Effect of microwave heating on the crystallization of glutathione (GSH) tripeptide using the metal-assisted and microwave-accelerated evaporative crystallization (MA-MAEC) technique is reported. GSH crystals were grown from supersaturated solutions of GSH (300–500 mg/mL) on the iCrystal plates with silver nanoparticle films (SNFs) and without SNFs in three different microwave systems operating at 2.45 GHz: conventional (multimode, fixed power at 900W), industrial (monomode, variable power up to 1200 W), and the iCrystal system (monomode, variable power up to 100 W). The efficacy of the MA-MAEC technique, in terms of improvement in the crystallization time, crystal size and quality of GSH, was compared between the three microwave systems and the crystallization at room temperature (no microwave heating, a control experiment). Optical microscopy was used to visualize and quantify the growth of GSH crystals during and after microwave heating. Powder X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy data showed that GSH crystals had identical crystal structure to those grown at room temperature and microwave heating did not alter the chemical structure of GSH molecules during microwave heating, respectively. Using the MA-MAEC technique, the iCrystal system yielded high quality GSH crystals in a rapid manner.

Effect of intermittent monomode microwave heating on the crystallization of glutathione (GSH) and lysozyme on indium tin oxide (ITO) films using the metal-assisted and microwave-accelerated evaporative crystallization (MA-MAEC) technique was investigated. Intermittent time intervals of 5, 10, 15, 30, 40, 60, 120, 180, 240 min and 30, 40, 60, 120, 180, 240 min were employed for microwave heating of solutions of GSH (500 mg/mL) and lysozyme (40 mg/mL) using a monomode microwave source at 70 W, respectively. Optical microscopy and ImageJ software were employed to quantify and compare the size and number of GSH and lysozyme crystals grown at different microwave heating time intervals. The rate of crystallization for GSH crystals was found to be the fastest at ~ 7.52 μm/ min for the 5 min interval of microwave heating and decreased to 0.57 μm/min as the time interval of microwave heating was increased to 240 min. The rate of crystallization for lysozyme crystals was found to be 0.20 ~ 0.27 μm/min for 30-120 min of microwave heating and decreased to 0.07 μm/min as the time interval of microwave heating was increased to 240 min. Intermittent microwave heating of GSH and lysozyme solutions were found to have a minimal influence on the size and count of the crystals produced. X-ray crystallography studies and Fourier transform infrared (FTIR) spectroscopic analysis of grown crystals confirmed that the duration of microwave heating have no or little effect on the crystal morphology and molecular structure of biomolecules studied.