We used Raman spectroscopy to study the conformational changes of DNA induced by Cd^2+ ions in different Cd^2+ concentrations solution. The experimental results show that when the Cd^2+/PO2^- ratio R increased from 0 to 3.0, the band 835.0cm^-1 shifted about 8cm^-1, and the overlapping spectra of 1446.0 and 1461.0cm^-1 separated and moved to 1441.0 and 1458.0cm^-1, respectively. This indicates that the conformation of DNA has changed from a 'normal' B-form to a 'modified' B′-form. At the same time, changes of other bands demonstrate that parts of base stacking collapse and some hydrogen bonds between AT are disrupted, AT base pairs are damaged more larger than GC base pairs.
A·C mismatches are studied by Raman spectral characterization of PolyA,PolyC,and their equimolar complex in solution of 0.14 mol/L Na^+,pH7.0.Experimental results show that A·C mismatches occur to be A/B(mainly A)conformers,and unlike Watson-Crick base pairing,this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H_2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger,and conformation of the backbone more ordered,which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.
