摘要:

AbstractA kinetic model for the metal organic chemical vapour deposition (MOCVD) growth of ZnTe is presented, taking into account the competitive adsorption of organometallic precursors. By assuming that diethylzinc (DEZn) and diethyltellurium (DETe) or di‐isopropyltellurium (DIpTe) are adsorbed onto the surface by two sites, the model yields the growth rate as a function of the gas‐phase concentrations of the constitutents and is corroborated by experimental results obtained by the MOCVD growth (at 400°C with DETe or 350°C with DIpTe), which shows asymmetric behaviour: for a given DETe or DIpTe pressure (10−4atm), the growth rate as a function of DEZn partial pressure passes through a maximum, whereas, at the same constant DEZn pressure, the growth rate increases monotonically when the DETe or DIpTe partial pressure i

ISSN:0268-2605    

DOI:10.1002/aoc.590080202

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPoly(methylsilanes) produced by sodium coupling of methyldichlorosilane (2:1 molar ratio) contain residual chlorine which can be removed by reduction with LiAlH4at low temperature. Following this reduction, the polymers contain catalytically active centers (presumed to be silyl anions) which, in THF solution, further polymerize and crosslink the polymer at room temperature, while in toluene solution they are inactive. The reduced polymethylsilane gives high yields (ca75%) of ceramic product on pyrolysis, but the composition is rich in silicon, compared with pure silicon carbide (SiC). Addition of catalytic amounts of dimethylzirconocene (DMZ) to this polymer gives a product which pyrolyzes to a product with stoichiometry close to that of SiC. It is concluded that the DMZ has an important influence in promoting Si–C bond formation, relative to Si–Si bond formation, during the pyroly

ISSN:0268-2605    

DOI:10.1002/aoc.590080203

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractSome organometallic compounds, e.g. Ph3SnCl, react on the surface of the smectite clay, laponite. Other compounds, e.g. Br3TeC6H4CH=NCH2CH2N=CHC6H4TeBr3, are sorbed onto the organophilic surface of cetylpyridinium‐ion‐exchanged Wyoming bentonite. X‐ray photoelectron spectroscopy (XPS) is an appropriate technique with which to examine the nature of the surface‐sorbed species; however, it is demonstrated that decomposition of the organometallic can occur when the clay surface is exposed over a period of time to energetic X‐rays. Thus, care must be taken with the interpretation of data of which some features may be the result of the XPS e

ISSN:0268-2605    

DOI:10.1002/aoc.590080204

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNa2[Cr(CO)5] (1) was found to be an efficient catalyst for the dimerization of aldehydes to carboxylic esters. Several aromatic aldehydes including furfural gave the corresponding esters in good yields. This reaction also proceeded intramolecularly to give phthalide from phthalaldehyde. Compared with M2[Fe(CO)4] (M = Na, K), 1 was found to be a more efficient catalyst for this reaction. However, aliphatic aldehydes gave aldolcondensation products instead of the corresponding esters. In the reactions ofp‐substituted benzaldehydes with 1, the reactivity decreased with the increase of the electron‐releasing ability of the substituents. However, evenp‐anisaldehyde, which hardly reacted with M2[Fe(CO)4], reacted with 1 to give the ester in moderate yield. The reaction mechanism, including the nucleophilic attack of the pentacarbonylchromate dianion on the carbonyl carbon, is disc

ISSN:0268-2605    

DOI:10.1002/aoc.590080205

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractStannacyclohexyl and stannacycloheptyl derivatives of dipeptides (CH2)nSnAA ·xH2O (H2AA = H2GlyGly, withn= 5,x= 2 or n = 6, x = 1; H2AA = H2GlyAla, H2GlyVal, H2GlyMet, withn= 5, 6,x= 1) and stannepinyl glycylglycinate monohydrate have been obtained by the reaction of (CH2)nSnCl2or stannepinyl dichloride with Na2AA. According to infrared and119Sn Mössbauer data of the solid compounds, AA acts as a tridentate ONN ligand and tin has a trigonalbipyramidal environment. An analogous structure has been inferred from1H,13C, and119Sn NMR data for the undissociated molecules in methanol solutio

ISSN:0268-2605    

DOI:10.1002/aoc.590080206

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractIn order to replace silicones in some of their biomedical applications, e.g. syringe lubrication, implants ets., a series of digermoxanes (R1R2R3Ge)2O (R = n–alkyl, aryl) were synthesized. These compounds are thermally stable oils; their viscosities, depending on the nature of substituents, lie in the range 1–72 cPo (mPa s) at 2

ISSN:0268-2605    

DOI:10.1002/aoc.590080207

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe HPLC separation of arsenite, arsenate, methylarsonic acid and dimethylarsinic acid has been studied in the past but not in a systematic manner. The dependence of the retention times of these arsenic compounds on the pH of the mobile phase, on the concentration and the chemical composition of buffer solutions (phosphate, acetate, potassium hydrogen phthalate) and on the presence of sodium sulfate or nickel sulfate in the mobile phase was investigated using a Hamilton PRP‐X100 anion‐exchange column. With a flame atomic absorption detector and arsenic concentrations of at least 10 mg dm−3all investigated mobile phases will separate the four arsenic compounds at appropriate pH values in the range 4–8. The shortest analysis time (˜3 min) was achieved with a 0.006 mol dm−3potassium hydrogen phthalate mobile phase at pH 4, the longest (˜10 min) with 0.006 mol dm−3sodium sulfate at pH 5.9 at a flow rate of 1.5 cm3min−1. With a graphite furnace atomic absorption detector at the required, much lower, flow rate of ˜0.2 cm3min−1acceptable separations were achievable only with the pH 6 phosphate buffer (0.03 mol dm−3) and the nickel sulfate solution (0.005 mol dm−3) as the mobile phase. To become detectable approximately 100 ng arsenic from each arsenic compound (100 μl injection) must be chromatographed with the phosphate buffer, and approximately 10 ng with the

ISSN:0268-2605    

DOI:10.1002/aoc.590080208

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractIn the soils and aquatic systems of coniferous forests, selenium is usually associated with humic substances. To clarify further some of the mechanisms involved, labelled and unlabelled selenite were added to two forest floors and to a brownwater lake. Sequential extraction procedures and chromatographic methods were used to evaluate the resulting association between selenium and humic substances. It was observed that the forest floors fixed most of the added selenite by means of microbial reductive incorporation and that selenium was preferentially incorporated into lowmolecular‐weight fractions of the humic substances. By contrast, selenium reduction was much slower in the brown‐water lake and instead, inorganic complexation of selenite to metal–humic complexes was important during the experiment, provided that the concentrations of competing ligands wer

ISSN:0268-2605    

DOI:10.1002/aoc.590080209

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractDibutyltin‐3‐hydroxyflavone, Bu2Sn(of), is a new fluorescence probe inhibitor of F1F0‐ATPase and oxidative phosphorylation which inhibits by titration of an unidentified component of F0. Its site of action is closely related to that of the trialkyltins and of venturicidin. This F0component is part of a pool of this component which is present in the heart mitochondrial inner membrane at levels of 5–7 nmol (mg protein)−1[18 ± 3 Bu2Sn(of) sites per mol F1F0‐ATPase]. However, ATPase activity in submitochondrial particles is near maximally inhibited by titration of approx. three Bu2Sn(of) sites per mol F1F0‐ATPase.Over 60% (60–80%) of the Bu2Sn(of) interaction sites can be lost during the purification of F1F0‐ATPase from submitochondrial particles. The number of Bu2Sn(of) interaction sites in various F1F0‐ATPase preparations is variable. The high numbers of Bu2Sn(of) sites per mol F1F0‐ATPase for heart mitochondria (18–21) and submitochondrial particles (15–19.5) decline in ATP synthase (11–15) to the low values obtained in Complex V (7–10.5) and the minimal values observed in highly purified F1F0−ATPase (3.5–5.6), thus indicating a variable dissociable component or cofactor of ATP synthase.The Bu2Sn(of) interaction site, a component of ATP synthase, is responsive to the redox status of the respiratory chain and the interaction with Bu2Sn(of) is with the reduced form of this component. Fluorescence titration studies show that this component is in redox equilibrium with the ubiquinone pool of the respiratory chain. It is proposed that this redox component serves as an inhibitor titratable cofactor pool which cycles through an F0interaction site (or sites) via a system which serves as an energy‐transfer link between th

ISSN:0268-2605    

DOI:10.1002/aoc.590080210

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0268-2605    

DOI:10.1002/aoc.590080213

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY