CONFORMATIONAL TRANSITIONS OF POLY(DI-DC) IN AQUEOUS-SOLUTION AS STUDIED BY CLASSICAL RAMAN-SPECTROSCOPY

Poly(dI-dC) in aqueous solution can undergo different equilibrium geom etries which strongly depend on the salt nature and the concentration. These structures were studied by classical Raman spectroscopy (RS). S pectral changes depending on NaCl concentration and on the presence of Ni2+ ions were observed and interpreted on tile basis of previously o btained results from resonance RS studies of poly(dI-dC) and classical RS studies for other alternating purine-pyrimidine polydeoxyribonucle otides, i.e. poly(dG-dC), poly(dA-dT) and poly(dA-dC)(dG-dT), which al so showed B to Z conformational transitions upon varying the salt conc entrations. It is shown that: i) The low-salt structure (0.1 mol/l NaC l) is in the pure canonical B conformation. ii) The high-salt (5 mol/l NaCl) Raman spectrum is similar to that obtained for the low-salt con centration. Thus the high-salt structure corresponds to the right-hand ed polymer with characteristic bands for both the B (predominant) and A conformations with some weak Z conformation markers which indicate a tendency for B to Z conformational transition of the polymer. iii) Th e addition of 9 . 10(-3) mol/l NiCl2 to the high-salt solution induces Z-conformation of the polymer.