Modification of morphology of polycarbonate/thermoplastic elastomer blends by supercritical CO2

The effect of supercritical CO2 on the morphological features of blends of polycarbonate and a commercial thermoplastic elastomer was investigated. The as-prepared films of the blend showed phase separated domains of the elastomer. With the combination of pressure and temperature, the large domains were "burst" into smaller domains. Temperatures higher than the critical temperature are required to cause any change in the morphology. The size distribution of the elastomer domains is effectively narrowed by the supercritical CO2 treatment. The time of exposure also plays a role. It was also seen that above 60 °C, crystallization of polycarbonate begins. Based on the previous work on this system, it is proposed that enhancement of elongation, Young's modulus and abrasion resistance would occur due to the reduction in the domain size and distribution

Orthogonally protected building blocks for automated glycan assembly

Summary Following an introduction to solid-phase carbohydrate chemistry and automated glycan assembly, we discuss the specific requirements for protecting groups (PGs) used in solid-phase chemistry. Besides routinely applied permanent and temporary PGs, specialized solutions for specific problems such as the introduction of β-mannosides are covered. Based on the available orthogonal PGs, a general strategy for the design of suitable building blocks for a given oligosaccharide target is proposed. A set of “approved” monosaccharide building blocks that have been successfully applied in the assembly of various oligosaccharides is presented. Exemplary syntheses of mammalian, microbial, and plant oligosaccharides are described to demonstrate the importance of choosing suitable orthogonally protected building blocks. Finally, an update on commercial automated oligosaccharide synthesizers is provided as well as a short outlook on the chances and challenges of automated glycan assembly

Function of the hydration layer around an antifreeze protein revealed by atomistic molecular dynamics simulations

Atomistic molecular dynamics simulations are used to investigate the mechanism by which the antifreeze protein from the spruce budworm, Choristoneura fumiferana, binds to ice. Comparison of structural and dynamic properties of the water around the three faces of the triangular prism-shaped protein in aqueous solution reveals that at low temperature the water structure is ordered and the dynamics slowed down around the ice-binding face of the protein, with a disordering effect observed around the other two faces. These results suggest a dual role for the solvation water around the protein. The preconfigured solvation shell around the ice-binding face is involved in the initial recognition and binding of the antifreeze protein to ice by lowering the barrier for binding and consolidation of the protein:ice interaction surface. Thus, the antifreeze protein can bind to the molecularly rough ice surface by becoming actively involved in the formation of its own binding site. Also, the disruption of water structure around the rest of the protein helps prevent the adsorbed protein becoming covered by further ice growth