Of ¦Á-glycine Crystal Preparation And Its Temperature-dependent Raman Spectroscopy Study

Glycine, a biologically important compound, is the simplest and uniquely achiral among the amino acids. Investigation of glycine could be far-reaching with respect to protein structure and the origins of biochirality. In the crystalline state, glycine hasα,βandγ-polymorphs, existing as zwitterionic form (NH3+CH2COO?).α-glycine has monoclinic structure (space group symmetry P21/n) with four formula units per unit cell. High-purity single crystals ofα-glycine were grown from saturated aqueous solution ofα-glycine by slow evaporation at 277K. In 1999, Chilcott found that electrical impedance measurements of single crystal glycine revealed anomalous temperature dependence of the conductance and capacitance around 304K. This unusual electric behavior was not explained by the conduction mechanism. The present paper investigates temperature-dependent Raman spectra ofα-glycine single crystal at different temperatures. We find a discontinuous frequency variation of the NH3+ torsional mode ofα-glycine crystal around 304K, which was assumed due to the NH3+ torsion mode splitting and deformations. The electrical dipoles of NH3+CH2COO? are reoriented and the crystal had to undergo a ferroelectric transition around 304K.Raman spectra ofα-glycine polycrystalline powder are also studied from 90 to 400K. we found frequency variation of the NH3+ torsional mode in polycrystalline powder exhibits a similar discontinuous change around 304K. Because the polarization of a ferroelectric is an effect inherent in the entire structure of the crystal, polycrystalline powder could also undergo a ferroelectric transition around 304K. 162cm-1 ,CH2 twist ,CH2bend ,CH2 asym str, COO -1bend, COO -1asym str, CN str , NH3+ torsion and NH3+ sym def mode show splitting , the reasons of which are explained.