[Conformation of nucleotides, oligonucleotides and their analogues in aqueous solution. II. Syn-anti-equilibrium in solutions of adenosine, 5'-AMP, 3'-AMP, 5'-CMP and 3'-CMP].

A method for determining the equilibrium constant of sin-anti-states in the aqueous solution of purine and pyrimidine nucleotides and nucleosides has been proposed. This method is based on the measurement of the spin-lattice relaxation rate of H(1') atom of purine nucleotides before and after exchange of H(8) deuterium in the case of purine nucleotides or H(1') and H(5) atoms of pyrimidine nucleotides. The results obtained were interpreted by the two-state dynamic model. The method applied for investigation of the conformation situation in solutions of Ado, 5'-AMP, 3'-AMP, 5'-CMP and 3'-CMP. 5'-AMP and 5'-CMP were shown to exist predominantly in the anti-state (90%). In the case of 3'-nucleotides the enhancement of the relativity weight of sin-populations to 0.2 and 0.85 for 3'-CMP and 3'-AMP, respectively, was found. In the solution Ado both anti- and sin-state were equiprobable. Experimentally measured relaxation rates of H(8) of adenine or H (6) of cytosine nucleotides were used for determination of the time average orientation of nucleic bases towards the ribose ring in the anti-state. For all compounds investigated with the exception of 3'-AMP the "normal" anti-conformation was confirmed. The 3'-AMP was found to be characterized by high anti-conformation. The probable causes of the conformational situation organization and correlation between the N/S and sin/anti rations are discussed.