THE INTERACTION OF COPPER TETRAKIS(4-N-METHYLPYRIDYL) PORPHINE WITH POLYNUCLEOTIDES STUDIED BY ULTRAVIOLET RESONANCE RAMAN-SPECTROSCOPY

Resonance Raman spectra are reported for poly[dA . dT](2), poly[dA]. poly[dT], poly[dG . dC](2), poly[dG]. poly[dC], poly[dA . dC]. poly[dG . dT] and Calf Thymus DNA in interaction with the porphyrin Cu(TMpy-P4). The spectra were obtained under conditions of low salinity and a ratio of porphyrin molecules to nucleotide base pairs of r=0.05, with an excitation wavelength of 257 nm The differences between the spectra in interaction with Cu(TMpy-P4) and those of the unmodified nucleic acids are interpreted in terms of the structural changes imposed by the porphyrin. Two different binding modes have been reported in previous studies, a 5'-CG-3' specific intercalative mode and an A-T specific outside binding mode. Our results suggest that this latter mode may show a preference for A-A or T-T sites. Furthermore a transition in structure, while remaining within the B-form family of structures, is indicated for both poly[dA]. poly[dT] and poly[dG . dC](2) upon addition of Cu(TMpy-P4).