XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
80
T2: O–12
Comparative study of binding interactions between porphyrin
systems and aromatic compounds of biological importance
by multiple spectroscopic techniques
Magdalena Makarska-Białokoz
1
1
Faculty of Chemistry, Maria Curie-Sklodowska University, M. Curie-Sklodowska Sq. 2, 20-031
Lublin, Poland, e-mail: makarska@hektor.umcs.lublin.pl
The specific spectroscopic and redox properties of porphyrin systems, especially their high ability
to emit fluorescence, predestine this class of compounds to fulfill the role of sensors during
interacting with different biologically active substances. Monitoring of binding interactions in the
systems porphyrin-biologically active compound is a key question not only in the field of
physiological functions of life organisms, but also in environmental protection, notably in the light of
the rapidly growing drug consumption and concurrently the production of drug effluents.
Not always beneficial action of the compounds mentioned above on natural porphyrin systems
(e.g. chlorophyll), induces to further studies, with commercially available porphyrins as the model
systems. Therefore the binding process between several water-soluble porphyrins (4,4’,4’’,4’’’-
(21H,23H-porphine-5,10,15,20-tetrayl)tetrakis-(benzoic
acid),
5,10,15,20-tetrakis
(4-
sulfonatophenyl)-21H,23H-porphine, 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21H, 23H-
porphine tetra-p-tosylate, 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine tetra-p-tosylate,
the Cu(II) complexes of H
2
TTMePP and H
2
TMePyP), as well as chlorophyll a, and a series of
biologically active compounds, such as caffeine [1], guanine [2,3], theophylline, theobromine,
xanthine [4], uric acid and its sodium salt [5], has been studied in different aqueous solutions
analysing their absorption and steady-state fluorescence spectra. The fluorescence lifetimes and the
quantum yields of the porphyrins examined were also established. The comparison of the binding (K
a
)
and fluorescence quenching (K
SV
) constants for all the systems studied was presented. The magnitude
of K
a
and K
SV
values for particular quenchers decreases in a series: uric acid>guanine>caffeine>
theophylline>theobromine>xanthine. Within methylxanthines the manner and magnitude of
quenching depend on the number and position of –CH
3
groups of particular xanthine compounds.
The porphyrin fluorescence quenching can be explain by the process of the photoinduced
intermolecular electron transfer from aromatic compound to the center of the porphyrin molecule,
playing the role of the binding site. Calculated parameters suggest that in all the systems studied there
are obviously characters of static quenching, as a consequence of the π-π-stacked non-covalent and
non-fluorescent complexes formation between porphyrins and interacting compounds, accompanied
simultaneously by the additional specific binding interactions, proceeding in all probability in the
aftermath of the existence of different forms of the fluorophore (porphyrin), which do not have an
identical accessibility to the quencher. The formation of different porphyrin forms depends on the
conditions of the microenvironment in the particular systems.
Presented results can be valuable for designing of new fluorescent porphyrin chemosensors or
monitoring of drug traces in aqueous solutions. The obtained outcomes have as well the toxicological
and medical importance, providing insight into the interactions of the water-soluble porphyrin with
biologically active substances.
Keywords: Porphyrins; Methylxanthines; Guanine; Uric acid
Acknowledgment
The research was carried out with the equipment purchased thanks to the financial support of the European
Regional Development Fund in the framework of the Operational Program Development of Eastern Poland 2007-
2013 (Contract No. POPW 01.03.00-06-017/09).
References
[1] M. Makarska-Białokoz, J. Fluoresc. 22 (2012) 1521.
[2] M. Makarska-Białokoz, Cent. Eur. J. Chem. 11 (2013) 1360.
[3] M. Makarska-Białokoz, J. Lumin. 147 (2014) 27.
[4] M. Makarska-Białokoz, J. Mol. Struct. 1081 (2015) 224.
[5] M. Makarska-Białokoz, P. Borowski, J. Lumin. 160 (2015) 110.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
81
T2: O–13
The C-O vibrational frequency as a measure of the protein electric field
in carbonmonoxy heme proteins
Aleksander Gorski
1
, and Solomon S. Stavrov
2
1
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw,
Poland
2
Sackler Institute of Molecular Medicine, Department of Human Molecular Genetics and
Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel,
e-mail: stavrov@post.tau.ac.il
In carbonmonoxy heme proteins (HPs) protein electric field (PEF) was shown to strongly
affect vibrational frequency (ν
CO
) of carbon monoxide (CO) molecule coordinated by the heme
iron of HPs [1, 2].
The dependence of ν
CO
on the protein dynamics is studied using ultrafast two-dimensional
infrared vibrational echo spectroscopy. To interpret the experimental results it was assumed that
ν
CO
linearly depends on the electric field on CO (Stark effect). However, this approach failed to
describe the protein dynamics of carbonmonoxy myoglobin.
On the other hand, earlier the effect of different charges located at different positions with
respect to heme-porphin-imidazole-CO complex on ν
CO
was computed [1, 2]. The results of
these studies show that in case of charges located in non-axial positions the ν
CO
change cannot
be described in terms of the Stark-effect. ν
CO
linearly depends on the electric filed on CO in the
case of axial charges, however the coefficients of the linear dependence for distal and proximal
charges are very different. Consequently the Stark-effect approach to the problem is limited to
the case of changing or moving axial charges located on one side of the porphyrin ring.
Fig. 1. Active center of carbonmonoxy myoglobin [3].
Such a dependence is studied by DFT computing of the effect of different sub-structures of
the distal histidine observed in X-ray studies (Fig. 1) on ν
CO
. It is shown that ν
CO
is very
sensitive to the distal environment, and, in particular, the observed different X-ray sub-structures
correspond to the A
0
, A
1
, and A
3
conformational substates
Keywords: protein dynamics, myoglobin, quantum chemistry
Acknowledgment
This work was supported European Union’s Horizon 2020 research and innovation programme under grant
agreement No 645628
References
[1] B. Kushkuley, S.S. Stavrov, Biophys. J. 70 (1996) 1214.
[2] B. Kushkuley, S.S. Stavrov, Biophys. J. 72 (1997) 899.
[3] J. Vojtechovsky, K. Chu, J. Berendzen, R.M. Sweet, I. Schlichting, Biophys. J. 77 (1999) 2153.
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