VIBRATIONAL SPECTROSCOPIC STUDIES OF THE DIVALENT METAL-ION EFFECT ONDNA STRUCTURAL TRANSITIONS

Raman spectroscopy is used to study DNA complexes with Cu2+, Mn2+ and Ca2+ ions in 0.001 M NaCl, pH 7.0. The changes observed in the spectra permit us to conclude that all the ions interact both with the DNA ph osphate groups and with the nucleic bases, changing the DNA structure. Ca2+ and Mn2+ ions bind to N7 of guanine and adenine only, but Cu2+ i ons can probably bind to N7, 06 of guanine and N3 of cytosine as well. The latter type of binding occurs as the base is turning around the g lycoside bonds and a G-C pair transition from anti to syn conformation takes place. Besides, at high concentrations of Ca2+ ions a partial B -A transition takes place in DNA. (C) 1997 Elsevier Science B.V.