title: Dynamics and thermodynamics of crystalline polymorphs. 2. β-Glycine, analysis of variable-temperature atomic displacement parameters.
abstract: The molecular dynamics in the crystal and the thermodynamic functions of the β-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(DFT:PM3) calculations on a 15-molecule β-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 β-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 β-phase with higher H and G is found to be less stable than the α-phase in the temperature range of the experiment.
authors.affiliation: Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. thammarat.aree@gmail.com
authors.forename: Thammarat
authors.initials: T
authors.lastname: Aree
authors.forename: Hans-Beat
authors.initials: HB
authors.lastname: Bürgi
authors.forename: Vasily S
authors.initials: VS
authors.lastname: Minkov
authors.forename: Elena V
authors.initials: EV
authors.lastname: Boldyreva
authors.forename: Dmitry
authors.initials: D
authors.lastname: Chernyshov
authors.forename: Karl W
authors.initials: KW
authors.lastname: Törnroos
mesh_terms: D003460:Crystallization; D005998:Glycine / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D013696:Temperature; D013816:Thermodynamics
chemical_list: D005998:Glycine