Mechanism and kinetics of the silane decomposition in the presence of acetylene and in the presence of olefins

Kinetic data and product studies are reported for the silane pyrolysis in the presence of olefins and acetylene. The kinetics of silane loss in the presence of acetylene was found to be identical to the initial gas phase silane decomposition step (SiH₄ + M → SiH₂ + H₂ + M) when corrected for pressure fall-off effects. This result and the absence of methane or ethane from the pyrolysis of SiH₄ in the presence of 1-butene or 1-pentene demonstrate that silyl radicals and H atoms are not involved in silane-olefin or silane-acetylene reactions. Qualitative aspects and kinetic data from the SiH₄ pyrolysis in the presence of propylene are in accord with propylsilane formation via propylsilylene formed by silylene addition to propylene.     

聚丙烯和聚乙烯熔融接枝改性及增容

近年来,有关高分子改性研究已引起人们的广泛关注。本文对热塑性塑料聚丙烯和聚乙烯熔融接枝改性的常用单体、提高接枝率的方法、增容作用和接枝物的表征等方面进行了综述。     

Induction by Cytodef of the biosynthesis of endogenous ethylene and cellulase and the change in the composition of the proteins in the leaf-shedding zone of the cotton plant

The influence of the defoliant Cytodef (Tsitodef) on the formation of ethylene and the activity of cellulase in the separating zone of cottonplant leaves has been investigated. It has been established that Cytodef is an inductor of a number of biochemical reactions taking place at the membrane and genetic levels and leading to leaf shedding.Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 463–466, May–June, 1995. Original article submitted October 5, 1994.     

Analysis and assessment of the occurrence, the fate and the behavior of nanomaterials in the environment

Nanomaterials have one dimension <100 nm and possess physico-chemical properties dictated by their unusually small size, large surface area, shape and chemical composition. New properties of nanomaterials have boosted their production and industrial applications in many fields (e.g., microelectronics, catalysis, fuel cells, materials science, textiles, biotechnology and medicine). In biomedical fields, nanomaterials are of the appropriate dimensions to interact with biological matter. However, they may also have negative effects on biological systems. Nanotechnology is a major, innovative, scientific and economic growth area, but the increasing production and use of nanomaterials have led to calls for more information regarding the potential impacts that their release may have on human health and the environment.This review addresses analytical approaches for characterization and quantification of nanomaterials in the environment and recent studies on their occurrence, fate and behavior.     

Curve-fitting overlapped bands: quantification and improvement of curve-fitting robustness in the presence of errors in the model and in the data

Estimation of the band parameters of overlapped bands often relies on curve-fitting. It has been demonstrated that curve-fitting provides the maximum likelihood estimation of band parameters under a series of assumptions. One of these assumptions is that the curve-fitting model is correct and any error in the data is random. Under real conditions, we have to acknowledge the unavoidable presence of errors in the model and systematic errors in the data. Here, we derive an expression for the estimation of how these errors affect the quality of the parameters obtained from curve-fitting. In addition, we derive theoretical expressions to quantify the extent to which different methods can improve the curve-fitting robustness to these errors. The methods considered are: (i) deterministic and (ii) probabilistic constraints in the band parameters, (iii) curve-fitting band-narrowed data, and (iv) building a more accurate model. The theoretical expressions obtained are tested in the curve-fitting of a synthetic noisy spectrum with either baseline or band shape errors, and in the curve-fitting of the experimental infrared amide I band of the membrane protein bacteriorhodopsin.     

Synergism in the extraction of europium in the presence of alkylphosphates and sulphoxides

Synergism in the extraction of europium(III) has been investigated using a mixture of naphthoyltrifluoroacetone and synergists like trioctylphosphine-oxide (TOPO), tributylphosphate (TBP), trihexylphosphate (THP), diphenylsulphoxide (DPSO) and benzylsulphoxide (BSO). Synergism decreases in the order: TOPO < TBP ≃THP < BSO < DPSO indicating a correlation between electron density at the donor atom and extent of synergism. The equilibrium constants for adduct formation have also been evaluated.     

Use of the salet phenomenon in the determination of sulfur and phosphorus in aqueous and organic samples

The history of the Salet phenomenon is summarized. Various experimental configurations are studied for the measurement of the S₂ and HPO emission from different sulfur and phosphorus species in low-temperature flames. Analysis of petroleum fractions for sulfur, and insecticides for phosphorus is discussed.     

Theoretical studies of the structure and stability of protonated olefins in the gas phase and in solution

The calculation of carbenium and carbonium type cations resulting from the protonation of olefins with growing length and increasing chain branching was carried out by quantum chemical methods which were tested elsewhere.One result is the distinction of olefins with an equal number of alkyl substituents on both sides of the double bond and other ones with different number. In the latter case generally no bridged structures could be defined.The influence of nucleophilic solvents on the stability of the cationic structures is simulated on the basis of Klopman's solvaton model. These calculations show that solvents may change the gas phase data in a remarkable way.     

Pharmacokinetics of protein-unbound linezolid in the blood and the mechanism of hepatobiliary excretion in the rat

Linezolid (Zyvox), an oxazolidinones antibiotic, was developed for the treatment of infectious diseases caused by gram-positive pathogens. To investigate the mechanism of hepatobiliary excretion of linezolid, a parallel study design used two groups; in the control group, rats received linezolid alone (3 or 10 mg/kg, i.v.). In the drug-treated groups, 10 min prior to linezolid administration, cyclosporin A (CsA; 10 mg/kg, i.v.), a P-glycoprotein (P-gp) inhibitor, was given in the rats. The microdialysis probes were implanted into the jugular vein toward right atrium and the bile duct of Sprague-Dawley rats for multiple biological fluid sampling. Separation was performed using a reversed phase C₁₈ (4.6 mm × 150 mm i.d., 5 μm) with mobile phase of acetonitrile-methanol-1% 1-octanesulfonic acid in water of 30:10:60 (v/v/v) at flow rate of 1 ml/min. The UV detection for linezolid was set at a wavelength of 260 nm. Following linezolid (10 mg/kg, i.v.) administration, the concentration of linezolid in the brain was less than the limit of quantification and the area-under the concentration curve versus time curve (AUC) of blood and bile were 1780 ± 50 and 2850 ± 276 (min μg/ml), respectively. The bile-to-blood distribution ratio was 1.6 ± 0.2 (n = 6), which was defined as AUC_bile/AUC_blood. The results demonstrated that the transportation of linezolid into bile might be mediated by active transport. However, after treatment with CsA, the linezolid AUC in bile was 3060 ± 411 (min μg/ml) which did not indicate a significant difference with linezolid alone. These results suggest that the hepatobiliary excretion of linezolid might not be regulated by P-gp transportation.     

Catalytic asymmetric alkylation in water in the presence of surfactants: influence of the nature of the nucleophile and the allylic acetate on the activity and enantioselectivity

Asymmetric palladium-catalyzed alkylation of 1,3-diphenyl-2-propenyl acetate with carbon and nitrogen nucleophiles occurs in water in the presence of a surfactant, a base, and Binap as the chiral ligand. Enantioselectivities up to 91% were obtained using carbon nucleophiles, and 93% using nitrogen nucleophiles, in the presence of CTHASO₄ as the surfactant. While the efficiency of the catalyst was higher in water in the presence of the surfactant in the case of carbon nucleophiles, no micellar effects were observed using the nitrogen nucleophiles. The alkylation was extended to other allylic acetates, but the efficiency as well the enantioselectivity of the coupling were lower.     

Changes in the Activity of Lipases in the Presence of Synthetic and Natural Polymers

Moscow University Chemistry Bulletin - Abstract—Both synthetic and natural polymers are promising carriers for the immobilization of enzymes, including lipases from different sources. This...     

Quantum-chemical study of the mechanism of the hydrolysis of amides in the gas phase and in aqueous solution

The MNDO, AM1, and MNDO/M methods have been used to calculate the profile of the potential energy surface for the hydrolysis of formamide in the gas phase and in aqueous solution. Estimates have been made of the changes in the energy barrier in specific acid and base catalysis, and it is shown that in the absence of proton exchange between the reacting system and the solvent the interaction of the charged reactants with a polar medium impedes the reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1785–1792, August 1989.     

正常小儿血清锌铜含量测定及几种疾病中锌、铜含量变化的观察报告

报道２３５名正常小儿血清锌、铜参考值（μｍｏｌ／Ｌ）：新生儿１３．３±１．９、１２．６±２．２，１～３个月龄时偏低，４月龄后增加，且恒定在１５．６±３．２、１７．４±３．４。铜／锌比值为１．１±０．２。疾病组１８０例患儿血清锌降低，以厌食、缺铁性贫血降低明显。血清铜增加，以恶性血液病增加显著，且与病情相关。Ｇ６ＰＤ缺陷溶血组血清锌减少比非溶血组减少明显．与Ｇ６ＰＤ活性、Ｇ６ＰＤ缺陷致溶血之间存在着一定的关系。了解血清钟、铜含量及其比值，对某些小儿疾病的诊断、治疗和预后均有一定的参考价值。     

聚氨酯/聚丙烯酸酯复合乳液的研制进展

概述聚氨酯－聚丙烯酸酯复合乳液的制备方法。特别对聚氨酯－聚丙烯酸酯复合乳液共聚法作了较为系统的介绍和讨论。     

Global energy and climate of the planet in the XXI century in the context of historical trends

The paper deals with global energy perspectives and forthcoming changes in the atmosphere and climate under the influence of anthropogenic and natural factors. In the framework of the historical approach to energy development the forecast of the future global energy consumption for the present century is made, and its resource base and the global consequences of the impact of the power sector on the atmosphere and climate on the background of natural factors are studied. It is shown that, following the historical tendency for global energy evolution, the global energy consumption by the end of the century will remain within 26 bln. tce, with CO₂ emissions peaking in the middle of the century. In this scenario, the CO₂ concentrations will not exceed 500 ppm, and the global temperature should rise by 1.5 degree by 2100, with the growth rate not exceeding the adaptation limits of the biosphere.     

Sulfoxides in the allylation of aldehydes in the presence of silicon tetrachloride and allyltributylstannane

SiCl₄ can be conveniently activated by catalytic amounts of dimethyl sulfoxide or other readily-available sulfoxides for the allylation of aromatic, hetero-aromatic and unsaturated aldehydes in the presence of allyltributyl stannane. Chiral aryl methyl sulfoxides have been used to develop asymmetric allylation methods, as well as probe the aldehyde substrate scope.     

环糊精对阿斯巴甜的甜感增强作用及二者相互作用热力学

目前环糊精（CD）对阿斯巴甜（ASP）甜感强度的影响研究主要集中在环糊精对阿斯巴甜的稳定性研究。我们认为CD对ASP甜感强度的提升与其和ASP的结合常数有一定的关系。本文选择了五种环糊精,α-环糊精（α-CD）、β-环糊精（β-CD）、γ-环糊精（γ-CD）、羟丙基-β-环糊精（HP-β-CD）、甲基-β-环糊精（Met-β-CD）,研究了这些环糊精存在下ASP的感官甜度的变化及二者的相互作用。结果表明,β-CD可以明显提升ASP的甜感强度。等温滴定量热（ITC）和荧光光谱对ASP与CDs结合过程亲和力的研究表明,ASP与β-CD的结合是自发的,并且具有最大的结合常数。差示扫描量热（DSC）、核磁共振（¹H NMR）以及傅里叶变换红外（FT-IR）揭示了其结合过程的机制。本研究对理解甜味剂甜感强度与热力学结合常数的关系具有重要的意义,也为基于结合常数筛选风味保持剂的方法提供有益的基础。