engleski

The effect of magnesium ions on the structure of thin DNA thin films: an infrared spectroscopy study

Previous research showed that under influence of Mg+2 cations DNA undergoes structural and conformational changes. It was pointed out by many authors that regardless of the conditions, Mg ions show great affinity toward phosphate groups of DNA, thus neutralizing and stabilizing double helical structure. Interaction of the Mg ions with the base sites, however, still remains unclear as different authors report different affinities and preferable sites of Mg-base coordination [1, 2, 6]. In order of finding the best model, we developed protocols where Mg-DNA interaction can be tested with and without intrinsic Na cations, and over large interval of molar concentrations ratio (r =[magnesium]/[phosphate]). Utilizing Fourier transform infrared spectroscopy we have investigated the vibrational spectrum of thin dsDNA films with intrinsic Na cations in order to track the structural changes upon addition of magnesium ions. In the range of low magnesium concentration (r < 0.5), both the red shift and the intensity of asymmetric PO2 stretching band decrease, indicating an increase of magnesium–phosphate binding in the backbone region. Vibration characteristics of the A-conformation of the dsDNA vanish, whereas those characterizing the B-conformation become fully stabilized. In the crossover range with comparable Mg and intrinsic Na DNA ions (r ≈ 1) B-conformation remains stable ; vibrational spectra show moderate intensity changes and a prominent blue shift, indicating a reinforcement of the bonds and binding in both the phosphate and the base regions. At high Mg contents (r > 10), the vibrational spectra broaden and show a striking intensity rise, while the base stacking remains unaffected. Also, in order to eliminate/determine influence of sodium ions extensive dialysis was performed, and the vibrational spectrum of thin films without intrinsic Na cations upon addition of magnesium ions that will be compared with samples containing sodium ions.

thin films; FTIR; DNA; Mg ions

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