REVERSIBLE CRYSTAL TRANSITION OF GUANOSINE BETWEEN THE DIHYDRATE AND ANHYDROUS STATES COUPLED WITH ADSORPTION-DESORPTION PROCESS

Relative humidity induces the reversible crystal transition of guanosi ne between the dihydrate and the anhydrous state. The characteristics of the transition was investigated by means of X-ray powder diffractio n analysis and high-resolution solid-state C-13 NMR spectroscopy. Adso rption-desorption hysteresis was observed. Guanosine dihydrate (the H- state) which is crystallized from an aqueous solution rapidly loses cr ystal water below 10% relative humidity (rh), and is anhydrous at 0% r h (the A-state). The crystals gradually recover the II-state at approx imate 20% rh. In the adsorption process between 10-20% rh, there exist s one intermediate state, M, with 1.2-1.3 moles water per mole guanosi ne. The lattice of the M-state was determined to be orthorhombic with the cell parameters of a = 16.248(1), b = 11.603(1), and c = 13.643(2) Angstrom. The base-stacking structure is retained throughout the trans ition. On the other hand, conformational changes of the riboses and br eak of the hydrogen-bonding network between the bases would be induced in the A-state in conformity with lack of crystal water.