On the origin of optical activity in tris-diamine complexes of Co(III) and Rh(III): a simple model based on time-dependent density function theory

Time-dependent density functional theory (TD-DFT) is applied to the CD spectra of Lambda(deltadeltadelta)-(+)-[Co(S-pn)n(en)(3-n)]3+ (n = 1, 2, 3) and Lambda(deltadeltadelta)-(+)-[Co(en)3]3+ as well as the stereoisomers Delta-((delta)n(lambda)(3-n))-(-)-[Co(S-pn)n(en)(3-n)]3+ (n = 1, 2, 3) and Delta(deltadeltadelta)-(-)-[Co(en)3]3+. Theory is able to reproduce the major differences in the CD spectra of the species with a Lambda-configuration and their isomers with a Delta-configuration in both the d-d and ligand-to-metal CT region. It is further possible to rationalize the trend in terms of a larger azimuthal distortion away from the octahedral geometry in the Lambda-conformation compared to the Delta-configuration. Considerations were also given to the CD spectra of the lel3-isomer, Delta(lambdalambdalambda)-(-)-[Rh(R-pn)3]3+ and the ob-isomer, Lambda(lambdalambdalambda)-(+)-[Rh(S-pn)3]3+.     

High stability amperometric biosensor based on enzyme entrapment in microgels

The preparation and characterization of an amperometric glucose biosensor based on the entrapment of glucose oxidase (GOx) in a polyacrylamide microgel is described. This study proves that polyacrylamide microgels provide an excellent matrix for GOx immobilization that can be used as a biological material in amperometric biosensors. The interference produced by ascorbic and uric acid has been eliminated by including acrylic acid in the polymeric matrix. With this modification, we obtain an adequate device for glucose determination in complex samples such as blood and serum. The study of the temperature effect in the response of biosensors indicates that swelling of the microgels directly influences the enzymatic activity. Thus, the behaviour of the enzyme in the swollen microgels is similar to the enzyme in solution, but the enzyme's activation energy increases when the water content in the microgels decreases. One important property of these biosensors is their remarkable stability. After 4 months of its manufacture, there is no loss in the initial response. Furthermore, the enzymatic activity of freeze-dried microgels containing enzyme remains unaltered for at least 18 months.     

Regioselective palladium-catalyzed alkylation of allylic halides with benzylic grignard reagents. Two-step synthesis of abietane terpenes and tetracyclic polyprenoid compounds

A highly regioselective palladium-catalyzed alpha-alkylation of allylic bromides 1a,c-e and chloride 1b with substituted and unsubstituted benzylic Grignard reagents is reported. The resulting all-trans polyenehomobenzene derivatives were obtained in excellent yields and regioselectivity. These products were easily converted to abietane-type diterpenes (10-12) and tetracyclic polyprenoid compounds (13, 14) through a Lewis acid-promoted cascade polyene cyclization reaction.     

Elucidation of the pore structure of SBA-2 using Monte Carlo simulation to interpret experimental data for the adsorption of light hydrocarbons

We have measured the adsorption of methane and ethane to high pressure on SBA-2, a structured mesoporous silica composed of spheres connected by narrow channels. The experimental data were analyzed by carrying out Monte Carlo simulations of adsorption in pore structure models of different complexity and then adjusting the parameters of the models to match the Monte Carlo results to the experimental data. We found that a model based on single-sized spherical cavities was inadequate and that it is necessary to explicitly account for the interconnecting channels. Further, we found that despite the basic regularity of the SBA-2 structure, it is necessary to allow for a distribution of the sizes of both the cavities and the channels. These size distributions were obtained by fitting the parameters of the model to the experimental adsorption data, revealing detailed structural information not previously known for this material. The channels were found to be 5-15 A in diameter, while the cavities were 40-50 A in diameter. There is some evidence that the distribution of channel sizes leads to a percolation effect whereby the pore structure is not equally accessible to all adsorptives.     

Determination of oxidized and reduced glutathione, by capillary zone electrophoresis, in Brassica juncea plants treated with copper and cadmium

A rapid method of capillary zone electrophoresis is described to determine the oxidized (GSSG) and reduced (GSH) form of glutathione in plant tissue. In order to separate both analytes in a fused-silica capillary, the pH and composition of the electrolyte solution were optimized. The electrolyte composition was 100 mmol/L, borate 25 mmol/L Tris, and 0.2% w/v metaphosphoric acid (MPA), pH 8.2. Some instrumental conditions used to run the samples were hydrostatic injection for 30 s, 30 kV applied voltage, and UV detection (185 nm) at 25 degrees C. Linearity and useful range obtained for the calibration curves were optimum, with correlation coefficients about 0.999 in the 0-120 micromol/L range. The migration time was highly reproducible, less than 5 min being afforded to run a sample. Electrolyte buffer and samples required a careful pH control for optimal separation of both analytes. This aspect constitutes a critical analytical step when acids are used in the procedure for sample preparation. Simultaneous analysis of GSH and GSSG may provide a useful tool for comparative studies of plants in order to select those species with a potential capacity for detoxification from toxic elements or those appearing promising from phytoremediation for these elements.     

Transport in ceria electrolytes modified with sintering aids: effects on oxygen reduction kinetics

Small (2 mol%) cobalt oxide additions to ceria-gadolinia (CGO) materials considerably improve sinterability, making it possible to obtain ceramics with 95–99% density and sub-micrometre grain sizes at 1,170–1,370 K. The addition of Co causes a significant shift of the electrolytic domain to lower pO₂. This modification to the minor electronic conductivity of the electrolyte material has influence on the cathodic oxygen reduction reaction. The impedance technique is shown to provide information not only about polarisation resistance, but also about the active electrode area from analysis of the current constriction resistance. It is demonstrated that this current constriction resistance can be related to the minor electronic contributions to total conductivity in these materials. A simple imbedded grid approach gives control of the contact area allowing the properties of the electrolyte materials to be studied. A much lower polarisation resistance for the Co-containing CGO electrolyte is observed, which can be clearly attributed to an increased three-phase reaction area in the Co-containing material, as a consequence of elevated p-type conductivity.     

NADH Electrooxidation Using Bis(1,10-phenanthroline-5,6-dione) (2,2'-bipyridine)ruthenium(II)-Exchanged Zirconium Phosphate Modified Carbon Paste Electrodes

We present a carbon paste electrode (CPE) modified using the electron mediator bis(1,10‐phenanthroline‐5,6‐dione)(2,2′‐bipyridine)ruthenium(II) ([Ru(phend)₂bpy]²⁺) exchanged into the inorganic layered material zirconium phosphate (ZrP). X‐Ray powder diffraction showed that the interlayer distance of ZrP increases upon [Ru(phend)₂bpy]²⁺ intercalation from 10.3 Å to 14.2 Å. The UV‐vis and IR spectroscopies results showed the characteristic peaks expected for [Ru(phend)₂bpy]²⁺. The UV‐vis spectrophotometric results indicate that the [Ru(phend)₂bpy]²⁺ concentration inside the ZrP layers increased as a function of the loading level. The exchanged [Ru(phend)₂bpy]²⁺ exhibited luminescence even at low concentration. Modified CPEs were constructed and analyzed using cyclic voltammetry. The intercalated mediator remained electroactive within the layers (E°′=–38.5 mV vs. Ag/AgCl, 3.5 M NaCl) and electrocatalysis of NADH oxidation was observed. The kinetics of the modified CPE shows a Michaelis–Menten behavior. This CPE was used for the oxidation of NADH in the presence of Bakers' yeast alcohol dehydrogenase. A calibration plot for ethanol is presented.     

Ab initio molecular dynamics simulation of a room temperature ionic liquid

Ab initio molecular dynamics simulations have been performed for the first time on the room-temperature organic ionic liquid dimethyl imidazolium chloride [DMIM][Cl] using density functional theory. The aim is to compare the local liquid structure with both that obtained from two different classical force fields and from neutron scattering experiments. The local structure around the cation shows significant differences compared to both the classical calculations and the neutron results. In particular, and unlike in the gas-phase ion pair, chloride ions tend to be located near a ring C-H proton in a position suggesting hydrogen bonding. The results are used to suggest ways in which the classical potentials may be improved.