No abstract

Salt, glycerol, and dimethyl sulfoxide (DMSO) are used to modify the properties of protein solutions. We experimentally determined the effect of these additives on the phase behavior of lysozyme solutions. Upon the addition of glycerol and DMSO, the fluid-solid transition and the gas-liquid coexistence curve (binodal) shift to lower temperatures and the gap between them increases. The experimentally observed trends are consistent with our theoretical predictions based on the thermodynamic perturbation theory and the Derjaguin-Landau-Verwey-Overbeek model for the lysozyme-lysozyme pair interactions. The values of the parameters describing the interactions, namely the refractive indices, dielectric constants, Hamaker constant and cut-off length, are extracted from literature or are experimentally determined by independent experiments, including static light scattering, to determine the second virial coefficient. We observe that both, glycerol and DMSO, render the potential more repulsive, while sodium chloride reduces the repulsion.

To gain insight into the fundamental processes determining the motion of macromolecules in polymeric matrices, the dynamical hindrance of polymeric dextran molecules diffusing as probe through a polyacrylamide hydrogel is systematically explored. Three complementary experimental methods combined with Brownian dynamics simulations are used to study a broad range of dextran molecular weights and salt concentrations. While multi-parameter fluorescence image spectroscopy (MFIS) is applied to investigate the local diffusion of single molecules on a microscopic length scale inside the hydrogel, a macroscopic transmission imaging (MTI) fluorescence technique and nuclear magnetic resonance (NMR) are used to study the collective motion of dextrans on the macroscopic scale. These fundamentally different experimental methods, probing different length scales of the system, yield long-time diffusion coefficients for the dextran molecules which agree quantitatively. The measured diffusion coefficients decay markedly with increasing molecular weight of the dextran and fall onto a master curve. The observed trends of the hindrance factors are consistent with Brownian dynamics simulations. The simulations also allow us to estimate the mean pore size for the herein investigated experimental conditions. In addition to the diffusing molecules, MFIS detects temporarily trapped molecules inside the matrix with diffusion times above 10 ms, which is also confirmed by anisotropy analysis. The fraction of bound molecules depends on the ionic strength of the solution and the charge of the dye. Using fluorescence intensity analysis, also MTI confirms the observation of the interaction of dextrans with the hydrogel. Moreover, pixelwise analysis permits to show significant heterogeneity of the gel on the microscopic scale.

Ceramic composites found in nature, such as bone, nacre, and sponge spicule, often provide an effective resolution to a wellknown conflict between materials' strength and toughness. This arises, on the one hand, from their high ceramic content that ensures high strength of the material. On the other hand, various pathways are provided for stress dissipation, and thus toughness, due to their intricate hierarchical architectures. Such pathways include crack bridging, crack deflection, and delamination in the case of layered structures. On the basis of these inspiring ideas, we attempted here to create simultaneously strong and tough laminated alumina composite with high ceramic content. Composites were prepared from highgrade commercial alumina with spin-coated interlayers of ductile polymers (PMMA and PVA). The specimens' ultimate properties (strength, fracture toughness, and work of fracture) were measured by a four-point bending method. In some cases, fracture toughness of the composites was increased by up to an order of magnitude, reminiscent of the natural layered composites. It is proposed that this increase may be attributed to an interlocking mechanism, often encountered in biological composites. The significance of sample architecture and the role of the interfacial and bulk properties of the interlayer material are discussed. J ournalspicule. The structural architecture and interlayer adhesion will be viewed as variable parameters, the optimized values of which will hopefully lead to a tough and strong composite with high ceramic content. Emphasis is put here on the use of simple, affordable materials and techniques so as to demonstrate the universality and applicability of bioinspired toughening mechanisms. Supporting InformationAdditional Supporting Information may be found in the online version of this article:

Protein phase behavior and protein-protein interactions can be tuned by additives. We experimentally determined the phase behavior of lysozyme solutions, namely, the cloud-point temperature (CPT), in the presence of two additives, sodium chloride (NaCl) and guanidine hydrochloride (GuHCl). Their concentrations are chosen to maintain the secondary structure, as verified by CD spectroscopy. Our data indicate that the salts affect the CPT through electrostatic screening and salt-specific contributions. At high salt concentrations, the CPT is a linear function of the additive concentration for the salts NaCl and GuHCl as well as for a nonionic additive, glycerol, and a solvent, dimethyl sulfoxide (DMSO). Their molar temperature increments, which rank their specific effects on the CPT (NaCl > 0 > DMSO > glycerol > GuHCl), are found to be essentially independent of the protein concentration. In particular, the specific effects of NaCl and GuHCl in mixtures are found to be additive, indicating the absence of synergies or suppressions between both salts. Thus, molar temperature increments represent a characteristic measure for the specific effects of additives on protein interactions, which is easily accessible in lab experiments and which will help to characterize the effects of additives on protein interactions and phase behavior.