Face-selective crystal growth behavior of l-aspartic acid in the presence of l-asparagine

The kinetic mechanism of l-asparagine (l-Asn) action on l-aspartic acid (l-Asp) crystal growth, namely the face-selective effect of l-Asn on the l-Asp crystal growth rate in each direction, was examined. In the a-axis direction, the effect of l-Asn on the l-Asp crystal growth rate was small. Enhancement and inhibition of l-Asp crystal growth, and interestingly the dissolution of the l-Asp crystal face, were observed in the b-axis direction, depending on the amount of l-Asn added. In the c-axis direction, the l-Asp crystal growth rate decreased with the increase in the amount of l-Asn added, and the experimental results were well fitted with a Langmuir adsorption isotherm. The study showed that there were crystal growth conditions where enhancement and inhibition, as well as inhibition and dissolution, coexisted in the presence of an additive with a structure similar to the growing crystal.