engleski

The Interaction of New 4.9-Diazapyrenium Compounds with Double Stranded Nucleic Acids

Interactions of double stranded nucleic acids were studied with 4, 9-diazapyrenium compounds, includingmonofunctional monocationic derivatives [4-methyl- (1) and 4-benzyl- (2)], monofunctional dicationicderivatives [4, 9-dimethyl- with substituents H- (3) or Ph- (4) in the 5, 10 positions and Me- (5) in the 2, 7-positions], and bifunctional derivatives [4, 4
-p- (6) and m- (7) xylylene bridged], which were described in thepreceding paper. NMR spectra indicate intercalation for all ligands, with line width increases of up to 70 Hz.Thermal melting experiments and UV or fluorescence titrations were used to characterize affinities ; these areessentially independent of the number of charges present in the ring systems, in line with negligible electrostaticbinding contributions and with the corresponding affinities towards nucleotides (reported in the preceding paper).Substituents at the pyrenium rings have relatively little influence on the binding, with the exception of two phenylgroups, which lower the affinity, probably due to steric hindrance. Several melting curves are biphasic ; in particularwith the RNA-type polyA-polyU one observes transition points above and below the original denaturation point.Ligands containing two diazapyrenium rings bridged either by a m- or by a p-xylylene unit show distinctly higheraffinities for the latter, and in Scatchard analyses a ligand to nucleotide ratio of n=0.08, suggesting bisintercalation.Viscometry, however, shows a rather uniform length increase of the calf thymus DNA double helix with slopes ofα=1.1, similar to the known monointercalator ethidium bromide (α=1.0). The monofunctional compounds exhibitsome noteworthy RNA selectivity

diazapyrenium ; intercalation ; spectroscopy ; nucleotide

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