A Resonance Light-Scattering Analysis of the Suprahelical Helixes of Nucleic Acids Induced by 5,10,15,20-Tetrakis[4-(trimethyammonio)phenyl]porphine

This paper discusses the usefulness of resonance light-scattering spectroscopy (RLSS), which can be obtained by using an ordinary spectrofluorimeter, for the analysis of the suprahelical helixes of nucleic acids induced by 5,10,15,20-tetrakis[4-(trimethyammonio)phenyl]porphine (H2tapp). Depending on the acidity of the aqueous solution, the titled porphyrin has two species, [H2tapp]4+ and [H4tapp]6+. Both species can stack on appropriate conditions along the surface of nucleic acids in the mode of long-range assembly; and this leads to the formation of suprahelical helixes of nucleic acids. Enhanced resonance light-scattering signals can be observed for the porphyrin-induced suprahelical helixes of nucleic acids with the maximal resonance light scattering near to 432 nm for [H2tapp]4+ and near to 452 nm for [H4tapp]6+. The exciton splitting signals, which are generally associated with the aggregation of porphyrins, as described by molecular-exciton theory, are observed at 428 nm in the RLS spectra, analogous to the circular dichroism spectra when the molar ratio of [H2tapp]4+ to nucleic acids (R) is greater than 0.89. These results indicate that porphyrin–porphyrin interactions occur in the suprahelical helixes of nucleic acids.