engleski

Recognition of nucleotides and polynucleotides by phenanthridinium and diazapyrenium derivatives in aqueous media

Interactions of 4, 9-diazapyrenium cations with nucleotides and polynucleotides was studied in buffered aqueous solution (pH 5 or 7) by UV-Vis, fluorescence, NMR and viscometry. The formation of stacked nucleotide / 4, 9-diazapyrenium and nucleotide-phenanthridinium complexes of 1:1 stoichiometry with log Ks 1.6 &#8211; 2.8 and log Ks <1 to 2.3, respectively, suggest that larger surface of the former cationic heteroaromatics does not considerably enhance nucleotide binding. The stability constants were found independent on nucleotide charge suggesting the dominance of aromatic stacking over coulombic interactions in such complexes. Monomeric 4, 9-diazapyrenium cations bind to ss- and ds-polynucleotides by intercalation. Affinities were found to be essentially independent on the number of permanent charges present in the aromatic system but strongly dependent on a type of substituents attached. 2, 7- Diamino substituted 4, 9-diazapyrenium derivative has shown the highest affinity toward polynucleotides, the highest double helix stabilisation and highly specific fluorescence response on binding to double-stranded G - C (quenching) and A &#8211; U(T) (emission increase) polymers. Interactions of 2, 7-diamino-4, 9-diazapyrenium derivative with ss-polynucleotides, in contrast to other derivatives, depend strikingly on the nucleobase composition and in some cases on pH. The bis(4, 9-diazapyrenium) dicationic derivatives differing in rigidity and length of the linkers connecting diazapyrenium units were found to bind ds-polynucleotides by monointercalation ; some of them exhibited strong additional interactions of the non-intercalated diazapyrenium unit with the outer surface of a polynucleotide.

recognition; nucleotides; polynucleotides; phenanthridinium; diazapyrenium

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