Divergent and stereoselective synthesis of dafachronic acids

A new divergent synthesis of DAF-12 ligands, namely Δ⁴- and Δ⁷-dafachronic acid, is described starting from the natural bile acid hyodeoxycholic acid. Homologation of the side chain followed by stereoselective reduction of the Δ²⁴ olefinic linkage, 6α-dehydroxylation and C₃-oxidation affords dafachronic acids in good yields and high diastereoselectivity making this approach easily accessible and scalable.     

Conditional reversible work method for molecular coarse graining applications

Systematically coarse grained models for complex fluids usually lack chemical and thermodynamic transferability. Efforts to improve transferability require the development of effective potentials with unequivocal physical significance. In this paper, we introduce conditional reversible work (CRW) potentials that describe nonbonded interactions in coarse grained models at the pair level. The method used to obtain these potentials is straightforward to implement, can be readily extended to compute hydration contributions in implicit-solvent potentials, and is easy to automize. As a first illustration of the method, we present CRW potentials for 3-site models of hexane and toluene. The temperature-transferability of the liquid phase density obtained with these potentials has been investigated, and a comparison has been made with effective potentials obtained by the iterative Boltzmann inversion method.     

Cosolvent gel-like materials from partially hydrolyzed poly(vinyl acetate)s and borax

A gel-like, high-viscosity polymeric dispersion (HVPD) based on cross-linked borate, partially hydrolyzed poly(vinyl acetate) (xPVAc, where x is the percent hydrolysis) is described. Unlike hydro-HVPDs prepared from poly(vinyl alcohol) (PVA) and borate, the liquid portion of these materials can be composed of up to 75% of an organic cosolvent because of the influence of residual acetate groups on the polymer backbone. The effects of the degree of hydrolysis, molecular weight, polymer and cross-linker concentrations, and type and amount of organic cosolvent on the rheological and structural properties of the materials are investigated. The stability of the systems is explored through rheological and melting-range studies. (11)B NMR and small-angle neutron scattering (SANS) are used to probe the structure of the dispersions. The addition of an organic liquid to the xPVAc-borate HVPDs results in a drastic increase in the number of cross-linked borate species as well as the agglomeration of the polymer into bundles. These effects result in an increase in the relaxation time and thermal stability of the networks. The ability to make xPVAc-borate HVPDs with very large amounts of and rather different organic liquids, with very different rheological properties that can be controlled easily, opens new possibilities for applications of PVAc-based dispersions.     

Electric-field gradients at Ta impurities in Sc2O3 semiconductor

In this work we present an ab initio study of Ta-doped Sc₂O₃ semiconductor. Calculations were performed at dilute Ta impurities located at both cationic sites of the host structure, using the Augmented Plane Wave plus Local Orbitals (APW+lo) method. The structural atomic relaxations and the electric-field gradients (EFG) were studied for different charge states of the cell in order to simulate different ionization states of the double-donor Ta impurity. From the results for the EFG tensor at Ta impurity sites and the comparison with experimental results obtained using the Time-Differential γ–γ Perturbed-Angular-Correlations technique we could determined the structural distortions induced by the Ta impurity and the electronic structure of the doped-semiconductor.     

A multiplex molecular assay for the detection of uniparental disomy for human chromosome 7

Uniparental disomy (UPD) describes the inheritance of both homologues of a pair of chromosomes from only one parent. This condition is often caused by nondisjunction events during meiosis. UPD has been reported as a rare cause of the autosomal recessive disorder and aberrant expression of imprinted genes that are expressed from only one parental allele, either maternal or paternal. Maternal and/or paternal UPD for chromosome 7 is the most frequently observed UPD after UPD15. Here we developed and validated, for the first time, an effective, CE‐based method for a rapid and economic detection based on two‐fluorescent STR multiplexes.     

Responsive Metal Complexes: A Click‐Based “Allosteric Scorpionate” Complex Permits the Detection of a Biological Recognition Event by EPR/ENDOR Spectroscopy

Click to detect! Azamacrocyclic complexes with a triazole scorpion ligand may be easily assembled, as shown for a biotin‐functionalised cyclam derivative. Coordination of the triazole to the metal is perturbed by the binding of avidin to the pendant ligand (see scheme). This event can be sensitively detected with EPR and ENDOR spectroscopy, which confirm the loss of the axial triazole nitrogen donor upon avidin binding. This general strategy may have wide applications in imaging and therapeutics.

     

Chemical Modification of Glycosaminoglycan Polysaccharides

The linear anionic class of polysaccharides, glycosaminoglycans (GAGs), are critical throughout the animal kingdom for developmental processes and the maintenance of healthy tissues. They are also of interest as a means of influencing biochemical processes. One member of the GAG family, heparin, is exploited globally as a major anticoagulant pharmaceutical and there is a growing interest in the potential of other GAGs for diverse applications ranging from skin care to the treatment of neurodegenerative conditions, and from the treatment and prevention of microbial infection to biotechnology. To realize the potential of GAGs, however, it is necessary to develop effective tools that are able to exploit the chemical manipulations to which GAGs are susceptible. Here, the current knowledge concerning the chemical modification of GAGs, one of the principal approaches for the study of the structure-function relationships in these molecules, is reviewed. Some additional methods that were applied successfully to the analysis and/or processing of other carbohydrates, but which could be suitable in GAG chemistry, are also discussed.     

Peptide‐Directed DNA‐Templated Protein Labelling for The Assembly of a Pseudo‐IgM

The development of methods for conjugation of DNA to proteins is of high relevance for the integration of protein function and DNA structures. Here, we demonstrate that protein‐binding peptides can direct a DNA‐templated reaction, selectively furnishing DNA–protein conjugates with one DNA label. Quantitative conversion of oligonucleotides is achieved at low stoichiometries and the reaction can be performed in complex biological matrixes, such as cell lysates. Further, we have used a star‐like pentameric DNA nanostructure to assemble five DNA–Rituximab conjugates, made by our reported method, into a pseudo‐IgM antibody structure that was subsequently characterized by negative‐stain transmission electron microscopy (nsTEM) analysis.     

Temperature and potential-dependent structural changes in a Pt cathode electrocatalyst viewed by in situ XAFS

The paper presents an X-ray absorption fine structure (XAFS) investigation of Pt supported on Vulcan XC-72 operating as a cathode catalyst in a polymer electrolyte membrane fuel cell (PEM FC). XAFS spectroscopy was performed in situ using a cell developed by the authors and optimized for absorption measurements. Low-noise spectra were obtained using the transmission mode over the Pt L₃ XAFS range, enabling multiple-scattering XAFS data-analysis for the Pt nanocrystalline system under operating conditions. Accurate measurements of the local structure were performed at various potentials and working temperatures. Changes in the near-edge structures reflecting variations in the Pt electronic structure were observed for various potential values in the cathode activation region. The Pt average local geometric structure was found to be practically potential-independent. The increase in structural disorder caused by the higher working FC temperature was not found to affect the catalyst’s performance in the kinetically controlled region.