A comparative study of the interaction of 5,10,15,20-tetrakis (N-methylpyridinium-4-yl)porphyrin and its zinc complex with DNA using fluorescence spectroscopy and topoisomerisation

摘要

Binding of 5,10,15,20-tetrakis(N-methylpyridiniutn-4-yl)porphyrin (H₂TMPyP4+) and its zinc complex (ZnTMPyP4+) to DNA is demonstrated by their coelectrophoresis and by absorption and fluorescence spectroscopic methods. Topoisoinerisation of pBR322 DNA shows that H₂TMPyP4+ unwinds DNA as efficiently as ethidium bromide showing that it intercalates at many sites. ZnTMPyP4+ may cause limited unwinding. Marked changes in the fluorescence spectra of the porphyrins are found in the presence of DNA. The fluorescence intensity of either H or ZnTMPyP4+ is enhanced in the presence of poly (d(A–T)), whereas in the presence of poly (d(G–C)) the fluorescence intensity of ZnTMPyP4+ is only slightly affected and that of H₂TMPyP4+ markedly reduced. Both the porphyrins photosensitise the cleavage of DNA in aerated solution upon visible light irradiation.