Homogeneous and heterogeneous dynamics in native and denatured bovine serum albumin.

A characteristic property of unfolded and disordered proteins is their high molecular flexibility, which enables the exploration of a large conformational space. We present neutron scattering experiments on the dynamics of denatured and native folded bovine serum albumin (BSA) in solution. Global protein diffusion and internal macromolecular dynamics were measured using quasielastic neutron time-of-flight and backscattering spectroscopy on the picosecond to nanosecond time- and Ångstrom length-scale. Internal protein dynamics were analysed in a first approach using stretched exponential functions. In denatured BSA predominantly slow heterogeneous dynamics dominates the observed macromolecular motions. Reduction of disulphide bridges in denatured BSA does not significantly alter the visible motions. In native folded BSA fast homogeneous dynamics and slow heterogeneous dynamics were observed. In an alternative data analysis approach, internal protein dynamics was interpreted using the analytical model of the overdamped Brownian oscillator, which allowed us to extract mean square displacements of protein internal dynamics and the fraction of hydrogen atoms participating in the observed motions. Our results demonstrate that denaturation modifies the physical nature of internal protein dynamics significantly as compared to the native folded structure.

Dynamics of water confined in mesoporous magnesium carbonate.

We have measured the dynamics of water confined in a porous magnesium carbonate material, Upsalite®, using the high-resolution neutron backscattering spectrometer SPHERES. We found quasielastic scattering that does not flatten out up to 360 K, which means that the dynamics of water are much slower than in other matrix materials. Specifically, a single Lorentzian line could be fitted to the quasielastic part of the acquired spectra between 220 and 360 K. This, accompanied by an elastic line from dynamically frozen water present at all experimental temperatures, even above the melting point, signaled a significant amount of bound or slow water.

Polymer confinement effects in aligned carbon nanotubes arrays.

We present experimental and theoretical studies on the infiltration of polymers (polystyrene (PS), polymethylmethacrylate (PMMA)) into the free interstices of 3D aligned carbon nanotube arrays. The 3D aligned CNT structures were prepared by a template assisted non catalytic CVD approach. The infiltrated CNT/polymer composites were characterized by microscopic techniques such as infra-red and Raman spectroscopy. Small angle X-ray scattering (SAXS) has been employed to study the structural evolution and polymer confinement after the polymers are infiltrated in the aligned arrays of CNTs. A theoretical model has been used to understand and predict possible confinement effects of these polymers within the aligned CNT arrays, using self-consistent field theory (SCFT) and Monte-Carlo simulations based on the bond-fluctuation model.