Early stages in the degradation of metal-organic frameworks in liquid water from first-principles molecular dynamics

IRMOF-1 structures are known to suffer lattice break-up when exposed to water-rich environments, a limiting factor in their everyday use. To shed light on the underlying mechanism of disruption, the role of the metal in the secondary building unit (SBU) has been systematically investigated, and the global behaviour of IRMOF-1-type structures with the three metals Zn, Mg, and Be studied by Born-Oppenheimer Molecular Dynamics in liquid water. Results show that fully hydrated Be based compounds are stable up to 500 K while the equivalent structures with Mg or Zn break down already at 300 K. The reasons behind this instability are in the tendency of the metal atom to form penta- and hexa-coordination spheres and in the strength of the M-O bond. These are the key factors that generate unique breaking patterns for Mg and Zn IRMOF-1 analogues, as well as the reason for the high hydrothermal stability of the Be-IRMOF-1.     

The effect of an amino-containing modifier on properties of ethylene copolymers

The effect of some aminosilanes on the complex of properties of ethylene copolymers with vinylacetate, acrylates, and ternary ethylene copolymers with vinylacetate or acrylates and maleic anhydride is studied.     

An a priori error analysis of a type III thermoelastic problem with two porosities

In this work, we study, from the numerical point of view, a type III thermoelastic model with double porosity. The thermomechanical problem is written as a linear system composed of hyperbolic partial differential equations for the displacements and the two porosities, and a parabolic partial differential equation for the thermal displacement. An existence and uniqueness result is recalled. Then, we perform its a priori error numerical analysis approximating the resulting variational problem by using the finite element method and the implicit Euler scheme. The linear convergence of the algorithm is derived under suitable additional regularity conditions. Finally, some numerical simulations are shown to demonstrate the accuracy of the approximations and the dependence of the solution on a coupling coefficient.     

The renormalization of collective states and the improper initial or final states in NFT

The collective lines in a given diagram are renormalized by including higher order processes. The problem is cast into the form of a conventional linear algebraic matrix equation that allows a simple treatment of the normalization conditions. It is shown that the states entering in the renormalization of the phonons become improper initial or final states, if dressed phonons are used in the intermediate states. A simple extension of this argument allows one to justify one of the rules given in the formulation of the NFT.     

Electrochemical Studies of Ochratoxin A Mycotoxin at Gold Electrodes Modified with Cysteamine Self‐Assembled Monolayers. Its Ultrasensitive Quantification in Red Wine Samples

The quantification of ochratoxin A is studied at cysteamine self‐assembled monolayer modified gold electrodes in red wine samples by square wave voltammetry. Detection and quantification limits of 0.004 µg L^?1 and 0.012 µg L^?1, respectively, were determined. The recovery percentages were in the range from 146 % to 94.0 % at spiking levels ranging from 0.02 to 5 µg L^?1. The variation coefficients for within‐laboratory repeatability varied from 31.4 to 11.5 % for spiked level from 0.02 to 2.0 µg L^?1. The developed electrochemical method is efficient, reproducible, and ultrasensitive for the quantification of OTA in red wine samples.     

The effect of aminoalkoxy and glycidoxyalkoxy silanes on adhesion characteristics of double and triple copolymers of ethylene

The effect of aminoalkoxy and glycidoxyalkoxy silanes on strength of a polyethylene-modified copolymer-metal (polyethylene terephthalate) adhesion joint was studied for double and triple acetate copolymers of ethylene. It was shown that such modification resulted in an essential increase in the deformation-strength and adhesion characteristics of adhesive joints.     

An h-adaptive solution of the spherical blast wave problem

Shock waves and contact discontinuities usually appear in compressible flows, requiring a fine mesh in order to achieve an acceptable accuracy of the numerical solution. The usage of a mesh adaptation strategy is convenient as uniform refinement of the whole mesh becomes prohibitive in three-dimensional (3D) problems. An unsteady h-adaptive strategy for unstructured finite element meshes is introduced. Non-conformity of the refined mesh and a bounded decrease in the geometrical quality of the elements are some features of the refinement algorithm. A 3D extension of the well-known refinement constraint for 2D meshes is used to enforce a smooth size transition among neighbour elements with different levels of refinement. A density-based gradient indicator is used to track discontinuities. The solution procedure is partially parallelised, i.e. the inviscid flow equations are solved in parallel with a finite element SUPG formulation with shock capturing terms while the adaptation of the mesh is sequentially performed. Results are presented for a spherical blast wave driven by a point-like explosion with an initial pressure jump of 10⁵ atmospheres. The adapted solution is compared to that computed on a fixed mesh. Also, the results provided by the theory of self-similar solutions are considered for the analysis. In this particular problem, adapting the mesh to the solution accounts for approximately 4% of the total simulation time and the refinement algorithm scales almost linearly with the size of the problem.     

Kinetics of the reaction between 2-phenylpropionitrile and 2-chloro-5-nitrotrifluoromethylbenzene under phase-transfer catalysis

Phase-transfer catalysis (PTC) is a widely accepted methodology in organic synthesis. Although a great number of organic syntheses were reported in PTC conditions, systematic kinetic studies are scarce. In the present report, a detailed study of the kinetics of the reaction between 2-chloro-5-nitrotrifluoromethylbenzene (CNTFB) and 2-phenylpropionitrile anion (HPP-), under PTC, was performed under several conditions. The reaction was carried out either in toluene or chlorobenzene as the organic phase, in the presence of a concentrated aqueous solution of NaOH using tetraalkylammonium (Q+X-) salts as phase-transfer catalysts. The major product was 2-(4-nitro-2-trifluoromethylphenyl)-2-phenylpropionitrile, and its yield depends on the experimental conditions. Different aspects of the mechanism are discussed and quantified. Kinetic data were explained by means of an interfacial mechanism that involves the deprotonation of the adsorbed nucleophile precursor followed by its catalyst-mediated extraction to the organic phase. A multicomponent Langmuir-type interface was assumed. Although the extraction of OH- by catalyst to the organic phase is usually disregarded, the formation of the substrate hydrolysis product that leads to catalyst poisoning was also investigated. The influence of this side reaction on the yield of the main product was established. A discussion about the influence of this side process on the main reaction and the operating mechanism is presented.