On the concomitant crystallization of amino acid crystals upon dissolution of some amino acid salt crystals

During our in situ microscopy experiments we found that dissolution of glutamic acid, aspartic acid and leucine chloride single crystals leads to the spontaneous formation of numerous glutamic acid, aspartic acid and leucine crystals respectively. This phenomenon was not encountered during dissolution of monosodium glutamate single crystals. The observations are interpreted on the basis of calculated phase diagrams of the amino acid/HCl (/NaOH) systems. It was shown that upon dissolving the halide salts one enters the liquid–solid amino acid domain in the phase diagram, leading to the crystallization of the amino acids. The conclusions were confirmed by triple point composition measurements using several analytical methods.