Spectroscopic Study of the Effects of Bioprotectant Systems on the Protein Stability

In the present article the effect of kosmotrope compounds, i.e. systems having the capability to stabilize biological macromolecules, is investigated by using complementary techniques. The attention is focused on the kosmotrope character of trehalose, a glucose disaccharide, compared to its homologous maltose and sucrose. Complementary techniques of neutron scattering, such as Inelastic Neutron Scattering (INS) and Quasi Elastic Neutron Scattering (QENS) allow to point out the capability of trehalose to strongly affect both the structural and dynamical properties of water. Finally the stabilization effect of trehalose on a well know protein, lysozyme, is studied as a function of temperature by Small Angle Neutron Scattering (SANS)

Effect of chain length and topological constraints on segmental relaxation in cyclic PDMS

We present a detailed investigation of local dynamics of linear and cyclic poly(dimethylsiloxane) (PDMS) covering a wide range of molar masses. To aid interpretation of the experimental data, QENS measurements in the time scale from 2 to 200 ps and at Q = 0.3 to 1.8 Å–1 are complemented by theoretical calculations. These make use of a methodology developed by us elsewhere applicable to both simple chain models and real chains and applied here, for the first time, to cyclic PDMS. Analysis of the incoherent dynamic structure factor at T < Tm shows that the rotational motion of the methyl groups is unaffected by polymer topology. At higher temperatures, the QENS data are described by a model that consists of two dynamic contributions: methyl group rotation and segmental motion, the latter described by a stretched exponential function. Relaxation times of both linear and cyclic PDMS increase with increasing molar mass. Several features predicted by theory are also reproduced by the experimental data. We show, unambiguously, that rings have higher relaxation times for the segmental motion compared to linear chains of the same number of monomer units. Theoretical calculations support the idea that such slowing down of local dynamics is due to the topological constraint imposed by the ring closure, a constraint which becomes negligible for very large molar masses. Our calculations suggest that due to its albeit small conformational rigidity, cyclic PDMS undergoes an additional constraint which further increases the relaxation time, producing a shallow maximum for N ≈ 50 repeat units. A similar feature is also observed in the experimental QENS data. Values of activation energy, Ea, are derived from analysis of the temperature dependence of the quasi-elastic broadening and are found to be in agreement with viscosity measurements reported in the literature. Although the pronounced molar mass dependence of Ea for linear PDMS is certainly linked to the presence of mobile chain ends, for the cyclic polymers the behavior appears to be more complex than anticipated

Electron transfer in dextran probed by longitudinal field muon spin relaxation

Electron-transfer processes play a crucial role in bio-nanobattery design, the electron transfer rate through the organic material being a key parameter in determining the resistance, maximum current, power density, discharge rate and duty cycle of the cell. The labelled electron method using positive muons allows such transfer processes in macromolecules, such as polymers and proteins, to be probed on a microscopic level. Here we present the results of an experiment using the labelled electron method with longitudinal field muon spin relaxation (LF-μSR) to investigate electron-transfer processes in dextran. The data are well described using the Risch–Kehr model and the results suggest intra-chain diffusion is the dominant transport process in this systembetween 15 and 250 K. Intra-chain diffusion rates of 1013 s−1 have been determined

Electron transfer in dextran probed by longitudinal field muon spin relaxation

Electron-transfer processes play a crucial role in bio-nanobattery design, theelectron transfer rate through the organic material being a key parameter indetermining the resistance, maximum current, power density, discharge rate andduty cycle of the cell. The labelled electron method using positive muons allowssuch transfer processes in macromolecules, such as polymers and proteins, tobe probed on a microscopic level. Here we present the results of an experimentusing the labelled electron method with longitudinal field muon spin relaxation(LF-μSR) to investigate electron-transfer processes in dextran. The data arewell described using the Risch–Kehr model and the results suggest intra-chaindiffusion is the dominant transport process in this systembetween 15 and 250 K.Intra-chain diffusion rates of 1013 s−1 have been determined