Ultraviolet resonance Raman spectroscopy of distamycin complexes with poly(dA)-poly(dT) and poly(dA-dT): role of hydrogen bonding

摘要: Raman spectra are reported for distamycin, excited at 320 nm, in resonance with the first strong absorption band of chromophore. Qualitative assignments to pyrrole ring and amide modes made on basis frequency shifts observed D2O. When distamycin is dissolved dimethyl sulfoxide or dimethylformamide, large (30 cm-1) upshifts seen assigned I, while amides II III shift down appreciably. Similar but smaller when bound poly(dA-dT) poly(dA)-poly(dT). Examination literature data N-methylacetamide various solvents shows that I frequencies correlate well solvent acceptor number poorly donor number. This behavior implies interactions C = O group more important than N-H polarizing bond stabilizing zwitterionic form. The therefore imply groups, despite being exposed solvent, less strongly H-bonded polynucleotide complexes aqueous perhaps because orienting influences nearby backbone phosphate groups. In this respect, poly(dA)-poly(dT) same, showing same RR frequencies. Resonance were also obtained 200-nm excitation, where DNA residues enhanced. essentially without except a perceptable narrowing adenine poly(dA-dT), suggesting reduction conformational flexibility polymer upon drug binding.