Molecular and Quantum Acoustics vol. 28 (2007)
95
ACOUSTIC AND THERMODYNAMIC INVESTIGATIONS OF
AQUEOUS SOLUTIONS OF SOME CARBOHYDRATES
M. GEPERT and A. MOSKALUK
University of Silesia, Institute of Chemistry, Szkolna 9, 40-006 Katowice, POLAND
Acoustic and thermodynamic properties of aqueous solutions of three
carbohydrates: D-glucose, D-fructose and D-saccharose are discussed. Dglucose and D-fructose have different molecular structures; thus they interact in
different ways with the surrounding water molecules. Based on our experimental
results, we found that the thermodynamic properties of the aqueous solutions of
the two monosaccharides are similar, except the limiting apparent molar
compressibilities. As anticipated, the thermodynamic properties of an aqueous
solution of D-saccharose are mostly the resultant of the properties of both
monosaccharides. Any modifications of these properties are probably caused by
the specific linkage between two monosaccharide rings.
1. INTRODUCTION
Carbohydrates are the most exceptional class of organic compounds in biological
systems. They are the constituents of all living organisms, as well as very important
ingredients of food. Water is the most natural solvent for simpler saccharides; so many
researchers very often investigate the aqueous solutions of carbohydrates. The spectroscopic
investigations indicated that the orientation of saccharides in solutions reflect the “structure”
of solvent. Thus, the discussion in this paper is based on the properties of the solutions
obtained by other than the spectroscopic techniques. Specifically, the acoustic and
thermodynamic properties of the aqueous solutions of D-glucose, D-fructose and Dsaccharose
are
compared.
D-glucose
and
D-fructose
are
the
most
common
monocarbohydrates with the same chemical formula but different three-dimensional
structures. Such difference may cause the dissimilarity of some simple physico-chemical
properties of the solutions of these compounds. The compared properties are: the speed of
sound, adiabatic compressibility, apparent molar volume and apparent molar adiabatic
compressibility.
96
Gepert M., Moskaluk A.
2. EXPERIMENTAL
In all measurements, the sugars commonly available in pharmaceutical and food
industry were used. D-fructose (Biofan 99.9%, Langsteiner 99.8%), D-glucose (Microfarm,
Lefarm FP V) and D-saccharose (Świdnica S.A. 99.8%) were used without additional
purification. All aqueous solutions were prepared about twenty-four hours before the
measurements and were kept in sealed flasks. The concentrations of the solutions used in the
measurements were base on the necessity in data processing and were limited by the solubility
of the particular sugar (e.g. max. molar fraction for fructose solution was 0.1).
The measurements of the speed of sound (c) (f = 4 MHz) were carried out by the sing
around method with a precision of 5 × 10-3 % and accuracy about one order worse. All details
concerning the method used were described in literature [1-5].
Density measurements (ρ) were made with an Anton Paar DMA 5000 vibrating tube
densimeter. The accuracy of density measurements was assessed at 2⋅10-5 g⋅cm-3.
The speeds of sound and the densities were measured at 293.15 K, 298.15 K and 303.15 K
3. CALCULATIONS AND DISCUSSION
On the basis of densities and speeds of sound we calculated the adiabatic
compressibilities using the well-known formula: κ S = 1 ρc 2 . Speeds of sound and adiabatic
compressibilities at 298.15 K are drawn in the Figure 1. As can be seen in Fig. 1 the speeds of
sound and compressibilities of monosaccharides solutions are similar. The highest speeds and
the lowest compressibilities are observed for D-saccharose solutions.
The apparent molar volumes and apparent adiabatic molar compressibilities were
(ρ
− ρ)
M
0
calculated using the following equations: Vφ = mρρ + ρ2 and Κ S ,φ =
0
( ρ 0κ S − ρκ S ,0 ) + κ S M 2
mρρ 0
ρ
,
where M2 denotes molar mass of the sugar, m is the molality and subscript “0” refers to the
solvent. The apparent molar volumes and compressibilities of each sugar in infinite dilution
were calculated according Redlich-Meyer equation: X φ = X φ∞ + Am1 2 + Bm , where Xφ denotes
volume or compressibility; A and B are the empirical constants. The apparent molar volumes
and compressibilities of sugars are presented in the Figure 2. In the Figure 3 there are drawn
the limiting apparent molar volumes and compressibilities for all saccharides in aqueous
solutions at 293.15 K, 298.15 K and 303.15 K.
The comparison the limiting apparent volumes and limiting apparent compressibilities
obtained during this work with some literature ones is presented in the Table 1.
Molecular and Quantum Acoustics vol. 28 (2007)
97
1800
5.0
1750
4.5
1650
1600
fructose soln
glucose soln
saccharose soln
1550
1500
1450
0.00
0.02
0.04
0.06
x2
0.08
0.10
κ S 10 10 /(m 2/N)
c /(m/s)
1700
fructose soln
glucose soln
saccharose soln
4.0
3.5
3.0
2.5
2.0
0.00
0.02
0.04
0.06
0.08
0.10
x2
Fig. 1. Speeds of sound (left) and adiabatic compressibilities (right) of aqueous solutions of
fructose, glucose and saccharose (298.15 K).
Fig. 2. Apparent molar volumes (left) and apparent adiabatic molar compressibilities (right) of
fructose, glucose and saccharose in aqueous solutions (298.15 K).
98
Gepert M., Moskaluk A.
Tab. 1. Comparison of the limiting apparent molar volumes and limiting molar
compressibilities of sugars at 298.15 K with the literature data
Sugar
D-fructose
Vφ∞
Quantity
10 /(m3 mol-1)
K S∞,φ 1014/(m5 N-1 mol-1)
This work
110.3 ± 0.1
-2.2 ± 0.1
Literature values
110.4a, b
-1.979a
D-glucose
Vφ∞ 106/(m3
111.3 ± 0.1
110.9c; 111.4a;
-1.8 ± 0.1
111.9d; 112.2b;
-2.013a; -1.93c; -1.6d
210.5 ± 0.1
210.2b; 211.32e;
-1.66 ± 0.05
211.8a
-2.853a; -1.856e
K S∞,φ
D-
6
mol-1)
1014/(m5 N-1 mol-1)
Vφ∞ 106/(m3
mol-1)
saccharose
K S∞,φ
e)
1014/(m5 N-1 mol-1)
a)
[7]; b) [8] c) [9] d) [10] [11]
From the inspection of the Figure 2 it can be said that the apparent molar volumes of Dfructose and D-glucose are very similar, the different and much higher are the apparent
volumes of D-saccharose. The apparent molar adiabatic compressibilites of all sugars are
negative and became similar at lower molarities. The negative Κ s,φ values may be interpreted
in terms of the specific interactions between the solute and solvent that lead to the diminishing
the compressibility the water near sugar compared to the pure water. This effect became
probably more prominent in the lowest concentration of sugars where the association process
between solute molecules is less effective.
The limiting apparent molar quantities ( Vφ∞ , K s∞,φ ) are often treated as a sum of the
intrinsic volume or intrinsic adiabatic compressibility of solute and the contributions taking
account all changes of volume and compressibility of solvent evoked by the solute presence in
solution. According to this assumption, it may be noticed that the influence of D-fructose and
D-glucose on the volume of surrounding water at all regarded temperatures is very similar.
Larger limiting apparent volumes of D-saccharose are obvious, because larger molecules may
cause higher changes of volumes than smaller monocarbohydrates.
The monosaccharides chosen for our investigations have the same number of the
hydroxyl groups in the molecule, thus any differences in the limiting adiabatic
compressibilities of these sugars may be interpreted in terms of different amount of α and/or
β forms of pyranose and furanose rings of D-fructose and D-glucose in aqueous solutions. It
is well known that the β anomers have the larger number of the hydroxyl groups of equatorial
position (i.e. groups paralleled to the sugar ring’s plane) than α ones. As the consequence, in
the β anomers two or more oxygen atoms in the hydroxyl groups achieve the comparable
distance with the characteristic for oxygen atoms in pure water what causes that the hydration
Molecular and Quantum Acoustics vol. 28 (2007)
99
process increases cooperatively [3-5]. Thus, it is not surprising that in aqueous solutions of D∞
fructose and D-glucose the β - anomers prevails. The K S ,φ values for D-fructose are lower
than those observed for D-glucose. Thus, it seems that the presence of the not only β pyranose but also the β - furanose rings in aqueous D-fructose solutions may cause larger
“stiffening” the water molecules around sugar than in D-glucose solutions where only β pyranose forms occurs. Finally, the highest, but still negative limiting apparent
compressibility of D-saccharose means that the large disaccharide molecules may modify the
structure of water significantly, yet the change is the weakest in regarded of the row of the
saccharides. The temperature dependences of the limiting apparent molar quantities are also
very interesting., because the limiting apparent molar volumes of all saccharides in aqueous
solutions change only slightly from 293.15 K to 303.15 K, whereas the limiting apparent
molar adiabatic compressibilities increase sharply with the temperature. It means that the
temperature increase causes the loosing of the water shell surrounding the sugar with retaining
almost the same distances between molecules. The temperature dependence of limiting
apparent molar quantities of D-saccharose in aqueous solution reveals that in spite of the
glucoside linkage between two monosaccharide rings that force them to achieve a specific
anomeric configuration (α for glucose and β for fructose) the influence this sugar on the
structure of water results from specific interactions water-sugar of both monosaccharides.
Fig. 3. Limiting apparent molar volumes (left) and adiabatic compressibilities (right) of
carbohydrates in aqueous solutions at 293.15 K, 298.15 K and 303.15 K.
4. CONCLUSIONS
The results of our investigation show that the properties of the aqueous solutions of Dfructose and D-glucose such as the speeds of sound, adiabatic compressibilities, as well as
apparent molar volumes are similar. However, the limiting apparent molar compressibilities
of monosaccharides in aqueous solutions are different; it may indicate that both sugars
100
Gepert M., Moskaluk A.
influence the structure of water in little different way. Eventually, the properties of aqueous
solutions of D-saccharose are generally the resultants of properties of aqueous solutions of
monosaccharides.
The temperature dependences of apparent molar quantities indicate that loosening of the
structure of water near the sugar molecules almost not cause the volume change for all
regarded saccharides in aqueous solutions.
REFERENCES
1. S. Ernst, et al., Acoustics Letters 15, 123-130 (1992) .
2. E. Zorebski, Molecular and Quantum Acoustics 24, 261-270 (2003).
3. E. Zorebski, M. Zorebski, S. Ernst, J. Phys. IV France 129, 79-82 (2005).
4. E. Zorebski, Molecular and Quantum Acoustics 26, 317-326 (2005).
5. E. Zorebski, Molecular and Quantum Acoustics 27, 327-336 (2006).
6. T.V. Chalikian, J. Phys. Chem. B 102, 6921-6926 (1998).
7. F. Franks ed., Water, A Comprehensive Treatise, vol. 2, Plenum Press–New York–
London 1973.
8. M.V. Kaulgud, S.S. Dhondge, Ind. J. Chem. 27A, 6-11 (1988).
9. F. Shahidi, P.G. Farell, J.T. Edward, J. Solution Chem. 5, 807-816 (1976).
10. F. Franks, J.R. Ravenhill, D.S. Reid, J. Solution Chem. 1, 3-16 (1971).
11. A. Lo Surdo, Ch. Shin, F.J. Millero, J. Chem. Eng. Data 23, 197-201 (1978).