Document Detail

Structure-property relationships in the crystals of the smallest amino acid: an incoherent inelastic neutron scattering study of the glycine polymorphs.
MedLine Citation:
PMID:  18578525     Owner:  NLM     Status:  MEDLINE    
Incoherent inelastic neutron scattering spectra for the three crystalline polymorphs (alpha- P2(1)/n, beta- P2(1), gamma- P3(1)) of glycine (C2H5NO2) at temperatures between 5 and 300 K (using the time-of-flight (ToF) spectrometer NEAT at HMI) and at pressures from ambient up to 1 GPa (using the ToF spectrometer IN6 at the ILL) were measured. Significant differences in the band positions and their relative intensities in the density of states (DoS) were observed for the three polymorphs, which can be related to the different intermolecular interactions. The mean-squared displacement, <u(2)>(T), dependence reveals a change in dynamic properties at about the same temperature (150 K) for all the three forms, which can be related to the reorientation of the NH3 group. Besides, a dynamic transition in beta-glycine at about 230-250 K on cooling was also observed, supporting previously obtained adiabatic calorimetry data. This behavior is similar to that already observed in amorphous solids, on approaching the glass transition temperatures, as well as in biological systems. It suggests the onset of degrees of freedom most likely related to transitions between slightly different conformational orientations. The DoS obtained as a function of pressure has confirmed the stability of the alpha-form with respect to pressure and also depicted a sign of the previously reported reversible beta-beta' glycine phase transition in between 0.6 and 0.8 GPa. Moreover, a remarkable kinetic effect in the pressure-induced phase transition in gamma-glycine was revealed. After the sample was kept at 0.8 GPa for an hour in the neutron beam, an irreversible transition into a high-pressure form (different from the beta'-form) occurred, although previously in X-Ray diffraction and Raman spectroscopy experiments a gamma- to delta-glycine phase transition was observed above 3.5 GPa only.
Heloisa N Bordallo; Elena V Boldyreva; Alexandra Buchsteiner; Michael Marek Koza; Sven Landsgesell
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2008-06-26
Journal Detail:
Title:  The journal of physical chemistry. B     Volume:  112     ISSN:  1520-6106     ISO Abbreviation:  J Phys Chem B     Publication Date:  2008 Jul 
Date Detail:
Created Date:  2008-07-21     Completed Date:  2008-11-13     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101157530     Medline TA:  J Phys Chem B     Country:  United States    
Other Details:
Languages:  eng     Pagination:  8748-59     Citation Subset:  IM    
Hahn-Meitner-Institut, Glienicker Strasse, 100 14109 Berlin, Germany.
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MeSH Terms
Amino Acids / chemistry*
Calorimetry, Differential Scanning
Glycine / chemistry*
Models, Molecular
Phase Transition
Spectrum Analysis, Raman
X-Ray Diffraction
Reg. No./Substance:
0/Amino Acids; 56-40-6/Glycine

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