Direct participation of counter anion in acid hydrolysis of glycoside

The mechanism of acid hydrolysis of glycoside has been investigated since the end of the 19th century accompanied by lots of literatures published on the mechanism, although little attention has surprisingly been paid to the action of counter anion of acid. In this paper, it was investigated whether or not counter anion of acid directly participates in acid hydrolysis of glycosides, methyl α- and β-d-glucopyranosides (MGP) in water, aqueous 74%, and 82% 1,4-dioxane systems. Because proton activity of a reaction system is the important rate-determining parameter in the universally acknowledged mechanism, it was carefully estimated in this study. The results suggested that bromide anion directly participates in the acid hydrolysis reaction of MGP in a water solvent system and the participation of bromide anion is further pronounced in aqueous 74% and 82% 1,4-dioxane solvent systems. It was also suggested that chloride anion directly participates in these dioxane solvent systems.     

Synthesis of heparin oligosaccharides and their interaction with eosinophil-derived neurotoxin

A convenient route for the synthesis of heparin oligosaccharides involving regioselective protection of D-glucosamine and a concise preparation of rare L-ido sugars from diacetone α-D-glucose is described. Stereoselective coupling of a D-glucosamine-derived trichloroacetimidate with a 1,6-anhydro-β-L-idopyranosyl 4-alcohol gave the desired α-linked disaccharide, which was used as repeating unit for dual chain elongation and termination. Stepwise assembly from the reducing to the non-reducing end with a D-glucosamine-derived monosaccharide as starting unit furnished the oligosaccharide skeletons having different chain lengths. A series of functional group transformations afforded the expected heparin oligosaccharides with 3, 5 and 7 sugar units. Interaction of these oligosaccharides with eosinophil-derived neurotoxin (EDN), a cationic ribonuclease and a mediator produced by human eosinophils, was further investigated. The results revealed that at 5 μg mL(-1), the heptasaccharide has sufficiently strong interference to block EDN binding to Beas-2B cells. The tri- and pentasaccharides have moderate inhibitory properties at 50 μg mL(-1) concentration, but no inhibition has been observed at 10 μg mL(-1). The IC(50) values of the tri-, penta- and heptasaccharides are 69.4, 47.2 and 0.225 μg mL(-1), respectively.     

The first synthesis of an epidiselenodiketopiperazine

Epidithiodiketopiperazines (ETPs) are natural products (e.g., gliotoxin) with varied and important biological activity, which often is attributed to the redox properties of the disulfide moiety. As such, analogs with altered redox properties and similar structural characteristics would be of value to biological investigations. The use of an ETP as the point of departure in the first synthesis of an epidiselenodiketopiperazine (ESeP) and its activity against Mycobacterium tuberculosis (MTB) is reported.     

Pathway-Selective Sensitization of Mycobacterium tuberculosis for Target-Based Whole-Cell Screening

Whole-cell screening of Mycobacterium tuberculosis (Mtb) remains a mainstay of drug discovery, but subsequent target elucidation often proves difficult. Conditional mutants that underexpress essential genes have been used to identify compounds with known mechanism of action by target-based whole-cell screening (TB-WCS). Here, the feasibility of TB-WCS in Mtb was assessed by generating mutants that conditionally express pantothenate synthetase (panC), diaminopimelate decarboxylase (lysA), and isocitrate lyase (icl1). The essentiality of panC and lysA, and conditional essentiality of icl1 for growth on fatty acids, was confirmed. Depletion of PanC and Icl1 rendered mutants hypersensitive to target-specific inhibitors. Stable reporter strains were generated for use in high-throughput screening, and their utility was demonstrated by identifying compounds that display greater potency against a PanC-depleted strain. These findings illustrate the power of TB-WCS as a tool for tuberculosis drug discovery.     

Avoidance of Majorana resonances in periodic topological superconductor-nanowire structures

Semiconducting nanowires in proximity to superconductors are promising experimental systems for Majorana fermions which may ultimately be used as building blocks for topological quantum computers. A serious challenge in the experimental realization of the Majorana fermion in these semiconductor-superconductor-nanowire structures is tuning the semiconductor chemical potential in close proximity to the metallic superconductor. We show that presently realizable structures in experiments with tunable chemical potential lead to Majorana resonances, which are interesting in their own right, but do not manifest non-Abelian statistics. To resolve this crucial barrier to the solid state realization of Majorana fermions, we propose a new topological superconducting array structure where introducing the superconducting proximity effect from adjacent nanowires generates Majorana fermions with non-Abelian statistics.     

Ab initio study of shear strain effects on ferroelectricity at PbTiO3 thin films

Ferroelectric thin film with the perovskite ABO₃ structure have been widely used in technology applications, e.g., actuators in MEMS/NEMS and nonvolatile random access memories (FeRAM). In order to clarify the effect of the shear strain on the ferroelectricity, the PbTiO₃ thin film as a typical one is chosen. The focus of this study is to put on the PbO-terminated (1? × ?1) and c(2? × ?2) surfaces and the TiO₂-terminated (1? × ?1) surface. Based on ab initio density functional theory calculations with the local density approximation, we have found out that in both the PbO and TiO₂-terminated (1? × ?1) models, the ferroelectricity in the PbO layers was enhanced under the positive shear strain while it was suppressed under the negative one. For the TiO₂ layers, the ferroelectricity was slightly enhanced and sharply suppressed under the positive and negative shear strains, respectively. In the PbO-terminated (2? × ?2) model, the AFE phase was suppressed by the FE phase under the positive shear strain while the opposite trend was found under the negative shear strain. For the PbO layers, the ferroelectricity was enhanced under the positive and negative shear strains. For the TiO₂ layers, the influence of the negative shear strain on the ferroelectricity was larger than that of the positive one. In addition, the ideal strength of the PbTiO₃ thin film with the different terminations was investigated as well.     

Restricted Normal Cones and the Method of Alternating Projections: Applications

The method of alternating projections (MAP) is a common method for solving feasibility problems. While employed traditionally to subspaces or to convex sets, little was known about the behavior of the MAP in the nonconvex case until 2009, when Lewis, Luke, and Malick derived local linear convergence results provided that a condition involving normal cones holds and at least one of the sets is superregular (a property less restrictive than convexity). However, their results failed to capture very simple classical convex instances such as two lines in a three-dimensional space. In this paper, we extend and develop the Lewis-Luke-Malick framework so that not only any two linear subspaces but also any two closed convex sets whose relative interiors meet are covered. We also allow for sets that are more structured such as unions of convex sets. The key tool required is the restricted normal cone, which is a generalization of the classical Mordukhovich normal cone. Numerous examples are provided to illustrate the theory.     

On groups with large character degree sums

Let G be a finite group, and let T(G) be the sum of all complex irreducible character degrees of G. Define ${f(G) = \frac{T(G)}{|G|}}$ . In this paper, we show that if G is a finite group and ${f(G) > \frac{4}{15}}$ , then G is solvable.     

MALDI-TOF MS analysis of native and permethylated or benzimidazole-derivatized polysaccharides

MALDI-TOF MS provides rapid and sensitive analyses of larger biomolecules. However, MS analyses of polysaccharide have been reported to have lower sensitivity compared to peptides and proteins. Here, we investigated some polysaccharides chemically derivatized by permethylation and ortho-phenylene diamine (OPD) tagging. Methylated glycan is obviously able to improve the sensitivity for mass spectrometry detection. Oxidative condensation by UV-activation tagging to saccharides by OPD and peptide-OPD also improve the sensitivity of MALDI-TOF MS analyses. Polysaccharides including dextran, glucomannan, arabinoxylan, arabinogalactan and beta-1,3-glucan, isolated from nutritional supplements of Ganoderma lucidum and Saccharomyces pastorianus were measured using MALDI-TOF MS with 2,5-dihydroxybenzoic acid (2,5-DHB) as the matrix. These glycans were also derivatized to methylated and benzimidazole-tagged glycans by chemical transformation for molecular weight analysis. The derivatized polysaccharides showed excellent MALDI-TOF MS signal enhancement in the molecular weight range from 1 to 5 kDa. Here, we demonstrate an efficient method to give glycan-benzimidazole (glycan-BIM) derivatives for polysaccharide determination in MALDI-TOF MS. Therefore, permethylated or benzimidazole-derivatized polysaccharides provide a new option for polysaccharide analysis using MALDI-TOF MS.