480—Redox and adsorption behaviour of some redox coenzymes involved in an electron-transport chain studied by the electro-optical technique

The redox and adsorption behaviour of some redox coenzymes involved in an electron-transport chain, i.e. ubiquinone-10 (CoQ), flavocoenzymes [flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)] and nicotinamide adenine dinucleotide (NAD⁺), has been studied at a gold electrode by cyclic voltammetry and specular reflectivity measurement. All the coenzymes investigated were found to participate in electron transport in adsorbed states on the electrode surface. Adsorbed CoQ and flavocoenzymes are reduced and the resulting products remain adsorbed at the surface. Contrary to them, adsorbed NAD⁺ is reduced and then desorbed immediately. Possible models for the surface orientation of adsorbed molecules were proposed based on the experimental data.Some analogies can be noted between the interfacial behaviour of these coenzymes at the electrode and that in mitochondria.     

Matrix polycondensation through hydrogen bonding interaction

Polycondensation of diesters having hydroxyl or pyridine groups was carried out with hexamethylenediamine (HMD) in the presence of (vinyl alcohol/vinyl acetate) copolymers as a matrix polymer. Apparent rates of the polycondensation of dimethyl tartrate (DMT) with HMD increased with increasing contents of PVA units in the copolymers and a strong entanglement between growing polyamide chains and PVA copolymers took place through the adsorption of HMD and DMT on the matrix copolymers. 2,6-Dimethyl pyridine dicarboxylate (2,6-DMP) reacted with HMD in the presence of the PVA copolymers or polysaccharide, while the rate enhancement effect of the matrix polymers was not significantly observed, as in the case of DMT. The effect of the matrix polymers on the polycondensation was discussed in terms of hydrogen bonding interactions.     

A sensitive spectrofluorimetric determination of human serum albumin with chrome azurol S

A simple and sensitive method for assay of human serum albumin (5–80 μg) is based on binding of chrome azurol S by the albumin and determination of the bound dye spectrofluorimetrically. The method is sufficiently sensitive for application to spinal fluid (20–100 μl).     

Effect of water treatment and Ce doping of Pt/Al2O3 catalysts on Pt sintering and propane oxidation

The effect of Ce doping and pretreatment of Pt/Al₂O₃ on its catalysis of propane oxidation was investigated after aging the catalysts. The Ce amount and pretreatment conditions were varied, and the propane oxidation activity was measured. The properties of the catalysts were investigated by means of XRD, STEM-EDX, FT-IR, and H₂-TPR. The size of the Pt nanoparticles (PtNPs) decreased for water-treated catalysts doped with a small amount of Ce, suggesting that water treatment of Ce-doped catalysts inhibits Pt sintering. The minimum PtNP size was obtained with ca. 3.6 wt% of Ce. The Ce species with less than 3.6 wt% existed in a dispersed state, whereas above this value, CeO₂ particulates co-existed. The propane oxidation temperature of the water-treated catalysts was lowered to an extent that depended on the Ce content. This tendency is consistent with the PtNP size in the catalysts. It is considered that highly dispersed Ce species take a primary role in promoting propane oxidation on PtNPs. The reduction temperature of Ce species on water-treated catalysts was lower than that of untreated catalysts, probably owing to a stronger interaction between Pt and Ce, demonstrated by FT-IR measurements. The increased reducibility of Ce species may be the reason for the improved oxidation activity of the catalysts.

Graphic abstract

     

Sequence distribution of 1,4 and 3,4 units in polyisoprenes

The ¹³C-NMR spectra of hydrogenated polyisoprenes were investigated. Polyisoprenes containing various ratios of 1,4 and 3,4 units were prepared with n-BuLi/Et₂O and were hydrogenated by using p-toluenesulfonylhydrazide. ¹³C-NMR signals of the hydrogenated polymers were assigned for the triad sequences arising respectively from the 1, 4 and 3, 4 units of polyisoprenes. On the basis of these assignments it was confirmed that 1,4 and 3,4 units were randomly distributed in the polyisoprenes prepared with n-BuLi and that these polymers did not contain appreciable amounts of head-to-head or tail-to-tail 1,4 linkages.     

A direct method for the separation and quantification of bile acid acyl glycosides by high-performance liquid chromatography with an evaporative light scattering detector

A direct method for the separation and quantification of a series of bile acid acyl glycosides using high-performance liquid chromatography coupled to an evaporative light scattering detector (HPLC-ELSD) is described. Complete separation of each of 15 bile acid acyl 24-alpha-glucosides and their 24-beta-anomers and 24-beta-galactosides was achieved by the stepwise gradient elution mode on a C18 column using a mixture of acetonitrile-methanol (8:2, v/v) and 1% aqueous acetic acid as the mobile phase. 24-beta-Galactosides were always eluted faster than the corresponding 24-beta-glucosides, which eluted after the corresponding 24-alpha-anomers. Calibration curves of different 24-beta-galactosides were linear over a range of 0.2-40 nmol of injected amount and the detection limits (S/N > 3) were from 0.08 to 0.1 nmol. The present HPLC-ELSD method may provide an insight into the separation and quantification of the biologically interesting neutral bile acids.     

Synthesis of D- and L-selenomethionine double-labeled with deuterium and selenium-82

The synthesis of D- and L-selenomethionine labeled with ?2Se and three deuteriums at Se-methyl group (D- and L-[2H?, ?2Se]selenomethionine) was described. D- And L-[2H?, ?2Se]selenomethionine were prepared by condensation of (R)- and (S)-2-amino-4-bromobutylic acid with lithium [2H?, ?2Se]methaneselenolate, which was prepared from metal (82)Se and [2H?]methyl iodide. The optical purities of D- and L-[2H?, ?2Se]selenomethionine were determined by HPLC with a chiral stationary phase column and were found more than 99% ee. The chemical ionization mass spectra showed that the molecular related ion for N-isobutyloxycarbonyl ethyl ester derivatives of [2H?, ?2Se]selenomethionine did not overlap with the m/z values known from that of non-labeled selenomethionine.     

Direct detection of OH radicals diffused to the gas phase from the UV-irradiated photocatalytic TiO2 surfaces by means of laser-induced fluorescence spectroscopy

The important roles of OH radicals for remote oxidation using TiO(2) photocatalysts were evidenced by the in situ detection of OH radicals in the gas phase using the laser-induced fluorescence (LIF) technique. The appearance of OD-LIF intensities after the exposure of D(2)O vapors over TiO(2) powders and the decrease of the time-resolved signals of OH-LIF intensities with increasing calcined temperatures of TiO(2) powders suggested that the exchangeable water at the TiO(2) surface is the origin of the diffused OH radicals.