Sequence selective photoinduced electron transfer of a pyrene-porphyrin dyad to DNA

Abstract

The binding modes of a pyrene-porphyrin dyad, (1-pyrenyl)-tris(N-methyl-p-pyridino) porphyrin (PyTMpyP), to various DNAs (calf thymus DNA (Ct-DNA), poly[d(G-C)(2)], and poly[d(A-T)(2)]) have been investigated using circular dichroism and linear dichroism measurements. Based on the polarization spectroscopic results, it can be shown that the pyrenyl and porphryin planes are skewed to a large extent for PyTMPyP in an aqueous environment and in the binding site of poly[d(G-C)(2)]. In this complex, a photoinduced electron transfer (PET) process between the pyrenyl and porphyrin moieties occurs. On the other hand, PET was not observed in the PyTMPyP-poly[d(A-T)(2)] complex, whereas the fluorescence intensity of TMPyP was enhanced. The molecular planes of the pyrene and porphyrin moieties are almost parallel in the poly[d(A-T)(2)] and Ct-DNA adducts. Moreover, the generation of O-1(2) species occurs only for the PyTMPyP-Ct-DNA and PyTMPyP-poly[d(A-T)(2)] complexes. We discuss the photophysical properties of PyTMPyP which are attributed to the binding patterns and the sequence of DNA bases.