Crystal Engineering of l-Alanine with l-Leucine Additive using Metal-Assisted and Microwave-Accelerated Evaporative Crystallization

Abstract

In this work, we demonstrated that the change in the morphology of l-alanine crystals can be controlled with the addition of l-leucine using the metal-assisted and microwave accelerated evaporative crystallization (MA-MAEC) technique. Crystallization experiments, where an increasing stoichiometric amount of l-leucine is added to initial l-alanine solutions, were carried out on circular poly(methyl methacrylate) (PMMA) disks modified with a 21-well capacity silicon isolator and silver nanoparticle films using microwave heating (MA-MAEC) and at room temperature (control experiments). The use of the MA-MAEC technique afforded for the growth of l-alanine crystals with different morphologies up to ∼10-fold faster than those grown at room temperature. In addition, the length of l-alanine crystals was systematically increased from ∼380 to ∼2000 μm using the MA-MAEC technique. Optical microscope images revealed that the shape of l-alanine crystals was changed from tetragonal shape (without l-leucine additive) to more elongated and wire-like structures with the addition of the l-leucine additive. Further characterization of l-alanine crystals was undertaken by Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy and powder X-ray diffraction (PXRD) measurements. In order to elucidate the growth mechanism of l-alanine crystals, theoretical simulations of l-alanine’s morphology with and without l-leucine additive were carried out using Materials Studio software in conjunction with our experimental data. Theoretical simulations revealed that the growth of l-alanine’s {011} and {120} crystal faces were inhibited due to the incorporation of l-leucine into these crystal faces in selected positions.

Crystallization of Lysozyme on Metal Surfaces Using a Monomode Microwave System

“…Subsequently, w e e x p e r i m e n t a l l y d e m o n s t r a t e d t h e r a p i d crystallization of amino acids and drug molecules on surfaces modified with silver nanoparticles using the MA-MAEC technique to date. Our initial experimental results indicated that the use of chemically deposited silver island films (a dis-continuous silvered surface) resulted in the rapid growth of crystals in conjunction with microwave heating [18,19,3,20,21,22]. In addition, we also demonstrated the proof-of-principle of the MA-MAEC technique for the crystallization of lysozyme using SNFs and a 700 W conventional microwave cavity [23].…”

Effect of Microwave Heating on the Crystallization of Glutathione Tripeptide on Silver Nanoparticle Films

“…Metal nanostructures of silver, gold, copper, nickel, and indium tin oxide are deposited onto poly(methyl methacrylate) (PMMA) platforms combined with silicon isolators (i.e., the iCrystal plates). 12–16 The unique design of the iCrystal plates ensures that microwave radiation is distributed homogeneously across the wells formed by the silicon isolator. 17,18 In studies based on the MA-MAEC technique by our research group to date, two different microwave systems operating at 2.45 GHz was employed: a multimode conventional microwave system (fixed power, 7001000 W) 10,11 and the iCrystal system (monomode, variable power up to 100 W).…”

“…19 Conventional microwave system is a commercially available microwave oven that was initially used to demonstrate the proof-of-principle demonstration and applications of the MA-MAEC technique for the crystallization of biological compounds. 11–16 The iCrystal microwave system is an instrument developed by our research group and was also employed for the crystallization of a variety of biomolecules. 19…”

Microwave intensified synthesis of regular shaped sodium bisulfate crystal

“…Microwave heating techniques, offers many advantages in terms of enhanced diffusion processes and significantly reduced processing times [10], are preferable for their high-efficiency in chemical synthesis and dehydration [11,12]. The microwave heating technology has also been applied into some fields such as material sciences [13,14], and pharmaceutical molecule crystallization [15][16][17].…”

“…It was found that microwave irradiation for evaporative crystallization of niflumic acid results in crystal size reduction due to the high evaporation rates [17]. However, the size of ʟ-Alanine crystals increase when utilizing microwave heating [15]. The consequences resulted from the nucleation and crystal growth in microwave were different because the properties of material such as structural and dielectric properties were different [20,21].…”