Factors Influencing Additive Interactions with Calcium Hydrogenphosphate Dihydrate Crystals

The effect of aspartic acid, glutamic acid, hexaammonium tetrapolyphosphate, calcium phytate, and polyaspartic acid on calcium hydrogenphosphate dihydrate (CaHPO4·2H2O, DCPD) crystal growth morphology was studied. The mechanism of additive−DCPD crystal interaction depends on the size and structure of the additive molecule and the structural fit between the organic molecule and the ionic structure of particular crystal face. Small molecules with low charge (aspartic and glutamic acid) do not have a significant effect, whereas small molecules with several functional groups (citrate and hexaammonium tetrapolyphosphate) adsorb on lateral faces primarily by electrostatic interactions. Molecules with hindered structures (phytate) and macromolecules (polyaspartic acid) specifically adsorb on the dominant (010) face, for which a certain degree of structural fit is necessary.