The crystal structure of guanosine dihydrate and inosine dihydrate.

Crystals of the dihydrates of guanosine (C10H13NsOs) and inosine (C10H12N405) are nearly isostructural. They are monoclinic, space group P21, with cell dimensions a= 17·518, b= 11 ·502, c= 6·658 A, P=98·17° (guanosine) and a=17·573, b=11·278, c=6-654A, P=98·23° (inosine). There are two nucleoside molecules and four water molecules per asymmetric unit. Data were collected on an automated diffractometer; the structures were solved by Patterson and trial-and-error methods and refined to R indices of about 0·035. The structure features hydrogen bonding between purine bases to form ribbons parallel to b and parallel stacking of purine bases along c; the separation between adjacent rings within a stack is 3·3 A. The conformations about the glycosidic C-N bond and the puckerings of the sugar rings arc quite different for the two molecules in the asymmetric unit.