Aspirin-DNA interaction studied by FTIR and laser Raman difference spectroscopy.

The interaction of calf-thymus DNA with aspirin is investigated in aqueous solution at pH 7-6 with drug/DNA (phosphate) molar ratios of r = 1/40, 1/20, 1/10, 1/5, 1/2, 1 and 2. Fourier transform infrared (FTIR) and laser Raman difference spectroscopy are used to determine drug binding sites, sequence preference and DNA secondary structure, as well as the structural variations of aspirin-DNA complexes in aqueous solution. Spectroscopic evidence showed that at low aspirin concentration (r =1/40), drug-DNA interaction is mainly through the backbone PO2 groups and the A-T base pairs. Such interaction largely perturbs the phosphate vibration at 1222 cm(-1) and the A-T bands at 1663 and 1609 cm(-1) with no major helix destabilization. At higher drug concentration (r > 1/20), the participation of the G-C bases in drug-DNA complexation was evident by strong perturbations of the guanine and cytosine vibrations at 1717 and 1494 cm(-1), with a partial helix destabilization. A major alteration of the B-DNA structure towards A-DNA occurs on drug complexation. The aspirin interaction was through anion CO and COOCH3 donor atoms with those of the backbone PO2 group and DNA bases donor sites (directly or indirectly via H2O molecules).