Assay for the enantiomeric analysis of [2H1]-fluoroacetic acid: insight into the stereochemical course of fluorination during fluorometabolite biosynthesis in streptomyces cattleya

A sensitive method for the configurational analysis of (R)- and (S)-[2H1]-fluoroacetate has been developed using 2H[1H]-NMR in a chiral liquid crystalline solvent. This has enabled biosynthetic experiments to be conducted which reveal stereochemical details on biological fluorination occurring during the biosynthesis of fluoroacetate and 4-fluorothreonine in the bacterium Streptomyces cattleya. In particular, feeding experiments to S. cattleya with isotopically labeled (1R, 2R)- and (1S, 2R)-[1-2H1]-glycerol 3d and 3e and [2,3-2H(4)]-succinate 4a gave rise to samples of enantiomerically enriched [2-2H1]-fluoroacetates 1a. The predominant enantiomer resulting from each experiment suggests that the stereochemical course of biological fluorination takes place with an overall retention of configuration between a glycolytic intermediate and fluoroacetate 1. Consequently, this outcome suggests that the stereochemical course of the recently identified fluorinase enzyme which mediates a reaction between fluoride ion and S-adenosyl-l-methionine (SAM), occurs with an inversion of configuration.     

A constant enclosure method for validating existence and uniqueness of the solution of an initial value problem for a fractional differential equation

This paper presents a new method for validating existence and uniqueness of the solution of an initial value problems for fractional differential equations. An algorithm selecting a stepsize and computing a priori constant enclosure of the solution is proposed. Several illustrative examples, with linear and nonlinear fractional differential equations, are given to demonstrate the effectiveness of the method.     

Cation-Induced Macroscopic Ordering of Non-Mesomorphic Modules—A New Application for Metallohelicates

The subtle balance between organized and chaotic domains in the nondiscoidal ligand in the helicate 1 , which displays liquid crystalline properties, represents the key element which enables the local molecular architecture to be integrated into an organized macroscopic ensemble.     

Asymptotically symmetric embeddings and symmetric quasicircles

A well-known characterization of quasicircles is the following: A Jordan curve in the complex plane is a quasicircle if and only if it is the image of the unit circle under a quasisymmetric embedding. In this paper we try to characterize a subclass of quasicircles, namely, symmetric quasicircles, by introducing the concept of asymptotically symmetric embeddings. We show that a Jordan curve in the complex plane is a symmetric quasicircle if and only if it is the image of the unit circle under an asymptotically symmetric embedding.

     

The Cyclic Thermomechanical Coupled Problem of Thermal Gradients in Friction Railway Disc Brakes

The emergency braking distance of a TGV train at a speed of 320 km/h is almost 3000 m. Dry running brakes are reliable due to their predictable response to external stress and are thus used in such applications. The kinetic energy is dissipated proportionately into the brake disc and brake pad. This induced dissipation of energy and the high frequency of brake application cause high temperatures. These immense temperature changes could cause macroscopic cracks leading to failure of discs and accidents [1]. Generally, hot spotting describes the development of thermal localizations and can lead to early damage, early wear, pad performance loss, and squeal noise [2]. The aim of the present study is to improve a disc-pad transient numerical model by use of a coupled thermomechanical method. It is based on full 3-d thermomechanical calculations taking disc rotation into account. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and textural features of TiO<Subscript>2</Subscript>/SAPO-34 nanocomposite prepared by the sol–gel method

This paper focuses on the synthesis of nanocomposite materials, TiO₂/SAPO-34, using the sol–gel method, which involves preparing a mixture between as-synthesized or calcined SAPO-34 zeolite and TiO₂ gel under hydrothermal crystallization and then calcining it at 400 °C for the formation of the TiO₂ anatase phase. The structural and textural features of the obtained materials were determined by various physico-chemical techniques such as thermogravimetric analysis, X-ray diffraction, scanning electronic microscopy, nitrogen sorption at 77 K, energy dispersive X-ray analysis and ultraviolet–visible spectrometry. The DRX results showed that calcination at 400 °C of the mixture between the calcined SAPO-34 and TiO₂ gel led to the collapse of the original framework of zeolite, but formed the anatase TiO₂ in a nano-spherical morphology; however, the use of as-synthesized SAPO-34 supports provides a mixture phase between SAPO-34 and TiO₂ anatase after calcination. The photocatalytic properties of the SAPO-34/TiO₂ and TiO₂-type materials were tested for the removal of methylene blue (MB) dye. The MB degradation proved to increase as a function of contact time, catalyst mass and the initial concentration of MB.     

In vitro effect of wheat bran (Triticum aestivum) extract on calcium oxalate urolithiasis crystallization

Urolithiasis can lead to the loss of renal function in some cases. In this study, we tested the inhibiting effect of wheat bran (Triticum aestivum L) extract on calcium oxalate crystallization in a turbidimetric model, by FTIR spectroscopy, and polarized microscopy. The results show that this plant extract has a major inhibitory effect on calcium oxalate crystallization.     

SBA-15-Type Organosilica with 4-Mercapto-N,N-bis-(3-Si-propyl)butanamide for Palladium Scavenging and Cross-Coupling Catalysis

This work describes the synthesis of novel functional silica materials with difunctional thiol-amide substructures and featuring regular architectures on a mesoscopic level. The functional materials were synthesised by both one-pot co-condensation and post-grafting approaches. The thiol groups confined in the matrix were found to be efficient for palladium entrapment, leading to highly active and reusable heterogeneous catalysts for Sonogashira and Suzuki-Miyaura cross-coupling reactions. This work evidences the crucial role of both the thiol precursor and the condensation degree of the silica scaffold in view of the design of stable and reusable tailor-made mesoporous catalytic silica materials.