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31.
Parr and Chattaraj proposed a principle of maximum hardness for stable molecular structures. Pearson and Palke used ab initio SCF MO calculations for ammonia and ethane to demonstrate the operation of the principle. In this paper, we present ab initio SCF MO results for five isomeric forms of the homoatomic P6 cluster as further support for the principle of maximum hardness. © 1994 John Wiley & Sons, Inc. 相似文献
32.
Dalgarno SJ Hardie MJ Warren JE Raston CL 《Dalton transactions (Cambridge, England : 2003)》2004,(16):2413-2416
Two types of arrays are formed in water involving aza-crown ethers, p-sulfonatocalix[5]arene and europium(III) ions. One is a co-ordination polymer connecting calixarenes, sodium ions and lanthanide ions based on "ferris wheel" moieties incorporating aza-18-crown-6 and sodium ions. The second structure is a host-guest arrangement with di-protonated diaza-18-crown-6 in the cavity of the calixarenes as part of secondary coordination spheres of aquated europium(iii) ions. 相似文献
33.
The metal complexes [Os(byp)(2)(pic)](+) and [Ru(byp)(2)(pic)](+) where byp is 2,2'-bipyridine and HPic is o-picolinic acid were synthesised and characterised using spectroscopic and electrochemical techniques. These complexes were then evaluated as mediators for a glucose oxidase (GOx)-based biosensor. Results demonstrate the electrocatalytic behaviour of both metal couples towards regeneration of the flavoprotein GOx (FADH(2)) group, when co-immobilised with glucose oxidase. Surface immobilisation was achieved by potential cycling in aqueous solutions of the metal complexes at a glucose oxidase (GOx)/Nafion modified electrode. This proved successful in terms of catalytic efficiency and stability of redox sites. Kinetic parameters associated with both enzymatic and mediator reactions were estimated and the stability/performance properties of the sensor were tested. 相似文献
34.
Modifications of the SCF-LCAO-π-MO method analysed in the previous paper are described in which provision is made for the incorporation of Variable Bond Order and Variable Electronegativity procedures. A comparison is made with the results of other π-electron calculations and values are reported for twenty hydrocarbon systems. 相似文献
35.
Warren DB Grieser F Perera JM Stevens GW 《Langmuir : the ACS journal of surfaces and colloids》2005,21(7):2822-2826
A model to calculate the interfacial concentration of competing surface active species in a two-phase oil/water system was developed. To enable the calculation of the surface excess of 2-hydroxy-5-nonylacetophenone oxime (HNAPO, active ingredient of LIX 84) in the presence of surfactants competing for interfacial area, an interfacial adsorption competition model was derived for noninteracting surface active species in a n-heptane/aqueous system, assuming ideal enthalpy and entropy of mixing. The model was found to be valid for HNAPO in the presence of sodium dodecyl sulfate (SDS) or dodecyldimethyl(3-sulfopropyl)ammonium (DDSA). In the case of dodecyltrimethylammonium chloride (DTAC) or octa(ethylene glycol) mono-n-dodecyl ether (C12E8) as the competing surfactants with HNAPO, the predicted surface excess values from the model fit less favorably. The difference was shown to not be due to nonideal entropy of mixing. 相似文献
36.
In 1959, Horner showed that metalated alkyldiphenylphosphane oxides react with aldehydes or ketones to give alkenes. With this reaction, the diphenylphosphoryl (Ph2PO) group made its entrance into synthetic organic chemistry. In the thirty-six years since that date, extensive research has shown that this olefination, the Horner–Wittig reaction, has unique properties that make it much more than simply the phosphane oxide cousin of the more famous phosphorus-based olefinations—the Wittig reaction (based on phosphonium salts) and the Wadsworth–Emmons reaction (based on phosphonate esters). Early work on the Horner–Wittig reaction concentrated on the reactivity of phosphane oxides and the regioselectivity of their reactions, but more recently the power of the Ph2PO group to control the stereochemistry of alkenes, and to produce “on demand” either stereoisomer in high stereochemical purity, has emerged. From the study of these stereocontrolled Horner–Wittig reactions arose the realization that the Ph2PO group is useful not only for the control of the two-dimensional stereochemistry of alkenes, but also of three-dimensional stereochemistry in general. After a brief introduction to phosphane oxide chemistry, this review will examine the Horner–Wittig reaction, in both its original and “stereocontrolled” varieties. From there, we will move on to an account of the stereoselective construction of molecules containing the Ph2PO group, concentrating on the stereochemical directing effects of the Ph2PO group and on the role of its unique combination of attributes—steric bulk, electronegativity, and Lewis basicity—in controlling these reactions. Finally, we will present what is intended as a practical guide to this chemistry, covering the type of functionalized alkenes that have been made with the help of the Ph2PO group and giving guidelines that we hope will help the organic chemist to make the most of the chemistry the Ph2PO group has to offer. 相似文献
37.
Mario H. Gutierrez Warren T. Ford 《Journal of polymer science. Part A, Polymer chemistry》1986,24(4):655-663
Glass transition temperatures have been determined for polystyrenes crosslinked with 1–10% divinylbenzene and swollen with toluene, chloroform, N,N-dimethylformamide, and tetrahydrofuran to as high as 0.7 weight fraction solvent. The Tg′s depend approximately on the weight fractions and the Tg′s of the components according to the empirical equation 1nTg = m1 1nTg1 + m2 1nTg2 of Pochan. The Tg′s of the networks swollen with toluene also fit approximately a quasithermodynamic equation of Karasz based on the Tg′s and the ΔCp′s at Tg of the components. 相似文献
38.
The title compounds may be made from bis(phenylthio) acetals and aldehydes by routes involving PhS migration. 相似文献
39.
S. G. Yunusova S. D. Gusakova A. I. Glushenkova U. K. Nadzhimov Sh. Turabekov SA. Musaev 《Chemistry of Natural Compounds》1991,27(2):147-150
A comparative analysis has been made of the amounts of lipids and their fatty-acid compositions in the seeds of the lines of agenetic collection of cotton plants of the speciesGossypium hirsutum and their hybrids and the variety Tashkent-1. The results obtained on the fatty-acid compositions of some hybrids make it possible to recommend the use of individual lines of cotton plants as donors for improving the food-value indices of cottonseed oil.Institute of Chemsitry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 173–176, March–April, 1991. 相似文献
40.
Wehmschulte RJ Grigsby WJ Schiemenz B Bartlett RA Power PP 《Inorganic chemistry》1996,35(23):6694-6702
The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects. 相似文献