title: Z form of poly d(A-C).poly d(G-T) in solution studied by Raman spectroscopy.
abstract: Poly d(A-C).poly d(G-T) structures have been studied in solution by Raman spectroscopy, in presence of Na+, Mn2+ and Ni2+ counterions. Increase of the Na+ concentration or addition of Mn2+ ions up to 1M MnCl2 does not modify the B geometry of the polynucleotide. On the contrary, in conditions of low water activity (4M NaCl), the presence of small amounts of nickel ions (65 mM) induces a left-handed geometry of the DNA. The shift of the guanine line located at 682 cm-1 in B form to 622 cm-1 reflects unambiguously the C2'-endo/anti-greater than C3'-endo/syn reorientation of the deoxyribose-purine entities. Moreover modifications in the phosphate backbone lines indicate that the polymer is in a Z conformation. New or displaced lines corresponding to adenosine vibrations are correlated with the left-handed structure. An interaction of the Ni2+ ions specifically with the N7 site of purines, combined with a low water activity is necessary to promote the B-greater than Z transition.
mesh_terms: D002412:Cations; D008345:Manganese; D009532:Nickel; D009690:Nucleic Acid Conformation; D011089:Polydeoxyribonucleotides; D012964:Sodium; D013059:Spectrum Analysis, Raman / Q000379:methods
chemical_list: D002412:Cations; D011089:Polydeoxyribonucleotides; D008345:Manganese; C028333:poly(d(A-C).d(G-T)); D009532:Nickel; D012964:Sodium