Synthesis, Optical Properties and DNA-Binding Behavior of a Quinoxaline Ring-Fused pi-Elongated Chlorin - Efforts Towards Preparation of Long Wavelength Absorbing Porphyrinoids

摘要

A porphyrinoid containing cis-diol pyrroline subunit and fused nitro-quinoxaline pi-elongated unit at its peripheral beta,beta'-positions was prepared. The UV-visible spectrum exhibits typical chlorin-like sharp Q(y)-band, but significantly more red-shifted (687 nm) and more intense than for a normal diol chlorin. The precursor porphyrin exhibited weak Q-bands slightly above 650 nm. The same porphyrin exhibited a low pH dependent similar to 40 nm red-shift in its UV-visible spectrum. Analysis of the frontier molecular orbital energies using electrochemical techniques and theoretical analysis of the lowest energy geometry of the porphyrin confirmed the roles of non-planar conformation and electronic charge redistribution in inducing this spectral feature. In addition, biophysical and computational analysis of DNA-binding behavior of these porphyrinoids indicated that groove binding induced by Van der Waals contacts was the preferred mode of interaction.