Physicochemical studies on calcium glycerophosphate. I. X-ray diffraction study of calcium glycerophosphate crystals and their water of crystallization.

Abstract

Calcium dl-α-glycerophosphate (α-CaG) has three crystal forms (anhydrate, mono-and di-hydrates), and calcium β-glycerophosphate (β-CaG) has two (anhydrate and monohydrate). The X-ray diffraction patterns of these crystals show a characteristic strong peak at a Bragg angle (2θ) of 6° to 8°. This peak is very sensitive to de-and rehydration of the hydrate crystals ; for α-CaG hydrates, the 2θ angle of the peak shifts, while that of β-CaG hydrate does not change, but its intensity changes. Since the dehydrated CaG hydrates recover their original hydrate forms at appropriate relative humidities without any crystal damage, the rate constants of rehydration were measured using the gravimetry and X-ray intensity methods. β-CaG monohydrate has a smaller value of the rate constant than the α-CaG dihydrate, indicating that the dehydrated crystals of the former are more stable than those of the latter, and that water of crystallization in the former may not play as important a role in crystal growth as in the latter. As for α-CaG dihydrate, the rate of rehydration through the incorporation of water into the dehydrated crystal is smaller than the total velocity of water gain (involving water of crystallization and adsorbed water), suggesting that the water molecule is first adsorbed onto the dehydrated crystal and is then incorporated into the crystal. The formation of the different CaG crystals may be a result of differences in the mode of interaction between the water molecules and calcium ions.