1Institute of Physics, Charles University, Ke
Karlovu 5, CZ-121 16 Prague 2, Czech Republic
2B. I. Stepanov Institute of Physics, National
Academy of Sciences of Belarus, 70 F. Skaryna Ave., Minsk 220072, Belarus
3L.P.B.C., Université P. & M. Curie,
mailbox 138, 4 Place Jussieu, F-75252 Paris 5, France
Complexes
of water-soluble cationic (metallo)porphyrins with nucleic acids (DNA and RNA)
are widely investigated owning to their possible use in photodynamic therapy of
cancer. Since absorption, CD, luminescence and vibrational spectra of the
(metallo)porphyrins are quite sensitive to their binding modes and local structure
of the binding sites, some (metallo)porphyrins can be applied as spectroscopic
probes for relaying information about local base-pair composition/sequence,
structure, conformation and dynamics of nucleic acids [1]. Among various metalloporphyrins studied in
complexes with nucleic acids, the copper(II) derivatives attracted a particular
interest owing to their ability to form reversibly - in copper-centred (d,d)
photoexcited electronic states – transient axially coordinated complexes,
so-called exciplexes, with convenient electron-donating groups from their close
proximity [1-5]. Due to competitive relaxation pathways asserting in
non-coordinating microenvironments, and due to very fast kinetics of exciplex
formation (t < 1 ps), any relocation of the photoexcited
porphyrin within its binding site is improbable [3]. Consequently,
electron-donating groups participating as axial ligands in the exciplex
formation have to be present at the proper position before the porphyrin
photoexcitation. Thus, the yield of exciplex formation provides specific
information about microenvironment of the porphyrin as shaped by its binding to
nucleic acid in its ground electronic state. Exciplex formation of the copper
porphyrins can be conveniently monitored by resonance Raman spectroscopy due to
well-established exciplex Raman markers [2].
Complexes
of water-soluble cationic copper(II) 5,10,15,20-tetrakis[4-(N-methylpyridyl)] porphyrin (CuP) with DNA-model single- and
double-stranded oligo/polynucleotides consisting of various
nucleobases have been studied to reveal correlation between nucleobase
composition/sequence, nucleic acid structure and/or conformation, preferred
binding mode and structural features of the complex, and ability to form
exciplex. Our results clearly demonstrate that exocyclic C=O groups as well as
endocyclic nitrogens of all nucleobases with exception of guanine residues can
serve as electron-density donors [2-5], nevertheless, only if the CuP is fixed
to nucleic acid otherwise then by intercalation. In such a way, CuP exciplex
formation can be considered as a special marker for non-intercalative binding
mode.
Financial supports awarded by the Ministry of Education (Kontakt ME557, VZ 113200001), and by the Grant Agency of the Czech Republic (203/04/0688) are gratefully acknowledged.
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98 (1998) 1201–1219.
[2] P. Mojzes, L. Chinsky, P.-Y. Turpin, J.
Phys. Chem. 97 (1993)
4841–4847.
[3] S. G.
Kruglik, P. Mojzes, Y. Mizutani, T. Kitagawa, P.-Y. Turpin, J. Phys. Chem. B 105 (2001) 5018–5031.
[4] P. Mojzes, P.
Praus, V. Baumruk, P.-Y. Turpin, P. Matousek, Biopolymers (Biospectroscopy)
67 (2002) 278–281.
[5] P. Mojzes, S.
G. Kruglik, V. Baumruk, P.-Y. Turpin, J. Phys. Chem. B 107 (2003)
7532–7535.