Protein crystallization in vivo

Protein crystallization in vivo provides some fascinating examples of biological self-assembly. Here, we provide a selective survey to show the diversity of functions for which protein crystals are used, and the physical properties of the crystals thatare exploited. Where known, we emphasize how the nature of the protein-protein interactions leads to control of the crystallization behaviour.Comment: 17 pages, 1 figur

On polydispersity and the hard-sphere glass transition

We simulate the dynamics of polydisperse hard spheres at high packing fractions, $\phi$, with an experimentally-realistic particle size distribution (PSD) and other commonly-used PSDs such as gaussian or top hat. We find that the mode of kinetic arrest depends on the PSD's shape and not only on its variance. For the experimentally-realistic PSD, the largest particles undergo an ideal glass transition at $\phi\sim 0.588$ while the smallest particles remain mobile. Such species-specific localisation was previously observed only in asymmetric binary mixtures. Our findings suggest that the recent observation of ergodic behavior up to $\phi \sim 0.6$ in a hard-sphere system is not evidence for activated dynamics, but an effect of polydispersity

Evaporation of Concentrated Polymer Solutions is Insensitive to Relative Humidity

A recent theory suggests that the evaporation kinetics of macromolecular solutions is insensitive to the ambient relative humidity (RH) due to the formation of a ‘polarisation layer’ of solutes at the air-solution interface. We confirm this insensitivity up to RH ≈ 80% in the evaporation of polyvinylalcohol solutions from open-ended capillaries. To explain the observed drop in evaporation rate at higher RH, we need to invoke compressive stresses due to interfacial polymer gelation. Moreover, RH-insensitive evaporation sets in earlier than theory predicts, suggesting a further role for a gelled ‘skin’. We discuss the relevance of these observations for respiratory virus transmission via aerosols

Turning a yield-stress calcite suspension into a shear-thickening one by tuning inter-particle friction

We show that a suspension of non-Brownian calcite particles in glycerol-water mixtures can be tuned continuously from being a yield-stress suspension to a shear-thickening suspension--without a measurable yield stress--by the addition of various surfactants. We interpret our results within a recent theoretical framework that models the rheological effects of stress-dependent constraints on inter-particle motion. Bare calcite particle suspensions are found to have finite yield stresses. In these suspensions, frictional contacts that constrain inter-particle sliding form at an infinitesimal applied stress and remain thereafter, while adhesive bonds that constrain inter-particle rotation are broken as the applied stress increases. Adding surfactants reduces the yield stress of such suspensions. We show that, contrary to the case of surfactant added to colloidal suspensions, this effect in non-Brownian suspensions is attributable to the emergence of a finite onset stress for the formation of frictional contacts. Our data suggest that the magnitude of this onset stress is set by the strength of surfactant adsorption to the particle surfaces, which therefore constitutes a new design principle for using surfactants to tune the rheology of formulations consisting of suspensions of adhesive non-Brownian particulates.Comment: 8 pages, 7 figure