Resonance Raman and absorption characterization of cationic Co(II)-porphyrin in its complexes with nucleic acids: binding modes, nucleic base specificity and role of water in Co(II) oxidation processes

Abstract

A comparative study of Co(II) and Co(III) complexes of the water-soluble cationic tetrakis(N-methyl-4-pyridiniumyl)porphyrin [Co II -and Co III TMpyP(4)] with calf thymus DNA (CT DNA) and synthetic double-stranded (ds) and single-stranded (ss) polynucleotides, namely, poly(dA-dT) 2 , poly(dG-dC) 2 , [poly(dA)·poly(dT)], poly(A), poly(dT), poly(G) and poly(C) was carried out by resonance Raman (RR) as well as stationary absorption spectroscopy. It is shown that free Co II TMpyP(4) in aqueous solution is easily oxidized to Co III TMpyP(4) by dissolved molecular oxygen, but Co(II) to Co(III) oxidation ability fundamentally changes when Co II TMpyP(4) is bound to nucleic acids (NA). In double helical DNA and AT-containing polynucleotides, where the porphyrin is assumed to be outside bound mainly in the minor groove near AT sites, Co(II) is stable for weeks and even months. It is suggested that Co(II) axial ligation by immobilized water (i.e. water molecule that is hydrogen bound to O or N atoms from DNA bases) resultsin such Co II TMpyP(4) stabilization. In contrast, Co II TMpyP(4) binding with ds and ss guanine-containing polynucleotides results in instantaneous Co(II) to Co(III) transformation. This can be explained by Co ion ligation by the guanine N7 atoms, which are known to be strong electron-donating ligands. It is assumed that partial intercalation occurs when Co II TMpyP(4) is bound with poly(dG-dC) 2 , in particular, at low ionic strength values, where cobalt ion is Co(III) in character.

Recent Advances in linear and nonlinear Raman spectroscopy I

“…A Raman study of DNA structure at low pH in the presence of Mn 2C was performed by Muntean et al 154 The diversity of porphyrin structures results in various porphyrin-binding modes to nucleic acids. Terekhov et al 155 carried out a resonance Raman and absorption characterization of cationic Co(II)-porphyrin in its complexes with nucleic acids and studied the binding modes, nucleic base specificity, and role of water in Co(II) oxidation processes. Terekhov et al 155 carried out a resonance Raman and absorption characterization of cationic Co(II)-porphyrin in its complexes with nucleic acids and studied the binding modes, nucleic base specificity, and role of water in Co(II) oxidation processes.…”

Photoinduced Species of Cationic CoII Porphyrin in Complexes with AT-Containing Nucleic Acids Characterized by Resonance Raman and Transient Absorption Spectroscopies

“…From our observations reported earlier [22] it was assumed that Co II TMpyP(4) in the presence of DNA, poly(dA-dT) 2 and poly(dT) is stable. In contrast, it is rapidly oxidized to Co III species upon complexation with poly(dG-dC) 2 and poly(G).…”

“…We believe that such a flattening of the porphyrin structure is favourable for its disposition within narrow DNA grooves, especially minor groove (such kind of binding mode was proposed for Co II TMpyP(4)-DNA complex. [22] ) Moreover, electronic structure and photophysics of namely cationic tetramethylpyridyl-substituted porphyrins can be strongly influenced by such structure dependent charge transfer processes since they possess a large charge located on the pyridyl rings, whereas the porphyrin core is scarce with electron density. Earlier similar conjugation-dependent decrease of the rate of CT state decay has been observed for tetraruthenated cobalt porphyrins.…”

“…They are also known to be growth inhibitors of human malignant melanoma cells. [22] We have earlier reported the study of steady-state interaction of Co II TMpyP(4) with DNA and model polynucleotides. [22] Porphyrin binding modes to a set of AT-and GC-containing NA have been proposed.…”

“…[22] We have earlier reported the study of steady-state interaction of Co II TMpyP(4) with DNA and model polynucleotides. [22] Porphyrin binding modes to a set of AT-and GC-containing NA have been proposed. Here we report the study of the excited Co II TMpyP(4) complexes with AT-containing NA by using resonance Raman and TA porphyrin were analyzed by using the results of the work [22] and of our earlier RR data acquired for free Co II TMpyP(4) solutions.…”