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International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
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Electronic states of sterically hindered meso-phenyl-substituted
Pd-octaethylporphyrins
Aleksander Gorski
1
, Michał Kijak
1
, Valery Knyukshto
2
, Eduard Zenkevich
2
,
Alexander Starukhin
2
, Jędrzej Solarski
1
, and Patrycja Kowalska
1
1
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw,
Poland, e-mail: agorski@ichf.edu.pl
2
B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Independence Av. 68,
220072, Minsk, Belarus
The tetrapyrrolic compounds like porphyrin and its derivatives are relevant in biological
processes including electron transfer, oxidation catalysis and photosynthesis. The spatial organization
of tetrapyrrole complexes, in which chromophore molecules assume non-planar conformations, is a
key to subtle control of excited-state characteristics as well as spectral and photophysical properties of
natural tetrapyrrolic pigments. Therefore, it is important to get information concerning the influence
of increasing number of alkyl substituents on excited state geometry of tetrapyrrolic
metallocomplexes.
A
B
Fig. 1. Chemical structures of two from four meso-phenyl-substituted derivatives of Pd-porphyrin: Pd-5-phenyl-
2,3,7,8,12,13,17,18-octaethylporphyrin (left) and Pd-5,10,15,20-tetraphenyl-2,3,7,8,12,13,17,18-
octaethylporphyrin (right) and its MCD (top) and absorption (bottom) spectra.
Magnetic circular dichroism (MCD) is one of the powerful tools of investigation of excited states
properties of organic molecules. The shape and sign of MCD spectra of tetrapyrrolic compounds
such as porphyrin or its isomers can be easily predicted theoretically even without engaging the time-
consuming quantum-chemical calculations [1]. In this work, MCD studies were performed for a series
of Pd-octaethylporphyrin derivatives (Pd-OEP) with different number of bulky meso-phenyl
substituents (Fig. 1). In results it was possible to separate and locate electronic transitions in the
regions of Q and Soret bands for four different derivatives. Analysis of the experimental spectra
together with results of quantum chemical calculations shows that, in the case of meso-phenyl
substituted Pd-OEPs, significant folding of the porphyrinoid macrocycle with increasing of number of
alkyl substituents induces a high changes in MCD signals (Faraday A terms) providing the direct
spectroscopic evidence of ligand nonplanarity.
Keywords: magnetic circular dichroism; excited states properties; Pd-octaethylporphyrin derivatives
Acknowledgment
This work was supported by the European Union’s Horizon 2020 research and innovation programme under grant
agreement No 645628 and Foundation for Fundamental Research of Republic of Belarus (project Ph16R-084).
References
[1] J. Waluk, J. Michl, J. Org. Chem. 56 (1991) 2729.
C
2
C
2
C
2
C
2
H
C
2
H
H
5
H
5
C
2
N
N
N
N
P
C
2
H
C
2
H
C
2
H
C
2
H
C
2
H
H
5
H
5
C
2
N
N
N
N
P
XIV
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International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
235
T2: P–20
Spectroscopic characterization of interactions of mouse thymidylate
synthase with N
4
OH-dCMP
Małgorzata Prokopowicz
1,2
, and Wojciech Rode
3
1
Interdisciplinary Doctoral Studies in Natural Sciences and Mathematics, College of Inter-Faculty
Individual Studies in Mathematics and Natural Sciences , 2C Banacha St., 02-097 Warszawa,
e-mail: malgorzata.prokopowicz@student.uw.edu.pl
2
Biophysics Division, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, 93
Ż
wirki i Wigury St., 02-089 Warszawa
3
Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur St, 02-093
Warszawa, Poland
Thymidylate synthase (TS) is an essential enzyme in the de novo biosynthesis of
thymidylate (dTMP), one of DNA building nucleotides. The enzyme, recognized a target in
antiviral, anticancer, antifungal and antiparasite therapy [1–3], catalyzes the reductive
methylation of C(5) in 2'-deoxyuridine-5'-monophosphate (dUMP), via simultaneous N5,10-
methyltetrahydrofolate (mTHF) methylene group transfer and reduction, leading to formation of
dTMP and 7,8-dihydrofolate [4].
Between numerous dUMP analogues, known to inhibit TS-catalyzed reaction, N4OH-dCMP
(NOH) appears unique by using an unusual, and still not fully understood mechanism of enzyme
inhibition. It provokes an abortive reaction, leading to a covalent complex formations with TS.
Moreover, in contrast to well understood inhibition by FdUMP, the enzyme interaction with
NOH appears to result in a transfer of the aforementioned methylene group to a so far unknown
destination and reduction by tetrahydrofolate of NOH pyrimidine ring [5, 6]. Thus the inhibitor
appears to uncouple TS-catalyzed reactions of methylene transfer and reduction.
Results concerning NOH complex with recombinant mouse TS (mTS), obtained using UV
absorption, fluorescence spectroscopy and time correlated single photon counting (TCSPC) are
presented. The presence of tryptophan (Trp) and tyrosine (Tyr) (aromatic amino acids) in the
structure of mTS allows to employ spectroscopy that provide with important information
concerning structural rearrangements [7, 8]. Preliminary results indicate essential changes in the
fluorescence lifetime and fluorescence spectra of mTS interacting with NOH, suggesting
important spatial changes that need to be clarified.
Keywords: thymidylate synthase; N4-hydroxy- 2'-deoxycytidine-5'-monophosphate (NOH); UV spectroscopy;
time correlated singe photon counting; fluorescence; tryptophan; fluorescence lifetime
Acknowledgment
The study was done in the Biophysics Division, Institute of Experimental Physics, Faculty of Physics,
University of Warsaw. Supported by the National Science Center grant no. 2016/21/B/NZ1/00288.
References
[1] W.H. Wolberg, Cancer Research 29 (1969) 2137.
[2] P. Singh, A. Bhardwaj, Mini Reviews in Medicinal Chemistry 8 (2008) 388.
[3] W. Rode, A. Leś, Acta Biochimica Polonica 43 (1996) 133.
[4] N. Kanaan, S. Martí, V. Moliner, A. Kohen, Biochemistry 46 (2007) 3704.
[5] A. Dowierciał, A. Jarmuła, P. Wilk, W. Rypniewski, B. Kierdaszuk, W. Rode, Pteridines 24 (2013)
93.
[6] W. Rode, Z. Zieliński, J.M. Dzik, T. Kulikowski, M. Bretner, B. Kierdaszuk, J. Cieśla, D. Shugar,
Biochemistry 29 (1990) 10835.
[7] J.R. Lakowicz, Springer (2006) ISBN-10: 0-387-31278-1. Principles of Fluorescence Spectroscopy
3rd Eddition.
[8] J.B.A. Ross, W.R. Laws, K.W. Rousslang, H.R. Wyssbrod, [in:] J.R. Lakowicz (Ed.), Biochemical
Applications
. Plenum Press 3 (1992) 1.
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