The interaction of small and macromolecules with growing calcium hydrogenphosphate dihydrate crystals

Abstract

The influence of glutamate, aspartate, citrate and polyaspartate (MW=5–15 kDa) on the growth morphology of calcium hydrogenphosphate dihydrate (CaHPO₄·2H₂O, DCPD) was studied.

DCPD crystals were prepared under controlled conditions by fast mixing of the anionic and cationic reactant solutions and subsequent growth without further stirring in the course of 24 h at 37 °C. The initial conditions were: c(CaCl₂)=c(Na₂HPO₄)=0.021 mol dm⁻³, c(NaCl)=0.3 mol dm⁻³, pH 5.5. The respective additive was added to the ionic component prior to pH adjustment. The affected crystal faces were identified by light and scanning electron microscopy.

In the control system mostly large (approx. 200 µm×100 µm) thin platelets with prominent (010) faces were obtained. Glutamate and aspartate had no significant effect, but both citrate and polyaspartic acid significantly inhibited DCPD crystallization and changed the morphology of the crystals by specifically affecting different crystal faces. Crystals grown in the presence of citrate ions appeared rod-like. When grown in the presence of polyaspartic acid crystals appeared much larger than in the control systems but the basic orientation was unchanged, indicating that polyaspartic acid adsorbs on (010) face.