Crystal structure and sequential dehydration transitions of disodium guanosine 5'-monophosphate tetrahydrate.

Disodium guanosine 5'-monophosphate was reported previously to crystallize as both the tetrahydrate and the heptahydrate. We herein report a determination of the molecular and crystal structures of the title tetrahydrated salt, 2Na·CHNOP·4HO. It was found that the structure differs markedly from that of the heptahydrate, but greatly resembles that of disodium deoxyguanosine 5'-monophosphate tetrahydrate. The C2'-O2'H moiety of ribose is surrounded by hydrophilic moieties and is disordered over two sites. The sugar puckering mode is O4'-endo-C1'-exo at both sites and the conformation around the C4'-C5' bond is gauche-trans. Powder X-ray diffraction and thermal analyses revealed that the temperature-controlled transition from the tetrahydrate to the anhydride proceeded through three intermediate phases between 40 and 60 °C at 0% relative humidity. Large induction periods were observed.