Preparation and Formation Mechanism of l-Valine Spherulites via Evaporation Crystallization

Abstract

L-Valine crystallizes in a flake-like shape generally; however, compared with the flake-like products, spherulitic L-valine has better filterability, flowability, and bulk density and has potential for wider industrial applications in the future. In this study, L-valine spherulites have been successfully prepared by an evaporative crystallization method in the presence of no more than 0.5% hydroxypropyl methyl cellulose (HPMC). The spheroidization of L-valine proceeds via a layer-by-layer transformation from an initial flake-like shape to a petal-like form, and then it continues to grow into the final sphere-like shape. Molecular dynamics simulations show that HPMC interacts with hydrophilic (001) faces preferentially and promotes the continuous layer growth process. Only the substituent groups of hydroxypropyl and methyl exist simultaneously within a certain spatial distance and, in a viscosity of 40−50 mPa•s, can promote the formation of L-valine spherulites. The particle size increased with the increase in the HPMC dosage and decrease of temperature or evaporation rate. This effect of HPMC promoting the spherical formation provides a method to enrich the design of spherulites and new insights into the fabrication mechanism of spherulitic growth.

Modified Stranski–Krastanov Growth of Amino Acid Arrays toward Piezoelectric Energy Harvesting

“…Both the BFDH method and the simulation by the Materials Studio suggested valine molecules stack along the cdirection (001) into a large plane. 17 those with the largest interplanar distances, which is consistent with our obverse sheet structures (Figure 4d). The hydrogen bond networks of the valine sheet crystal were clearly observed from the top view of the predicated BFDH morphology (Figure 4e).…”

“…Valine sheets showed smooth and straight surfaces and faceted edges, leucine sheets were curled and thinner, and isoleucine sheets were similar to valine sheets but with smoother edges (Figure b–d). The X-ray diffraction (XRD) measurements matched the simulated XRD result for valine, leucine, and isoleucine arrays, confirming these amino acid sheets had a noncentrosymmetric crystal structure with space groups P 2 1 (Figure e–g). − The amino acids assembled into a double-layer structure (Figure S2). ,, Within layers, head-to-tail α-amine and α-carboxyl groups interact with each other to form a stable single-layer structure.…”

“…The X-ray diffraction (XRD) measurements matched the simulated XRD result for valine, leucine, and isoleucine arrays, confirming these amino acid sheets had a noncentrosymmetric crystal structure with space groups P 2 1 (Figure e–g). − The amino acids assembled into a double-layer structure (Figure S2). ,, Within layers, head-to-tail α-amine and α-carboxyl groups interact with each other to form a stable single-layer structure. The van der Waals forces between adjacent double-layer structures drove the assembly extending parallel to the (001) plane.…”

“…The periodical packing of the unit cell eventually resulted in the valine crystal and vertical sheets (Figure b,c). Both the BFDH method and the simulation by the Materials Studio suggested valine molecules stack along the c -direction (001) into a large plane . The (001) plane of the valine crystal in Figure c has the largest d values (12.063 Å).…”

“…17−19 The amino acids assembled into a double-layer structure (Figure S2). 17,20,21 Within layers, head-to-tail α-amine and α-carboxyl groups interact with each other to form a stable single-layer structure. The van der Waals forces between adjacent double-layer structures drove the assembly extending parallel to the (001) plane.…”