Symmetric low-frequency motion in incompressible transversely isotropic elastic plates

The problem of long-wave low-frequency extensional (symmetric) motion in a layer composed of incompressible, transversely isotropic elastic material is investigated. Motivated by appropriate approximations of the dispersion relation, a hierarchy of asymptotically approximate boundary value problems is set up and solved. A leading order system of equations is obtained for the governing extensions, together with a refined system for their second order counterparts. A one-dimensional model problem, involving impact edge loading, is set up and solved in order to illustrate the derived theory.     

Exactness of direct limits for abelian categories with an injective cogenerator

We prove that the exactness of direct limits in an abelian category with products and an injective cogenerator J is equivalent to a condition on J which is well-known to characterize pure-injectivity in module categories, and we describe an application of this result to the tilting theory. We derive our result as a consequence of a more general characterization of when inverse limits in the Eilenberg–Moore category of a monad on the category of sets preserve regular epimorphisms.     

Correction to: Peculiarities of chromium electrodeposition from water − dimethylformamide solutions

Journal of Solid State Electrochemistry - This original article contained a mistake. The page numbers of reference Kuznetsov et al. 2000 are incorrect, “853–858” should be...     

Molecular clips based on diphenylglycoluril and benzocrown ethers: promising complexing agents for the alkali metal cations

The interaction of new molecular clips containing diphenylglycoluril and benzocrown ethers moieties with alkali metals ions was studied. Stability constants were determined by spectrophotometric titrations with chloride salts in methanol. Complex stability and cation binding selectivity were shown to be dependent on the size of the crown ether moiety. The “sandwich-type” 1:1 (clip to cation) complexes and the “classical” 1:2 complexes were found. Their ratio varies depending on the molecular clips nature and on the cation type. It was found an unexpected selectivity of the molecular clip with benzo-15-crown-5 moieties toward K⁺ and Rb⁺ cations. The molecular structure of the clip complex with benzo-15-crown-5 fragments and sodium picrate was determined by X-ray crystallography. The crystal structure and solution-state structure were proven to be similar.     

Theory of Gradient Elution Liquid Chromatography with Linear Solvent Strength: Part 2. Peak Width Formation

The process of formation of the width (σ _b) of a solute band migrating along a column and its effect on the width (σ) of a corresponding peak in a chromatogram are quantified along with the extra-column contributions (Δσ _b and Δσ) to these parameters due to insufficiently narrow injection plugs. Previously unknown expressions for σ _b and Δσ _b as functions of the band migration distance and time were found. The negative gradients in the solvent strength cause the fronts of the solute bands to travel slower than their tails. This compresses the bands (reduces their widths). Previously unknown expressions describing the band compression process as functions of the band migration distance and time are found. The band compression tends to narrow the peaks. However, as shown here, the gradients that compress the bands also reduce their elution speeds. This tends to broaden the peaks (typically ignored phenomenon) and, as shown here, can cause a slight net peak broadening under normal conditions (in spite of general expectations that the gradients should narrow the peaks). On the other hand, as shown here, the gradients can significantly suppress the harmful effect of the extra-column peak broadening.     

Polymer Dynamics in a Polymer-Solid Interphase: Molecular Dynamics Simulations of 1,4-Polybutadiene At a Graphite Surface

A chemically realistic model of 1,4-polybutadiene confined by graphite walls in a thin film geometry was studied by molecular dynamics simulations. The chemically realistic approach allows for a quantitative determination of a variety of experimentally accessible relaxation functions (e.g., dielectric, NMR, or neutron scattering responses). The simulations yield these experimental observables. Additionally, the simulations can be resolved as a function of distance to the solid interface on a much finer scale than experimentally possible, providing a detailed mechanistic picture of the segmental and large scale motions of polymers in the interfacial region between bulk polymer melts and solid walls. Extending the study of 1,4-polybutadiene on graphite to temperatures close to the glass transition temperature, we also address the question to what extent growing length scales associated with the glass transition influence the melt dynamics in the interphase. It was found that there is an interplay of this intrinsic slowing down with the adsorption/desorption kinetics of the chains close to the wall. It is argued that the monomer density changes near the wall can overcome the effect of rotational barriers only in a region of about 2 nm next to the wall.     

Advances in chiral separations of small peptides by capillary electrophoresis and chromatography

Many chemical and biological processes are controlled by the stereochemistry of small polypeptides (di‐, tri‐, tetra‐, penta‐, hexapeptides, etc). The biological importance of peptide stereoisomers is of great value. Therefore, the chiral resolution of peptides is an important issue in biological and medicinal sciences and drug industries. The chiral resolutions of peptide racemates have been discussed with the use of capillary electrophoresis and chromatographic techniques. The various chiral selectors used were polysaccharides, cyclodextrins, Pirkle types, macrocyclic antibiotics, crown ethers, imprinted polymers, etc. The stereochemistry of dipeptides is also discussed. Besides, efforts are made to explain the chiral recognition mechanisms, which will be helpful in understanding existing and developing new stereoselective analyses. Future perspectives of enantiomeric resolution are also predicted. Finally, the review concludes with the demand of enantiomeric resolution of all naturally occurring and synthetic peptides.     

Highly Efficient Phase Boundary Biocatalysis with Enzymogel Nanoparticles

The enzymogel nanoparticle made of a magnetic core and polymer brush shell demonstrates a novel type of remote controlled phase‐boundary biocatalysis that involves remotely directed binding to and engulfing insoluble substrates, high mobility, and stability of the catalytic centers. The mobile enzymes reside in the polymer brush scaffold and shuttle between the enzymogel interior and surface of the engulfed substrate in the bioconversion process. Biocatalytic activity of the mobile enzymes is preserved in the enzymogel while the brush‐like architecture favors the efficient interfacial interaction when the enzymogel spreads over the substrate and extends substantially the reaction area as compared with rigid particles.     

Theoretical and experimental study of 15N NMR protonation shifts

A combined theoretical and experimental study revealed that the nature of the upfield (shielding) protonation effect in ¹⁵N NMR originates in the change of the contribution of the sp²‐hybridized nitrogen lone pair on protonation resulting in a marked shielding of nitrogen of about 100 ppm. On the contrary, for amine‐type nitrogen, protonation of the nitrogen lone pair results in the deshielding protonation effect of about 25 ppm, so that the total deshielding protonation effect of about 10 ppm is due to the interplay of the contributions of adjacent natural bond orbitals. A versatile computational scheme for the calculation of ¹⁵N NMR chemical shifts of protonated nitrogen species and their neutral precursors is proposed at the density functional theory level taking into account solvent effects within the supermolecule solvation model. Copyright © 2015 John Wiley & Sons, Ltd.