The Intramolecular Conformation of Adenosine 5′-Monophosphate in Aqueous Solution as Studied by Fast Fourier Transform 1H and 1H-{31P} Nuclear Magnetic Resonance Spectroscopy

Abstract

Abstract Nuclear magnetic resonance spectra of 5'-AMP were examined over a concentration range of 0.001 to 2.2 m in the Fourier mode in the 1H and 1H-{31P} configuration and were analyzed by computer simulation. The principal conclusions with respect to the solution conformation of 5'-AMP are as follows. (a) The exocyclic C(5')—O(5') and C(4')—C(5') bonds are flexible, and preferentially exist in the gauche-gauche conformation with a W relationship across H(4')—C(4')—C(5')—O(5')—P(5') in which the above atoms lie in one plane as in its crystal structure. (b) The ribose moiety exists as a flexible ring system undergoing interconversion between the 3E and 2E conformations. The sugar ring conformation is strongly concentration dependent, being 63 ± 10% 2E and 37 ± 10% 3E at concentrations below 0.01 m. At higher concentrations, the population of the 3E form increases at the expense of the 2E form, and at 2.0 m, 3E is the preferred conformation. In the solid state the conformation of the sugar ring is 3E for 5'-AMP.