Highly efficient synthesis of ketoheptoses

A reliable, facile, high overall yielding and diastereoselective synthesis of ketoheptoses was developed and applied for preparation of the two most diabetogenic ketoheptoses as well as in a modified version for the synthesis of kamusol.     

Conductivity of water-in-oil microemulsions stabilized by mixed surfactants

The electrical conductivity of D2O-in-n-heptane microemulsions stabilized by cationic/nonionic surfactant mixtures was studied as a function of D2O content, surfactant concentration, and surfactant mixture composition. The surfactants employed were cationic di-n-didodecyldimethylammonium bromide, DDAB, nonionic poly(oxyethylene) monododecyl ethers, C12EJ, with J=3-8 and 23, nonionic polymeric surfactants of the type PEO-PPO-PEO (Pluronic), and the reverse structure analogues (Pluronic R). Qualitative structural information was drawn from a comparison between the measured conductivity and that predicted by the charge fluctuation model for spherical droplets. The conductivity versus water content curves were found to be typical for water-in-oil systems composed of spherical droplets. From the effect of blending nonionic surfactant with DDAB on the measured conductivities, it was concluded that microemulsion conductivity is independent of the concentration of cationic surfactant (DDAB). This finding agrees well with theoretical microemulsion conductivity models.     

Microemulsions with Didodecyldimethylammonium Bromide Studied by Neutron Contrast Variation

The structure of water-in-oil microemulsion droplets, stabilized by didodecyldimethylammonium bromide (DDAB), has been investigated by small-angle neutron scattering (SANS). Detailed information about the curved surfactant film has been obtained by selectively deuterating the water, DDAB, and cyclohexane components. For each surfactanth-DDAB andd-DDAB and concentration, three sets of complementary neutron contrast data were analyzed together in terms of a Schultz distribution of core–shell particles. The modeling was consistent with a simple liquid-like surfactant layer, of density 0.80 g cm⁻³, with no evidence for any solvent penetration. This film thickness was found to be 11–12 Å, about 70% of an all-transC₁₂chain length. At the water interface the area per head was 56–61 Ų, while for the alkyl chains at the outer surface it was 90–125 Ų(15–30% lower than that for a truncated cone molecular configuration). The cyclohexane–water interfacial tensions γ_o/w, measured by surface light scattering, were used along with the droplet polydispersities to find that the rigidity of the DDAB film, 2K+ is close to 1.0k_BT. This means that rather than acting as an effective parameter in the SANS analysis, the polydispersity is a natural consequence of the film rigidity. These results show that the film bending energy model accounts well for the behavior of such DDAB microemulsions.     

CHARTING ARGUMENTATION SPACE IN CONCEPTUAL LOCALES: TOOLS AT THE BOUNDARY BETWEEN RESEARCH AND PRACTICE

We describe a procedure for developing pedagogical knowledge about the argumentation of groups of children in relation to conceptual locales. The method involved the collection of small groups of children who had made different but significant responses to diagnostic test items, the recording and analysis of their subsequent researcher-managed discourses, and the mapping of the main productive elements of argument and charting a flow through it. Two examples of the method are presented which show how children can develop argument, and how these can be charted. These charts and other tools encapsulate research knowledge on children's learning in a form designed to help teachers to plan argumentation in their classroom practice: i.e. as pedagogical content knowledge. In addition to content-focused results, we also find general teaching strategies which appear to be effective generally, i.e. across conceptual locales. We discuss the relationship of this work to the development of teacher's pedagogical content knowledge and practice.     

Partitioning a graph into monochromatic connected subgraphs

We show that every -edge-colored graph on vertices with minimum degree at least can be partitioned into two monochromatic connected subgraphs, provided is sufficiently large. This minimum degree condition is tight and the result proves a conjecture of Bal and DeBiasio. We also make progress on another conjecture of Bal and DeBiasio on covering graphs with large minimum degree with monochromatic components of distinct colors.     

Coupled McKean–Vlasov diffusions: wellposedness,propagation of chaos and invariant measures

In this paper, we study a two-species model in the form of a coupled system of nonlinear stochastic differential equations (SDEs) that arises from a variety of applications such as aggregation of biological cells and pedestrian movements. The evolution of each process is influenced by four different forces, namely an external force, a self-interacting force, a cross-interacting force and a stochastic noise where the two interactions depend on the laws of the two processes. We also consider a many-particle system and a (nonlinear) partial differential equation (PDE) system that associate to the model. We prove the wellposedness of the SDEs, the propagation of chaos of the particle system, and the existence and (non)-uniqueness of invariant measures of the PDE system.     

The Mechanism Behind Top-Down UVPD Experiments: Making Sense of Apparent Contradictions

Top-down ultraviolet photodissociation (UVPD) allows greater sequence coverage than any other currently available method, often fracturing the vast majority of peptide bonds in whole proteins. At the same time, UVPD can be used to dissociate noncovalent complexes assembled from multiple proteins without breaking any covalent bonds. Although the utility of these experiments is unquestioned, the mechanism underlying these seemingly contradictory results has been the subject of many discussions. Herein, some fundamental considerations of photochemistry are briefly summarized within the context of a proposed mechanism that rationalizes the experimental results obtained by UVPD. Considerations for future instrument design, in terms of wavelength choice and power, are briefly discussed.

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Graphical Abstract ?

     

Metal-selective coordination and enhanced fluorescence of a self-assembling ligand scaffold

A fluorescent hydroxyiminonicotinonitile (HINT) coordinating group can be incorporated into self-assembling ligand scaffolds, and shows metal-selective assembly and enhanced fluorescence. The assembly process is dependent on ligand coordination angle, and coordination only occurs for oxophilic first row transition metal ions, with affinity enhanced by the supramolecular assembly process. The ligands are weakly emissive, and show strong enhancement in fluorescence upon Zn²⁺ coordination, whereas Co²⁺ or Fe²⁺ cause complete quenching.