Rheological and thermal properties of agarose aqueous solutions and hydrogels

In this article, we report on the rheological properties of agarose aqueous solutions and gels. Viscosity curves were determined for homogeneous agarose aqueous solutions at different temperatures (from 68 to 38 °C) to study the viscosity behavior as the systems undergo gelation. The gelation phenomenon of agarose solutions was also investigated by shear oscillation experiments and differential scanning calorimetry. The gelation and melting temperature as a function of agarose concentration were determined together with the gelation and melting enthalpies. The results obtained were interpreted using the two‐step model describing the gelation of agarose in water. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 322–328, 2008     

Small cliques in random graphs

For d ≥ 1, a d-clique in a graph G is a complete d-vertex subgraph not contained in any larger complete subgraph of G. We investigate the limit distribution of the number of d-cliques in the binomial random graph G(n, p), p = p(n), n→∞.     

On the optimality equation for average cost Markov control processes with Feller transition probabilities

We consider Markov control processes with Borel state space and Feller transition probabilities, satisfying some generalized geometric ergodicity conditions. We provide a new theorem on the existence of a solution to the average cost optimality equation.     

Reaction of 3-chloroquinoline-2,4-diones with ethanolamine and rearrangement of the reaction products

The reaction of tertiary α-chloroketones with ethanolamine has not been hitherto described in the literature. Herein, we describe the reaction of tertiary 3-chloroquinoline-2,4-diones with ethanolamine to give novel 3-(2-hydroxyethylamino)quinoline-2,4-diones. These compounds provide 3-(2-oxooxazolidin-3-yl)quinoline-2,4(1H,3H)-diones and new compounds with dimeric character after reaction with triphosgene. Molecular rearrangement proceeds during the reaction of 3-(2-hydroxyethylamino)quinoline-2,4-diones with isocyanic acid. Three types of reaction products arise: 2-(2-hydroxyethyl)imidazo[1,5-c]quinazoline-3,5-diones, 3-(2-hydroxyethyl)-3,3a-dihydro-2H-imidazo[4,5-]quinoline-4(5H)diones and primarily 5-hydroxy-1-(hydroxyethyl)-1′H-spiro[imidazolidine-5,3′-indole]-2,2′-diones. The reaction mechanism and product stereochemistry are discussed. The ¹H, ¹³C and ¹⁵N NMR spectra of the prepared compounds were measured, and all resonances were assigned from appropriate two-dimensional experiments.     

Switchable solvent based liquid phase microextraction of palladium coupled with determination by flame atomic absorption spectrometry

A switchable solvent-based micro-extraction method for pre-concentration and separation of ultratrace palladium was developed prior to its flame atomic absorption spectrometric detection. Reverse change of hydrophilicity of N,N-dimethylcyclohexylamine (DMA) was achieved by reaction with carbonated water. The hydrophilic bicarbonate salt of the protonated DMA was used as extractant for palladium complexed with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). Formation of the hydrophobic form of switchable solvent from hydrophilic form of switchable solvent phase was achieved by addition of sodium hydroxide into the extractant-sample solution. The effect of key parameters affected extraction recovery was studied and optimised by using Plackett–Burman design, central composite design and three dimension (3D) surfaces response. The calibration plot was linear in the range 0.015–1.6 mg L^?1 of palladium with a correlation coefficient of 0.999. The limit of detections values of palladium for liquid and solid samples were 4.28 μg L^?1 and 0.54 µg g^?1, respectively. The pre-concentration factor was 37.5. The accuracy was confirmed by determination of palladium in certified reference material. The procedure was also applied for determination of palladium content of real samples as automotive catalytic converter, roadside dust, sea water and river water.     

Textile‐based Electrochemical Sensing: Effect of Fabric Substrate and Detection of Nitroaromatic Explosives

This study examines the influence of textile substrates upon the behavior of wearable screen‐printed electrodes and demonstrates the attractive sensing properties of these sensors towards the detection of nitroaromatic explosives. Compared to electrodes printed on common cotton or polyester substrates, GORE‐TEX‐based electrochemical sensors display reproducible background cyclic voltammograms, reflecting the excellent water‐repellant properties of the GORE‐TEX fabric. The wetting properties of different printed textile electrodes are elucidated using contact angle measurements. The influence of laundry washing and mechanical stress is explored. The GORE‐TEX‐based printed electrodes exhibit favorable detection of 2,4‐dinitrotoluene (DNT) and 2,4,6‐trinitrotoluene (TNT) explosives, including rapid detection of DNT vapor.     

The possible production of natural flavours by amino acid degradation

Abstract  

This work describes the degradation of phenylalanine and tryptophane catalysed by their complexes with Fe(II), Co(II), and Cu(II). The influences of the central atom and of the reaction conditions on the degradation of the amino acids were observed. The necessary condition of the degradation is the possibility of a redox reaction on the central atom between M(II) and M(III). Moreover, the coordination sphere of the central cation of the transition metal must not be sterically shielded. The necessary conditions are fulfilled only in the Fe(II) complexes. The degradation is strictly anaerobic because due to the influence of oxygen, an irreversible oxidation of Fe(II) to Fe(III) proceeds. This reaction results in 5-hydroxy-1H-indol instead of the mixture of the degradation products, such as benzaldehyde, phenylacetaldehyde, and phenylacetic acid. The influence of the temperature on the catabolism is very important because the reaction accelerates with temperature increase. The phenylalanine anion acts as a reducing agent, and Fe(II) is spontaneously reduced to Fe(0).