Thiophene and butadiene-thiolate complexes of molybdenum: observations relevant to the mechanism of hydrodesulfurization

Mo(PMe3)6 reacts with thiophene to give the eta5-thiophene complex (eta5-C4H4S)Mo(PMe3)3 and the eta5-butadiene-thiolate complex (eta5-C4H5S)Mo(PMe3)2(eta2-CH2PMe2), which are the first examples of (i) eta5-thiophene coordination and (ii) C-S cleavage and hydrogenation by a molybdenum compound. Deuterium labeling studies suggest that the hydrogenation of thiophene may involve an alkylidene intermediate, an observation that has ramifications for the mechanisms of hydrodesulfurization.     

A novel derivative free algorithm with seventh order convergence for solving systems of nonlinear equations

We present a seventh order iterative method for solving systems of nonlinear equations. The algorithm is derivative free per full iteration. A comparison between the computational efficiencies of proposed technique and existing techniques of similar nature is made. It is shown that for large system the new method is more efficient. The performance is tested through numerical experimentation which also confirms the theoretical results.     

Simulation of winter air pollution dispersion mechanism of Kathmandu valley by water-tank experiment

The air pollution concentration in Kathmandu valley in the winter season was found to be higher than in the summer season due to the formation of the inversion layer. This mechanism was simulated in the water-tank experiment by measuring the temperature and flow field using liquid crystal thermometry and particle image velocimetry. Thermal stratification was made at the beginning of the experiment and the surface temperature of the valley model was changed with 12 minutes period matching the diurnal field temperature pattern of the Kathmandu valley. The updraft wind and Bernard convection occurred during daytime and downdraft wind and inversion layer were realized during nighttime. The temperature, flow field and mass dispersion characteristics obtained in the water-tank experiment explained clearly the mechanism of air pollution in Kathmandu valley.     

Computational evidence that the inverse kinetic isotope effect for reductive elimination of methane from a tungstenocene methyl-hydride complex is associated with the inverse equilibrium isotope effect for formation of a sigma-complex intermediate

Calculations on [H2Si(C5H4)2]W(Me)H demonstrate that the interconversion between [H2Si(C5H4)2]W(Me)H and the sigma-complex [H2Si(C5H4)2]W(sigma-HMe) is characterized by normal kinetic isotope effects for both reductive coupling and oxidative cleavage; the equilibrium isotope effect, however, is inverse and is the origin of the inverse kinetic isotope effect for the overall reductive elimination of methane.     

Efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921

[reaction: see text] An efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921 was accomplished. Two short enantioselective syntheses of the common key intermediate (S)-alpha-aminoazepinone 6b were developed. Olefin 3 was converted to 6b via asymmetric hydrogenation. Alternatively, enyne 12 was converted to racemic alpha-aminoazepinone 15b, which was transformed to 6b by a practical dynamic resolution.     

Expression and Production of Therapeutic Recombinant Human Platelet-Derived Growth Factor-BB in <Emphasis Type="Italic">Pleurotus eryngii</Emphasis>

Recombinant human platelet-derived growth factor-BB (rhPDGF-BB) is widely used in many therapeutic applications. Until now, there has been no report on rhPDGF-BB expressed in fungi. In this study, we tested whether Pleurotus eryngii could support the expression of human therapeutic rhPDGF-BB protein. A binary vector pCAMBIA1304 containing the hPDGF-BB gene was constructed and introduced into P. eryngii via Agrobacterium tumefaciens-mediated transformation. The transformation of hPDGF-BB gene was confirmed by Southern blot and PCR, whereas the expression was confirmed by Western blot analysis. The recombinant hPDGF-BB reached a maximum expression level of 1.98% of total soluble protein in transgenic mycelia and was in dimeric form. A bioassay revealed that hPDGF-BB expressed in P. eryngii increased proliferation of NIH-3T3 cells similarly to standard material. These results suggest that P. eryngii can be a robust system for the production of human therapeutic proteins including the hPDGF-BB.     

New third and fourth order nonlinear solvers for computing multiple roots

We present a new third order method for finding multiple roots of nonlinear equations based on the scheme for simple roots developed by Kou et al. [J. Kou, Y. Li, X. Wang, A family of fourth-order methods for solving non-linear equations, Appl. Math. Comput. 188 (2007) 1031-1036]. Further investigation gives rise to new third and fourth order families of methods which do not require second derivative. The fourth order family has optimal order, since it requires three evaluations per step, namely one evaluation of function and two evaluations of first derivative. The efficacy is tested on a number of relevant numerical problems. Computational results ascertain that the present methods are competitive with other similar robust methods.     

Desulfation and rearrangement of tigemonam to an isoxazolidin-5-one and the synthesis of the rearrangement product

The β-lactam antibiotic Tigemonam 2 undergoes desulfation to the N-hydroxyazetidinone 4 , which rearranges to the isoxazolidin-5-one 6 . The structure of the rearrangement product 6 was confirmed by synthesis.     

Unusual regiospecificity in the enolization of a ketone as the result of differences in energy to achieve the best overlap of an alpha hydrogen

A case of ketone enolization which seems governed by geometry is discussed.