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Abstract
In this paper we examine the interactions of Calf Thymus DNA and the model polynucleotides poly(dA).poly(dT), poly(dAdT)2 and poly(dG.dC)2 with a group of metallopor- phyrins derived from the freebase porphyrin tetrakis(4-N-methylpyridyl)porphine, H2 (TMpy- P4), by means of ultraviolet absorption spectroscopy, circular dichroism spectroscopy and microcalorimetry. We have studied the interactions of the copper, cobalt, nickel and zinc derivatives of H2 (TMpy-P4) in addition to the free base porphyrin itself. We have found strong evidence for an external self-stacking interaction of the Cu(TMpy-P4) and Zn(TMpy-P4) derivatives with poly(dA).poly(dT) and poly(dAdT)2 even at low concentrations of porphyrin, and all of the porphyrin derivatives studied appear to display such a self-stacking in interaction with poly(dA.dT)2 at sufficiently high ratios of porphyrin to polynucleotide.
