Molecular dynamics in DTGS ND3 by quasielastic and inelastic neutron scattering

The paper presents the last of our QENS and INS measurements on triglycine sulphate DTGS ND3 at NEAT BENSC neutron spectrometer. Using an energy window of 0.093 meV we have completed the information obtained in our previous measurements that were carried on non deuterated TGS. By replacing the protons from amino groups of TGS with deuterons we have been able to observe the dynamical changes in the QENS pattern. The quasielastic line broadening in this case is mainly due to the flip jump diffusion motion of the protons which belong to CH2 group of the GI glycine molecule in DTGS. The residence time associated to this motion is about 4.2 ps. The second part of the paper is devoted to lattice phonons and internal molecular normal modes. The peaks observed in the generalized density of states were compared with optical spectroscopy data. The agreement is goo

An equipment for Rayleigh scattering of Mössbauer radiation

A personal computer driven equipment designed for Rayleigh scattering of Mössbauer radiation experiments at room temperature is described. The performances of the system were tested using like scatterers crystals with different mosaic divergences: lithium fluoride (LiF) and pyrolytic graphite (C). The equipment, suitable for any kind of Mössbauer scattering experiments, permits low and adjustable horizontal divergences of the incident beam

Dynamics of amino GI glycine molecule in triglycine sulphate by incoherent quasielastic neutron scattering

In the present work we present our experimental results concerning the molecular dynamics on a TGS polycrystaline sample, at different temperatures, using the Incoherent Quasi Elastic Neutron Scattering TOF method. The measurements were carried out above and below the critical temperature associated with ferroelectric paraelectric phase transition, which characterize the TGS compound. The dynamics of GI glycine molecule consists of two main motions The flip motion of the GI molecule from one side to another side of the mirror symmetry planes that are present at b 1 4 and b 3 4 in TGS unit cell. The rotational motion of the amino group around C N molecular axis during the flipping. By using the advantages provided by IQENS technique and applying the most suited models we have evaluated the characteristic times and energy levels of these molecular motion

Molecular dynamics in triglycine sulphate by cold neutron spectroscopy

Molecular dynamics of the ferroelectric compound triglycine sulphate (TGS) was studied by quasi-elastic neutron scattering. From among the three glycine molecules forming the unit cell the non-planar GI molecule is responsible for the polarisation which occurs in crystal and for the order-disorder ferroelectric phase transition at T-c = 49 degrees C. This molecule also shows a complex dynamics much faster than that performed by the other glycine molecules. The key group of this molecule is the amino group that, on one hand, seems to be responsible for the phase transition and, on the other hand, performs motional processes spread on a wide time scale. These motions have been detailed studied by means of different energy resolution windows within the quasi-clastic scattering range. We found that the dynamics of this group develops in a restricted spatial volume and consists in a faster rotational diffusion around the molecular axis of the group and a slower flipping dynamics between two symmetrical positions on both sides of a mirror plane containing the molecular axis of GI molecule. (c) 2005 Elsevier B.V. All rights reserved

Hydration of Sodium Alginate in Aqueous Solution

Alginates are naturally occurring biocompatible polysaccharides. They have a broad range of applications, mainly in connection to their ability to control the rheol. of aq. solns. Specifically, addn. of a small amt. of alginate (10% wt) leads to a ~100-fold increase in viscosity. Here we explore whether that pronounced retardation of the long-range correlations is accompanied by mol.-level changes of the water structure. We employ viscometry, dielec. spectroscopy (DS) and femtosecond IR (fs-IR) pump-probe spectroscopy to study water dynamics in sodium alginate solns. Remarkably, despite the large rheol. effects of alginates in soln., the rotational dynamics of water are remarkably similar to those obsd. in bulk water. Only a small subensemble of water mols. is slowed down significantly, amounting to 6 ± 2 water mols. per saccharide unit. Furthermore, DS measurements reveal an addnl. ~5 water mols. to be slowed down by the counterion (Na+). Our results reveal that the effect of alginate on the dynamics of water is restricted to the first hydration shell. This indicates that the large viscosity increase is detd. by the polysaccharide network, with large water pools present between the polysaccharide chains. [on SciFinder(R)