Intercalative and nonintercalative binding of large cationic porphyrin ligands to polynucleotides

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Abstract
The interactions of two positional isomers and one analogue of meso-tetra(4-N-methylpyridvi)porphine, with the synthetic polynu-cleotides poly[d(A-T)] *poly[d(A-T)] and poly[d(G-C)]* poly[d(G-C ) ] have been Investiqated by circular dichroism. All four porphyrins were found to bind to the polynucleot1des as shown by the Induction of circular dichroism 1n their Soret bands. Furthermore, the sign of the Induced elliptidty reflects selective occupation of binding sites by the porphyrin ligands. The conformational lability of poly[d(A-T)] *poly[d(A-T)] was found to be appreciable as micromolar amounts of meso-substituted 4-N-methylpyridyl, 3-N-methylpyridyl , and p-N-trimethylanilinium porphines induced a CD spectrum similar but not Identical to that of DNA 1n the Z-form, i.e. a negative band at 280 nm and a positive band at 259 nm. The effect of porphyrin binding to poly[d(G-C)] *poly[d(G-C)] was less pronounced and dissimilar to that seen 1n the AT polymer.