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⁺·C₁₀H₁₂N₅O₈P^2-·4H₂O. 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.