Comparison of two hydrated forms of sodium inosine 5'-monophosphate.

The crystal and molecular structure of a decahydrated form of the sodium salt of inosine 5'-monophosphate (C10H12N4O8P-.Na+.10H2O) was solved to study the effect of hydration on the conformation of nucleic acids. Monoclinic, space group P2(1), a = 8.730 (3), b = 22.349 (7), c = 12.282 (4) A, beta = 109.68 (3) degrees, V = 2256.52 A3, Mr = 550.34, Z = 4, F(000) = 1196, Dx = 1.62 g cm-3, mu = 21.7 cm-1, lambda(Cu K alpha) = 1.54056 A, R = 0.070, wR = 0.102 for 3404 unique [Inet greater than 2 sigma (Inet)] observed reflections out of 3457 unique reflections. The two molecules (A and B) in the asymmetric unit differ in the arrangement of the first shell of hydration and in the torsion angles of the ribose and phosphate. The bond lengths and angles are similar to those of the structure of a less hydrated ('dry') form of the same nucleotide (C10H12N4O8P-.Na+.8H2O) determined previously in space group C222(1) [Rao & Sundaraligam (1969). J. Am. Chem. Soc. 91, 1210-1217]. The twofold symmetry in the 'dry' form is destroyed in the present crystal structure due to the relative displacement of the two independent molecules and reorganization of the hydration shell. Molecule A is different from (r.m.s. = 0.190 A) while molecule B is similar to (r.m.s. = 0.093 A) that of the 'dry' form. The conformation adopted is influenced mainly by the differences in the endocyclic torsion angles of the ribose.