Locally Preferred Structure and Frustration in Glassforming Liquids: A Clue to Polyamorphism?

We propose that the concept of liquids characterized by a given locally preferred structure (LPS) could help in understanding the observed phenomenon of polyamorphism. ``True polyamorphism'' would involve the competition between two (or more) distinct LPS, one favored at low pressure because of its low energy and one favored at high pressure because of its small specific volume, as in tetrahedrally coordinated systems. ``Apparent polyamorphism'' could be associated with the existence of a poorly crystallized defect-ordered phase with a large unit cell and small crystallites, which may be illustrated by the metastable glacial phase of the fragile glassformer triphenylphosphite; the apparent polyamorphism might result from structural frustration, i. e., a competition between the tendency to extend the LPS and a global constraint that prevents tiling of the whole space by the LPS.Comment: 11, 6 figures, Proceedings of the Conference "Horizons in Complex Systems", Messina; in honor of the 60th birthday of H.E. Stanle

Time-temperature superposition in viscous liquids

Dielectric relaxation measurements on supercooled triphenyl phosphite show that at low temperatures time-temperature superposition (TTS) is accurately obeyed for the primary (alpha) relaxation process. Measurements on 6 other molecular liquids close to the calorimetric glass transition indicate that TTS is linked to an $\omega^{-1/2}$ high-frequency decay of the alpha loss, while the loss peak width is nonuniversal.Comment: 4 page

Terahertz underdamped vibrational motion governs protein-ligand binding in solution

Low-frequency collective vibrational modes in proteins have been proposed as being responsible for efficiently directing biochemical reactions and biological energy transport. However, evidence of the existence of delocalized vibrational modes is scarce and proof of their involvement in biological function absent. Here we apply extremely sensitive femtosecond optical Kerr-effect spectroscopy to study the depolarized Raman spectra of lysozyme and its complex with the inhibitor triacetylchitotriose in solution. Underdamped delocalized vibrational modes in the terahertz frequency domain are identified and shown to blue-shift and strengthen upon inhibitor binding. This demonstrates that the ligand-binding coordinate in proteins is underdamped and not simply solvent-controlled as previously assumed. The presence of such underdamped delocalized modes in proteins may have significant implications for the understanding of the efficiency of ligand binding and protein–molecule interactions, and has wider implications for biochemical reactivity and biological function

Etude de la dynamique en régimes quasiharmonique et anharmonique de la phase basse température de la triéthylènediamine par diffusion cohérente inélastique des neutrons

Triethylenediamine N(CH2CH2)3N grows up to Tc in hexagonal compact ordered solid phase. Coherent inelastic neutron scattering in the low temperature phase has been used to understand the martensitic transition process at Tc from the evolution with temperature of the dynamical parameters. Thus, dispersion curves have been determined at 190 K, 245 K and 295 K. Measurements at room température have allowed to fit dispersion curves with a quasi-harmonic model. Then anharmonicity of librational phonons has been studied up to T c in several points of the Brillouin zone, in order to describe the motions which could possibly drive the h.c.p. → f.c.c. transition at Tc.La triéthylènediamine N(CH2CH2)3N cristallise jusqu'à Tc = 351 K dans une phase solide ordonnée de symétrie hexagonale compacte. Les expériences de diffusion cohérente inélastique des neutrons réalisées dans la phase basse température s'inscrivent dans le cadre de l'étude du processus de la transition martensitique à Tc à partir de l'évolution avec la température des paramètres dynamiques. Ainsi les courbes de dispersion ont été déterminées à 190 K, 245 K et 295 K. Les mesures effectuées à température ambiante ont permis d'ajuster les courbes de dispersion théoriques, calculées suivant un modèle quasi harmonique. Une étude de l'anharmonicité des modes de libration a été réalisée jusqu'à Tc en plusieurs points de la zone de Brillouin afin de décrire les mouvements susceptibles de piloter la transition h.c.p. → f.c.c. à Tc

Etude de la structure de la phase haute température de la triéthylènediamine sur des monocristaux fabriqués à 388 K

Triethylenediamine (N[CH2CH2]3N) undergoes a solid state structural transition at 351 K. Single crystals of phase I (above 351 K) have been grown in situ on the diffractometer by the Bridgmann method. The structure has been determined at T = 388 K. To solve the structure, two refinement procedures have been used : Frenkel model and decomposition of the orientational average density of the atoms on symmetry-adapted functions. The results confirm the space group Fm3m and coincidence of the three fold molecular and crystal axes. Around each direction there are two orientations separated by a 60° rotation about that direction.Le triéthylènediamine (N[CH2CH2]3N) présente une transition de phase solide ordonné-solide plastique à Tc = 351 K. Des monocristaux de triéthylènediamine dans sa phase haute température ont été obtenus in situ sur le diffractomètre par la méthode de Bridgmann. La structure a été déterminée à T = 388 K. Deux modèles ont été utilisés pour résoudre la structure ; le premier est un modèle de désordre statique, le second consiste à développer sur une base de fonctions adaptées à la symétrie du site et de la molécule le facteur de structure. Les résultats confirment le groupe spatial Fm3m ainsi que l'orientation de l'axe d'ordre trois moléculaire le long de la direction du cube avec deux positions d'équilibre

Solid-state loading of organic molecular materials within mesoporous silica matrix: Application to ibuprofen

International audienc

Analysis of the local order in the glacial state of triphenyl phosphite by neutron diffraction

A neutron diffraction study over a wide Q-range (Qmax = 16 Å-1 has been made in order to analyze the change of the local order of triphenyl phosphite through the isothermal transformation between the supercooled liquid into the glacial state at different temperatures Ta. Direct evidence is given from the analysis of the time-dependence of diffraction pattern, both in the low Q- and high Q-regimes that the structural changes observed during the glaciation are the signature of a crystallization process. Consequently, the transformation of the supercooled liquid into the glacial state can be interpreted as an abortive crystallization into a sub-microcrystalline state.status: publishe