title: Effect of magnesium ions on the structure of DNA thin films: an infrared spectroscopy study.
abstract: Utilizing Fourier transform infrared spectroscopy we have investigated the vibrational spectrum of thin dsDNA films in order to track the structural changes upon addition of magnesium ions. In the range of low magnesium concentration ([magnesium]/[phosphate] = [Mg]/[P] < 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 ([Mg]/[P] ≈ 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. The obtained results reflect the modified screening and local charge neutralization of the dsDNA backbone charge, thus consistently demonstrating that the added Mg ions interact with DNA via long-range electrostatic forces. At high Mg contents ([Mg]/[P] > 10), the vibrational spectra broaden and show a striking intensity rise, while the base stacking remains unaffected. We argue that at these extreme conditions, where a charge compensation by vicinal counterions reaches 92-94%, DNA may undergo a structural transition into a more compact form.
authors.affiliation: Department of Physics and Biophysics, School of Medicine, University of Zagreb, Zagreb, 10000, Croatia kristinaserec@gmail.com.
authors.forename: Kristina
authors.identifier: 0000-0001-6163-1584
authors.initials: K
authors.lastname: Serec
authors.affiliation: Department of Physics and Biophysics, School of Medicine, University of Zagreb, Zagreb, 10000, Croatia sanja.dolanski.babic@gmail.com.
authors.forename: Sanja Dolanski
authors.initials: SD
authors.lastname: Babić
authors.affiliation: Department of Theoretical Physics, J. Stefan Institute, Ljubljana, 1000, Slovenia Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, 1000, Slovenia.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Podgornik
authors.affiliation: Institute of Physics, Zagreb, 10000, Croatia.
authors.forename: Silvia
authors.initials: S
authors.lastname: Tomić
mesh_terms: D000818:Animals; D004247:DNA / Q000737:chemistry*; D007477:Ions; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D010100:Oxygen / Q000378:metabolism; D012474:Salmon; D012964:Sodium / Q000494:pharmacology; D017550:Spectroscopy, Fourier Transform Infrared; D014732:Vibration
chemical_list: D007477:Ions; D004247:DNA; D012964:Sodium; D008274:Magnesium; D010100:Oxygen