AN FTIR SPECTROSCOPIC STUDY OF CALF-THYMUS DNA COMPLEXATION WITH AL(III) AND GA(III) CATIONS

The interaction of calf-thymus DNA with trivalent Al and Ga cations, i n aqueous solution at pH =6-7 with cation/DNA(P) (P=phosphate) molar r atios (r) 1/80, 1/40, 1/20, 1/10, 1/4 and 1/2 was characterized by Fou rier Transform infrared (FTIR) difference spectroscopy. Spectroscopic results show the formation of several types of cation-DNA complexes. A t low metal ion concentration (r=1/80, 1/40), both cations bind mainly to the backbone PO2 group and the guanine N-7 site of the G-C base pa irs (chelation). Evidence for cation chelate formation comes from majo r shifting and intensity increase of the phosphate antisymmetric stret ch at 1222 cm(-1) and the mainly guanine band at 1717 cm(-1). The pert urbations of A-T base pairs occur at high cation concentration with ma jor helix destabilization. Evidence for cation binding to A-T bases co mes from major spectral changes of the bands at 1663 and 1609 cm(-1) r elated mainly to the thymine and adenine in-plane vibrations. A major reduction of the B-DNA structure occurs in favor of A-DNA upon trivale nt cation coordination.