Crystal growth of α and γ glycine polymorphs and their polymorphic phase transformations

Journal of Crystal Growth (Impact Factor: 1.69). 12/2008; 311(1):156-162. DOI: 10.1016/j.jcrysgro.2008.10.084

ABSTRACT The single crystals of α and γ polymorphs of glycine were grown from aqueous solutions at ambient conditions. The metastable α-form was crystallized from pure aqueous solution and the stable γ-form from aqueous solution in the presence of a critical concentration of a selective additive sodium chloride. Attempt to grow sizable β-form single crystals were not successful because of their high instability. In stability terms at ambient conditions these three glycine polymorphs are like this: β

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    ABSTRACT: Glycine is the simplest achiral amino acid that undergoes spontaneous mirror symmetry breaking when it crystallizes in its chiral γ-polymorphic modification. As a result of Ostwald ripening, its racemic mixture stochastically becomes optically active. The sense of the resulting handedness can be controlled by addition of one enantiomer of a simple chiral amino acid, the alanine.
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    ABSTRACT: In glycine crystal the transformation from γ to α modification has been investigated using differential scanning calorimetry (DSC) and low-frequency dielectric spectroscopy methods on powder and monocrystalline samples. In monocrystalline samples the transition begins at 457.5 K. The first step is connected with cracking of the sample and growing of the ac conductivity which reaches maximum at 458.5 K. Next, ac conductivity achieves a huge maximum at the transition point 462.8 K. Additional small anomaly in the complex dielectric constant was revealed at 335 K. In powder samples this transformation measured by the DSC method goes uniformly. For these samples the ac conductivity begins to grow rapidly from 455 K and grows 2.5 times in the range of 383–387 K. In powder samples the ac conductivity at the transition point is seven times greater than in the monocrystalline samples. Conductivity anomalies are accompanied by changes in the real part of the dielectric constant.
    Phase Transitions 11/2014; 87(10-11). DOI:10.1080/01411594.2014.953951 · 1.04 Impact Factor