Infrared absorption detection of metal ion-deoxyguanosine monophosphate binding: experimental and theoretical study.

Metal ion interactions with nucleic acids attract attention because of the environmental and biological consequences. The formation of the complex is often monitored by the vibrational spectroscopy. To identify characteristic binding patterns and marker bands on a model DNA component, infrared absorption spectra of the deoxyguanosine monophosphate complexes with Na(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), Zn(2+), and Cd(2+) cations were recorded and interpreted on the basis of density-functional computations. The aqueous environment was simulated by continuum and combined continuum-explicit solvent models. For the binding to the N7 position of the guanine base, the computation predicted a characteristic frequency upshift and splitting of the 1578 cm(-1) band, which is in accord with available experimental data. Contrary to the expectation, the modeling suggests that the binding to the carbonyl group might not be detectable, as the metal causes smaller spectral changes if compared to the hydrogen-bound water molecules. The binding to the phosphate group causes significant spectral changes in the sugar-phosphate vibrating region ( approximately 800-1200 cm(-1)), but also notable frequency shifts of the carbonyl vibrations. The Cu(2+) and Zn(2+) ions induced the largest alterations in observed vibrational absorption, which corresponds to the calculated strong interaction energies in the N7-complexes and to previous experimental experience. Additional changes in the vibrational spectra of the copper complexes were observed under high metal concentration, corresponding to the simultaneous binding to the phosphate residue. The two-step Cu(2+) binding process was also confirmed by the microcalorimetry titration curve. The computations and combination of more techniques thus help us to assign and localize spectral changes caused by the metal ion binding to nucleic acids.