Binding of Mg~2+,Cd~2+,and Ni~2+ to Liquid Crystalline NaDNA:Polarized Light Microscopy and NMR Investigations

摘要

The interaction of the divalent metal ions Mg~2+,Cd~2+,and Ni~2+ with liquid crystalline NaDNA solutions(molar ratios Me~2+/DNA-phosphate <=0.050)was investigated by polarized light microscopy and multinuclear ~31P,~2H,and ~23Na NMR.Our findings show that the state of the cholesteric NaDNA phase at equal MgCl_2,CdCl_2,or NiCl_2 concentration is affected in a different way and to a different extent by the nature of the divalent cation.Indeed,we found that the occurrence of an isotropic phase is markedly favored by Mg~2+,and to a lower extent by Cd~2+,and that the pitch of the cholesteric phase decreases in the presence of Cd~2+ or Ni~2+.~23Na NMR spectroscopy also shows differences between the binding behavior of Mg~2+ and the transition metal ions in the counterion atmosphere around DNA.The results are discussed in terms of different binding modes of the metal ions.