A High-pressure Vibrational Spectroscopie Study
of Polymorphism in Steroids: Progesterone and
Spironolactone
BY
Gisia L.Pisegna
A thesis submitted to the Faculty of Graduate Studies and Research of McGill
University in partial fulfiilntent of the requirements
for the degree of Master of Science
Novernber 1999
Departrnent of Chemistry
McGill University
Montréal, Québec, Canada
" ~ i s i aL.Pisegna
üibîiothèque nationale
du Canada
Acquisitions and
BiMiographic Services
Acquisitions et
senrices bibliographiques
The author has grantecl a nonexclusive licence dowing the
National L i h u y of Canada to
reprodoce, Ioan, distribute or seil
copies of this thesis in microform,
paper or electronic formats.
The author retains ownership of the
copyright in this thesis. Neither the
thesis nor substantial extracts lkom it
may be printed or otherwise
reproduced without the author's
permission.
L'auteur a accordé une licence non
exclusive permettant à la
Bibliothèque nationale du Canada de
reproduire, prêter, distribuer ou
vendre des copies de cette thèse sous
la forme de mic~che/nlm,de
reproduction sur papier ou sur format
électronique.
L'auteur conserve la propriété du
droit d'auteur qui protège cette thèse.
Ni la thèse ni des extraits substantiels
de celle-ci ne doivent 'être imprimés
ou autrement reproduits sans son
autorisation.
Abstract
The effect of high extemal pressures on the vibrational (IR and Raman)
spectra of the polymorphs of progestemne and spironolactone has been examined.
The high pressures were achieved with the aid of a diamond-anvil ce11 between
ambient pressure and 50 kbar (-50,000 atm). The pressure dependences of selected
vibrational modes were obtained. Wavenumber vs. pressure plots were used to
determine the dv/dp values. Progesterone exists in two polymorphic forms and Form
11 is more thermodynamically sensitive than is that of Form 1. Form 1 exhibited a
pressure-induced structural transition at
transition at
- 15 kbar.
- 20 kbar, whereas Form II exhibited a phase
Spironolactone aiso exists in two polymorphic forms, where
Form II is more thermodynamically sensitive. Form 1exhibited a structural transition
at
- 16 kbar and Forrn 11at - 12 kbar.
L'effet de hautes pressions externes sur les spectres vibrationnels (InfraRouge
et Raman) des polymorphes de la progestérone et de la pirolactone a et6 étudié. Les
hautes pressions, pouvant aller de la pression ambiante jusqu'à 50 kbar (-50,000 atm),
ont été atteintes à l'aide d'une cellule à enclumes de diamant. Les variations de
certains modes vibrationnels sélectionnés au préaiable, ont été enregistrés. Les
courbes des nombres d'onde en fonction de la pression ont été utilisées pour
déterminer les valeurs de dv/dp. La progestérone existe sous deux formes
polyrnorphiques et la Forme J I est plus thermodynamiquement sensible que la Forme
1. La Forme I possède une transition structurelle induite par la pression à -20 kbar
alors que la Forme 11 montre une transition de phase B
-15 kbar. La spirolactone
existe également sous deux formes polymorphiques et la Forme II est plus
-
thermodynamiquement sensible. La Forme 1possède une transition structurelle à 16
-
kbar et la Forme II à 12 kbar.
1 would fust like to thank my supervisor, Professor Ian Butler, for his support,
encouragement and enthusiasm throughout the course of this work.
1would also like to acknowledge:
Stephanie Warner for her endless support, encouragement and fkiendship.
Many thanks !
Dr. Zen Hua Xu, Clare Edwards, Heather Gass and my other lab #335
colleagues for their support. encouragement and friendship;
Shane Pawsey for his help @SC) and for his friendship. as well as my friends
from Otto Maass who made Montreal enjoyable;
Pierre Lesté-Lasserre for help with the translation of the abstract and his
friendship;
Michel Boulay for technical assistance with the IR and Raman spectrometers
and Dr. Anne-Marie Lebuis for the 'numerous' X-ray patterns and her support;
Ms. Renée Charon and dl the other office staff for taking care of the
administration, and
My family and friends for their endless support and encouragement.
Note on Units
The following units have been used in this thesis for historical reasons. Their
definitions and SI equivalents are given below:
Physical Q u m tity
Symbol
SI Units
Units Used
wavenumber
v
m"
cm-' (= 100 m")
pressure
P
Pa (Nm-2)
kbar (= 108Pa)
force constant
k
N m"
dyne cm-' (= 10.' N m-')
bond length
r
m
ce11 constants
& b, c
m
A (= IO-'' m)
A (= 10-'O m)
In the text of this thesis, the unit of vibrational wavenurnber is often referred
to as the vibrational frequency (v). These quantities are dirvctly proportional to one
another, v = c ,; where c is the speed of light.
List of Abbreviations
The followiny abbreviations have k e n used in ihis thesis:
Atmosphere
atm
Diamond-anvil ce11
DAC
Infrared
IR
N u c h Magnetic Resonance
NMFt
Differential Scanning Calorimetry
DSC
Potassium Bromide
KBr
vii
Table of Contents
Abstract.........................................................................................
..
..il
...
Resume ........................................................................................... 111
Acknow ledgments .............................................................................. iv
Note on Units ..................................................................................... v
List of Abbreviations........................................................................... vi
Chapter 1
Introduction.................................................................... 1
1.1
High-pressure DAC Technique...............................................2
1.2
Infrared and Raman Spectroscopy...........................................5
1.3
References.......................................................................7
Chapter 2
Polymorphisrn in the Pharmaceutid Industry
2.1
Introduction ...................................................................... 8
2.2
Applications of Polymorphism in the Pharmaceutical Industry..........9
2.3
Methods Used to Identify Polyrnorphs.................................... 10
2.4
FAQ's in the Identification of Polyrnorphs ................................ 13
2.5
Polymorphism of Certain Dmgs and Steroids............................13
2.6
References....................................................................
Chapter 3
-20
Experimental Section
3.1
High-pressure Micro-infrared Spectra..................................... 2
3.2
High-pressure Micro-Raman Spectra...................................... 24
3 -3
Data Error Anal ysis ........................................................... 25
3.4
Preparation of Progesterone Forms 1 and II .............................26
3.5
Preparation of Spironolactone - Forms 1 and lI...........................39
3.6
References.................................................................... -49
-
Chapter 4
High-pressure Study of Progesterone and Polymorphism
4.1
Introduction ................................................................. - 3 0
4.2
Polymorphism of Progesterone............................................ -50
4.3
Results and Discussion ..................................................... -53
IR and Rarnan Pressure Studies of Form I ........................ 57
4.3.2 IR and Rarnan Pressure Studies of Fonn II.....................-69
Conclusions .................................................................... 79
References.................................................................... -81
4.3.1
4.4
4.5
Chapter 5
High-pressure Study of Spironolactone and Polymorphism
5.1
Introduction .................................................................... 82
5.2
Spironolactone and Polymorphism....................................... - 3 3
5.3
Results and Discussion ..................................................... -85
5.5
IR and Raman Pressure Studies of Form I ........................ 93
5.3.2 IR and Raman Pressure Studies of Form I1..................... 108
Conclusions................................................................... 119
References................................................................... -121
Chapter 6
Conclusions and Future Suggestions................................... 122
6.1
References................................................................... -125
5.3.1
5.4
Chapter 1
Introduction
Polymorphism is a problem of particular importance to the pharmaceutical
industry. Different polymorphs of a dnig can have different dissolution rates, which
in turn c m affect bioavailability [1,2].
Much work has been done on the
thermodynarnic properties of various pol ymorphs, main1y temperature studies, to
investigate the relationships between the different forms. Numerous drugs such as,
barbiturates, steroids and antihistarnines exhibit poiymorphism [1,2]. Progesterone
and spironolactone, Figure 1.1, are the two steroids of focus in this thesis as little has
been reported on the physicochemical properties of their poiymorphic forms, which
will facilitate clarification of the inter-relationship between each forrn.
Figure 1.1 Chernical structures of a) pmgesterone and b) sphnolactone.
The overail objective of the research project was to provide information o n the
effect of high-pressure and other relevant properties of the steroids on their different
polymorphic States. The use of the diamond-anvil cell, DAC, has become a popular
approach for investigating materials under high pressure [3]. DACs have found their
way into many fields of study, such as Chemistry, Physics, Geology, Biochemistry
and Forensic Science. If certain polymorphs are known to interchange with each
other, for exarnple, if Form II of a given material can convert to Form 1 under certain
conditions
- or
vice versa, then pressure may be another variable to investigate
further this structural transition. Coupling of a diamond-anvil ce11 to an infrared or a
Raman spectrometer may prove to be a useful technique for monitoring such changes.
The thesis is divided into the following chapters; Chapter 1 will present a brief
summary of high-pressure, diamond-anvil ce11 infkared and Raman spectroscopy.
Chapter 2 will discuss the effect of polyrnorphism of dnigs, especially that of
steroids.
It will incorporate some of the main investigations to date and the
importance of polymorphs in the phamaceutical industry. Chapter 3 will describe
the various experiments undertaken in order to obtain the results presented in the
thesis.
Chapter 4 will discuss the results of the structural characterization of
progesterone and the high-pressure infrared and Raman investigations. Chapter 5 will
contain the results of a similar study for the steroid, spironolactone. Finally, Chapter
6 will surnmarize the overall conclusions of the project and also present some
suggestions for future research.
1.1 High-pressure Diamond-anvil Ceii (DAC) Technique
Temperature has traditionally k e n the cornmon rnethod of observation used
to examine the theories of interatomic and intermolecular interactions. In addition to
temperature, however, pressure is an ideal rnethod to observe these same phenornena
as al1 materiais are expected to undergo phase transitions if sufficient pressure is
applied. It was in 1958 that Charles Weir and Alvin Van Valkenburg, at the National
Bureau of Standards in Washington, D.C.invented the diamond-anvil cell, DAC, [4].
The simplicity of the design dong with the range of pressures attainable, arnbient to
100 kbar (-100,000 atm), makes the DAC an attractive technique to study materials
under compression. The anvil and lever arm design involves two polished diamonds
with flat faces which allows a minute amount of sample to be placed in a thin gasket
located between the two diamond faces. The diamonds act as both the pressurebearing medium and the optical windows. The transparency of the diamonds over the
whole electromagnetic spectrum allows materiais to be studied directly in the DAC at
high pressures by using techniques such as infrared absorption, Raman scattenng and
X-ray powder difiaction. In the case of the DAC, pressure is applied by simply
turning a special screw.
These vibrational techniques are useful tools to study the bonding interactions
in molecules.
With the aid of a diarnond-anvil cell, these interactions can be
investigated thoroughly. Pressure is an important variable that leads to a method for
changing artificially the distance between atoms and molecules without affecting
other parameters. Thus, high-pressure vibrational spectroscopy is an excellent way to
examine inter- and intramoleçular interactions. Changes in spectral parameters such
as, frequency, band shape, intensity and band splitting can provide a large amount of
information about the nature of bonding in materials [SI.
Pressure-induced frequency shifts are the most noticeable effect because the
application of pressure reflects changes in molecular force constants since both the
masses of atoms and the native vibrations remain the same [3,5]. In a completely
harmonic situation, where the force constant operating between two masses is truly a
constant and independent of the distance between the masses, the application of
pressure would cause no observed frequency shift at dl. Therefore, the study of
pressure-induced frequency shifts can be considered to be the snidy of the
anharmonicity of atomic andor molecular interactions, and is most often observed
with the application of pressure. When a rnolecular crystal is compressed, there is a
reduction in the interatomic distances between the atoms which leads to an increase in
force constants. This situation normally causes vibrational bands t o shift to higher
frequencies. The frequency shifts observed for most stretching modes with pressure
are 1-3 cm-' kbafl, while those for bending modes are 0.14.3 cm-' kbar-'. Deviations
fiom these estimates such as, large, small, or negative pressure dependences, may be
rationalized in terms of the type of bonding involved, the nature of the vibrational
mode or the inter- and intramolecular interactions.
Phase transitions, viewed when there is a discontinuity in the dope of the
wavenumber vs. pressure plots, are most interesting because they involve one
crystalline form changing into another upon the application of pressure.
Phase
transitions can be first-order or second-order. The Gibbs free energy, G, is defined
for a given mass of material by:
where U is the intemal energy, T is temperature, S is entropy, P is pressure and V is
volume. For two phases to be in themodynamic equilibrîum at a particular pressure
and temperature, the Gibbs free energy must be the same for the matenal in either
phase. A transition is referred to as-'first-order' if the first denvative of the free
energy is discontinuous at the phase change.
For example, if there is a volume
discontinuity, then this indicates a first-order transition because V = (M;/6P)T.
However, if there is no discontinuity in the first derivative of G, but there is a
discontinuity in the second derivative, then the transition is termed 'second-order' or
continuous. Thus, if the volume changes continuously, but the compressibility shows
a discontinuity, then this is a second-order transition and:
Plots of wavenumber vs. pressure reveal discontinuities in the slopes of the graphs at
the pressure where a phase transition occurs. Phase transitions normally result from
very dense packing 131.
There is no single straightforward explanation that can be used to understand
intensity and bandshape changes as a function of pressure in sirnilar manner to how
the frequencies were treated in terms of bond anharmonicities. For a given vibration.
that is both IR and Raman active, the frequency shift with pressure will be the same.
However, the band shapes can be quite different and change in a different way.
htensities are complementary, but both may increase, decrease, or change in opposite
senses upon the application of pressure. In most cases, any bandshape or intensity
changes observed are relatively smail. Any significant changes are generally
associated with a phase change, Fermi resonance, soft modes, hindered rotations, or,
uni-axial pressure.
1.2 Ixûrared and Raman Spectroscopy
Infrared spectroscopy is the result of absorption of electromagnetic i n h e d
radiation by vibrating molecuIes [6,7]. The interaction of infrared radiation with a
molecule involves interaction of the oscillating electnc field component of the
radiation with an oscillating electric dipole moment in the molecule. In order for a
molecule to absorb infrared radiation as vibrational excitation energy, there must be a
change in dipole moment of the molecule as it vibrates. Consequently, stretching of
homonuclear diatomic molecules will not give rise to infrared absorptions.
According to the selection rule, any change in direction or magnitude of the dipole
during a vibration gives rise to an oscillating dipole that c m interact with the
oscillating electric field component of infrared radiation, leading to absorption of
radiation.
Raman spectroscopy is concerned witb vibrational and rotational transitions,
and is similar to infiared spectroscopy [6,7]. The selection mle is different from that
of infrared, and the information obtained from Raman spectroscopy often
complements that obtained from an infrared snidy and provides valuable structural
information. The Raman effect results €rom the scattering of electromagnetic
radiation by vibrating molecules. In a Raman expriment, a monochromatic bearn of
light illuminates the sample. In order for a vibration to be Raman-active, there must
be a change in polarizability during the vibration.
When the incident light is
scattered, the majority of this radiation is scattered at the same frequency as the
incident light, v,, known as Rayleigh scattering. Some of the light is scattered
inelastically and therefore gives rise to scattered light with frequencies different from
that of the incident light and is referred to as Raman scattering. Bands found at
higher frequencies than v, are cdled anti-Stokes scattering, and those with lower
frequencies are termed Stokes scattering. Raman scattering is dependent on the
change in polarizability of a molecule once irradiated. The polarizability is a measure
of the ease with which the electron clouds around the atoms in the molecule can be
distorted. When a molecule is distorted during a vibration, a dipole is induced and
the molecule is said to be polarized.
1.3 References
1.
J. Haieblian and W. McCrone, J. P h a m . Sci., 58 (1969) 9 1 1-929.
3.
J. R. Ferraro, in Vibrational Spectroscopy at High External Pressures, The
Diamond Anvil Cell, Academic Press, Orlando, Flonda, 1984.
4.
RIM. Hazen, in The New Alchemists, Times Books, 1 993.
5.
W. F. Sherman and G. R. Wilkinson, in Advances in Infared and Raman
Spectoscopy, Vol. 6, (R. J. H.Clark and R. E. Hester, eds.), Heyden and Son,
London, 1980.
6.
R. S. Drago, in Physical Methodsfor C h i s t s (znded). Saunders College
Pubiishing, Orlando, Florida, 1992.
7.
1. S. Butler and J. F. Harrod, in Inorganic Chemistry: Principles and
Applications, Benjamin/Cummings Publishing Company, Menlo Park,
California, 1989.
Chapter 2
Polymorphism in the Pharmaceutical
Industry
2.1 Introduction
Polyrnorphism is well known in the pharmaceutical industry and in the
scientific literature. The tenu, polyrnorphism, is defined as the ability of any element
or compound to crystallize in more than one distinct crystal species
[Ml.
A simple
example is that of carbon as cubic diamond or hexagonal graphite. A polymorph is a
solid crystalline phase of a given material resulting fiom the possibility of at least two
different arrangements of the molecules in that matenal in the solid state [Ml.
Polymorphs of a given compound can be as different in structure and properties as are
the crystals of two different compounds. Physical properties, such as, solubility,
melting point, density, hardness. crystd shape, optical and electrical properties and
vapor pressure al1 vary with polyrnorphic fom [l]. These properties can affect the
pharmaceutical industry where dissolution rates, powder flow and tableting behavior
are of great importance for the preparation of drugs. Common methods of obtaining
different polymorphs involve changes in temperature, pressure, relative hurnidity,
crystallization form various solvents and grinding. Exposure to these conditions may
oçcur during processing of drug substances by drying, granulation, milling and
compression. The scientific literature includes numerous indications of pol ymorphism
and its importance in biomaterials such as barbiturates, antihistamines, steroids and a
number of other important drugs. Approximately 67% of steroids exhibit multiple
forrns. Polymorphs of a dmg can have significantly different bioactivities due to
varying rates of dissolution in the body [l-41. Ease of formulation, acceptability and
stability of formulation can be strongly dependent on the polymorph chosen.
2.2 Applications of Polymorphism in the Pharmaceutical Industry
One of the main applications of polymorphism in the pharmaceuticai industry
is in the preparation of physically stable dosage fonns. Roblems of dmg preparations
and dosage forms c m be affected by using the incorrect polymorph.
Although
polymorphisrn is less important for solution dosage forms and for drug substances
that are highly water-soluble, it does affect semi-solid dosage forrns, such as creams
and ointments. One method of dosage pmparation where polyrnorphism poses a
problem is in suspensions [Il. The use of a wrong polymorph can give nse to a phase
conversion from a metastable form to a more stable form. This conversion could
produce crystal growth resulting in undesirable particle size distribution and can
cause a problem with parental suspensions, mainly syringibility [ 11.
Another
difficulty that c m arise when the drug is altered by phase transitions, producing drug
particles with different solubilities, is the biological availabilities of the dmg. Nso,
caking in suspensions may produce suspensions that cannot be u n i f o d y resuspended
by shaking [l]. Polymorphisrn aiso affects the preparation of creams. The use of a
wrong polyrnorph can result in a phase inversion to a more stable phase and crystal
growth is the outcorne, yieIding gritty and cosmetically unacceptable products. The
problem lies in an unevenly distribution of the active ingredient. A second difficulty
lies in suppositories, where polymorphic changes of a suppository base could result in
a product that undergoes a change in its melting characteristics
[Il.
If a suppository
base is dependent on the melting at body temperatures to release the active ingredient,
then a small change in the melting point of the polymorph could have severe
consequences. A third problem rnay also appear in solution-based dmgs, where a
metastable form concentration exceeds the equilibrium solubility of a less soluble
form of the dug and a thermodynamically unstable fomulation anses. Problems such
as crystallization may occur and this is typically found in water-soluble dmgs.
23 Methods Used to Identay Polymorphs
There are several methods of examination to help identiQ polyrnorphs of a
compound. The techniques most commonly used are optical microscopy, hot stage
methods, X-ray powder diffraction, infiareci spectroscopy, nuclear magnetic
resonance spectroscopy (NMR),differential scanning calonmetry @SC) and electron
rnicroscopy 11.21.
Infrared spectroscopy was one of the first techniques used to
identify polymorphs and led to the discovery of interconversion or manipulation of
crystalline modifications. Polyrnorphism in steroids has been known for at least sixty
years and the subtle differences in the IR spectra of different forms have been
reported. Changes in IR spectra resulting From grinding with KBr have also k e n
reported to occur with steroids CS]. In some instances, these changes were attributed
to conversion of a crystalline form into an amorphous or a second crystalline form.
Sample preparation techniques can have a profound effect on the IR spectra of
steroids.
Solid-phase IR spectra are generally recorded for steroids because,
unfortunately, many of the physiologically important steroids are only sparingly
soluble in comrnonly used solvents. Thus. this makes the use of solid-phase spectra
unavoidable. Mesley et al. have recorded the IR spectra of numerous steroids and
their polymorphs [SI. Spectral evidence of polymorphism has been reported
particularly for cortisone acetate, estradiol, testosterone, prednisone, and a number of
other steroids [5,6].
Over the past decade, new types of instrumentation have been added to the list
which have eased the manipulation of the polymorphs and so lessen the possibilities
of interconversion.
Such instruments include FT-Raman, near-IR and solid-state
NMR spectroscopy [4,7-91.
Near-IR spectroscopy is one of the latest techniques
used to charactenze polymorphism, accompanied by the pattern recognition method;
it is able to detect small amounts of undesired or desired polymorphs of a d m g [4].
Because polyrnorphs are the result of different arrangements of molecules, their IR
spectra can be affected. Numerous authors have shown IR spectroscopy to be useful
in the study of polymorphism; however, the spectra may be affected when using KBr
pellets or Nujol mulls since sarnple preparation is required and the pressure applied to
prepare the samples can lead to interconversion &or
manipulation in the spectra If
grinding is needed to reduce particle size, this could m o d e the sample.
ET-Raman spectroscopy is a new technique that is k i n g used in the study of
polymorphism of drugs. The main attraction of Raman specuoscopy is that no
sample preparation is required. In general, the samples are powders and can be
packed into a sample cup for the spectra to be recorded. Thus, Raman spectroscopy
is finding its mark in the polymorphism area FT-Raman spectroscopy has been used
to identiq and differentiate among the polyrnorphs of spironolactone, a well-known
diuretic [lO]. NIR FT-Raman spectroscopy has been employed as a method of
quantitative analysis for cortisone acetate (Figure 2.1) and R69, a compound involved
in a heart disease project [Il].
The use of NIR FT-Raman spectroscopy as a
convenient tool for quantitative measurement of polyrnorphs can be of great value.
Figure 2.1 Chernical stmcture of cortisone acetate
SoIid-state NMR spectroscopy is the third new technique that is common in
the identification of polyrnorphs. This method has become particularly useful for the
investigation of dmg polymorphs and dmgs in their dosage forms. High-resolution
'
3
~
spectroscopy
~
~ in ~the solid-state, using the cross-polarization, magic-angle
spinning (CPMAS) suite of techniques has been shown to provide a powerf'ul method
of distinguishing polymorphs, of establishing chernical structures, and of obtaining
some crystallographic information [8,9]. A study conducted by Harris et al. used
solid-state N M R spectroscopy to investigate the six polymorphs of cortisone acetate
[9]. Cortisone acetate, in the form of an acetate ester, is used clinically as an anti-
inflammatory agent for the treatment of allergies and certain collagen diseases. They
analyzed nine different samples of cortisone acetate and found six polymorphs, eacb
giving a distinct NMR spectrum. Some of the samples were impure and mixtures of
polymorphs were readily analyzed and rninor components were detected by solidstate NMR spectroscopy. If a given polymorph is only found in an admixture with
another form, the spectnim of the former cm be ploned separately by difference
spectroscopy if the second polymorph is known in a pure state so as to provide as a
reference [9]. A second study performed by Byrn et al. demonstrated the usefulness
of solid-state NMR spectroscopy for characterizing polymorphs of benoxaprofen and
nabilone, and pseudopolymorphs of cefazolin, Figure 2.2
[a]. The data
led to the
conclusion that different crystal forms of dmgs have different solid-state NMR
spectra. The technique can also be used to study dosage forms and determine which
crystalline foms are present in these dosage forms.
Figure 2.2 Chemical structure of a) benoxaprofen,b) nabilone and c) cefazolin
2.4 FAQ's in the Identification of Polymorphs
In order for a compound to exhibit polymorphism and ascertain the number of
f o m s that do exist. certain questions must be addressed [LI: (1) How many
polymorphic forms are there? (2) Which forms are the most stable and to what
degree? Are certain forms metastable? (3) 1s there a noncrystalline glassy state and
what is its stability? (4) What are the tempera-
stabilizing ranges for each crystal
form? (5) What are the solubilities of each forrn? (6) How are the different forms
prepared? (7) WiIl the more soluble metastable form survive processing? (8) Does
the polymorph react with any other chernical compound during processing to form a
molecular addition compound? (9) If so, what are its physical properties such as.
stability, melting point, and c m it exist in a desirable metastable polymorphic form or
glass?
In general, the nomenclature of the polymorphs are assigned from stable to
least stable at room temperature and the names given are Form A, a,or 1 as the most
stable form [l]. The most stable form is generaily the one with the highest melting
point. The determination of transition temperatures further helps characterize the
forms, Le., the temperature at which both or al1 f o m s have identical free energies,
solubilities, and vapor pressures are specific examples. The closer the melting points
for each forrn, then the easier it is to obtain the unstable form. The difference
between melting points can be taken as a mesure of relative stability [l ] .
2.5 Polymorphism of Certain Drugs and Steroids
Numerous well-known dnigs exhibit polymorphism. The famous over-thecounter pain reliever, Aspirin, is known to exist in two polymorphic forms 1121.
Form 1 is crystallized from a saturated solution of commercial aspirin in 95% ethanol.
It has a melting point of 143-144 OC and has a monoclinic crystal structure. Form II
is crystallized from n-hexane at room temperature and has a melting point of 123-125
OC.
Differences in the X-ray powder diffraction patterns and the IR spectra indicate
different arrangements of the aspirin molecules in the crystal lattices of each fom.
Dissolution rates were also measured and Form II has a greater thermodynamic
activity and exhibits the higher dissolution rate 1121.
Another well-known compound in today's society is Aspartame, APM. the
commercial artificial sweetener, which also exhibits polymorphism [13]. Aspariame
exists as a hemihydrate, APM-0.SH20, which occurs in two polymorphic foms. Form
I refers to the known crystal structure of aspartame hemihydrate, determined by
Hatada et al. [14]. The commercial form, also a hemihydrate, is designated Form II.
Both forms give different powder diffractions; however, Form II upon ball-rnilling or
heating to 160 OC in the presence of stearn converts to Form 1 [13]. Characterization
of both foms was achieved by
using X-ray powder diffraction, DSC,
thermogravimetric analysis, FT-IR, solid-state
13cNMR
spectroscopy, scanning
electron rnicroscopy and particle size analysis. Measurements of tme density and
dissolution rates were also undertaken. Spectral cornparisons suggest that the crystal
structure of Form II is less symmetric than is that of Form 1. However, each of the
polymorphs converts to a dihemihydrate, APM-2.5Hfi, when subjected to water
vapor at relative humidities 2 58% or to liquid water.
A third drug that is in common public use is Ranitidine, which is used in the
treatrnent of peptic ulcers and related disorders. Ranitidine hydrochloride exists as
two polymorphs (m.p. 144.5 and 146.2 OC)and both forms have been characterized
by IR spectroscopy [15]. The spectra differ considerably in detail, especially in the
region above 3000 cm-' due to bonded N H absorptions. Numerous polymorphs of
dmgs have been characterized by IR spectroscopy because it is a fast and routine
method of identification.
Polymorphism is a particular problem with steroids. Mesley et al. have
investigated over 35 steroids, using IR spectroscopy, and found more than half
exhibited different crystalline modifications [5,6]. One of the first steroids found to
demonstrate the phenornenon of polymorphism is 17s-estradiol, Figure 2.3. Smakula
et al. showed by IR spectroscopy and X-ray powder diffraction the various
polymorphic forms of 17P-estradiol [IO]. With these two techniques. they found
estradiol exists in an amorphous state and at least four different polymorphs with a
common melting point. It was also shown that these modifications are selectively
interconvertible by varying degrees of thermal and mechanical agitation [163. They
observed interconversion when preparing KBr discs of the various foxms. The
preparation of KBr discs involve grinding, pressing, and heating which may lead to
spectrum of a different crystal form or a rnixed spectrum. The X-ray powder
diffraction patterns may also suffer due to the same effect.
The thermal and
mechanical conversion of the polymorphs into one common crystal form may prevent
the recognition of polymorphism by melting point determinations and X-ray
diffraction. However, Smakula et al. found that because of the drastically different
modes of hydrogen bonding in estradiol, they were able to characterize the IR spectra
of the various forms.
Figure X 3 Chernical structure of l'la-estradiol.
17P-Estradiol contains two hydroxyl groups, one phenolic and the other
alcoholic, which provide suitable conditions for different modes of hydrogen bonding
and lead to several crystalline modifications. Since molecules of a compound can
associate in altemate modes of hydrogen bonding of comparable stability, this could
be a major cause of polymorphism, thus causing differences in the solid-state spectra
of polymorphs.
The use of estradiol in Hormone Replacement Therapy (HRT)
ensures the replacement of estrogen which the body stops producing during
menopause. Studies have shown that crystal inclusions of estradiol are present in the
HRT patches and so the proper dosage is not delivered as it needs to be in solution-
state for permeability through the skin [17]. FT-Raman mapping was used to observe
the crystal inclusions, however, the polymorphic fonn was not identifiable.
Another steroid exhibiting polymorphism is dethoxyprone, Figure 2.4.
Dethoxyprone is a soluble steroid with potent anaesthetic properties and is known to
exist in two polymorphic foms 118-201.
Palmer et al. detemiined the crystal
structure of each form and showed Form 1 to be monoclinic with space group P2i,
whereas Form II is orthorombic with space group PZl2121. The forms were
characterized by X-ray crystallography, DSC and vibrational and solid-state NMR
spectroscopy.
Figure 2.4 Chernical structure of dethoxyprone.
The X-ray data of dethoxyprone demonstrate that there is one molecule in the
crystallographic asymmetric unit and that each polymorph shows hydrogen bonding
&roii,oh the C(3)-OH hydrogen atom. Form 1 molecules are linked in a head-to-head
ladder fashion throughout the structure, whereas Form II adopts a head-to-tail
structure. The geometrical data suggest that Form 1 has weaker hydrogen bonding
than does Form II [18-201. From the DSC studies, the results were inconclusive and
showed no evidence of reversible interconversion between the two forms. However,
the IR and Raman spectra chara~terizedeach form unambiguously. The carbonyl
stretching mode for the 20-keto group gave signals of 1709 (Fom 1) and 1688 cm-'
(Form II) [18]. This indicates that the fundamental difference lies within the crystal
lanice of the two forms. The OH-stretching region in the infrared also demonstrates
the varying strengths of the hydrogen bonding. The Fï-Raman spectra supported the
IR daîa, especially in the CO stretching region, and showed that the carbonyl is likely
to be involved in the different environments of the two forms. Therefore, the spectral
evidence agrees and supports the X-ray results.
PRmidone (Figure 2.5), an anticonvulsant, occurs in two polymorphic forms
[2 1,221. The crystal structure for Form A has been known for man y years, while that
of Form B has only been solved recently.
Rimidone has a strong &nity
for
hydrogen bonding and this is reflected in the packing arrangements of the crystal
structures.
The crystaî structure of Form A is monoclinic, whereas Form B is
orthorombic [2 1,221. Form A has two types of hydrogen bonds, one creating dimers
and the other linking those dimers into sheets of molecules. Form B has one type of
hydrogen bond forming sheets.
Figure 2.5 Chernical structure of primidone
Fluprednisolone, Figure 2.6, is another interesting steroid that exhibits
pol y morphism. The steroid crystallizes in several forms, including three anhydrous,
three solvates and one amorphous form [23]. Form 1 is the most stable at room
temperature, whereas Form EI slowly transforms to Form 1 in contact with air at
room temperature. Phase transitions occur under a variety of conditions, and al1
forms interconvert to the a-monohydrate, one of the solvate forms, in aqueous
suspension. The forms have k e n characterized by X-ray powder diffraction, DSC
and IR spectroscopy. The IR spectra illustrated small differences between each form
that are of sufficient magnitude to be of value in phase identification. The dissolution
rates of six phases of fluprednisolone in water were detennined [23]. Several phase
transitions were observed during the dissolution studies. Further in vitro and in vivo
studies anaiyzed the phase transitions and dissolution rates of the bioavailability of
fluprednisolone.
Figure 2.6 Chemiesl structure of fluprednisolone.
Crystallographically, different solid forms of a particular compound are
characterized by differences in the dimensions of their lattice unit cells.
Such
differences are most likely due to differing types of association between individual
molecules comprising the unit cell, which in tum, should be reflected in the IR
spectra. The most common form of association in the majority of compounds is
intermolecular hydrogen bonding between hydroxyl groups, however it is not always
the case.
Polymorphism has been found in two steroids, progesterone and
spironolactone, which contain no hydroxyl groups and the main form of association is
presumably dipolar interaction between two carbonyl groups [6]. While the subject
of polymorphism is extensively covered in the literature, there are relatively fewer
reports on the physicochernical properties of certain polymorphs.
Presently, the main approach to pressure-induced studies of steroids and their
polymorphs has been through the investigation of pressed KBr disc for IR spectra.
The literature explains the alteration of the IR spectra of steroids in KBr and how it
can play a role in the manipulation and interconversion of polymorphs [5,6,25,26].
Studies have shown that pïnding and bail-rniiling can alter the desireci polymorphs,
such as in the case of aspartame [13]. Most other studies have demonstrated that the
KBr disc can modify the spectrum of certain organic compounds [25,26]. Estradiol
was one of the first steroids to demonstrate interconversion of polymorphs through
the preparation of KBr discs [16]. As early as 1954, the detection of pressed KBr
discs has shown the modification of spectra of certain carbohydrates over several
days [25]. A sugar, such as a-D glucose, exhibited a modification in the IR specmim
after a three day period and was mainly observed in the OH stretching region at
approximately 3400 cm-'. Studies have also been reported on the alteration of spectra
of polyhydroxy steroids with the use of KBr discs [26].
Numerous organic
compounds are sensitive to KBr disc formation and alterations of their tnie spectra
are observed. Little or no work has been done on the investigation of polymorphs
using high-pressure spectroscopie techniques.
1.
J. Haleblian and W. McCrone, J. Pham. Sci., 58 (1969)91 1-929.
2.
T.L.Threlfall, Analyst, 120 (1995)2435-2460.
3.
P. K.Aidridge, C. L.Evans, H.W. Ward, II, S. T. Colgan, N. Boyer and P.J.
Gemperline, Anal. Chem., 68 (1996)997-1002.
4.
G.R. Desiraju, Science, 278 (1997)404-405.
5.
R.J. Mesley and C. A. Johnson, J. Pham. P h m a c o l . , 17 (1965)329-340.
6.
R.I. Mesley, Spectrochim Acta, 22 (1966) 889-917.
7.
C.M.Deeley and R. A. Spragg, Spectrochim. Acta, 47A (1991) 1217-1223.
8.
S. R. Bym, G. Gray, R. R. Pfeiffer and J. Frye, J. Piuznn. Sci., 74 (1985)565568.
9.
R. K.Harris, A. M. Kenwright, B. J. Say, R. R. Yeung, R. A. Fletton, R. W.
Lancaster and G. L. Hardgrove m.,Spectrochim. Acta, 46A (1990)927935.
IO.
G . A. Neville, H.D.Beckstead and H.F. Shurvell, J. P h a m . Sci., 81 (1992)
1141-1146.
11.
C . M. Deeley, R. A. Spragg and T. L. Threfall, Spectrochim. Acta, 47A (1991)
1217-1223.
12.
R.Tawashi,Science, 160 (1968)76.
13.
S.S. Leung, B. E. Padden, E. J. Munson and D. J. W. Grant, J. P h a m . Sci..
87 ( 1 998) 50 1 -507.
14.
M. Hatada, J. Jancarik, B. Graves and S.-H.
Kim,J. Am Chem. Soc., 107
( 1985)4279-4282.
15.
T. J. Cholerton, J. H. Hunt, G. Klinkert and M. Martin-Smith, J. Chern. Soc.
Perkin Trans 11, ( 1984) 1761 - 1766.
16.
E. Smakula, A. Gori and H. H.Wotiz, Spectrochirn. Acta, 9 ( 1 957)346-356.
17.
C.L.Armstrong, H.G.M.Edwards, D.W. Farwell and A. C. Williams, Vib.
Spectrosc., 11 (1996) t 05- 113.
18.
19.
R. K.Hamis, A. M.Kenwright, R. A. Fletton and R.W.Lancaster,
Spectrochim. Acta, 54A (1998) 1837-1847.
R. A. Palmer, H. T. Palmer and J. N. Lisgarten, Acta Cryst., C49 (1993) 721723.
20.
R.A. Palmer, H. T. Palmer, J. N. Lisgarten and R. Lancaster, J. CrystaLlogr.
Spect. Res., 23 (1993) 279-283.
21.
R. S. Payne, R.J. Roberts, R. C. Rowe, M. McPatiin and A. Bashal, Int. J.
Pham., 145 (1996) 165-173.
22.
R.S. Payne, R. J. Roberts, R. C. Rowe and R Docherty, Inr. J. Pham., 177
( 1999) 23 1-245.
23.
J. K.Haieblian, R.T.Koda and J. A. Biles, J. Pham. Sci., 60 (197 1) 14851488.
24.
J. K.Haieblian, R.T.Koda and J. A. Biles, J. P h a m Sei., 60 (1971) 14881491.
25.
S. A. Barker, E.J. Boume, W. B. Neel y and D. H. Whiffen, Chern. I d ,
(1954) 1418-1419.
26.
G . Roberts, Anal. Chem., 29 (1957) 9 11-916.
Chapter 3
Experimental Section
Infrared spectra (4000-600cm") were collected on a Bmker I F S 4 Fï-IR
spectrometer coupled to a Bruker A-590 infrared microscope (15X objective), a Sony
colour video system, and a liquid nitrogen-cooled, mercury-cadmiurn telluride
detector. The diarnond-anvil ce11 @AC), Figure 3.1, was purchased from HighPressure Diarnond Optics, Tucson, Arizona The ce11 contains two type IIa diamonds.
Type Da diarnonds are the most transparent in the IR, however, they have complete
absorption in the 2300- 1900 cm" region.
Figure 3.1 Schematic of the DAC.
A stainless-steel gasket (7 mm x 7 mm x 240 pm) with a 300 pdiarneter hole in its
center was mounted on the face of the lower diamond by means of small b a h of
plasticine.
The gasket ensured hydrostatic pressure and equal pressure in al1
directions. The sarnple and calibrant were then placed in the gasket hole with the aid
of an optical microscope. The ce11 was assembled and pressure was applied by
tuming the screw that resulted in a raising or lowering of the pressure plate.
The pressure calibrant used for the high-pressure micro-infrared experiments
was NaN03 diluted in a NaBr matrix (0.1-0.3 wt %) [l]. The pressure measurements
were monitored by following the behavior of the strong antisymmetric N-Ostretching
mode of the NO< ion, at 1401.3 cm-'at ambient pressure. The pressure is caiculated
using the following equation [2]:
P (kbar) = 1.775 Av - 0.7495 Av exp(-Av ff 8)
where Av is the ciifference between the peak positions of the nitrate peak at pressure P
and ambient pressure in cm-'. Figure 3.2 demonstrates the change in position of the
nitrate peak as the pressure is increased.
1460
1440
1420
1 400
1 380
1 360
W avenumber (cm")
Figure 3.2 The antisymmetric N-O stretching mode of the NO3- ion nt various
pressures.
The DAC was placed on an XYZ stage and was aligned with the aid of a
colour monitor. Infrared spectra were recorded at 1.O cm-' resolution and 10 0 scans
were collected.
The band intensities are expressed as absorbance rather than
transmittance.
3.2 High-pressure Micro-Raman Spectra
The Fï-Raman spectra were recorded on a Bniker IFS-88FT-IR spectrometer
furnished with a Bruker FRA-106 Raman attachment coupled to a Nikon Optiphot-2
optical microscope (20X objective). Near-infrared (N~'*:YAG) laser irradiation at
1064.1 nm was focused onto the sample at a laser power of 150 mW. The DAC was
loaded in similar fashion as the high-pressure infrared experiments, however, on1y
sample was placed inside the gasket hole. The higher energy component of the
t2,
phonon mode of the diamond, located at 1332.5 cm-' at ambient pressure, was used
in-siîu as the interna1 pressure calibrant 131. Figure 3.3 shows the diarnond line at
various pressures. The position of the calibration peak at the minimum point of its
second derivative was obtained. The frequency of the half-height of this position on
the calibration peak was placed into
following equation and then the pressure was
cdculated:
P (kbar) = S.S(v - 1336.8)
(3.2)
The equation was determined by the procedure reported by Markwell er al. [3,4].
The DAC was placed on an XYZ stage under the 20X objective of the optical
microscope. The high-pressure spectra were collected at regular intervals of 5000
scans at a resolution of 2.6 cm-'.
50.0 kbar
40 -6 kbar
Z . 0 bar
14.8 kbar
0.9 kbar
1
m
1350
1
I
1345
I
I
1340
1
1335
I
I
I
1330
1
1 325
Wavmumber (cm-')
Figure 3.3 The diamond line at various pressures.
3.3 Data Error Analysis
Data and spectral manipulations for IR and Raman experiments were made
using the Levenberg-Marquardt algorithm (Bruker OPUS" software). Linear leastsquares analyses were used to determine the pressure dependences, dv/dp.
The
values for dvldp are reported to two significant figure when the correlation
coefficient, ? > 0.95. Values with 0.80 c i s 0.95 are written with one significant
figure, and when r2 c 0.80, dv/dp are reported only if there are 10 or more data points.
The errors associated with the pressure calibration in the FI'-IR and Fï-Raman are
1.2 kbar and r 2 kbar, respectively.
*
-
3.4 Preparation of Progesterone Forms 1 and Iï
Form 1 was recovered from dissolvinp a commercial sarnple of progesterone
(Sigma) in a minimal arnount of cold chloroform. The solvent was then ailowed to
evaporate under a stream of air at room temperature [5]. The crystals were collected
and characterized by the following methods. (1) The strong IR absorption band at
870 cm-' [ 5 ] using the Bruker IFS-48FT-IRspectrometer coupled to a Bruker A-590
infrared microscope (15X objective), a Sony colour video system, and a liquid
nitrogen-cooled mercury-cadmium telluride detector. A single crystal was placed on
a NaCl salt plate and located under the microscope. Infrared spectra were recorded at
1.0 cm-' resolution and 200 scans were collected. (2) A Raman spectrum was also
collected using the Bruker IFS-88 FT-IR spectrometer fumished with a Bruker FRA106 Raman attachment. The sarnple was placed into a sarnple cup and the spectrum
was measured using the macro-chamber. The Raman spectra were recorded at 2.6
cm" resolution and 500 scans were collected. (3) I3cCPMAS spectra were acquired
at 25 MHz using a Chemagnetics Mlûû spectrometer. Samples were spun at 4 kHz,
the contact time was 3 ms and the recycle delay was 2
S.
(3) The differential scanning
caiorimetry thermogram of Form 1 was obtained using a Perkin Elmer DSC-7 at a
scan rate of 10 "/min from 25 to 150 OC in an atmosphere of nitrogen. A single peak
was observed at 130 OC,corresponding to the value found in the literature [6,7]. (5)
X-ray powder diffraction patterns were collected on a Siemens D-5000 using Copper
(CuKa) radiation.
Form II was prepared by dissolving progesterone in hot ethanol and the
solution was evaporated to dryness on a hot plate. The product was then dissolved in
cold acetone and the solvent was evaporated under a stream of air at room
temperature [ 5 ] . The form was characterized by the strong IR absorption band found
at 864 cm-' [ 5 ] . The IR spectrum was recorded using the same conditions as
described above for Forrn 1. Form II was also characterized fully by t h e other
methods mentioned above. The DSC thennogram showed a single peak at 124 OC.
which matched the value found in the literature [6,7].
Figure 3.13 Expanded (0-50 20-Scale) X-ray powder diffraction pattern of progesterone - Form I
ndd SO'CP
-
ndd LL'OO
+
-
3.5 Preparation of Sphnolactone Forms 1and II
Form 1 was prepared by dissolving a small arnount of commercial
spironolactone (Aldrich) in boiling acetone. The solution was cooled gradually to O
OC over a period of a few hours, and the crystais were coiïected [8]. Form 1 crystals
are long, flat, and transparent [8]. The same characterization methods used for
progesterone, except solid-state
I3c NlMR
spectroscopy, were also used for
spironolactone Form 1. The DSC thermogram exhibited a single peak at 208 O
C
[SI.
Further characterization was achieved by measuring single crystals of each fom.
Cell parameters for single crystais were obtained from a Rigaku AFC6S
diffractometer using MoKa radiation and the values matched those in the literature
[S,91.
Form II was prepared by dissolving a srnaII amount of commercial
spironolactone in acetone and the solvent was allowed to evaporate spontaneously at
room temperature [8]. The crystals obtained were clear and pnsmatic. The same
characterization methods mentioned above, except solid-state "C N M R spectroscopy
were followed. The DSC thermogram exhibited a single peak at 208
matched the literature value [8].
OC,
which
Ce11 parameters for single crystals were also
calculated and matched those in the titerature [8,10].
O
O
O
F
O
O
V)
F
O
O
O
(U
O
O
V)
CV
O
O
O
CC)
O
O
V>
CC)
-
Figure 3.22 X-ray powder diffraction pattern of spironolactone Form 1
-
Figure 3.23 X-ray powder diffraction pattern of spironolactone Form II
D. D.Klug and E. Whalley, Rev. Sci. I n s r n . , 54 (1983) 1205-1208.
D. A. Skoog and J. J. Leary, in Principles ofInstrumental Anulysis (4& ed),
Saunders College Riblishing, Orlando, Florida, 1 992.
R. D. Markwell and 1. S. Butler, Cm. J. Chem., 73 (1995) 1019- 1022.
R. D. Markwell, 1. S. Butler and C. M. Edwards, Spectrochim. Acta, 53A
(1998) 2253-2259.
R.J. Mesley and C. A. Johnson, I. Pharm. Pharmacol., 17 (1965) 329-340.
M. Muramatsu, M. Iwahashi and U. Takeuchi, J. Pharm. Sci., 68 (1979) 175177.
(a) R. Carneroni, G. Gamberini, M. T. Bernabei and M. Facchini, II Farmaco,
Ed. Pr., 28 (1973) 621-635.(b) R. Camcroni, G. Gamberini, M. T. Bemabei
and M. Facchini, Il Farmaco,Ed. Pr., 28 (1973) 636-641. (c) R. Carneroni,
G. Gamberini, M. T.Bernabei and M. Facchini, II Farmaco, Ed. Pr., 29
(1974) 184-191.
V. Agafonov, B. Legendre, N. Rodier, D. Wouessidjewe and J.-M. Cense, J.
Pharm. Sci., 80 (1991) 18 1-185.
V. Agafonov, B. Legendre and N. Rodier, Acta Cryst., C45 ( 1 989) 166 1- 1663.
O. Dideberg and L.Dupont, Acta Cryst., B28 (1972) 3014-3022.
Chapter 4
High-pressure Study of Progesterone
and Polymorphism
4.1 Introduction
Progestins and estrogens are the two major classes of female sex hormones.
Together they serve important functions in the development of female secondary sex
characteristics, control of pregnancy, control of ovulatory/menstnial cycle, and
modulation of many metabolic processes [l]. Progesterone, a natural progestin and
steroid hormone. is produced by the corpus luteum. Its function is in the preparation
of the lining of the uterus for the implantation of the fertilized ovum. Progesterone is
also partial1y responsible for mammary glandular development and may play a role in
ductal growth. The important pharrnacological use of estrogens and progestins is as
oral contraceptives. Estrogens and progestins act primarily to decrease the production
of gonadotropins, follicle-stimulating hormones (FSH),and luteinizing hormones
(LH) at the pituitary-hypothalamus axis. This inhibits the rnidcycle LH surge and
thus prevents ovulation.
Progesterone is a poorly water-soluble d m g
[Il. Oral progesterone is alrnost
completely inactivated in the liver and, therefore, synthetic modifications are
necessary in order to produce the oral active progestins. Progesterone can be given
parenterally; however, has an elimination half-live of only a few minutes.
It is
converted in the Iiver to pregnanediol and conjugated with glucoronic acid at the C3
position, and the conjugate is excreted mainly in unne.
4.2 Polymorphism of Progesterone
Progesterone, Figure 4.1, is known to occur in two polymorphic forms [2- 123.
Many studies have been done to characterize both forms by differential scanning
calorimetry @SC), X-ray powder diffraction, and IR spectroscopy [2-121. Studies
have been conducted in order to increase the solubility of progesterone by using solid
dispersion technology to increase the dissolution and oral absorption [2]. The
investigation
showed
that,
progesterone/polyoxyethylene
by
using
two
glycol
6ûûû
solid
different
dispersion
carriers,
and
progesterone/saccharose distearate solid dispersion, progesterone in its metastable
form could induce drug polytransformation with aging. Thus, carriers can influence
the polymorphisrn of progesterone.
Figure 4.1 Chemical stmcture of progesterone.
The two polymorphic forms, 1 and II, are prepared differently. Form 1 is
crystallized frorn chloroform, whereas Form II is crystallized from hot ethanol
followed by cold acetone. From DSC studies, Form 1 has a melting point of 130-13 1
O
C
and Fom II melts at 123-124 O C [3.4]. When observing their IR spectra. Form 1
has a strong absorption band at 870 cm-', whereas F o m
band at 864 cm-' [4-61.
LI has a strong IR absorption
The crystal data of Form 1 demonstrates that it is
orthorhombic and tends to crystallize with a prismatic morphology associated with
the P21212ispace group, with a = 12.559, b = 13.798, and c = 10.340 A, with Z = 4.
The packing is due to cohesion of crystals associated with Van der Waals interactions
[7,8]. F o m II is also orthorhombic with the same space group P212i2i,where a =
6.252, b = 12.593, and c = 22.498
A,
with Z = 4 [9]. From the crystal data. ir is
evident that the polymorphic differences are due to different packing forces because
progesterone is a typical steroid with limited flexibility.
Some therrnodynamic differences between the polymorphic crystals are
revealed in orientational changes of the mololecules in insoluble monolayen at airsolution interfaces when the polymorphic transformation is associated essentially
with a conformational change of the molecules in the two-dimensional film [3]. The
thermodynamic properties of the two polymorphic forms of progesterone are
important for pharmacological purities for quality control and are aiso important for a
quantitative understanding of the surface chernical properties of progesterone 131.
The study performed by Muramatsu et al. demonstrated that when molten
progesterone undergoes equilibrium melting at 85 OC in air, Nz,or He, Form 1crystals
are always formed [3]. However, when the molten liquid was in a vacuum (2-3 torr),
Form II crystals are produced At room temperature, both forms are stable and no
polymorphic transformation seems to occur for several months. However, at higher
temperatures, a unilateral transformation of Form II to Form 1takes place. It has been
estimated that Form 1 is more stable thermodynamicdly than is Form II by 1.1
kcaümol [3]. Polymorphs may be characterized by the dissimilarity in the packing
mode of their molecules without a significant difference in their conformation.
Carnpsteyn et al. have reported that the intermolecular cohesion in Form 1 is due
mainly to Van der Waals attraction [7]. Foresti-Serantoni et al. have indicated that
the molecular conformation in Form I is similar to that in the crystals of Form II and
that the packing forces in these crystals have little correlation to molecular
conformation Cg]. Therefore, the thermodynamic difference cornes from a different
mode of rnolecular packing, rather than molecular conformation, in the unit cells.
Neither f o m contains molecular interactions that would normally be regarded as
hydrogen bonds, because, although progesterone has ketone hydrogen bond
acceptors, it has no conventional hydrogen bond donors [IO].
To date, no high-pressure vibrational spectroscopie studies of the two
progesterone polymorphs have been reported.
Therefore, high-pressure IR and
Raman experiments were performed between ambient pressure and 50 kbar to
examine the phase transition behavior and the bonding in these forms, in order to
provide more information of the polymorphism of progesterone. The results are
presented and discussed in this chapter.
4.3 Results and Discussion
The FT-IR spectra of Forms 1 and II c m be found in Chapter 3. Expanded
Fï-IR spectra of both forms, recorded in the 1100-650 cm-' region. are shown in
Figure 4.2- The major peaks of interest, which characterize each form. appear in the
875-860 cm-' region.
More specifically, Fonn 1, crystallized frorn chloroforrn is
characterized by the strong IR absorption band at 870 cm-' [4-61.
Form II is
characterized by the strong IR absorption band at 864 cm-' 14-61. The remainder of
the spectra shows subtle differences between the two forms. The differential scanning
calorimetry thermo,orams, shown in Chapter 3, correspond to those reported in the
literature. where Form I exhibits a single peak at 130 OC and Form LI has a single peak
ar 123 OC [3,4]. No evidence of supercooling was observed. The FT-Raman spectra
of both forms are shown in Chapter 3 and expanded spectra of the lattice region (300-
20 cm-') and the 180-1550 cm-' region can be seen in Figures 1.3 and 1.4.
respectively. In the FT-Raman spectra of the two forms, there are subtle differences
in the 1800-1550 cm-' region associated with the v c a and v c s modes. The vc-0
modes for Form 1 are at 1664 and 1699 cm-' and the v c x mode is at 16 16 cm-'. Form
II has
vc=o modes at 1667 and 1706 cm-' and a vc.c
mode at 1616 cm-'. The
distinction is seen from the v c a stretching modes with approxirnately 5 cm"
difference between each form. Moreover, with the major difference occurring in the
lattice region, it can be concluded that the polymorphic differences are due chiefly to
the packing arrangement of the molecules in the crystal structures.
Further
characterization using X-ray powder diffraction patterns distinguished between each
form. However, the Form II pattern exhibits a mixture with Form 1 suggesting further
that Form 1 is thermodynarnically more favorable (Chapter 3). Although solid-state
'
3
~NMR
spectroscopy has been found to be a useful technique in the
characterization of polymorphs, this was not the case in the polymorphs of
progesterone. The
')c NMR spectra of both forrns are identical
characteristic of either form (Chapter 3). The slight changes
between both spectra are attributed to expenmental error.
with no peak being
(-
0.15 ppm) found
cm"
-Forrn II
*---*-
900
800
Wavenumber (cm-')
Figure 4.2 Expanded FT-IR spectra of progesterone Forms 1 and II (1100650
cm").
Fonn I
200
150
Wavenumber (cm*')
Figure 4.3 Expanded FT-Raman spectra of progesterone Forms 1and II
( Lattice region 300-20 cm-').
-
F m II
.--..Form 1
Wavenimber (cm")
Figure 4.4 Expanded FP-Raman spectra of progesterone Foms 1and II (18001550 cm").
4.3.1 IR and Raman Pressure Studies of Form 1
IR
The vibrational assignments and pressure dependences for the observed
infrared peaks of Form I are presented in Table 4.1.
Discontinuities in the
wavenumber vs. pressure plots, Figures 4.5 to 4.7, were found for a number of the
modes examined over a pressure range from 16-27 kbar. These discontinuities
provide evidence for a pressure-induced structural change. The appearance of new
peaks at pressures above 16 kbar a€fords further evidence of a structural change. The
spectra in boih phases are quite sirnilar and the changes in the pressure dependences
are gradual, occumng over a 16-27 kbar range. Therefore, this transition is most
likely to be second-order with the structures of both phases k i n g quite similar.
Table 4.1 Infrared modes and tbeir pressure dependences for progestetone Form 1.
Wavenumber Low-pressure Phase Wavenumber High-pressure Phase
(cm-')
dv/dp (cm-' kbaf ')
(cm-')
dv/db (cm-'kbar-')
687.0
0.24
692.7
0.22
0.40
0.41
0.26
0.25
0.23
0.30
0.29
Assignments [Il]
-
C-C-C bending
Ring deformation
C-Hout-of-plane
bending
0.24
0.52
0.32
O. 19
O. 19
0.2
0.20
0.31
0.26
0.26
o. 1
0.25
0.43
0.29
0.30
0.29
0.29
Ring suetching
C-Hin-plane bending
Pressure (kbar)
Figure 4.5 Wavenumber vs. pressure plots for seiected IR vibrational bands of
Form 1.
*re
4.6 Wavenmber vs. preaure plok for seleclrd n< vibrational ban& of
Form 1.
O
1O
20
30
40
50
Pmssure (bar)
Figure 4.7 Wavenumber vs. pressure plots for selected IR vibrational bands of
Form 1.
The vc.~,vc+ and v w stretching regions were not easily recorded in the IR
with tbe DAC, and their pressure dependence values were not determined due to the
complexity of the progesterone structure. Thus, regions below 1100 cm-' are only
presented in this study. Al1 the vibrational modes analyzed exhibited a continuous
change in wavenumber over the pressure range studied. The C-H out-of-plane
bending modes are positioned between 1000-800 cm" (Figure 4.8) [Il].
Al1 bands
exhibited typical shifts to higher energy with an increase in pressure. The bands at
921 and 870 cm" have the greatest pressure dependences in the low-pressure phase
while the 921 cm-' band is the most sensitive in the high-pressure phase. The major
peak observed is that characteristic of Form 1 situated at 870 cm-L,which bas a
pressure dependence of 0.56 cm-' kbar-'. Bending modes are generaily expected to
have pressure shifts of the order of 0.1-0.3 cm-'kbar" 1131. It is noticed in Figure 4.8
that the 870 cm" band quickiy approaches the 893 cm-' band with increasing
pressure. The 870 cm-' band is the most pressure sensitive and intense band in the
spectra The region between 1100 and 1000 c d , Figure 4.9, aiso demonstrates
typical shifts to higher frequencies with increasing pressure. At ambient pressure, the
C-C-C bending mode at 687 cm", Figure 4.10, has a pressure dependence of 0.24
cm-' kbar-' in the low-pressure phase. while in the high-pressure phase, it is 0.22 cm-'
kbar-'. The second C-C-C bending mode, at 710 cm-', has pressure dependences of
0.34 and 0.25 cm-' kbafl, for the low- and high-pressure phases, respectively. The
bands in Figure 4.10, at 778 and 746 cm" are assigned to ring deformation modes
[I 11. Both bands demonstrate typical frequency shifts with increasing pressure. The
appearance of two new peaks, at 1012 and 992 cm-', may give hirther indication of a
pressure-induced structural change.
1000
980
960
940
920
900
880
860
840
Wavenumber (cm-')
-
Figure 4.8 Mrareù high-pressure spectra of progesterone Form 1 in the 1000800 cm-' region at (A)0.4, (B)6.6, (C)16.6, (ID) 27.0, (E)36.8, (F) 48.7 kbar.
820
1060
1040
W avenumber (cm')
Figure 4.9 Infmed high-pressure spectra of progesterone - Form 1 in 11001000 cm-' region at (A)0.4, (B) 6.6, (C)16.6, (Dl 27.0, (E)36.8, O 48.7 kbar.
-
Figure 4.10 Infrared high-pressure spectra of progesterone Form 1in the 8006ûû cm-' region at (A) 0.4, (B)6.6, (C) 16.6, @) 27.0, (E)36.8, (F) 48.7 kbar.
Raman
The Fï-Raman high-pressure study is exclusive to the region between 18001500 cm-'. The remainder of the spectra was tao weak to analyze as the signal-to-
noise ratio aHected the intensities of the majority of the peaks when using the
diamond-anvil cell. This spectral region is characteristic of v-
and v-
modes and the data complement the hi@-pressure IR study.
stretching
The proposed
vibrational assignments and the wavenumber us. pressure plots for the Raman studies
of Form 1 are shown in Table 4.2 and Figure 4.11, respectively.
A distinct
discontinuity occurs between 23 and 29 kbar.
Table 4.2 Raman modes and their pressure dependences for progesterone
Form 1.
Wavenumber Low -pressure Phase Wavenumber
(cm- 1)
civ/cip (cm-' kbaf')
(cm- i)
1616.8
0.33
1627.5
1664.2
-0.02
1665.0
High-pressure Phase
dv/dp (cm-' kbar- )
'
0.35
0.03
-
Assignments
VG-C
VC=O
Figure 4.11 Wavenumber vs. pressure plots for selected Raman vibrational
bands of Form 1.
1720
1700
1680
1660
1640
1620
1 600
Wavenumber (cm")
-
Figure 4.12 Raman hi@-pressure spectra of progesterone Form 1in the 18001500 cm-' region at (A)O, (B) 11.0, (C)173,@) 23.1, (E)29.4, (F)34.5, (6)
44.7
kbar.
1580
The two intense bands appear at 1664 and 1616 cm-', and are amibuted to
C=O and C=C stretching modes, respectively. Although, it appears that there is littie
change in the spectra with incmasing pressure, Figure 4.12, subtle changes in band
shape and relative intensities are, in fact, occurring. The 1616 cm-'band has a
pressure dependence of 0.33 cm-' kbar-' in the low-pressure phase, while in the highpressure phase the value is 0.35 cm-' kbaf
'. These are typical values for stretching
modes where values generally range between 0.3-1 cm-' kbar-' [13]. The pressure
dependences for the 1664 cm-'band are -0.02 cm-' kbar" and 0.03 cm-' kbar-' for the
low- and hi&-pressure phase, respectively. The values are near zero for both phases
and suggest that the applied pressure does not really influence these vibrations, thus
indicating that the CIO bonds are not truly afTected by pressure. These bands
complement the infrared high-pressure data where the vc- and v~
stretching modes
were unable to be monitored. The Raman high-pressure data give further insight into
the pressure-induced structural transition.
4.3.2 IR and Raman Pressure Studies of Form II
IR
The vibrational assignments and pressure dependences for the observed
infrared peaks of Form II are presented in Table 4.3.
Discontinuities in the
wavenumber vs. pressure plots, Figures 4.13 and 4.14, were found for a number of the
modes examined over a pressure range from 14-26 kbar.
These discontinuities
provide evidence for a pressure-induced structural change. The appearance of a new
peak at pressures above 14 kbar affords further evidence of a structural change. The
spectra in both phases are quite similar and the changes in the pressure dependences
are gradual, occurring over a 14-26 kbar range. Similar to Form 1, this transition is
most likely to be second-order with the structure of both phases being very similar.
Table 4 3 Infrared modes and their pressure dependences for progesterone
-
Form II.
Wavenumber Low-pressure Phase Wavenumber
(cm-')
dv/dp (cm-'
kbar-')
(cm" )
685.9
0.27
695.4
High-pressure Phase
dv/dp (cm-'kbar-')
Assignmen ts [ 1 1]
0.47
C-C-Cbending
-
Ring deformation
-
-
1.17
0.34
0.33
-
----
0.55
C-Hout-of-plane
0.37
0.36
0.44
0.59
Ring stretching
0.32
C-H in-plane bending
bending
Figure 4.13 Wavenumber us. pressure plots for selected IR vibrationai bands of
Form II.
Figure 4.14 Wavenumber vs. pressure plots for selected IR vibrationai bands of
Form LI.
As mentioned above, the vc.~, v m , v ~ stretching modes were not easily
detected in the IR when using the DAC, and their pressure dependences values were
not measured due to the complexity of the progesterone structure. Thus, regions
below 1100 cm-' are presented in this study. Al1 the vibrational modes analyzed
exhibited a continuous change in frequency over the pressure range studied. The C-H
out-of-plane bending modes appear between 1150-800 cm-', Figure 4.15 and 4.1 6.
Al1 exhibit typical shifts to higher energies with an increase in pressure. The bands at
950 and 913 cm-' have the greatest pressure dependences in the low-pressure phase,
while the 1026 and 913 cm*' band are the most sensitive in the high-pressure phase.
The major peak observed is at 862 cm-', characteristic of Form II, and has a pressure
dependence of 0.15 cm-' kbaf' in the low-pressure phase, whereas it has a value of
0.34 cm-' kbaf' in the high-pressure phase. As mentioned earlier, bending modes are
generally expected to have a pressure shift of the order of 0.1-0.3 cm" kbar-' [13].
The 862 cm-' band is the most intense band in the spectra, although it loses intensity
with increasing pressure. A small shoulder at approximately 875 cm'' appears in the
high-pressure phase with a pressure dependence of 0.33 cm-'kbar-'. The C-C-C
bending mode, found at 685 cm-', has a pressure dependence of 0.27 cm-'kbar-' in the
low-pressure phase, while in the high-pressure phase, it is 0.47 cm-' kbar-'. The band
observed at 777 cm-'in Figure 4.15 is assigned as a ring deformation mode, which
displays typical frequency shifts with increasing pressure. Four peaks disappear in
the high-pressure phase, originally found at 709,745, 1066, and 1080 cm-'in the lowpressure phase. The first two bands become too weak in intensity to follow at high
pressures due to poor signal-to-noise ratios, while the last two disappear completely.
These observations, together with the presence of a new peak at approximately 875
cm-',provide further evidence of a structural change with the application of pressure.
1000
950
900
850
800
750
700
Wavenumber (cm")
-
Figure 4.15 Infrared high-pressure spectra of progesterone Form II in the
lOûû-675 cm-'region at (A) 0.3, (B)3.4, (C)14.1, (D) 26.3, (E) 32.3, (F) 40.7 kbar.
1150
1100
1050
1000
950
900
Wavenumber (cm-' )
-
Figure 4.16 Infrared high-pressure spectra of progesterone Form I in the
1150-880 cm-'region at (A) 0.3, (B)3.4, (C)14.1, (D) 26m3, (E)323,(F) 40.7 k b a ~
Raman
The Fï-Raman high-pressure study is, again, exclusive to the region between
1800-1500 c d due to the weak intensity of the remainder of peaks. This region is
characteristic of vcd and v~
stretching modes. The table of assignments and the
wavenumber vs. pressure plots for the Raman studies of Form II are shown in Table
4.4 and Figure 4.17, respectively. A distinct discontinuity occurs between 18 and 22
kbar.
Table 4.4 Raman d e s and their pressure dependences for progesterone
Form II.
Wavenumber
(cm‘' )
-
Low-pressure Phase
dv/& (cm-'
kbai')
-
Wavenumber High-pressure Phase
(cm-')
dv/dp (cm-'kbafl)
1609.1
0.12
-
Assignments
Pies sure (kbar)
Figure 4.17 Wavenumber us. pressure plots for selected Raman vibrational
bands of Form II,
1720
1700
1680
1660
1620
1640
1600
W avenumber (cm")
-
Figure 4.18 Raman high-pressure specba of progesterone Fonn II in the 18001500 cm-' region at (A) O, (B)15.1, (C) 185,@) 26.0, (E) 28.9, (F) 34.1 kbar.
1580
The two most intense bands are at 1667 and 1616 cm-'. Figure 4.18. They are
assigned to C=O and C=C stretching modes, respectively. Another vc=o mode at
1706 cm-' was monitored but exhibited little change in the spectra with increasing
pressure. subtle changes in band shape and relative intensity do occur. The 1616 cm-'
band has a pressure dependence of 0.29 cm-' k b i d in the low-pressure phase while in
the high-pressure phase a value of 0.16 cm-' kbar-' is obtained. These values are a
little lower than normal, 0.3-1 cm-' kbaf' [13]. The pressure dependences for the
1667 cm-' band are 0.06 cm-' kbaf' and -0.05cm-' kbaf' for the low- and highpressure phase, respectively. As mentioned above, for Form 1, these values are near
zero for both phases and suggest that pressure does not influence these vibrations,
thus indicating that the C=O bonds are not particularly affected by pressure. It should
be rnentioned, however, that in this case there is a possibility of coupling (Fermi
resonance) between the two C=O vibrations thereby minimizing the movement of the
two bands. These bands complement the high-pressure IR data, as the vc=o and vc=c
stretching modes were unable to be monitored. The appearance of a new band at
1609 cm-' in the high-pressure phase is of particular interest. It is cenainly indicative
of a structural remangement,
4.4 Conclusions
Progesterone exists in two polymorphic forms; however, Form LI generally
occurs in mixtures with Form 1. Thus, Form II is less thermodynamically stable than
is Form 1 and is often found to convert to Form 1 within a 36-hour period. This
observation is quite remarkabie. It was hoped that the high-pressure work reported
here would
provide more information.
However. no clear and distinct
interconversion was observed. The crystals needed for the high-pressure studies were
easily accessible through prelirninary examination using the microscope and the FT-
IR instrument, which made it easy to collect pressure data for the correct forrn.
The Raman and IR pressure data, for Form 1, display a distinct break in the
slopes of the wavenumber vs. pressure plots between 16 and 29 kbar and is indicative
of a pressure-induced structurai transition. The Raman and IR pressure spectra are
very similar for both the low- and high-pressure phases suggesting that the two
phases are also quite similar. From the wavenumber vs. pressure plots, the phase
change is relatively slow and certain bands show a curved response to pressure.
The results for Form II were interesting, especially with the appearance of a
new peak in the high-pressure phase in the Raman spectra together with a shoulder in
the IR next to the characteristic band at 862 cm-'.
These observations suggest a
structural remangement and demonstrate that Form II is thermodynamicatly
sensitive. Conversion to Form 1 with pressure was difficult to deduce since the highpressure data collected did not clearly demonstrate spectra illustrative of Forni 1.
In conclusion, a pressure-induced structural transition occurs for both forms.
A11 the vibrational bands in the IR and Raman spectra increase in energy with
increasing pressure. Form II demonstrates a different son of structural transition than
that for Form 1. From the high-pressure studies, we can conclude that Fonn II is less
thermodynamically stable.
4.5 References
T. M. Brody, J. Larner, K. P. Minneman and H. C. Neu, in Human
Phamcology, Molecuiar to Clinical, (2d ed.), Mosby-Year Bwk, Inc.,
1994.
R.Duclos, J. M. Saiter, J. Grenet and A. M. Orecchioni, J. Thermal. Anal., 37
(1991) 1869-1875.
M. Muramatsu, M. Iwahashi and U.Takeuchi, J. Phann. Sci., 68 (1979) 175(a) R. Cameroni, G. Gamberini, M. T. Bernabei and M. Facchini,Il F a m c o ,
Ed. Pr., 28 (1973) 621-635. (b) R. Cameroni, G. Gamberini, M. T. Bemabei
and M. Facchini, Il F a m c o , Ed. Pr., 28 (1973) 636-641. (c) R.Carneroni,
G. Gamberini, M. T. Bernabei and M. Facchini, II Fannaco, Ed. Pr., 29
(1974) 184-191.
R.J. Mesley and C. A. Johnson, J. Phann. Phannacol., 17 (1965) 329-340.
R. J. Mesley, Spectrochim. Acta, 22 (1966) 889-9 17.
H. Campsteyn, L. Dupont and 0. Dideberg, Acta Cryst., 828 (1972) 30323042.
H. Campsteyn, L. Dupont and 0. Didieberg, Cryst. Struct. Comm., 1 (1972)
2 19-222.
E. Foresti Serantoni, A. Krajewski, R. Mongiorgi, L. Riva di Sanseverino and
R. Carneroni, Cryst. Struct. Comm., 4 (1975) 189-192.
R.S. Payne, R. J. Roberts, R. C. Rowe and R. Docherty, In?.J. Pharm., 177
(1999) 23 1-245.
S. Narayana Kalkura and S. Devanaraynan, J. Mater. Sci. Le#.. 7 (1988) 827829.
J. Parsons and W. T. Beher, Anal. Chem., 27 (1955) 514-5 17.
W. F.Sherman and G. R. Wilkinson, in Advances in Infrared and Raman
Spectoscopy, Vol. 6, (R. J. H. Clark and R. E. Hester, eds.), Heyden and Son,
London, 1980.
Chapter 5
High-Pressure Study of Spironolactone
and Polymorphism
5.1 Introduction
Spironolactone, Figure 5.1, is a synthetic steroid that functions as a diuretic.
Diuretics are dmgs that increase the excretion of water and electrolytes by increasing
the rate of urine flow [Il. The primary effect is to increase solute excretion, which
consists mainly of sodium salts. A h a d l expansion of volume of extracellular fluid
(ECF)is characteristic of diseases such as congestive heart failure, cirrhosis of liver,
and nephrosis.
The classic use of diuretics is to effect a reduction in ECF by
enhancing the excretion of salts (NaCl)and water [l]. Diuretics inhibit the tubular
absorption of sodium ions.
Figure 5.1 Chemical structure of spironolactone
Spironolactone is an analog of aidosterone and is a potassium-sparing agonist.
The site of action is at the cortical collecting tubule cl]. Spironolactone and its
metabolite, canrenone, attach to aldosterone receptors in the kidney and elsewhere,
and act as cornpetitive inhibitors of the endogenous hormone, thus resulting in a
longer duration of action [l]. Spironolactone is poorly soluble in aqueous fluids. Its
bioavailabitlity of an oral dose is approximately 90%. and is rapidly metabolized in
the liver. The major metabolite, canrenone, is responsible for 80% of the potassium-
sparing effect. The onset of action is extremely slow, with a peak response generally
1-2 days after the first dose and an elimination half-life of 2-3 days [l]. The dnig acts
as an androgen antagonist by binding to the androgen receptor, which in m m blocks
androgen activity.
5.2 Spironolactone and Polymorphism
In 1983, El-Dash et al. studied the phenornenon of polymorphism of
spironolactone and reported the preparaîion of different polymorphs by crystallization
fiom acetonitrile, ethanol, chloroform, and ethyl acetate [2]. They found that the
different forms varied in their rate of dissolution in water:rnethanol mixtures.
Moreover, they noted that the IR spectra, using KBr pellets, were not useful in
distinguishing arnong the forms and differential thermal analysis study proved the
absence of any solvates.
Salole and Al-Sarraj later showed, by using various
crystallization techniques, the preparation of three polymorphs and five solvates
which they were able to differentiate and CO-identifyby
IR spectroscopy, more
specifically with Nujol mulls, and by thermogravimetric and differentiai thermal
analysis [3,4]. However, they did not report the degree of solvation of their solvates,
nor did they index the X-ray powder diffraction patterns to permit cornparison and
identification of such forms prepared by others. Recently, Agafonov et al. have
characterized two polymorphs and five solvates using X-ray crystailographic
techniques [5]. The five solvates formed by crystallization in absolute methanol,
acetonitrile, absolute ethanol, ethyl acetate, and benzene were funher characterized
by Beckstead er al. using FI'-Raman and FT-IRdiffuse reflectance spectroscopy [6].
They found al1 forms to be monosolvated, except that with acetonitrile, which gave a
2:l complex as determined by elemental rnicroanalysis and crystallographic data
[6,7l.
As mentioned already, the latest evidence reveals that spironolactone occurs
in two polymorphic and five solvate forms [SI. Form 1 is prepared by cooling a
supersaturated solution of spironolactone in acetone [5,8]. The crystal data indicate
parameters of a = 10.584, b = 11.005, and c = 18.996
A,
with Z = 4. The single
crystals are orthorhombic with the space group P212121. The A-ring conformation is
near that of a sofa, where the B- and C-rings are chair shaped. The D-ring is a
distorted 13P envelope and the E-ring is aimost a plane [SI. The molecules in the
crystal structure are held together by Van der Waals forces and Form 1 is the more
stable of the two forms.
Form II, described by Dupont et al., is prepared by
recrystallizing spironolactone from acetone and allowing the solvent to evaporate
spontaneously at room temperature. Form II demonstrates crystal parameters of a =
9.979, b = 35.576, c = 6.225 A and Z 4,
with the space group P2,2,2, [9,10]. The Aring is highly distorted because of the
double bond and the ketone group. The B-
and C-rings are chair shaped. The D-ring is a distorted haif-chair and the E-ring is a
half chair. Again, the molecules are held together in the crystalline state by Van der
Waals forces [9].
The main difference between the two fonns lies in the
conformations of the A, D, and E rings.
The two polymorphic forms of spironolactone are known to undergo structural
rearrangement upon heating 16-11- 131.
Due to such facile rearrangement,
spironolactone c m show variable and incornplete behavior following oral
administration because of poor water solubility and dissolution rate. It is for this
particular reason that we felt a high-pressure infrared and Raman investigation rnight
help to further understand the inter- and intramolecular properties of each form.
5.3 Resdts and Discussion
The preparation rnethods were not difficult procedures; however Form II was
at times difficult to obtain and crystds of Form 1 were usually colIected. Cornpiete
FT-IR spectra of Forms 1 and II can be found in Chapter 3. Expanded FT-IR spectra
of both forms, recorded in the 1100-600 cm-' and 3600-2600 cm-' regions, are shown
in Figures 5.2. and 5.3, respectively. Complete IR and Raman spectra of the two
polymorphs, characterized by Agafonov et ai., are not found in the literature. Neville
et al. have examined thirteen bulk pharrnaceutical preparations of spironolactone,
some polyrnorphs and others solvates, by FT-Raman and FT-IR d i f i s e reflectance
spectroscopy (DRIFTS)[ 121. These authors observed four di fferent representative
polymorphic sarnples of spironolactone by monitoring the overtone region 136003200cm-'), of the fundamental stretching frequencies for the C=O and C=C bonds. by
the DRIFTS technique. The FT-IR spectra recorded for this study, identified a few
characteristic bands for each form in the 1 0 - 6 0 0 cm-' region. The major peaks of
interest for Form 1 are the 101 1, 864 and 8 10 cm-', whereas for Form II the bands are
found at 1019, 870 and 814 cm-'. al1 characteristic of C-H out-of-plane bending
modes, Figure 5.2. The overtone region (3600-3200 cm-') of the fundamental C=O
and C=C stretching modes demonstrate differences in the spectra, Figure 5.3, as do
the C-Hstretches, which further illustrate the differences in crystallographic packing.
-Form II
--.--.
Fonn I
900
800
W avenumber (cm")
Figure 5.2 Expanded FT-IR spectra of spironolactone Forms 1 and II (1100-600
cm-').
- - . -Form
-- 1
Form II
3200
3000
Wavenumber (cm-')
Figure 5.3 Expanded FT-IR spectra of spironolactone Forms 1 and II (37002600 cm").
The FT-Raman s p w a of both forms illustrate signif~cantdifferences in the
lattice region (30-20 cm-') observed in Figure 5.4, which indicates that the two
forms are slightly different in their crystal paclcing arrangement. The other region
that R-Raman helps in charactenzing these polymorphs is the 1800-1500 cm-'
region, Figure 5.5. Both forms show subtle differences at approximately 1765 cm",
charactenstic of the vc=o mode for the y-lactone keto group. Subtle differences are
also present at approximately 1690 cm-', assigned to the v c . =mode for the thioacetyl
keto group [12]. Further differences for each form are illustrated at approximately
1667 cm-'. Form 1has an intense Raman line situated at 1669 cm-', presumably due to
enhanced polarization of the keto goup through conjugation with the adjacent double
bond [12], and is situated at 1663 cm-' for Form II, Figure 5.5. This polarizability of
the double bond (C=O) must contribute to the greater Raman intensity of the steroidal
C=C stretching mode at 1616 cm-', where it is situated at 1619 cm" for Form II.
Again, this leads to further justification of the different crystai packing. A third
distinction between the two forms in the FT-Raman spectra is observed in the region
between 660-630cm-', Figure 5.6. The weak Raman lines at 640 and 636 cm" for
Form 1 and II, respectively, are assigned to the vcs mode remote from the carbonyl
group [12). The intense Raman lines found at 659 and 656 cm-' for Form 1 and II,
respectively, are assigned to the v s c d mode, which is attnbuted to the S-C bond
conjugated to the thioacetyl carbonyl group [12]. Again, the intense Raman lines are
due to enhanced polarization of the keto group.
Further characterization of the foms was achieved by X-ray powder
diffraction pattern (Chapter 3). The patterns illustrated different peaks for each form
and most of the peaks matched the values found by Agafonov et al [5]. Single
crystais were also exarnined in order to select and isolate the correct crystals for the
high-pressure spectroscopie studies. The values matched the crystal parameters
found for each form reported in the literature. Form 1crystal data are a = 10.584, b =
11.OS, and c = 18.996 A [5,8]. Form II crystal data are a = 9.979, b = 35.576, and c
= 6.225
A
[5,9,10]. The differential scanning calorimetry data did not demonstrate
the melting point differences, and Form 1 and II both melted at the same temperature.
Solid-state NMR spectra were not conducted due to an insufficient amount of Form II
which was difficult to obtain.
-----
200
150
100
Wavenumber (cm4)
Figure 5.4 Expanded FT-Raman spectra of spironolactone Forms 1 and 11
(Lattice region 300-20 cm").
*
Fum l
Forrn II
1700
1650
Wavenurnber (cm")
Figure 5.5 Expanded FI'-Raman spectra of spironolactone Forms 1 and 11
(18W-15ûû cm-').
Form I
*-...Fom II
600
500
W avenum ber (cm-')
Figure 5.6 Expanded FT-Raman spectra of spironolactone Forms I and II ( 8 0 400 cm-').
5.3.1 IR and Raman high-pressure studies of Form 1
IR
The vibrationai assignments and pressure dependences for the observed IR
peaks of Form 1 are presented in Table 5.1. Discontinuities in the wavenumber vs.
pressure plots, Figures 5.7 to 5.9, are observed for a number of the modes exarnined
over a pressure range from 13-23 kbar. Attempts were made, without success, to
obtain further points within this pressure range.
These discontinuities provide
evidence for a pressure-induced structural change. The appearance of new peaks at
pressures above 13 kbar affords further evidence of a structural change. The spectra
in both phases are quite similar and the changes in the pressure dependences are
gradual, occumng over a 13-23 kbar range.
It is significant of a second-order
transition with the structures of both phases closely resembling each other.
Table 5.1 Infrared modes and their pressure dependences for spironolactone
Form 1.
Wavenumber Low-pressure Phase Wavenumber
(cm")
dv/dp (cm-'kbai')
(cm- )
769.5
762.9
0.26
'
High-pressure Phase
dvldp (cm" kbar-')
0.27
-
Assignments
Ring deformation
C-H out-of-p lane
bending
Ring streiching
-
C-H in-plane
bending
1239.8
125 1.7
1366.0
1286.1
1304.2
1316.6
133 1.2
1350.2
1377.S
0.20
1242.7
1255.9
1272.6
1289.7
1308.3
1319.8
1334.3
0.1 1
-0.01
0.1
0.20
O. 10
1354.8
1380.1
0.37
O. 12
O. 10
0.16
0.25
0.18
0.17
0.1
0.20
0.30
0.36
O. 12
-----C H 3 deformaiion
modes
Pressure (kbar)
Figure 5.7 Wavenumber vs. pressure plots for selected IR vibrational bands of
Form 1.
Figure 5.8 Wavenumber vs. pressum plots for sekW IR vibrational bands of
Form 1.
w
u
-
=
-
a
Figure 5.9 Wavenumber vs. pressure plots for selected IR vibrational bands of
Form 1.
The v c - ~v~
,
and v-
stretching regions were not easily recorded with the
DAC, and their pressure dependences were not detemiined because of the complexity
of the spironolactone structure. Thus, regions below 1400 cm-'are only presented in
this study. AU the vibrational modes analyzed exhibited a continuous change in
wavenumber over the pressure range studied. At ambient pressure, the bands at 770
and 762 cm-' are assigned to ring deformation modes. These bands, Figure 5.10,
demonstrate typical frequency shifis with increasing pressure.
One of the
characteristic bands of Form 1, situated at 810 cm-', is assiped C-H out-of-plane
bending mode. This band has a pressure dependence of 0.27 cm-' kbaf' in the lowpressure phase, while it has a pressure dependence of 0.60 cm-'kbar-l in the highpressure phase. The band loses intensity and broadens with increasing pressure,
making it difficult to observe in the hi&-pressure phase due to the fringing effect.
However, the band is sensitive in the high-pressure phase suggestive of a pressureinduced structural rearrangement.
A second
C-H out-of-plane bending mode,
characteristic of Form 1, appears at 834 cm-'. The band demonstrates a typical shifi in
energy with an increase in pressure. The pressure dependence value is 0.22 cm-' kbaf
' in the low-pressure phase, whereas it is 0.13 cm" kbaf' in the high-pressure phase.
The C-H out-of-plane bending mode at 848 cm-' has a pressure dependence of 0.01
cm" kbar-' in the low-pressure phase, thus it is not particularly sensitive to pressure.
The 834 cm-' band moves quickly into the 848 cm-' band and they blend into one
another with the pressure dependence value being relatively smaH in the highpressure phase, indicative of a pressure-induced structural remangement. The third
characteristic band of Form 1, situated at 864 cm-', has a nez-zero pressure
dependence value of 0.09 cm-' kbaf' in the Low-pressure phase and has a pressure
dependence value of 0.37 cm-' kbar-' in the high-pressure phase. While it is not
particularly sensitive in the low-pressure phase, a shoulder develops around 880 cm-'
in the high-pressure phase. There is a band at 91 1 cm-', characteristic of C-Hout-of-
plane bending, which develops a shoulder in the high-pressure phase as well. The
918 cm-'band is the most sensitive with a pressure dependence of 0.69 cm-'kbai' in
the low-pressure phase. The bands situated at 981, 969 and 945 cm" demonstrate
typical frequency shifts with increasing pressure. The ring stretching modes, Figure
5.1 1, at 1060 and 1040 cm-' aiso demonstrate typical shifts to higher energies with an
increase in pressure. The C-H in-plane bending modes at 1197 and 1188 cm", Figure
5.12, are not particularly affected with pressure and demonstrate near-zero pressure
dependence values in the low-pressure phase.
The C-H in-plane bending mode,
situated at 1266 cm", is sharp and intense and demonstrates a typical shift to higher
energy with increasing pressure. The methyl deformation modes, situated between
1380-1300 cm-', aiso demonstrate typical fkequency shifts with an increase in
pressure.
Overall, the disappearance of two peaks, 1 188 and 848 cm-', and the
appearance of four peaks, 1163,913,880 and 813 cm-',provide a strong indication of
a pressure-induced structural phase transition.
900
880
860
840
820
800
780
760
Wavenu mber (cm-')
-
Figure 5.10 Infrared high-pressure spectra of spironolactone Form I in the
900-70 cm-' region at (A) 0.4, (B)7.5, (C) 13.1, (D) 23.2, (E)29.2, O 38.6, (G)
47.5 kbar.
740
1060
1060
1O40
1 OeO
1000
980
960
940
QO
Wavenunbr (cm-')
-
Figure 5.11 Infrared high-pressure spectra of spirowlactone Form 1 in the
1100-900 cm" region at (A) 0.4, (B)7.5, (C)13.1, 0 )23.2, (E) 29.2, (F) 38.6, (G)
47.5 kbar.
1380
1350
1320
1290
1260
1230
1200
1170
1140
W avenurnber (c m-')
-
Figure 5.12 Infrared high-pressure spectra of spironolactone Form 1 in the
1400-1100 cm" region at (A) 0.4, (B)7.5, (C)13.1, (D) 23.2, (E) 29.2, O 38.6, (G)
47.5 kbar.
1110
Ranian
The FT-Raman high-pressure study is exclusive to the regions between 18001500 cm-', characteristic of v c a and v-
stretching modes, and 680-600 cm-',
characteristic of the vc-s stretching mode of the thioacetyl rnoiety. The FT-Raman
high-pressure data complement the high-pressure IR study. The proposed vibrational
assignments and the wavenumber us. pressure plots for the Raman studies of Fom 1
are shown in Table 5.2 and Figure 5.13, respectively. A distinct discontinuity occurs
between 16-2 1 kbar.
Table 5.2 Raman modes and their pressure dependences for spironolactoneForm 1.
Wavenumber Low-pressure Phase Wavenumber
(cm-')
dv/dp (cm-' kbad)
(cm-')
1691.81
0.35
1699.45
High-pressure Phase
dvfdp (cm-'
kbar")
Assignments
0.5 1
v c a thioacetyl
Pressure ( b a r )
Figure 5.13 Wavenumber vs. pressure plots for selected Raman vibrational
bands of Form 1.
1720
1700
1680
1660
1640
1620
1600
W avenumber (cm-')
Figure 5.14 Raman high-pressure spectra of spironolactone - Form 1 in the
1800-1500 cm-' region at (A) O, (B)11.0, (O 15.8,8,) 21.2, (E) 28.7, (F') 35.7, (G)
38.2 kbar.
1580
680
660
640
Wavmumber (cm" )
Figure 5.15 Raman high-pressure spectra of spironolactone - Form 1 in the
1800-1500 cm" region at (A) O, (B) 11.0, (C) 15.8,8,) 21.2, (E)2û.7, O 35.7, (G)
38.2 kbar.
The two intense bands in Figure 5.14 are found at 1669 and 16 16 cm*' and are
assigned to C=O and C S stretching modes, respectively. The 1669 cm-' band is
characteristic of the keto group (C3)adjacent to the C=C double bond present in the
skeleton of the steroid. The pressure dependence is -0.23 cm-' kbar-' in the lowpressure phase while in the high-pressure phase the value is -0.07 cm-' kbar-'. The
pressure dependence values are negative and are clearly seen in the spectra, Figure
5.14.
The C=C suetching band at 1616 cm", demonstrates a pressure dependence of
0.31 cm" kbar-' and 0.30 cm-' kbafl in the low- and high-pressure phases,
respectively, typical values for stretching modes [14]. The pressure dependences for
the 169 1 cm" band, assigned to v ~ +thioacetyl mode, are 0.35 cm-' kbaf' for the
low-pressure phase, whereas it has a value of 0.51 cm-' kbar-' in the high-pressure
phase. In Figure 5.15, the two interesting bands are situated at 658 and 640 cm-',
which are assigned to the vs-ca and vcs modes, the latter remote from the carbonyl
group. The band at 658 cm-'has pressure dependences of 0.47 and 0.57 cm-' kbar" in
the low- and high-pressure phases, respectively. The pressure dependences for the
640 cm'' band are 0.65 cm-'kbar-' in the low-pressure phase while the value i s 0.54
cm-' kbar" in the high-pressure phase. Both bands show typical shifts to higher
energies with increasing pressure and their pressure dependences are aiso typicai of
stretching modes [14]. Again, the FT-Raman high-pressure study is indicative of a
pressure-induced structural rearrangement.
5.3.2
IR and Raman hi@-pressure studies of Form II
IR
The vibrational assignments and pressure dependences for the observed
infrared peaks of Form II are presented in Table 5.3.
Discontinuities in the
wavenumber vs. pressure plots, Figures 5.16 and 5.17, occur for a number of the
modes exarnined over a pressure range from 12-17 kbar. These discontinuities
provide evidence for a pressure-induced structural change. The appearance of a new
peak at pressures above 12 kbar affords M e r evidence of a structural change. There
are only subtle differences seen in the low- and high-pressure phases of the spectra.
This let us conclude that the transition is second-order with both structures closely
resernbling each other.
Table 53 Infrared modes and tbeir pressure dependences for spironolacîone Form II.
Wavenumber Low-pressure Phase Wavenumber High-pressure Phase
(cm-'
)
dvldp (cm-'
kbaf')
(cm")
dv/dp (cm-'
kbar-')
769.6
0.2
765-7
0.44
Assignments
Ring deformation
C-Hout-of-plane
bending
918.1
948.2
974.7
1019.3
1042.7
1059.7
1112.2
1141.5
1176.5
1209.9
0.46
0.05
0.23
0.69
0.4 1
0.5 1
0.73
0.7 1
-0.03
0.3
925.4
949.8
976.4
1031.1
1048.5
1066.3
1121.7
1150.5
1177.1
1212.3
0.25
0.2
0.4
0.37
0.24
0.27
0.2
0.1 1
0.39
0.1
-
-
1238.4
1273.0
1295.3
1310.3
1330.9
1354.0
0.22
0.3
O. 19
O. 17
0.24
0.2
0.48
-0.80
0.02
0.1
1378.9
0.28
1227.6
1243.4
1276.8
1297-5
1319.9
1333.2
1356.3
1382.5
0.6
0.17
0.2
0.22
Ring stretching
C-H in-plane
bending
CH3 deformation
Ples sure (bar)
Figure 516 Wavenumber us. pressure plots for seleîtd IR vibrational bands of
Form II.
B
œ
O
1O
20
m
w
w
30
m
i
40
r
50
6Q
Pies sure (kbar)
Figure 5.17 Wavenumber vs. pressure plots for selected IR vibrational bands of
Form II.
As mentioned above, the
VCH,
VC=O, VC=C
stretching modes were not easily
detected when using the DAC, and their pressure dependences were not monitored.
Thus, regions below 1400 cm-' are presented in this study. Al1 the vibrational modes
analyzed exhibited a continuous change in frequency over the pressure range studied,
Figures 5.18 and 5.19. The C-H out-of-plane bending modes appear between 1020800 cm-', Figure 5-18. Al1 exhibit typical shifts to higher energies with an increase in
pressure. The bands found at 782 and 765 cm-' are assigned as ring deformation
modes and demonstrate typical frequency shifts with increasing pressure. The first
major peak of interest, characteristic of Form II, is situated at 814 cm".
This band is
assigned as a C-H out-of-plane bending mode and has a pressure dependence of 0.33
cm-' kbar-' in the low-pressure phase, whereas it has a value of 0.45 cm-' kbar-' in the
high-pressure phase. Bending modes are generally expected to have a pressure shift
of the order of 0.1-0.3 cm-' kbaf' [14]. The second characteristic band of Form II, at
850 cm", has a pressure dependence value of 0.22 cm-' kbar-' in the low-pressure
phase, however it is difficult to monitor in the high-pressure phase due to the fringing
effect. The third charactenstic band, situated at 870 cm", is sharp and intense. It has
a pressure dependence value of 0.46 cm-' kbar-' in both phases, demonstrating typicai
shift to higher energy with an increase in pressure. The most sensitive band is found
at 1019 cm", charactenstic C-H out-of-plane bending, with a pressure dependence of
0.69 cm-' kbaf' in the low-pressure phase.
The appearance of a shoulder at
approximately 1227 cm", Figure 5.19, is broad and indicative of a pressure-induced
structural change. Again, the disappearance of a peak in the high-pressure phase, at
834 cm-',further demonstrates a pressure-induced structural change.
-
1100
1050
1O00
950
900
850
800
Wavenumber (cm-')
-
Figure 5.18 Infrared high-pressure spectra of spimnolactone Form Iï in the
1100-750 cm-' region at (A) 1.4, (B)5.1, (C) 12.0, (D) 17.4, (E)21.3, (F) 32.9, (G)
40.6 kbar.
750
1350
1300
1250
1200
1150
1 100
Wavenumber (cm")
-
Figure 5.19 Infrared high-pressure spectra of spironolactone Form II in the
1400-1100cm" region nt (A)1.4, (B)5.1, (C)12.0, (ID) 17.4, (E)21.3, (F)32.9, (G)
40.6 kbar.
Raman
The FT-Raman high-pressure study was also restricted to the regions between
1800-1500 cm-', characteristic of v m and vc= stretching modes, and 700-620 cm-',
characteristic of the vc-s stretching mode of the thioacetyl moiety. The FI'-Raman
high-pressure data complement the high-pressure IR results.
The proposed
vibrational assignments and the wavenumber us. pressure plots for the Raman studies
of Form 1 are shown in Table 5.4 and Figure 5.20, respectively.
A distinct
discontinuity occurs between 13- 16 kbar.
Table 5.4 Raman modes and their pressure dependences for spironolactoneForm II.
Wavenumber Low -pressure Phase Wavenumber
dv/dp (cm-'kbaf')
(cm-')
(cm-')
660.16
656.89
0.18
1619.75
1663.83
0.66
-0.1
1630.72
1663.1
High-pressure Phase
dv/dp (cm-' kbar-')
Assignments
0.4 1
0.26
O. 1
Vs-C=O
VC--C
VC=O
Figure 5.20 Wavenumber vs. pressure plots for selected Raman vibrational
bands of Form II.
Wavenumber (cm")
Figure 5.21 Raman high-pressure spectra of spuonolactone - Form II in the
180-150cmœ1
region at (A)O, (B)9.3, (C)12.7, @) 18.0, (E)23.1, (F) 27.5, (G)
37.7 kbar.
Figure 5.22 Raman high-pressure spectra of spùono~actone- Form II in the
7 0 - 6 2 û cm-' region at (A) O, (B)9.3, (C)12.7, (D) 18.0, (E)23.1, (F) 27.5, (G)
37.7 kbar.
The two intense bands, found at 1664 and 1620 cm-', are assigned to C=O and
C=C stretching modes, respectively. Although it appears that there is little change in
the specua with increasing pressure, subtle changes in band shape and relative
intensities are in fact occurring, Figure 5.21. The 1620 cm" band has a pressure
dependence of 0.66 cm-' kbar" in the low-pressure phase while in the hi@-pressure
phase a value of 0.26 cm-' kbar-' is obtained. It c m be seen that the band is sensitive
in the low-pressure phase as the pressure dependence value is rather high, indicative
of a pressure-induced structural change. The 1664 cm" band, vc*
mode of C3
position, has a near zero pressure dependence value of -0.05 cm-' kba? in the lowpressure phase while a value of 0.13 cm-' kbafl is obtained in the high-pressure
phase. As mentioned before, near zero values suggest that the pressure applied does
not particularly influence these vibrations, thus indicating that the C=O stretching
mode is not tnily affected by pressure. The 656 cm-' band, VS-C=O mode, has pressure
dependence values of 0.18 and 0.41 cm" kbar-l for the low- and high-pressure phases,
respectively, and are typical values for stretching modes, Figure 5.22. The bands at
1700 and 636 cm-' were difficult to observe due to poor signal-to-noise ratios.
Overall, the FT-Raman high-pressure data of Form II demonstrates the occurrence of
a pressure-induced structural change.
5.4 Conclusions
The two 'new' polymorphs of spironolactone have only recently been
discovered [ 5 ] . Studies have been perfomed earlier on spironolactone but the
polymorphs tumed out to be solvates rather than real polymorphs [2-41. Agafovov et
al. discovered two polymorphic forms and showed Form 1 to be thermodynarnically
more stable than is Form II [SI. However, the vibrational characterization of both
polymorphs has not been published.
Therefore, our study has focused on the
characterization of each form using IR and Raman spectroscopy, followed by highpressure vibrational studies of both forms. Crystals of Form II were difficult to obtain
and not al1 of the characterization methods were performed due to the insufficient
amount of Form II available, thus M e r work is nquired and these results must be
considered preliminary.
Sirnilar to the high-pressure spectroscopie results of progesterone, no clear
and distinct interconversion was observed. Al1 the vibrational bands in the IR and
Raman spectra increase in energy with incteasing pressure. The Raman and IR
pressure data display a distinct break in the slopes of the wavenumber vs. pressure
plots between 12-17 kbar for Form II and 16-21 kbar for Form I. The data are
indicative of a pressure-induced structural change for both forms. However Form II,
the least stable, demonstrates a change earlier on than does Form 1. In conclusion,
Form 1 demonsuates a different sort of pressure-induced structural transition than
does Form II.
5.5 References
T.M. Brody, J. Lamer, K. P. Mimeman and H.C . Neu, in Hulluut
Phannacology, Mdecular to CZinical (2d ed.), Mosby-Year Book,Inc., 1994.
S. S. El-dalsh, A. A. El-Sayed, A. A. Badawi, F. 1. Khattab and A. Fouli, Drug
Dev.Ind. Pham., 9 (1983) 877-894.
E. G. Salole and F. A. Al-Sarraj, Drug Dev. Ind Pham., 11 (1985) 855-864.
E. G. Saiole and F. A. Al-Sarraj, Drug Dev. Ind. Pham., 11 ( 1985) 206 12070.
V. Agafonov, B. Legendre, N. Roder, D. Wouessidjewe and J.-M. Cense, J.
Pham. Sei., 80 (1991) 181-185.
H. D. Beckstead, G. A. Neville and H. F. Shurvell, J. Anal. Chem., 345 (1993)
727-732.
V. Agafonov, B. Legendre and N. Rodier, Acta Cryst., C47 (199 1) 365-369.
V. Agafonov,B. Legendre and N. Rodier, Acta Cryst., C45 (1989) 1661- 1663.
O. Dideberg and L. Dupont, Acta
Cryst., B28 (1972) 3014-3022.
O. Dideberg and L. Dupont, Cryst. Struct. Comm., 1 (1972) 99-102.
R. J. Mesley and C. A. Johnson, J. Pham. P h m a c o l . , 17 (1965) 329-340.
G. A. Neville, H. D. Beckstead and H. F. Shurveil, J. P h a m . Sci., 81 (1992)
1141-1 146.
J. L. Sutter and P. K. Lau, in K. Fiorey (ed) Analytical profiles of drug
substances, vol. 4. Academic Press, London, 1975,43 1-451.
W. F.Sherman and G. R. Wilkinson, in Advances in Infrared and Raman
Spectoscopy,Vol. 6, (R. J. H. Clark and R. E. Hester, eds.), Heyden and Son,
London, 1980.
Chapter 6
Conclusions and Future Suggestions
It was thought that through high-pressure vibrationai
studies, the
interconversion between polymorphs would have been easity detected and funher
understanding of the inter- and intramolecular bonding and the different crystai
packing environrnents would be possible. Pmgesterone and spironolactone are two
steroids that exhibit polymorphism with no hydrogen bonding involved [l]. Thus, the
main fom of association is presumably dipolar interactions between the two carbonyl
groups through Van der Waals interactions. The high-pressure spectroscopic results
for the polymorphs of both progesterone and spironolactone demonstrated pressureinduced structural changes with increasing pressure. The studies did reveal certain
polymorphs to be more pressure sensitive than others. Form II of both progesterone
and spironolactone is more thermodynamically sensitive than Form I to the
application of pressure.
The two polymorphs of progesterone were not difficult to prepare and crystals
of both forms were readily obtained. The charactenzation process demonstrated
differences between each form. However, the solid-state "C NMR spectroscopy
results did not demonstrate any particular differences between forms. The Fï-Raman
spectra demonstrated subtle differences between each f o m and supported the
different crystal packing arrangements, indicated by the lattice region. Form II was
shown to be thermodynamically more sensitive than Form 1 through the high-pressure
spectroscopic work. It was also the more dificult to prepare of the two forms.
The polymorphs of spironolactone were quite difficult to prepare. Form II (by
crystallization from acetone at room temperature) was difficult to obtain and crystals
of Form 1 were often collected. Enough crystals of Form II were prepared, however,
to perform the high-pressure spectroscopic work. The characterization of Form II
was not completed and the characterization by solid-state "C NMR spectroscopy was
not performed due to an insuficient amount of crystais. However, the high-pressure
.
vibrational spectroscopic studies led to the conclusion that high pressures do not
facilitate interconversion between forms. We were hypothesizing that F o m II, being
the least thermodynamically stable of two, would convert to Form 1 under pressure.
Therefore, the polymorphs of spironolactone are relatively stable and mechanical
manipulation does not affect the forms. Also, studies concerning the dissolution of
spironolactone in
fluids have reponed that the use of carriers, such as
polyoxypropylene-polyoxyethylene
copolymers
"polaxamer",
increases
the
dissolution rate of spironlactone [2]. They observed no formation of polymorphs
during the method of preparation through differential thermograrns and IR
spectroscopy.
This demonstrates the relative stability of the polymorphs of
spironolactone.
OveralI. the high-pressure spectroscopie results for the polymorphs of
progesterone and spironolactone indicate that the mechanical manipulation used in
tableting behavior may not necessarily affect the dosage forms of these particular
steroids. Progesterone is an important steroid for the preparation of contraceptive
pills and spironolactone is a well-known diuretic where polymorphism could play an
important factor in their preparation methods.
Suggestions for future work include completion of the characterization of the
polymorphs of spironolactone, especially Form II. As mentioned in Chapter 2, near-
IR spectroscopy is a new and useful tool in the identification of polymorphs. Further
characterization of progesterone and spironolactone with nez-IR spectroscopy would
give additional information on the various polymorphs. Some preliminary reverse
experiments on the polymorphs of progesterone and spironolactone were undertaken,
but those proved inconclusive. This is an area for possible future examination. The
next step would be to examine other steroids and their polymorphs to further
investigate the effects of mechanical manipulations, such as ,g-inding,
in the
preparation of dosage forms and the bioavailabilty in the pharmaceutical industry.
Steroids and other important dnigs that exhibit polymorphism due to various degrees
of hydrogen bonding would be interesting to investigate [1.3].
Such studies would
further help understand the fundamentais of the crystal arrangement and how high
pressures could affect these environments.
Another suggestion would be to
investigate these polymorphs and others at ultra high-pressures (- 650 kbar) to
observe their properties at higher pressures. We now have a ce11 capable of achieving
such pressures.
6.1 References
1.
R. J. Mesley, Spectrochim. Acta, 22 (1966) 889-917.
7
A. S. Geneidi and H. Harnacher, P h a m . Ind., 42 ( 1980) 3 15-3 19.
3.
R. J. iMesley and C. A. Johnson, J. Pham. Pharmacol.. 17 ( 1965) 329-340.
W.