Emulsion Copolymerization of Vinyl Acetate and Vinyl Silanes: Kinetics and Development of Microstructure

The batch emulsion copolymerization of vinyl acetate with different vinyl silane functional monomers (vinyl trimethoxysilane [VTMS], vinyl triethoxysilane [VTES], and vinyl silanetriol [VSTO]) is studied. The nature of the silane strongly affects the development of the microstructure and crosslinking ability of the latexes. A combination of techniques (Soxhlet extraction, centrifugation, assymetric‐flow field flow fractionation AF4/MALS/RI) shows that the factor controlling the molar mass and crosslinking density is the degree of hydrolysis of the alkoxysilane, producing higher molar masses and degrees of crosslinking when the degree of hydrolysis is high. Thus, the copolymer containing VSTO produced a very crosslinked latex, the one with VTMS produced a latex with a low degree of crosslinking in the wet state that can yield high degrees of crosslinking upon drying, and the latex with VTES do not produce significant amounts of crosslinking neither before nor after drying.     

Comparison Theorems for Gibbs Measures

The Dobrushin comparison theorem is a powerful tool to bound the difference between the marginals of high-dimensional probability distributions in terms of their local specifications. Originally introduced to prove uniqueness and decay of correlations of Gibbs measures, it has been widely used in statistical mechanics as well as in the analysis of algorithms on random fields and interacting Markov chains. However, the classical comparison theorem requires validity of the Dobrushin uniqueness criterion, essentially restricting its applicability in most models to a small subset of the natural parameter space. In this paper we develop generalized Dobrushin comparison theorems in terms of influences between blocks of sites, in the spirit of Dobrushin–Shlosman and Weitz, that substantially extend the range of applicability of the classical comparison theorem. Our proofs are based on the analysis of an associated family of Markov chains. We develop in detail an application of our main results to the analysis of sequential Monte Carlo algorithms for filtering in high dimension.     

On the Caginalp phase‐field systems with two temperatures and the Maxwell–Cattaneo law

Our aim in this paper is to study generalizations of the nonconserved and conserved Caginalp phase‐field systems based on the Maxwell–Cattaneo law with two temperatures for heat conduction. In particular, we obtain well‐posedness results and study the dissipativity of the associated solution operators. Copyright © 2016 John Wiley & Sons, Ltd.     

Water-soluble carbosilane dendrimers protect phosphorothioate oligonucleotides from binding to serum proteins

Treatment of dendriplexes formed between water-soluble carbosilane dendrimers and phosphorothioate oligodeoxynucleotides (ODN) with the anionic detergent sodium dodecyl sulfate disrupted the complexes indicating that the nature of the union in such dendriplexes is merely electrostatic. However, dendriplexes were not dissociated by serum proteins like bovine or human serum albumins, as assessed by gel electrophoresis and fluorescence experiments. This would imply a dendrimer-mediated protective effect able to prevent ODN interactions with serum proteins and additionally could translate into a reduction of the ODN doses needed to achieve the biological effects. The employment of carbosilane dendrimers as carriers may solve the problem of ODN kidnapping by plasmatic proteins as a key drawback for therapeutics involving ODNs. As examples, transfection processes on normal primary peripheral blood cells and diagnosis of HIV infection in the presence of serum have been assayed.     

Hydrophobic amino acid and single-atom substitutions increase DNA polymerase selectivity

DNA polymerase fidelity is of immense biological importance due to the fundamental requirement for accurate DNA synthesis in both replicative and repair processes. Subtle hydrogen-bonding networks between DNA polymerases and their primer/template substrates are believed to have impact on DNA polymerase selectivity. We show that deleting defined interactions of that kind by rationally designed hydrophobic substitution mutations can result in a more selective enzyme. Furthermore, a single-atom replacement within the DNA substrate through chemical modification, which leads to an altered acceptor potential and steric demand of the DNA substrate, further increased the selectivity of the developed systems. Accordingly, this study about the impact of hydrophobic alterations on DNA polymerase selectivity--enzyme and substrate wise--further highlights the relevance of shape complementary and polar interactions on DNA polymerase selectivity.     

Organocatalytic asymmetric 5-hydroxyisoxazolidine synthesis: a highly enantioselective route to beta-amino acids

The highly chemo- and enantioselective organocatalytic tandem reaction between N-protected hydroxyl amines and alpha,beta-unsaturated aldehydes is presented; the reaction provides access to 5-hydroxyisoxazolidines and beta-amino acids in high yields and with 90-99% ee.     

Pyrylium-containing polymers as sensory materials for the colorimetric sensing of cyanide in water

A sensory polymeric material for the colorimetric sensing of cyanide in water has been developed based on the reactivity of this anion with the pyrylium cation.     

Improved determination of flavour compounds in butter by solid-phase (micro)extraction and comprehensive two-dimensional gas chromatography

The practicability and potential of comprehensive two-dimensional gas chromatography (GC x GC) coupled to both conventional flame ionisation (FID) and time-of-flight mass spectrometric (TOF-MS) detection, were compared with those of conventional one-dimensional (1D) GC, with the determination of flavour compounds in butter as an application. For polar flavour compounds, which were collected from the aqueous fraction of butter by means of solid-phase extraction (SPE), it was found that GC x GC dramatically improves the overall separation. Consequently, quantification and preliminary identification based on the use of ordered structures, can be performed more reliably. The improvement effected by replacing 1D-GC by GC x GC is considerable also in the case of TOF-MS detection, as illustrated by the high match factors generally obtained during identification. GC x GC was also used successfully for the characterisation of volatile flavour compounds in the headspace of butter collected by solid-phase microextraction (SPME) and to study the effect of heat treatment on the composition of butter samples in more detail.     

Enantioselective Organocatalytic Addition of Oxazolones to 1,1‐Bis(phenylsulfonyl)ethylene: A Convenient Asymmetric Synthesis of Quaternary α‐Amino Acids

A new, easy, and highly enantioselective method for the synthesis of quaternary α‐alkyl‐α‐amino acids based on organocatalysis is reported. The addition of oxazolones to 1,1‐bis(phenylsulfonyl)ethylene is efficiently catalyzed by simple chiral bases or thioureas. The reaction affords α,α‐disubstituted α‐amino acid derivatives with complete C4 regioselectivity and with excellent yields and enantioselectivities. This methodology is complementary to previously reported enantioselective approaches to quaternary α‐amino acids and allows the synthesis of α‐phenyl‐α‐alkyl‐α‐amino acids and α‐tert‐butyl‐α‐alkyl‐α‐amino acids. It has distinct advantages in terms of operational simplicity, enviromentally friendly conditions, and suitability for large‐scale reactions.     

Stochastic theory of large-scale enzyme-reaction networks: finite copy number corrections to rate equation models

Chemical reactions inside cells occur in compartment volumes in the range of atto- to femtoliters. Physiological concentrations realized in such small volumes imply low copy numbers of interacting molecules with the consequence of considerable fluctuations in the concentrations. In contrast, rate equation models are based on the implicit assumption of infinitely large numbers of interacting molecules, or equivalently, that reactions occur in infinite volumes at constant macroscopic concentrations. In this article we compute the finite-volume corrections (or equivalently the finite copy number corrections) to the solutions of the rate equations for chemical reaction networks composed of arbitrarily large numbers of enzyme-catalyzed reactions which are confined inside a small subcellular compartment. This is achieved by applying a mesoscopic version of the quasisteady-state assumption to the exact Fokker-Planck equation associated with the Poisson representation of the chemical master equation. The procedure yields impressively simple and compact expressions for the finite-volume corrections. We prove that the predictions of the rate equations will always underestimate the actual steady-state substrate concentrations for an enzyme-reaction network confined in a small volume. In particular we show that the finite-volume corrections increase with decreasing subcellular volume, decreasing Michaelis-Menten constants, and increasing enzyme saturation. The magnitude of the corrections depends sensitively on the topology of the network. The predictions of the theory are shown to be in excellent agreement with stochastic simulations for two types of networks typically associated with protein methylation and metabolism.