Application of high-melting pyridinium salts as ionic liquid catalysts and media for fischer esterification

Pyridinium methanesulfonate (m.p. 185°C) and pyridinium p-toluenesulfonate (m.p. 121°C) were used as catalysts and media for the esterification of carboxylic acids with primary alcohols to give the corresponding esters selectively in high yields. The high melting points of these pyridinium salts did not prevent their application as ionic liquid medium for these reactions which were performed at 90°C.     

Cyclodehydration of 1,4-butanediol catalyzed by metal(IV) phosphates

Metal(IV) phosphates of tin, zirconium and titanium in different morphological forms, viz. amorphous, calcined and crystalline, have been used as catalysts for selective cyclodehydration of 1,4-butanediol to tetrahydrofuran. A comparative study of the three catalysts for the above reaction has been carried out to understand the effect of their composition and morphology on the catalytic activity.     

Higher Order Mortar Finite Element Methods in 3D with Dual Lagrange Multiplier Bases

Mortar methods with dual Lagrange multiplier bases provide a flexible, efficient and optimal way to couple different discretization schemes or nonmatching triangulations. Here, we generalize the concept of dual Lagrange multiplier bases by relaxing the condition that the trace space of the approximation space at the slave side with zero boundary condition on the interface and the Lagrange multiplier space have the same dimension. We provide a new theoretical framework within this relaxed setting, which opens a new and simpler way to construct dual Lagrange multiplier bases for higher order finite element spaces. As examples, we consider quadratic and cubic tetrahedral elements and quadratic serendipity hexahedral elements. Numerical results illustrate the performance of our approach. This work was supported in part by the Deutsche Forschungsgemeinschaft, SFB 404, C12, the Netherlands Organization for Scientific Research and by the European Community's Human Potential Programme under contract HPRN-CT-2002-00286.     

A finite element method for a biharmonic equation based on gradient recovery operators

A new non-conforming finite element method is proposed for the approximation of the biharmonic equation with clamped boundary condition. The new formulation is based on a gradient recovery operator. Optimal a priori error estimates are proved for the proposed approach. The approach is also extended to cover a singularly perturbed problem.     

Structural insight into the inactivation of <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> non-classical transpeptidase Ldt<Subscript>Mt2</Subscript> by biapenem and tebipenem

Background

The carbapenem subclass of β-lactams is among the most potent antibiotics available today. Emerging evidence shows that, unlike other subclasses of β-lactams, carbapenems bind to and inhibit non-classical transpeptidases (L,D-transpeptidases) that generate 3 → 3 linkages in bacterial peptidoglycan. The carbapenems biapenem and tebipenem exhibit therapeutically valuable potencies against Mycobacterium tuberculosis (Mtb).

Results

Here, we report the X-ray crystal structures of Mtb L,D-transpeptidase-2 (Ldt_Mt2) complexed with biapenem or tebipenem. Despite significant variations in carbapenem sulfur side chains, biapenem and tebipenem ultimately form an identical adduct that docks to the outer cavity of Ldt_Mt2. We propose that this common adduct is an enzyme catalyzed decomposition of the carbapenem adduct by a mechanism similar to S-conjugate elimination by β-lyases.

Conclusion

The results presented here demonstrate biapenem and tebipenem bind to the outer cavity of Ldt_Mt2, covalently inactivate the enzyme, and subsequently degrade via an S-conjugate elimination mechanism. We discuss structure based drug design based on the findings and propose that the S-conjugate elimination can be leveraged to design novel agents to deliver and locally release antimicrobial factors to act synergistically with the carbapenem carrier.

     

Production, Purification, and Biochemical Characterization of a Fibrinolytic Enzyme from Thermophilic Streptomyces sp. MCMB-379

Production of the fibrinolytic enzyme was carried out using 2.5-L glass fermentor, culture of thermophilic Streptomyces sp., and glucose yeast extract peptone medium of pH 8.0. Five successive batches were carried out under controlled fermentation conditions viz., agitation 140 rpm, aeration 0.5 vvm, 55 °C, and 18 h. The total protein extracellularly produced in the cell-free broth was ~300-500 mg/L. The enzyme belongs to serine endopeptidase type. Studies on the fibrin degradation indicate that the enzyme degrades the fibrin into small molecular weight products as seen from HPLC profile. Phase-contrast microscopic structure of fibrin showed that enzyme cleaves the fibrin filaments. The ex vivo activity of the actinokinase was compared with 500 IU of urokinase and 350 IU of streptokinase. The ex vivo clot lysis was found to be faster as compared to the commercial available enzymes.     

Cobalt(II), nickel(II) and copper(II) with 2-substituted benzimidazole complexes

Summary Complexes of stoichiometries M(Acbim)₂X₂·nH₂O and M(Bzbim)₂X₂·nH₂O (M = Co, Ni or Cu; Acbim = 2-acetylbenzimidazole, Bzbim = 2-benzoylbenzimidazole; X = Cl, Br, NO₃ or ClO₄; n = 0, 1 or 2) have been prepared and characterised by spectroscopic and physicochemical methods. The ligands coordinate through carbonyl oxygen and tertiary nitrogen.     

Manganese(II) β-diketonate catalyzed oxidation of cyclohexane bytert-butyl hydroperoxide

Oxidation of cyclohexane bytert-butyl hydroperoxide was carried out in acetonitrile solution at room temperature in the presence of manganese(II) β-diketonate complexes, Mn(acac)₂, Mn(acac)₂.2H₂O, Mn(ba)₂.H₂O, Mn(dbm)₂ and Mn(dbm)₂.2H₂O (where acacH=acetylacetone, baH=benzoylacetone and dbmH=dibenzoyl-methane). Cyclohexanol and cyclohexanone were obtained as the products. Oxidation ofcis-cyclooctene gave the corresponding epoxide together with two minor byproducts in the presence of Mn(acac)₂.2H₂O and Mn(dbm)₂.2H₂O. A mechanistic pathway predominantly involving autoxidation is proposed. IPCL communication No. 322