Abstract:

The interactions of two groups of hydrated model crystals, CaHPO4.2H2O (DCPD) vs. Ca4(HPO4)(PO4)2 (OCP) and Ca oxalate monohydrate (COM) vs. Ca oxalate dihydrate (COD) with different org. additives are considered. DCPD ppts. as platelet-like crystals with the dominant faces shielded by hydrated layers and charged lateral faces. In the 2nd system COM has charged surfaces, while all faces of COD are covered with layers contg. water mols. The org. mols. tested include neg. charged, flexible and rigid small and macromols. (glutamic and aspartic acid, citrate, hexaammonium polyphosphate, phytate, and polyaspartate) and anionic surfactants (sodium dodecyl sulfate, SDS, sodium diisooctyl sulfosuccinate, AOT, sodium cholate NaC, and disodium oleoamido PEG-2 sulfosuccinate, PEG). Two types of effects were demonstrated: (i) effect on crystal growth morphol.: flexible org. mols. with high charge d. and anionic surfactants affected the growth morphol. of DCPD and COM by selectively interacting with the charged lateral faces while rigid mols. (phytate, polyaspartate) specifically recognized the dominant (010) face of DCPD due to structural and stereochem. compatibility. (ii) effect on phase compn.: anionic surfactants at concns. above the crit. micelle concn. promoted growth of OCP and COD resp. by selectively adsorbing at, and inhibiting growth of nuclei of DCPD and/or COM, which were dominant in the resp. control systems. The effect was esp. pronounced in the Ca oxalate pptn. system, where in some cases complete reversal of the phase compn. occurred. The important role of the hydrated layer, as part of the structure of the investigated crystal hydrates, in the above crystal additive interactions is discussed. [on SciFinder(R)]