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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 geometries which strongly depend on the salt nature and the concentration. These structures were studied by classical Raman spectroscopy (RS). Spectral changes depending on NaCl concentration and on the presence of Ni2+ ions were observed and interpreted on the basis of previously obtained results from resonance RS studies of poly(dI-dC) and classical RS studies for other alternating purine-pyrimidine polydeoxyribonucleotides, i.e. poly(dG-dC), poly(dA-dT) and poly(dA-dC)(dG-dT), which also showed B to Z conformational transitions upon varying the salt concentrations. It is shown that: i) The low-salt structure (0.1 mol/l NaCl) 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 concentration. Thus the high-salt structure corresponds to the right-handed 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) The addition of 9.10(-3) mol/l NiCl2 to the high-salt solution induces Z-conformation of the polymer.