Selective Oxidation of Phenol in the Presence of Transition-Metal Substituted Polyoxometalates

Tetrabutylammonium salts of lacunary Keggin anions with supported Co and Mn cations soluble in organic solvents were prepared and characterized by thermogravimetric analysis, FTIR spectroscopy and X-ray diffraction. These salts were applied as catalysts for phenol oxidation in acetonitrile solution with iodosobenzene diacetate as single oxygen donor. Deposition of cobalt ions in the lacunary Keggin anions strongly increases the catalytic activity. The conversion of phenol is proportional to concentrations of catalyst and single oxygen donor. The dependence of the conversion of phenol on time indicates that the reaction is 1st order with respect to phenol. The catalyst retains its activity after recycling. On the basis of catalytic results reaction mechanism was elucidated.     

Application of lyophilization to prepare the nitrifying bacterial biofilm for imaging with scanning electron microscopy

Structure of bacterial biofilms may be investigated using several variants of scanning electron microscopy (SEM). We apply lyophilization to prepare nitrifying bacterial biofilm for conventional SEM imaging in high-vacuum mode (CSEM). We therefore replace standard biofilm fixation in glutaraldehyde cross-linking, ethanol dehydration, and critical-point drying (CPD) with less-invasive low-temperature drying by sublimation in vacuum. We compare this approach with: (1) standard preparation with glutaraldehyde fixation, ethanol dehydration, and CPD before CSEM, (2) cryo-sputter preparation of rapidly frozen biofilm in hydrated state (cryo-SEM), and (3) in situ observation without any sample pretreatment in environmental SEM. Combined imaging with these modalities revealed two distinct immobilization patterns on the polyurethane foam: (1) large irregular aggregates (flocs) of bacterial biofilm that exist as irregular biofilm fragments, rope-like structures, or biofilm layers on the foam surface; (2) biofilm threads adherent to the surface of polyurethane foam. Our results indicate that lyophilization was suitable for preservation of bacterial cells and many forms of structure of extracellular matrix. The lyophilized material could be imaged with high resolution (using CSEM) to generate structural information complementary to that obtained with other SEM techniques.     

A Comparison of the Effect of Lead (Pb) on the Slow Vacuolar (SV) and Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

Little is known about the effect of lead on the activity of the vacuolar K⁺ channels. Here, the patch-clamp technique was used to compare the impact of lead (PbCl₂) on the slow-activating (SV) and fast-activating (FV) vacuolar channels. It was revealed that, under symmetrical 100-mM K⁺, the macroscopic currents of the SV channels exhibited a typical slow activation and a strong outward rectification of the steady-state currents, while the macroscopic currents of the FV channels displayed instantaneous currents, which, at the positive potentials, were about three-fold greater compared to the one at the negative potentials. When PbCl₂ was added to the bath solution at a final concentration of 100 µM, it decreased the macroscopic outward currents of both channels but did not change the inward currents. The single-channel recordings demonstrated that cytosolic lead causes this macroscopic effect by a decrease of the single-channel conductance and decreases the channel open probability. We propose that cytosolic lead reduces the current flowing through the SV and FV channels, which causes a decrease of the K⁺ fluxes from the cytosol to the vacuole. This finding may, at least in part, explain the mechanism by which cytosolic Pb²⁺ reduces the growth of plant cells.     

Effect of Antibiotic Amphotericin B Combinations with Selected 1,3,4-Thiadiazole Derivatives on RPTECs in an In Vitro Model

4-(5-methyl-1,3,4-thiadiazole-2-yl) benzene-1,3-diol (C1) and 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl] benzene1,3-diol (NTBD) are representative derivatives of the thiadiazole group, with a high antimycotic potential and minimal toxicity against normal human fibroblast cells. The present study has proved its ability to synergize with the antifungal activity of AmB. The aim of this work was to evaluate the cytotoxic effects of C1 or NTBD, alone or in combination with AmB, on human renal proximal tubule epithelial cells (RPTECs) in vitro. Cell viability was assessed with the MTT assay. Flow cytometry and spectrofluorimetric techniques were used to assess the type of cell death and production of reactive oxygen species (ROS), respectively. The ELISA assay was performed to measure the caspase-2, -3, and -9 activity. ATR-FTIR spectroscopy was used to evaluate biomolecular changes in RPTECs induced by the tested formulas. The combinations of C1/NTBD and AmB did not exert a strong inhibitory effect on the viability/growth of kidney cells, as evidenced by the negligible changes in the apoptotic/necrotic rate and caspase activity, compared to the control cells. Both NTBD and C1 displayed stronger anti-oxidant activity when combined with AmB. The relatively low nephrotoxicity of the thiadiazole derivative combinations and the protective activity against AmB-induced oxidative stress may indicate their potential use in the therapy of fungal infections.     

Evaluation of kinetic parameters of coal ignition

A method is presented of evaluating the kinetic parameters for the ignition reaction of coal based on the Semenov's thermal ignition theory adopted to coal particle ignition. The evaluated apparent activation energy, E, for bituminous coal, anthracite and bituminous coal char are in the range 46–103 kJ mol^?1. A verification was made by comparing the measured induction periods for the coal particles with those calculated numerically. The oxidation rate is controlled by diffusion into pores.     

Electron microscope investigations of activated chalcopyrite particles via the FLSmidth<Superscript>®</Superscript> ROL process

Because of its unique semiconductor properties, the world’s most abundant copper mineral, chalcopyrite (CuFeS₂), is refractory with respect to atmospheric leaching using traditional acidic ferric sulfate lixiviants. FLSmidth^® has developed a novel approach manipulating lattice properties of semi-conducting minerals with the benefit of increasing chemical reactivity and dissolution kinetics. In the FLSmidth^® Rapid Oxidative Leach (ROL) process, leach kinetics are still further enhanced by combining chemical and mechanical processes with the assistance of a Stirred Media Reactor. Due to the reduction in surface passivation problems associated with atmospheric leaching, this process is typically able to achieve copper recoveries exceeding 95% in 6 h. An important factor contributing to this extraordinary process performance is a mineral preconditioning step (the focus of this study), which uses between 0.1 and 5 mol percent of copper (II) to dope the lattice and thereby “activate” chalcopyrite. Since lattice restructuring can have such a dramatic influence on semiconductor reactivity, the associated physico-chemical phenomena are worth studying. In this regard, we investigate the relationship between chemical activation and deformation of the chalcopyrite crystal lattice through the use of electron microscopy. Although the activation process took only an hour and the extent of conversion was on the order of a few mol%, the lattice was found to be strained throughout the particle. This paper draws some insights into the impact of applying chemical activation as a pretreatment for mechanochemical processes.     

Experimental studies of momentum transfer in a gas-liquid system in the vicinity of an agitated vessel wall

The results of an experimental investigation of transport processes at the wall of an agitated vessel in a gas-liquid system are presented. Measurements were carried out by means of the electrochemical method. The experiments were performed in a standard agitated vessel of diameter 0.3 m, equipped with a Rushton disc turbine and baffles. The distributions of the diffusion current along the vessel wall were obtained for different values of agitator speed and superficial gas velocity. On the basis of these data, distributions of the shear rate, shear stress, dynamic velocity, friction coefficient and energy dissipated were evaluated. The mean values of the variables were approximated analytically. This paper was presented at the International Workshop on Electrodiffusion Diagnostics of Flows held in Dourdan, France, May 1993.     

Molecular tracking: A concept for side-draw distillation column design

A simple approach is introduced to locate a side-draw tray for ternary and multi-component mixtures with middle boiling component(s) present in the system at trace levels. The concept is based on a probability function defined by the thermodynamic properties of the system. The advantage of this method over existing methods is the ability to quickly and efficiently provide a feasible configuration of the distillation unit without relying on rigorous optimization or trial and error approaches. Moreover, it provides an intuitive understanding of the movements of the middle boiling components in the column.     

A mathematical model of mixing of particulate solids

A mathematical model of mixing of particulate solids accompanied by segregation is presented. The model has been constructed on the assumption of diffusional mechanisms of both phenomena occurring when the mixing takes place, i.e. homogenisation and segregation. For the mechanism of diffusional segregation a “Law of Diffusional Segregation” has been formulated, analogous to Fick's Second Law. The model has been solved for a two-component system mixed radially in a horizontal rotating drum mixer. A solution has been obtained in the form of the dependence of the concentration of the key component upon the time and position. After introducing the statistical definition of the degree of mixing, based on the concentration standard deviation in the system, a rate equation has been obtained.