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 . 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 . 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 .
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.
 D. R. McMillin, K. M. McNett, Chem. Rev. 98 (1998) 1201–1219.
 P. Mojzes, L. Chinsky, P.-Y. Turpin, J. Phys. Chem. 97 (1993) 4841–4847.
 S. G. Kruglik, P. Mojzes, Y. Mizutani, T. Kitagawa, P.-Y. Turpin, J. Phys. Chem. B 105 (2001) 5018–5031.
 P. Mojzes, P. Praus, V. Baumruk, P.-Y. Turpin, P. Matousek, Biopolymers (Biospectroscopy) 67 (2002) 278–281.
 P. Mojzes, S. G. Kruglik, V. Baumruk, P.-Y. Turpin, J. Phys. Chem. B 107 (2003) 7532–7535.