Dynamical and orientational structural crossovers in low-temperature glycerol

Abstract

Mean square displacements of hydrogen atoms in glass-forming materials and proteins, as reported by incoherent elastic neutron scattering, show kinks in their temperature dependence. This crossover, known as the dynamical transition, connects two approximately linear regimes. It is often assigned to the dynamical freezing of subsets of molecular modes at the point of equality between their corresponding relaxation times and the instrumental observation window. The origin of the dynamical transition in glass-forming glycerol is studied here by extensive molecular dynamics simulations. We find the dynamical transition to occur for both the center of mass translations and the molecular rotations at the same temperature, insensitive to changes of the observation window. Both the translational and rotational dynamics of glycerol show a dynamic crossover from the structural to a secondary relaxation at the temperature of the dynamical transition. A significant and discontinuous increase in the orientational Kirkwood factor and in the dielectric constant is observed in the same range of temperatures. We, however, do not find any indications of a true thermodynamic transition to an ordered low-temperature phase. We therefore suggest that all observed crossovers are dynamic in character. The increase in the dielectric constant is related to the dynamic freezing of dipolar domains on the time-scale of simulations.

Insights into Hydration Dynamics and Cooperative Interactions in Glycerol–Water Mixtures by Terahertz Dielectric Spectroscopy

“…is an important co-solvent in this context, which was a subject of numerous studies in molecular dynamics (MD) simulations [8][9][10][11][12][13] and experiments. [14][15][16] At ambient conditions, this trihydric alcohol with three hydroxyl groups is a colorless, sugar-like, highly viscous liquid.…”

“…The study of the dynamics of these chemical biomolecules is indispensable to get a comprehensive perception of their conduct in aqueous solutions. Glycerol (C 3 H 8 O 3 ) is an important cosolvent in this context, which was a subject of numerous studies in molecular dynamics (MD) simulations − and experiments. − At ambient conditions, this trihydric alcohol with three hydroxyl groups is a colorless, sugar-like, highly viscous liquid. The high flexibility and viscosity of glycerol make it an important system in studies of the glass transition .…”

Complex Dynamics of Water in Protein Confinement

“…To a good approximation, in particular for low values of k , the ISF can be split into the contribution from the center of mass motions and rotations about the center of mass − with F T ( k , t ) and F R ( k , t ) being the translational and rotational ISF, respectively. They are given by the following equations and In eqs and r 0 i are the center of mass positions of the water molecules and d i are the position of the hydrogen atoms relative to the center of mass.…”

Orientational dynamics in supercooled glycerol computed from MD simulations: self and cross contributions

“…Glycerol, by its apparent simplicity and its low tendency to crystallize, has long been the subject of extensive studies, by various techniques including dielectric spectroscopy, 2,11,[30][31][32] neutron spectroscopy, 33 nuclear magnetic resonance (NMR), 34 DDLS 35,36 and MD simulations. [37][38][39][40][41][42][43][44] Its dynamics is, however, not particularly simple. As a tri-alcool, it is subject to H-bonds but does not display a Debye peak that would result from linear supramolecular chains.…”