Alamethicin channels – modelling via restrained molecular dynamics simulations

AbstractAlamethicin channels have been modelled as approximately parallel bundles of transbilayer helices containing between N=4 and 8 helices per bundle. Initial models were generated by in vacuo restrained molecular dynamics (MD) simulations, and were refined by 60 ps MD simulations with water molecules present within and at the mouths of the central pore. The helix bundles were stabilized by networks of H-bonds between intra-pore water molecules and Gln-7 side-chains. Channel conductances were predicted on the basis of pore radius profiles, and suggested that the N=4 bundle formed an occluded pore, whereas pores with N≥5 helices per bundle were open. Continuum electrostatics calculations suggested that the N=6 pore is cation-selective, whereas pores with N≥7 helices per bundle were predicted to be somewhat less ion-selective

Dynamic mechanical thermal analysis of aqueous sugar solutions containing fructose, glucose, sucrose, maltose and lactose

The glass transition of glucose, fructose, lactose, maltose and sucrose solutions at maximum cryo-concentration was studied by Dynamic Mechanical Thermal Analysis (DMTA), using the disc bending technique. The glass transition temperatures were determined from the peaks in the loss modulus E′′, which corresponds theoretically to the resonance point (Maxwell model) for several input frequencies. The frequency dependence was well described by both an Arrhenius-type model and by the WLF (Williams, Landel and Ferry) equation, yielding glass transition temperatures for an average molecular vibration time of 100 s, which were similar to published midpoint temperatures determined by DSC scans. Some sugar mixtures were studied, yielding results that were well described by the Gordon–Taylor equation, using literature data. The frequency dependence of the viscoelastic ratio was also well approximated by an Arrhenius-type equation, with activation energies similar to those of the glass transition temperature and corresponded well to published values of the endset of glass transition

Horizontal effects in double-diffusive convection

SIGLEAvailable from British Library Document Supply Centre- DSC:DX81727 / BLDSC - British Library Document Supply CentreGBUnited Kingdo