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Various P (various + p)
Selected AbstractsChemInform Abstract: Various P*-Chiral Phosphite-Type Ligands: Their Synthesis, Stereochemistry and Use in Pd-Catalyzed Allylation.CHEMINFORM, Issue 11 2008Eduard B. Benetsky Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Gene-dropping vs. empirical variance estimation for allele-sharing linkage statisticsGENETIC EPIDEMIOLOGY, Issue 8 2006Jeesun Jung Abstract In this study, we compare the statistical properties of a number of methods for estimating P -values for allele-sharing statistics in non-parametric linkage analysis. Some of the methods are based on the normality assumption, using different variance estimation methods, and others use simulation (gene-dropping) to find empirical distributions of the test statistics. For variance estimation methods, we consider the perfect variance approximation and two empirical variance estimates. The simulation-based methods are gene-dropping with and without conditioning on the observed founder alleles. We also consider the Kong and Cox linear and exponential models and a Monte Carlo method modified from a method for finding genome-wide significance levels. We discuss the analytical properties of these various P -value estimation methods and then present simulation results comparing them. Assuming that the sample sizes are large enough to justify a normality assumption for the linkage statistic, the best P -value estimation method depends to some extent on the (unknown) genetic model and on the types of pedigrees in the sample. If the sample sizes are not large enough to justify a normality assumption, then gene-dropping is the best choice. We discuss the differences between conditional and unconditional gene-dropping. Genet. Epidemiol. 2006. © 2006 Wiley-Liss, Inc. [source] Phosphorylation of imidazo[2,1- b]thiazoles with phosphorus(III) halides in the presence of bases,HETEROATOM CHEMISTRY, Issue 7 2005Evgenij V. Zarudnitskii The reaction of phosphorus(III) halides with 6-substituted imidazo[2,1- b]thiazoles in the presence of bases proceeds regioselectively and affords 5-phosphinoimidazo[2,1- b]thiazoles, useful synthons for the preparation of various P(III) and P(V) derivatives. 5-Phosphinoimidazo[2,1- b]thiazoles are selectively alkylated at the phosphorus or heterocyclic nitrogen atom, depending on the alkylating agent. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:648,655, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20166 [source] Thermodynamics of Phase Behavior in PEO/P(EO- b -DMS) Homopolymer and Block Co-Oligomer Mixtures under PressureMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2003Shichun Jiang Abstract The cloud-point temperatures (Tcl's) of poly(ethylene oxide) (PEO) and poly(ethylene oxide)- block -polydimethylsiloxane (P(EO- b -DMS)) homopolymer and block-oligomer mixtures were determined by turbidity measurements over a range of temperatures (105 to 130,°C), pressures (1 to 800 bar), and compositions (10,40 wt.-% PEO). The system phase separates upon cooling and Tcl was found to decrease with an increase in pressure for a constant composition. In the absence of special effects, this finding indicates negative excess volumes. Special attention was paid to the demixing temperatures as a function of the pressure for the different polymer mixtures and the plots in the T - , plane (where , signifies volume fractions). The cloud-point curves of the polymer mixture under pressures were observed for different compositions. The Sanchez-Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified P(EO- b -DMS) scaling parameters with the new combining rules can describe the thermodynamics of the PEO/P(EO- b -DMS) system well with the SL theory. Cloud point curves for various PEO/P(EO- b -DMS) polymer mixtures at various pressures on the T - ,PEO plane. [source] The First General and Selective Palladium(II)-Catalyzed Alkoxycarbonylation of Arylboronates: Interplay among Benzoquinone-Ligated Palladium(0) Complex, Organoboron, and Alcohol SolventADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Yoshihiko Yamamoto Abstract Methoxycarbonylation of aryl- and alkenylboron compounds was performed using the palladium(II) acetate/triphenylphosphine [Pd(OAc)2/PPh3] catalyst with p -benzoquinone as a stoichiometric oxidant in methanol at ambient temperature to obtain the corresponding methyl esters in good yields. A wide variety of functional groups including various carbonyl functionalities, nitrile, nitro, sulfone, and unprotected pyrrole rings were tolerated in the methoxycarbonlation, while the use of higher alcohols except for tert -butanol afforded various p -chlorobenzoates in moderate to high yields. The catalytic alkoxycarbonylation proceeded without any acid or base additive, and an oxidative transmetalation step is proposed to explain the exceptional efficacy of this protocol. DFT and MP2 calculations support the proposed mechanism. [source] Properties and application of poly(methacrylic acid- co -dodecyl methacrylate- cl - N,N -methylene bisacrylamide) hydrogel immobilized Bacillus cereus MTCC 8372 lipase for the synthesis of geranyl acetateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Madan Lal Verma Abstract A range of fatty acid esters is now being produced commercially with immobilized microbial lipases (glycerol ester hydrolases; EC) in nonaqueous solvents. In this study, a synthetic hydrogel was prepared by the copolymerization of methacrylic acid and dodecyl methacrylate in the presence of a crosslinker, N,N -methylene bisacrylamide. A purified alkaline thermotolerant bacterial lipase from Bacilluscereus MTCC 8372 was immobilized on a poly(methacrylic acid- co -dodecyl methacrylate- cl - N,N -methylene bisacrylamide) hydrogel by an adsorption method. The hydrogel showed a 95% binding efficiency for the lipase. The bound lipase was evaluated for its hydrolytic potential toward various p -nitrophenyl acyl esters with various C chain lengths. The bound lipase showed optimal hydrolytic activity toward p -nitrophenyl palmitate at a pH of 8.5 and a temperature of 55°C. The hydrolytic activity of the hydrogel-bound lipase was enhanced by Hg2+, Fe3+, and NH ions at a concentration of 1 mM. The hydrogel-bound lipase was used to synthesize geranyl acetate from geraniol and acetic acid in n -heptane. The optimization of the reaction conditions, such as catalyst loading, effect of substrate concentration, solvent (n -pentane, n -hexane, n -heptane, n -octane, and n -nonane), reaction time, temperature, molecular sieve (3 Å × 1.5 mm) and scale up (at 50-mL level), was studied. The immobilized lipase (25 mg/mL) was used to perform an esterification in n -alkane(s) that resulted in the synthesis of approximately 82.8 mM geranyl acetate at 55°C in n -heptane under continuous shaking (160 rpm) after 15 h when geraniol and acetic acid were used in a ratio of 100 : 100 mM. The addition of a molecular sieve (3 Å × 1.5 mm) to the reaction system at a concentration of 40 mg/mL in reaction volume (2 mL) resulted in an increase in the conversion of reactants into geranyl acetate (90.0 mM). During the repetitive esterification under optimum conditions, the hydrogel-bound lipase produced ester (37.0 mM) after the eighth cycle of reuse. When the reaction volume was scaled up to 50 mL, the ester synthesized was 58.7 mM under optimized conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Properties of poly(AAc- co -HPMA- cl -EGDMA) hydrogel-bound lipase of Pseudomonas aeruginosa MTCC-4713 and its use in synthesis of methyl acrylateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Shamsher Singh Kanwar Abstract Microbial lipases (E.C. 3.1.1.3) are preferred biocatalysts for the synthesis of esters in organic solvents. Various extracellular thermoalkaliphilic lipases have been reported from Pseudomonas sp. In the present study, a purified alkaline thermoalkalophilic extracellular lipase of Pseudomonas aeruginosa MTCC-4713 was efficiently immobilized onto a synthetic poly(AAc- co -HPMA- cl -EGDMA) hydrogel by adsorption and the bound lipase was evaluated for its hydrolytic potential towards various p -nitrophenyl acyl esters varying in their C-chain lengths. The bound lipase showed optimal hydrolytic activity towards p -nitrophenyl palmitate (p -NPP) at pH 8.5 and temperature 45°C. The hydrolytic activity of the hydrogel-bound lipase was markedly enhanced by the presence of Hg2+, Fe3+, and NH salt ions in that order. The hydrogel-immobilized lipase (25 mg) was used to perform esterification in various n -alkane(s) that resulted in , 84.9 mM of methyl acrylate at 45°C in n -heptane under shaking (120 rpm) after 6 h, when methanol and acrylic acid were used in a ratio of 100 mM:100 mM, respectively. Addition of a molecular sieve (3Å × 1.5 mm) to the reaction system at a concentration of 100 mg/reaction vol (1 mL) resulted in a moderate enhancement in conversion of reactants into methyl acrylate (85.6 mM). During the repetitive esterification under optimum conditions, the hydrogel-bound lipase produced 71.3 mM of ester after 10th cycle of reuse. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 183,191, 2007 [source] Nickel-Catalyzed Mizoroki,Heck- versus Michael-Type Addition of Organoboronic Acids to ,,,-Unsaturated Alkenes through Fine-Tuning of LigandsCHEMISTRY - AN ASIAN JOURNAL, Issue 11 2007Pao-Shun Lin Abstract Various arylboronic acids reacted with activated alkenes in the presence of [Ni(dppe)Br2], ZnCl2, and H2O in CH3CN at 80,°C to give the corresponding Mizoroki,Heck-type addition products in good to excellent yields. Furthermore, 1,equivalent of the hydrogenation product of the activated alkene was also produced. By tuning the ligands of the nickel complexes and the reaction conditions, Michael-type addition was achieved in a very selective manner. Thus, various p- and o- substituted arylboronic acids or alkenylboronic acid reacted smoothly with activated alkenes in CH3CN at 80,°C for 12,h catalyzed by Ni(acac)2, P(o -anisyl)3, and K2CO3 to give the corresponding Michael-type addition products in excellent yields. However, for m- substituted arylboronic acids, the yields of Michael-type addition products are very low. The cause of this unusual meta -substitution effect is not clear. By altering the solvent or phosphine ligand, the product yields for m- substituted arylboronic acids were greatly improved. In contrast to previous results in the literature, the present catalytic reactions required water for Mizoroki,Heck-type products and dry reaction conditions for Michael-type addition products. Possible mechanistic pathways for both addition reactions are proposed. [source] | |||||||||||||