Flexibility of DNA and RNA upon binding to different metal cations. An investigation of the B to A to Z conformational transition by Fourier transform infrared spectroscopy.

The interaction of DNA and RNA with Cu(II), Mg(II), [Co(NH3)6]3+ [Co(NH3)5Cl]2+ chlorides and, cis- and trans-Pt(NH3)2Cl2 (CIS-DDP, trans-DDP) has been studied by Fourier Transform Infrared (FT-IR) spectroscopy and a correlation between metal-base binding and conformational transitions in the sugar pucker has been established. It has been found that RNA did not change from A-form on complexation with metals, whereas DNA exhibited a B to Z transition. The marker bands for the A-form (C3'-endo-anti conformation) were found to be near 810-816 cm-1, while the bands at 825 and 690 cm-1 are marker bands for the B-conformation (C2'-endo, anti). The B to Z (C3'-endo. syn conformation) transition is characterized by the shift of the band at 825 cm-1 to 810-816 cm-1 and the shift of the guanine band at 690 cm-1 to about 600-624 cm-1.