Factors determining the chemoselectivity of phosphorus-modified palladium catalysts in the hydrogenation of chloronitrobenzenes

The precursor nature effect on the state of the Pd–P surface layer in palladium catalysts and on their properties in the liquid-phase hydrogenation of chloronitrobenzenes under mild conditions has been investigated. A general feature of the Pd–P-containing nanoparticles obtained from different precursors and white phosphorus at P/Pd = 0.3 (PdCl₂ precursor) and 0.7 (Pd(acac)₂ precursor) is that their surface contains palladium in phosphide form (BE(Pd3d _5/2) = 336.2 eV and BE(Р2р) = 128.9 eV) and Pd(0) clusters (BE(Pd3d_5/2) = 335.7 eV). Factors having an effect on the chemoselectivity of the palladium catalysts in chloronitrobenzenes hydrogenation are considered, including the formation of small palladium clusters responsible for hydrogenation under mild conditions.     

The state of palladium in the nanosized hydrogenation catalysts modified with elemental phosphorus

The size, nature, and surface state of nanoparticles formed by reduction of Pd(acac)₂ with hydrogen in the presence of P₄ have been elucidated by means of X-ray photoelectron spectroscopy, X-ray powder diffraction analysis, and transmission electron microscopy. The nanoparticles (average diameter of 5.6 nm) consist of Pd₆P and palladium nanoclusters (at initial ratio P/Pd = 0.3). Dimethylammonium dihydro- and hydrophosphates are found in the surface layer of the catalyst nanoparticles. The nanoparticles are stabilized by ammonium salts formed via dimethylformamide hydrolysis.     

Study of conjugation effects by NMR spectroscopy. XXIV. Determination of the conformational composition of alkyl phenyl ethers with branched alkyl radicals from the13C-1H and13C-13C spin-spin coupling constants

Conclusions During analysis of the¹³C-¹-H and¹³C-¹³C spin-spin coupling constants of the phenyl group in alkyl phenyl ethers it was established that the steric inhibition of the conjugation due to increase in the branching of the alkyl group partial in nature and is strongest in 2-methyl-2-phenoxypropane, whereas further increase in the effective volume of the alkyl group leads to some decrease in the population of the orthogonal conformer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2463–2467, November, 1985.     

The 13C bicarbonate method: an inverse end product method for measuring CO2 production and energy expenditure

We reconsider the principle of the ¹³C bicarbonate (NaH¹³CO₃) method (¹³C-BM) for the determination of the CO₂ production to obtain an estimate of energy expenditure (EE). Its mathematical concept based on a three-compartmental model is related to the [¹⁵N]glycine end product method. The CO₂ production calculated by the ¹³C-BM, R_aCO₂(¹³C) is compared to the result from the indirect calorimetry, RCO₂(IC). In an interspecies comparison (dog, goat, horse, cattle, children, adult human; body mass ranging from 15 to 350?kg, resting and fasting conditions) we found an excellent correlation between the results of ¹³C-BM and IC with RCO₂(IC)?=?0.703?×?R_aCO₂(¹³C), (R²?=?0.99). The slope of this correlation corresponds to the fractional ¹³C recovery (RF(¹³C)) of ¹³C in breath CO₂ after administration of NaH¹³CO₃. Significant increase in RF(¹³C) was found in physically active dogs (0.95?±?0.14; n?=?5) vs. resting dogs (0.71?±?0.10, n?=?17; p?=?.015). The ¹³C recovery in young bulls was greater in blood CO₂ (0.81?±?0.05) vs. breath CO₂ (0.73?±?0.05, n?=?12, p?<?.001) and in ponies with oral (0.76?±?0.03, n?=?8) vs. intravenous administration of NaH¹³CO₃ (0.69?±?0.07; n?=?8; p?=?.026). We suggest considering the ¹³C-BM as a ‘stand-alone’ method to provide information on the total CO₂ production as an index of EE.     

Surface nanoscale relief of mineral crystals and its relation to nonautonomous phase formation

The features of the nanoscale relief of crystals formed under natural and experimental conditions are considered by examples of pyrite, sphalerite and its solid solutions, and native gold. Nonautonomous phases (NAPs), which differ from the bulk mineral by their chemical composition, stoichiometry, and structure, are fixed within an approximately half-micron surface layer. For pyrite crystals, the NAP composition and morphology vary depending on the genetic conditions. In the case of sphalerite, hierarchical fractal structures arise on the crystal surface due to the formation of NAPs of sulfate or sulfoxide composition. An increased content of admixed elements (Cd, Hg) is observed on the surface at the largest NAP development. Gold sulfide NAPs are observed to be stable at a relatively high temperature under hydrothermal conditions.     

Evaluation of the oral ¹³C-bicarbonate tracer technique for the estimation of CO₂ production and energy expenditure in dogs during rest and physical activity

For feeding of working dogs during their daily life, illness, routine jobs or sporting activities, an accurate determination of their nutritional requirements is essential to ensure their optimal health and performance. To predict the appropriate guidelines about how to feed dogs, it appears essential to determine the energy expenditure (EE) in a reliable and feasible way. In the present experiment, the non-invasive oral 13C-bicarbonate tracer technique (o13CT), i.e. collection of breath samples after oral administration of NaH13CO?, was used for the estimation of CO? production and EE in dogs. Measurements were conducted during two days of rest, and during three days with 3 h of exercise per day. Average EE was 483 and 876 kJ kg??·?? d?1 during rest and exercise, respectively. The o13CT seems appropriate to use as a minimal restrictive and non-invasive method to obtain reliable estimates of EE in dogs at different activity levels under near natural conditions.     

Gold distribution in pyrrhotite crystals grown under hydrothermal conditions

The distribution of gold between pyrrhotite and greenockite was studied by the method of hydrothermal thermal-gradient cocrystallization of the components at a temperature of 450°C, a pressure of 1 kbar, and different activities of sulfur in the presence of As and Se impurities. The structural component of Au impurity in these minerals was selected by studying statistical samplings of the analytical data for single crystals. Ferrous greenockite incorporates a maximum of 10 ± 2 ppm Au in solid solution. The incorporation limit of Au in stoichiometric pyrrhotite was estimated to be 25 ± 9 ppm; for nonstoichiometric pyrrhotites, it is lower. The As and Se impurities barely affect the concentration of structural gold in the minerals. It was shown that constitutional vacancies in pyrrhotite do not capture Au impurity. The observed phenomenon may be the growth effect related to the surface properties of nonstoichiometric pyrrhotite crystals grown under hydrothermal conditions. Differences in the surface structure of pyrrhotites of different composition and the products of their sorption of gold were revealed by X-ray photoelectron spectroscopy.     

On the mechanism of trace-element uptake during the hydrothermal growth of sulfide mineral crystals

The stable species of cadmium and mercury are formed in iron and lead sulfides at elevated temperatures and pressures under hydrothermal conditions. Their formation proceeds through different mechanisms. The most general mechanism involves the uptake of trace elements in the form of structural species due to isomorphous exchange. The results obtained for cadmium in pyrrhotite indicate that structural defects substantially affect the incorporation of impurities into the crystal structure. It is found that trace elements are accumulated on the surface in the absence of defects and are incorporated into the crystal bulk in the form of structural impurities in the presence of defects. Moreover, at elevated temperatures and pressures, trace elements can form their own (surface nonautonomous) phases. These phases are formed not only at trace-element concentrations close to saturation (Cd in Fe_1.0S) but also under conditions far from saturation as a result of the interaction of trace elements with the oxidized surface of the mineral (the cadmium uptake by galena with the formation of either a sulfate surface phase or a sulfate-chloride surface phase). An important mechanism of trace-element uptake by sulfides during the hydrothermal growth of crystals is associated with external and internal adsorption of impurities by defects. This adsorption manifests itself both in an increase in the content of sorbed mercury in galena at a high sulfur activity due to the interaction of mercury with lead vacancies and in the formation of dislocation cadmium species, which results in an increase in the coefficient of cadmium distribution in the crystal-solution system.