Abstract

L-Asparagine monohydrate crystals grown from 100–300% supersaturated solutions in the presence of 1–20 mg ml⁻¹ polyacrylic acid exhibit a needle-like morphology, instead of their normal prismatic morphology. A similar effect is observed for crystals grown in octanoic acid emulsions. In contrast, no growth modification is observed for L-asparagine monohydrate crystals grown in 20 mg ml⁻¹ sodium polyacrylate, sodium octanoate and propanoic acid. Polyamido amine (PAMAM) dendrimers (generations −0.5, 1.5, 3.5 and 4.5) end-capped with carboxylate groups also exhibit no growth inhibitory effect at 20 mg ml⁻¹, even after acidification to pH 2.8. The ability of the carboxylic acid functionality to potentially act as a growth inhibitor for L-asparagine when in solution, or emulsion droplets, is contrasted with the L-asparagine crystallization promotion produced by carboxylic acid films spread at the air–water interface.