Silicon and phosphorus alkoxide mixture: Sol-gel study by spectroscopic technics

Sol-gel synthesis of mixtures of tetraethoxysilane and a phosphorus alkoxide [P(OEt)₃ or (OEt)₂P-O-P(OEt)₂ or PO(OEt)₃] have been studied by ¹H, ¹³C²⁹Si and ³¹P liquid and solid state NMR, infrared and raman spectroscopies. This study shows different behaviors towards hydrolysis for these three different phosphates and phosphites. P(OEt)₃ almost instantly reacts with water to form an intermediate species HPO(OEt)₂, which slowly evolves first to HPO(OH)(OEt), then to HPO(OH)₂ a few days later. For (OEt)₂P-O-P(OEt)₂, the P-O-P bond is broken when water is added, then the same intermediates are formed faster. PO(OEt)₃ is hydrolyzed much slower than the other alkyl phosphates. After ten months, triethoxyphosphate is quantitatively present in the sol with little PO(OH)(OEt)₂ species. All these hydrolyzed species are well characterized. Only the system which contains the tetraethoxysilane and the triethoxyphosphite P(OEt)₃ forms a few P-O-P and P-O-Si bonds in the gel. Hydrolysis of tetraethoxysilane is much faster than that of phosphorus alkoxides and the conventional Q₂, Q₃ and Q₄ condensed silicon species form the gel three dimensional network.     

Studies toward gymnodimine: development of a single-pot Hua reaction for the synthesis of highly hindered cyclic imines

[structure: see text]. In studies directed toward gymnodimine and related marine toxins, a single-pot variation of the Hua cyclic imine synthesis has been developed. The reaction involves generation of N-trimethylsilyl lactams in situ followed by alkyllithium addition leading directly to cyclic imines. Importantly, this reaction proceeds efficiently with highly hindered alpha,alpha-dialkyl lactams, provided 1,2-dimethoxyethane (DME) is used as solvent, leading to stable cyclic imines. Overall, this transformation allows a one-pot coupling of an alkyliodide and a lactam to give a cyclic imine.     

General characterization of noncommercial microbial lipases in hydrolytic and synthetic reactions

Fourteen noncommercial preparations of microbial lipases were investigated with respect to their catalytic activity for hydrolysis and synthesis of ester bonds. Six of the lipases were derived from microorganisms that have not previously been described as lipase producers, and another four were characterized for the first time. The synthetic reactions were carried out in two solvents of different polarities (n-heptane and acetone) using a series of fatty acids and primary and secondary alcohols with different chain lengths. Under the culture conditions employed, Pseudomonas cepacia produced more active enzyme than the other microorganisms. The lipase preparations produced using Ovadendron sulphureo-ochraceum, Monascus mucoroides, Monascus sp., Fusarium oxysporum, Penicillium chrysogenum, Rhodotorula araucariae, Pseudomonas cepacia, Streptomyces halstedii, and Streptomyces sp. were the most efficient catalysts for hydrolysis at lipid-water interfaces. Enzyme preparations from P. cepacia, Streptomyces sp., S. halstedii, and R. araucariae were good biocatalysts for esterification in the polar medium (acetone). When the lipase preparations with the greatest activity for hydrolytic, reactions were excluded, regression analysis of the data for the hydrolytic and synthetic activities of the remaining lipase preparations yielded high multiple correllation coefficients for these reactions in both n-heptane and acetone (R=0.82 and 0.91, respectively).     

Centrality dependence of high-p(T) hadron suppression in Au+Au collisions at sqrt[s(NN)]=130 GeV

Inclusive transverse momentum distributions of charged hadrons within 0.2相似文献   

Therapeutic drug monitoring for sirolimus in whole blood of organ transplants by high-performance liquid chromatography with ultraviolet detection

We developed and validated an accurate, sensitive, precise and rapid HPLC method with UV detection for the determination of sirolimus in blood samples from renal, cardiac and hepatic transplants. This method overcomes most of the problems related to previously published assays using a narrow-bore column with base deactivated C18 reversed phase. Whole blood samples were purified by a combination of a precipitating blood matrix with zinc sulphate and a single step liquid-liquid extraction with acetone and 1-chlorobutane. Calibration curves (range 2.5-150 ng/ml), were linear with coefficients of correlation better than 0.996. The relative standard deviation was determined to be less than 8%. The present method has also been validated by a reference laboratory (St. George's Hospital Medical School, London, UK). More of 300 clinical samples have been analysed with this method.     

Azimuthal anisotropy and correlations in the hard scattering regime at RHIC

Azimuthal anisotropy (v(2)) and two-particle angular correlations of high p(T) charged hadrons have been measured in Au+Au collisions at sqrt[s(NN)]=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high p(T) partons. The monotonic rise of v(2)(p(T)) for p(T)<2 GeV/c is consistent with collective hydrodynamical flow calculations. At p(T)>3 GeV/c, a saturation of v(2) is observed which persists up to p(T)=6 GeV/c.