Gabriela DYRDA*, Rudolf SŁOTA – Division of General Chemistry, Opole University, Opole,
Poland; Giuseppe MELE – Dipartimento di Ingegneria dell’Innovazione, Università del Salento,
Lecce, Italy
Please cite as: CHEMIK 2014, 68, 4, 396–401
Introduction
Porphyrins, naturally occuring macrocyclic compounds due to their
unique physicochemical properties are the area of extensive research.
Chemistry of porphyrin sensors and biosensors is currently one of the
most quickly developing research direction for porphyrins [1÷5].
Porphyrin structure is based on the molecular frame of porphin
(Fig.1.), which might be substituted in meso or β positions. In
metalloporphyrins, metal ions might have axial functional groups.
Experimental part
Used materials
5,10,15,20-tetrakis-[-4–2-(3-pentadecylphenoxy)-ethoxy]
phenylporphyrin, H2Pp-R4 , was synthesized according to the procedure
from the literature [16].
Benzene, dichloromethane and used electron acceptors:
BF3· Et2O, CF3COOH (TFA) and HCl, all analytically pure, were
ordered from Sigma Aldrich.
As carrier thin glass plate (0.15 mm) was used (typical microscope
slide, 20×20 mm).
Instruments and test methods
Fig. 1. Porphin molecule and the meso-substituted porphyrin
Metal-porphyrin complexes have intensive absorption band
(Soret band) in range 400–420 nm and two weaker Q bands in
range 450–700 nm, while for metal-free porphyrins four Q bands
are observed. These differences arise due to the different electron
distribution density for metalloporphyrins (MPp) and hydrogenated
porphyrin (H2Pp) [6].
The porphyrins can bind gases, the phenomenon which is used
in chemosensor systems that usually are based on thin porphyrin
films deposited on the surface of specific carrier. The carriers might
be polymers (PCS, PS), silane gel [5, 7÷9] or glass [10]. Porphyrin
sensors might be used for detection of amines [9,11÷12], HCl and
NO2 [12÷14]. The porphyrins that do not contain complexed metal,
i.e. H2Pp, while affected by electron acceptors, change their colour –
from initial purple to green due to the redistribution of electron density
in the chromophor system of the macroring [15]. This is a specific
quality of these substances and might be a justification to carry out
research on porphyrins applications in sensors.
Under this project, the glass plate was used as a carrier on
which thin porphyrin film was deposited. The porphyrin contained
four 3-pentadecyl-phenoxyethoxyphenyl groups in “meso” position
(H2Pp-R4). R functional group is presented in Diagram 1.
Preparation of chemosensor and its interaction with electron
acceptor
The thin layer of chemosensor was obtained by the immersion of
the glass plate (carrier) in dichloromethane solution of studied porphyrin
(c = 1×10–4 mol/dm3). After drying up its quality was evaluated based
on UV-VIS spectrum. The procedure was repeated several times, till
uniform layer of porphyrin was formed on the plate surface.
The liquid phase (benzene) tests were carried out by addition
to the system such amount of acceptor to observe total conversion
of dissolved porphyrin to green form. In turn, plates with deposited
porphyrin film were directly subjected to vapours of given
electron acceptor.
Spectroscopic measurements
Absorption spectra were measured in range 250–800 nm using
spectrophotometer JASCO V-670 (software Jasco Spectra Manager
V.2) for porphyrin solution in benzene, while spectra of thin films were
measured directly on the plate.
Results and discussion
Interactions of porphyrin chemosensor with acceptors
in liquid phase
Diagram 1
The article discusses results obtained during preliminary
research. Its main objective was to validate usefulness of used
porphyrin as a chemosensor and evaluation of its lifetime in the
environment of selected electron acceptors. The tests were carried
out in the system: porphyrin sensor-gas phase using HCl, CF3COOH
(TFA) and BF3. For comparison, similar tests were carried out for
the same porphyrin in benzene.
Corresponding author:
Ph.D. Gabriela DYRDA, e-mail: [email protected]
nr 4/2014 • tom 68
Fig. 2. Changes in the UV-VIS spectrum of H2Pp-R4 in benzene due
to the effect of HCl gas, (a) initial form; (b) green form; (c) after
saturation with N2 gas (24 h)
The changes observed in the UV-VIS spectrum are presented in
Figure 2. They were similar in nature, regardless of used electron
• 399
50 Years of Chemistry in Opole
Porphyrin chemosensor. Interaction of 2H-porphyrins
with selected electron acceptors
50 Years of Chemistry in Opole
acceptor. Initially purple porphyrin solution (Fig.2a) during reaction
with electron acceptor changed its colour to green (Fig.2b). In the
spectrum of the green form, single Q band has appeared with higher
intensity than for initial form. The observed changes are attributed
to the formation of protonated forms [15,17, 18] or adducts 1: 1,
or 1:2 [19, 20].
The reverse process is also possible, i.e. reversion from green
to purple form, if stream of gaseous nitrogen is passed through the
tested solution. For tests in benzene such process was observed
only for HCl. It was found that in this reaction approx. 30% of
porphyrin has degraded. While for the reaction of porphyrin with
TFA and BF3, the reversal to initial form was only possible after
addition of some quantity of triethylamine (TEA) to the solution
containing green form.
Interaction of porphyrin chemosensor with acceptors
in solid phase
Table 2
Degradation degree of the porphyrin due to interaction with the
electron acceptors
Acceptor
HCl
TFA
BF3
Degradation degree
3%
30 %
15 %
Summary
The carried out tests indicate that the studied porphyrin in form
of thin films effectively interacts with electron acceptors such as:
HCl, TFA, or BF3. It can be observed visually, but the system, while
affected by acceptor, changes its colour from purple to green and
this process is (at least partially) reversible. At this stage of research
it could not be established which factors have essential impact on
the observed porphyrin degradation. At the same the nature of
response of studied porphyrin to the presence of electron acceptor
shows features typical for chemosensors. Therefore this direction
of the research will be continued.
Literature
Fig. 3. The reaction of H2Pp-R4 with TFA
Absorption spectrum measured for thin film of studied
porphyrin is presented in Figure 3. (line a). It has characteristic
features for porphyrins without metal [6]. Under the influence of
acceptor, similarly to benzene, the conversion from initial purple
form to green one occurs (Fig.3, line b). In all studied cases the
nature of this transformation was similar as in the system with TFA.
The only differences were for position of individual bands in UV-VIS
spectrum (Tab.1).
Table 1
Position of absorption bands (λmax) in the UV-Vis spectrum of the
green porphyrin form depending on the electron acceptor used
Acceptor
HCl
TFA
BF3
λmax, nm
477 722
464 715
473 729
It was concluded that the reversion from green to purple form
is possible when the plate with adsorbed acceptor is placed under
the stream of gaseous nitrogen. The process takes a long time and
only for system with HCl it was possible to recover initial form
after 130 h of saturation with N2 gas. For other acceptors, TFA
and BF3 changes in UV-VIS spectrum in similar range were minor.
It proves that these acceptors are bonded more strongly to thin
chemosensor film.
Regardless of the type of used acceptor, the recovery of purple
initial form is possible by treating the plates with generated green
form of porphyrin with TEA vapors. In such case, the reversal to the
initial purple form was instantenous.
For each studied system partial degradation of porphyrin was
observed (Tab.2). The highest degree of degradation was observed for
system subjected to TFA (30%).
400 •
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nr 4/2014 • tom 68
Rudolf SŁOTA – Ph.D. (Eng.), Assoc Professor, is a graduate of the
Faculty Chemistry of the Wrocław University of Technology, he received
Ph.D. degree from the Faculty of Chemistry, Warsaw University of
Technology. After obtaining a doctorate he earned habilitation in the
field of chemical sciences from the Faculty of Chemistry, Wroclaw
University of Technology. Currently he serves as a Head of the Division
of General Chemistry of the University of Opole. Scientific interests:
physicochemistry of phtalocyanines and porphyrins, photochemistry,
photocatalysis, electron spectroscopy.
Professor Giuseppe MELE is a graduate in the field of chemistry of
* Gabriela DYRDA is a graduate of the Faculty of Mathematics, Physics
University of Bari, Italy, from which also received degree of the doctor
and Chemistry of the University of Opole, from which she also received
of chemical sciences. He works as Associate Professor at Dipartimento
title of the doctor of chemical sciences. She is a lecturer at the Division of
di Ingegneria dell’Innovazione, in Università del Salento in Lecce, Italy.
General Chemistry, University of Opole. Scientific interests: photochemical
Scientific interests: catalysis and photocatalysis, synthesis of organic
and biochemical activity of phtalocyanines and porphyrins, photocatalysis.
and metalorganic compounds, porphyrins and phtalocyanines in hybrid
e-mail: [email protected]; phone: +48 77 452 731
materials.
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nr 4/2014 • tom 68
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50 Years of Chemistry in Opole
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G.: Synthesis of novel lipophilic porphyrin-cardanol derivatives. Journal of
Porphyrins and Phthalocyanines 2004, 8, 1276–1284.
17. Weinkauf J. R., Cooper S.W., Schweiger A., Wamser C.C.: Substituent and Solvent
Effects on the Hyperporphyrin Spectra of Diprotonated Tetraphenylporphyrin.,
The Journal of Physics Chemistry A 2003, 107, 3486–3496.
18. Rudine A.B., Del Fatti B.D., Wamser C.C.: Spectroscopy of Protonated
Tetraphenylporphyrins with Amino/ Carbomethoxy Substituents:
Hyperporphyrin Effects and Evidence for a Monoprotonated Porphyrin. The
Journal of Organic Chemistry 2013, 78, 6040−6049.
19. Mohajer D., S. Zakavi, S. Rayati, M. Zahedi, N. Safari, H. Reza Khavasi,
S. Shahbazian: Unique 1 : 2 adduct formation of meso-tetraarylporphyrins
and meso-tetraalkylporphyrins with BF3: a spectroscopic and ab initio
study. New Journal of Chemistry 2004, 28, 1600–1607.
20. Molami H., Dehghani H.: Synthesis and characterization of new molecular
complexation between free base meso-tetraarylporphyrins and nitrosonium
ion as π-acceptor. Inorganica Chimica Acta 2012, 384, 133–136