TY - JOUR

T1 - Structure-property relationships in the crystals of the smallest amino acid

T2 - An incoherent inelastic neutron scattering study of the glycine polymorphs

AU - Bordallo, Heloisa N.

AU - Boldyreva, Elena V.

AU - Buchsteiner, Alexandra

AU - Koza, Michael Marek

AU - Landsgesell, Sven

PY - 2008/7/24

Y1 - 2008/7/24

N2 - Incoherent inelastic neutron scattering spectra for the three crystalline polymorphs (α- P21/n, β- P21, γ- 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 β-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 α-form with respect to pressure and also depicted a sign of the previously reported reversible β-β′ glycine phase transition in between 0.6 and 0.8 GPa. Moreover, a remarkable kinetic effect in the pressure-induced phase transition in γ-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 β′-form) occurred, although previously in X-Ray diffraction and Raman spectroscopy experiments a γ- to δ-glycine phase transition was observed above 3.5 GPa only.

AB - Incoherent inelastic neutron scattering spectra for the three crystalline polymorphs (α- P21/n, β- P21, γ- 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 β-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 α-form with respect to pressure and also depicted a sign of the previously reported reversible β-β′ glycine phase transition in between 0.6 and 0.8 GPa. Moreover, a remarkable kinetic effect in the pressure-induced phase transition in γ-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 β′-form) occurred, although previously in X-Ray diffraction and Raman spectroscopy experiments a γ- to δ-glycine phase transition was observed above 3.5 GPa only.

UR - http://www.scopus.com/inward/record.url?scp=49149093516&partnerID=8YFLogxK

U2 - 10.1021/jp8014723

DO - 10.1021/jp8014723

M3 - Journal article

AN - SCOPUS:49149093516

VL - 112

SP - 8748

EP - 8759

JO - Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical

JF - Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical

SN - 1520-6106

IS - 29

ER -