Dendritic Growth of Glycine from Nonphotochemical Laser-Induced Nucleation of Supersaturated Aqueous Solutions in Agarose Gels

We have observed two new morphologies of crystalline glycine grown from supersaturated aqueous solutions in agarose gels: tree-branch dendrites that nucleate spontaneously from a solution interface or by non-photochemical laser-induced nucleation (NPLIN) at the air-solution interface, and stellar dendrites that nucleate in the bulk of the solution induced only by laser irradiation. The tree-branch dendrites always consist of parallel, needle-like microcrystals of alpha-glycine and always grow unidirectionally in the c-direction, forming branches with small branching angles. The four-armed stellar dendrites consist of conglomerates of plate-like microcrystals of either alpha- or gamma-glycine or a mixture of microcrystals of the two polymorphs, with the gamma-glycine microcrystals concentrated in the core of the dendrite. The plate-like microcrystals of alpha-glycine grow primarily in the c- and a-directions. The stellar dendrite arm orientation is uncorrelated with the plane of polarization of the incident light, which does not lend support to the induced-polarization mechanism for NPLIN.