Selective Fabrication of alpha- and gamma-Polymorphs of Glycine by Intense Polarized Continuous Wave Laser Beams

Abstract

The polymorph control of glycine in D2O solution is successfully demonstrated by a laser trapping technique using a linearly or circularly polarized CW near-infrared laser beam. Focusing each laser beam into an air/solution interface of the solution always generates the stable crystal polymorph of either alpha- or gamma-form at the focal spot. The formation probability of each polymorph strongly depends on various experimental conditions of laser polarization, power, and solution concentration. For the supersaturated and saturated solutions, circularly polarized laser irradiation enhances gamma-crystal formation, while for the unsaturated solution the laser polarization effect becomes prominent and linearly polarized laser light at a specific power provides the maximum gamma-crystal probability of 90%. The present polymorphism is achieved by laser-induced effects such as concentration increase, temperature elevation, and molecular rearrangement, whose mechanism is discussed in view of laser polarization dependence of these effects.