Stabilization of α-l-glutamic acid on chiral thin films—A theoretical and experimental study

Self-assembled monolayers and multilayers (SAMs) are employed for controlling the polymorphic nature of different crystal systems. Previously, we reported the stabilization of the metastable α-l-glutamic acid on self-assembled multilayers of a phenylalanine derivative. In order to understand the inclination of phenylalanine moieties to stabilize the metastable α-form, we performed comparative theoretical calculations (molecular dynamics) of α-l-glutamic crystals in three environments: regular growth (gas phase), phenylalanine and cysteine additives. These energy calculations, combined with experimental data (XRD and SEM), showed that the absence of the (0 1 1) and (2 0 0) facets is crucial in stabilizing the α-l-glutamic form, and in preventing its transformation to the stable β-form. The crystallization of metastable polymorphs on thin films constructed from amino acid moieties may be applicable to other polymorphic systems, such as glycine. Moreover, the possibility of using SAM surfaces to stabilize thermodynamically metastable structures as demonstrated in this work, and the understanding of the chemical and physical attributes to the control of polymorphs, is of prime importance to fundamental science and may have further implications in the industrial world.