Dynamics and thermodynamics of crystalline polymorphs. 2. ß-Glycine, analysis of variable-temperature atomic displacement parameters.
J Phys Chem A
; 117(33): 8001-9, 2013 Aug 22.
Article
em En
| MEDLINE
| ID: mdl-23865724
ABSTRACT
The molecular dynamics in the crystal and the thermodynamic functions of the ß-polymorph of glycine have been determined from a combination of molecular translation-libration frequencies reflecting the temperature dependence of atomic displacement parameters (ADPs), with frequencies derived from ONIOM(DFTPM3) calculations on a 15-molecule ß-glycine cluster. ADPs have been obtained from variable-temperature diffraction data to 0.5 Å resolution collected with X-ray synchrotron (10-300 K) and sealed tube radiation (50-298 K). At the higher temperatures, the ADPs of ß-glycine from synchrotron are larger than those from sealed tube probably due to different experimental conditions. The lattice vibration frequencies from normal-mode analysis of ADPs and the internal vibration frequencies from ONIOM(B3LYP/6-311+G(2d,p)PM3) calculations agree with those from spectroscopy. Estimation of thermodynamic functions using the vibrational frequencies, the Einstein and Debye models of heat capacity, and the room-temperature compressibility provides C(p), H(vib), and S(vib) that agree with those from calorimetry. The ß-phase with higher H and G is found to be less stable than the α-phase in the temperature range of the experiment.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Temperatura
/
Termodinâmica
/
Simulação de Dinâmica Molecular
/
Glicina
Tipo de estudo:
Prognostic_studies
Idioma:
En
Revista:
J Phys Chem A
Assunto da revista:
QUIMICA
Ano de publicação:
2013
Tipo de documento:
Article
País de afiliação:
Tailândia