Lipase from Mucor miehei (MML) has been selected as the most suitable enzyme to catalyze the efficient monobenzoylation of 1,4-diols using vinyl benzoate as acyl transfer reagent in tert-butyl methyl ether. The regioselectivity of the monobenzoylation of 2-substituted-1,4-diols has been studied as well. 相似文献
Scopo del lavoro è di studiare la stabilità asintotica per le soluzioni di problemi di evoluzione astratti. Si considerano
operatori differenziali quali ilp-Laplaciano, e il poliarmonico, termini smorzanti e fortemente smorzanti, potenziali di richiamo o di sorgente.
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We present a proof of the exponential convergence to equilibrium of single-spin-flip stochastic dynamics for the two-dimensional Ising ferromagnet in the low-temperature case with not too small external magnetic fieldh uniformly in the volume and in the boundary conditions. 相似文献
We apply previous results on the pathwise exponential loss of memory of the initial condition for stochastic differential equations with small diffusion to the problem of the asymptotic distribution of the first exit times from an attracted domain. We show under general hypotheses that the suitably rescaled exit time converges in the zero-noise limit to an exponential random variable. Then we extend the results to an infinite-dimensional case obtained by adding a small random perturbation to a nonlinear heat equation. 相似文献
Abstract— The spectroscopic characterization of the photoreceptor pigment is one of the main questions in the study of the photosensory transduction chains in photomotile microorganisms. One of the possible techniques that can be used is in vivo microspectrofluorometry. By means of a tunable dye-laser microspectrofiuorometer developed by us, we have investigated some of the spectroscopic properties of the photoreceptor pigment of the green flagellate Euglena gracilis. The in vivo fluorescence excitation spectrum has been determined and the fluorescence quantum yield has been measured. The results show that flavins are indeed present in the paraflagellar body of E. gracilis and that their fluorescence quantum yield is much lower than that of a free flavin. An estimate of the order of magnitude of the rate constants for primary molecular reactions is tentatively given. 相似文献
This paper reports the results of a study carried out to evaluate the potentiality of combining selective solvent extraction and linear gradient elution reversed-phase high performance liquid chromatography (RP-HPLC) for characterizing soil organic matter on the basis of polarity of its constituting organic compounds. Such approach comprises the sequential extraction of soil organic matter with organic solvents of increasing polarity in a Soxhlet extractor and the subsequent separation of each extract by RP-HPLC. Accordingly, each soil sample has been subjected to cycles of sequential extraction with n-hexane, dichloromethane, ethyl acetate, and methanol. Each sample extracted by one of the four solvents have been dried in a rotary evaporator device at 40°C and then dissolved again in the proper volume of extraction solvent to obtaining sample solutions of concentration ranging from 5.0 to 15 mg ml−1. These sample solutions have been subjected to RP-HPLC separation using a Supelcosil LC-ABZ column that has been eluted by a linear acetonitrile gradient in water, having the same profile for all samples. The study has evidenced the possibility of producing highly repeatable chromatographic profiles, which are correlated to the polarity of organic solvents employed for extracting the organic matter in the Soxhlet extractor.
The synthesis of cis- and trans-2-methyl-3-phenyl-1,4-benzodioxans 4 and 5 , from 1-phenyl-2-[2-(hydroxy)-phenoxy]propanols threo 2 and erythro 3 are described. 相似文献
Head-space sampling (HS) has been combined with enantioselective gas chromatography (GC) for the analysis of chiral and non-chiral monoterpenes present in the cortical tissues of five different Norway spruce clones. (1S)-(-)-alpha-Pinene, (1S,5S)-(-)sabinene, (1S)-(-)-beta-pinene, and (4S)-(-)limonene dominated over (1R)-(+)-alpha-pinene, (1R,5R)-(+)-sabinene, (1R)-(+)-beta-pinene, and (4R)-(+)-limonene. Results showed a large variation in the enantiomeric composition of cortical tissues between different clones. The development of HS-GC greatly increased the speed of precise analyses of chiral monoterpenes in small samples and therefore offer excellent opportunities in studies on the ecophysiological and chemotaxomic roles of these chiral components. 相似文献
Summary. This review reveals that, in contrast to the general opinion, the aqueous speciation of nickel is poorly known. Besides the
fairly well established first hydrolysis constant, data are scarce and only poor estimates can be derived for higher Ni hydrolysis
constants from a few solubility studies. The situation is even worse in the case of aqueous carbonate complexes. No reliable
experimental study has been published so far and almost all numbers reported in thermodynamic databases are unacceptable estimates.
In this review we scrutinise all these published estimates and propose expectation ranges of nickel carbonate complex stability
through correlation with other known thermodynamic constants. Solubility constants for a few simple nickel solids are known
or have been estimated from thermochemical data. However, none of these simple solids is of geochemical relevance at ambient
conditions. Based on field evidence, classes of solids are identified which potentially govern nickel concentrations in ground
and surface waters. Recent spectroscopic data indicate that magnesium clay minerals and layered double hydroxides are the
most prominent candidates for nickel-bearing solids at ambient conditions.
Corresponding author. E-mail: wolfgang.hummel@psi.ch
Dedicated to the memory of Prof. Rolf Grauer
Received January 14, 2003; accepted January 24, 2003
Published online May 15, 2003 相似文献