The reactive intermediates and mechanisms of oxygenation of olefins by manganese complexes were investigated by treating olefins with newly synthesized [MnIV(Me2EBC)(OH)2](PF6)2 in the presence and absence of peroxide and by studying its catalytic epoxidation reaction in normal aqueous solution and, individually, with isotopically labeled H218O, 18O2, and H218O2. The manganese oxo species is not the reactive intermediate for the oxygen transfer process mediated by this manganese complex. A novel manganese(IV) peroxide intermediate, MnIV(Me2EBC)(O)(OOH)+, was captured by mass spectrometry and is proposed as the intermediate that oxygenates olefins in this catalytic system. 相似文献
Dichloro-2,3,3-trimethyl-1-platinocyclobutane, , prepared by the metathetical reaction of Zeise's dimer and 1,1,2-trimethylcyclopropane, reacts with pyridine in chloroform to produce a platinum complex of 2,3-dimethyl-1-butene . Reaction of I with pyridine at low temperatures (ca. ?40° C) leads to a pyridine addition compound (III) in which the platinocyclobutane ring remains intact. The thermal isomerization of III, which may be conveniently studied using NMR, produces a mixture of II and the free olefin. 相似文献
In recent years the need to standardize measurement protocols for quantifying the degree of ultraviolet radiation (UVR) protection provided by clothing has led to the introduction of a number of standards around the world. To date, these standards have specified spectral measurements of UVR transmission by clothing and fabrics. Development of a standard test method has become an important part of the testing process, and this article presents results from an intercomparison involving 10 independent testing laboratories and 11 different UVR transmission measurement instruments. In addition to comparing the measured ultraviolet protection factors (UPF), this intercomparison also incorporates detailed scan results from all 10 laboratories and highlights differences in performance of the various instruments in different wavelength regions. Careful examination of these differences can indicate where changes to the systems could be made to allow improvements both in equipment performance and in agreement of the final results. The variability in the measurements of UPF in this study suggest that the protection categories in standards may need to be broadened. 相似文献
A cluster expansion of the Lanczos recursion for non-extensive systems is developed based on the plaquette expansion for extensive systems, in which an auxiliary scaling parameter, Ω, plays the role of volume and introduces extensivity into the problem. Connected Hamiltonian moments of the non-extensive system are computed and introduced into the plaquette expansion in the usual way with Ω. The extensive energy is calculated for increasing orders of the expansion in 1/Ω and the ground state and mass gap of the finite few body problem recovered in the limit Ω → ∞. This new non-perturbative method is applied to the case of N bosons interacting harmonically in one dimension and the ground state energy and mass gap in the vacuum sector are calculated exactly. 相似文献
The crystal structures of PrPO4 and NdPO4 have been determined by single crystal X-ray diffraction techniques. The structures are isostructural with CePO4 and LaPO4, and are monoclinic in space group . The cell constants are a = 6.741(3), b = 6.961(4), c = 6.416(3) Å, and β = 103.63(3)° for PrPO4 and a = 6.722(1), b = 6.933(1), c = 6.390(2) Å, and β = 103.72(2)° for NdPO4. The least-squares structural refinements of PrPO4 and NdPO4 yielded R values of 0.034 and 0.038 based on 810 and 947 unique reflections, respectively. The lanthanide metal atoms are coordinated with nine oxygens and are linked together by very slightly distorted tetrahedral phosphate groups. The nine oxygen atoms ligating the lanthanide atoms form a polyhedron that is best described as a pentagonal interpenetrating tetrahedron. 相似文献
Reaction rate measurements show that a Michaelis-Menten model proposed earlier is inadequate to describe the full course of the polymerization of 2,6-dimethylphenol to poly(2,6-dimethyl-1,4-phenylene oxide). Modification of this model to include the effects of catalyst deactivation during the reaction and difference in reactivity between the monomer and other oligomers resulted in much greater accuracy. The kinetic constants in the modified model were influenced by reaction temperature, system composition, and method of catalyst component addition. 相似文献
Metalloprotein tethered CdSe nanoparticles have been generated to provide selective and reagentless maltose biosensing. As opposed to cell or protein detection by semiconducting nanoparticle bioconjugates, a modular method for small-molecule detection using semiconducting nanoparticle bioconjugates has been difficult. Here we report a method for reagentless protein-based semiconducting nanoparticle biosensors. This method uses Ru(II) complex-CdSe nanoparticle interactions and the maltose-induced conformation changes of maltose binding protein to alter the CdSe nanoparticle fluorescence emission intensity. In this proof-of-principle system, the maltose-induced protein conformation changes alter the Ru(II) complex-CdSe nanoparticle interaction, which increases the CdSe emission intensity. Altered CdSe emission intensity effects are best described as electron transfer from the Ru(II) complex to the CdSe excited state forming the nonfluorescent CdSe anion. Four surface-cysteine, Ru(II) complex-attached maltose-binding proteins have been studied for maltose dependent alteration of CdSe emission intensities. With 3.0-3.5 nm diameter CdSe nanoparticles, all ruthenated maltose-binding proteins display similar maltose-dependent increases (1.4-fold) in CdSe emission intensity and maltose binding affinities (KA = 3 x 106 M-1). For these four systems, the only difference was the sample-to-sample variation in maltose-dependent responses. Thus, very few surface cysteine mutations need to be examined to find a successful biosensor, as opposed to analogous systems using organic fluorophores. This strategy generates a unimolecular, or reagentless, semiconducting nanoparticle biosensor for maltose, which could be applied to other proteins with ligand-dependent conformation changes. 相似文献
The kinetics of iron colloid aggregation in estuaries have been simulated with a model estuary in which seawater is continuously pumped into a reservoir initially containing river water. Profiles of colloidal Fe concentration versus salinity produced in this apparatus closely resembled field data for actual estuaries. Synthetic Fe colloids prepared by peptising Fe(OH)3 with humic acid and phosphate showed very similar kinetic behaviour. Aggregation rate was found to be almost independent of velocity shear rate, implying that most aggregations are induced by brownian interparticle collisions. A heterogeneous kinetic model is proposed to explain the kinetic behaviour of Fe colloids during seawater-induced aggregation. This model describes kinetic behaviour in terms of a log-normal distribution of rate constants characterised by a mean value k and a standard deviation γ. Experiments showed that k is linearly related to the rate constant for salinity increase during mixing. This coupling of salinity changes and aggregation rate leads to Fe-salinity profiles that are nearly independent of the rate of salinity change, but which are dependent on γ. 相似文献
The effects of changes in sample size and/or sample acceptance level on the performance of aflatoxin sampling plans for shelled corn were investigated. Six sampling plans were evaluated for a range of sample sizes and sample acceptance levels. For a given sample size, decreasing the sample acceptance level decreases the percentage of lots accepted while increasing the percentage of lots rejected at all aflatoxin concentrations, and decreases the average aflatoxin concentration in lots accepted and lots rejected. For a given sample size where the sample acceptance level decreases relative to a fixed regulatory guideline, the number of false positives increases and the number of false negatives decreases. For a given sample size where the sample acceptance level increases relative to a fixed regulatory guideline, the number of false positives decreases and the number of false negatives increases. For a given sample acceptance level, increasing the sample size increases the percentage of lots accepted at concentrations below the regulatory guideline while increasing the percentage of lots rejected at concentrations above the regulatory guideline, and decreases the average aflatoxin concentration in the lots accepted while increasing the average aflatoxin concentration in the rejected lots. For a given sample acceptance level that equals the regulatory guideline, increasing the sample size decreases misclassification of lots, both false positives and false negatives. 相似文献