Effect of Amino Acid Additives on the Crystallization of l -Glutamic Acid

The influence of a range of amino acid additives on the crystallization of l -glutamic acid has been investigated. The presence of a bulky side chain (phenyl) in l -phenylalanine and l -tyrosine was identified as an essential feature in achieving stabilization of the α-polymorph at low additive concentrations. Minute quantities of these additives were incorporated into the α- l -glutamic acid product crystals when the additive/ l -glutamic molar ratio was 1:30 in solution; in this condition no β-form inclusions were observed inside the α-form crystals. At higher additive/ l -glutamic acid molar ratios in solution (1:6), a significant amount of additive uptake was observed and changes in α-form morphology were noted under these conditions. A key feature was the disappearance of the {011} and {001} facets of α- l -glutamic acid and the emergence of the {111}and {110} facets. The overall hypothesis is that additives disrupt the developing β/α interface and this stabilizes the α-form.