Synthesis,Characterization and Crystal Structure of the Bis(2,4-dinitrobenzoato)tetrabutyldistannoxane(IV) Dimer

Abstract The title compound, bis(2,4-dinitrobenzoato)tetrabutyldistannoxane(IV), was obtained from the reaction of di-n-butyltin(IV) oxide with 2,4-dinitrobenzoic acid. It crystallizes out as the usual dicarboxylatotetrabutyldistannoxane(IV) dimer. In the monoclinic system P2₁/c, a = 12.391(3) ?, b = 19.937(5) ?, c = 15.026(4) ?, α = γ = 90°, β = 102.857(2)°, V = 3618.95(16) ?³ and Z = 2. A crystal structure determination of the title compound reveals the presence of a centrosymmetric planar Sn₂O₂, with two different environments for tin atoms and two distinct carboxylate groups. Two of the carboxylate groups are bonded to the exocyclic tin atom in a bidentate bridging manner and the remaining two carboxylate groups are bonded to the tin atom in a monodentate manner. As a result, both the tin atoms moieties in the complex are five coordinate and exhibit trigonal bipyramid geometry. Index Abstract Synthesis, Characterization and Crystal Structure of the Bis(2,4-dinitrobenzoato)tetrabutyldistannoxane(IV) Dimer Yip Foo Win, Teoh Siang Guan, Lim Eng Khoon, Shea Lin Ng, Hoong Kun Fun A crystal structure determination of the title compound reveals the presence of a centrosymmetric planar Sn₂O₂, with two different environments for tin atoms and two distinct carboxylate groups.      

Brillouin light scattering from poly(vinyl chloride) gels

The hypersonic velocity and attenuation in PVC gels have been measured as a function of gel network volume fraction, using the technique of Brillouin light scattering. The experimental data have been analysed using the full theory for the elastodynamics of gels proposed recently by Johnson. It has been found that for two asymptotic approximations of the dynamic damping factor the tortuosity parameter is nearly always less than unity, contrary to the theoretical expectation.     

Role of energy irradiation in aiding pretreatment of lignocellulosic biomass for improving reducing sugar recovery

With the depletion of crude oil reserves, the ever-increasing global energy consumption encourages the efforts to find alternative renewable sources for production of biofuels and value-added chemicals. The conversions of lignocellulosic biomass into biofuels and commodity chemicals via the biotechnological pathway have been the recent trend. Specifically, these products can be obtained through fermentation of reducing sugars, which are the main but basic derivatives from the biomass. In order to overcome the recalcitrant structure of the biomass for effective reducing sugar recovery, a pretreatment stage is normally required. Currently, one of the most novel forms of biomass pretreatment is using energy irradiation methods such as electron beam, gamma ray, pulsed electrical field, microwave and ultrasound. In general, these technologies are often used together with other more conventional chemical and/or biological pretreatment techniques for enhancing sugar recovery. Nevertheless, energy irradiation offers significant improvement in terms of possible cost reduction opportunities and reduced toxicity. Hence, this review highlights the recent studies of using energy irradiation for pretreating biomass as well as the industrial applications of reducing sugars in biotechnological, chemical and fuel sectors. In short, more research needs to be done at the scientific, engineering and economic levels to make energy irradiation one of the front runners in the field of biomass pretreatment.     

Liquid chromatographic assay for the simultaneous determination of pyrazinamide and rifampicin in serum samples from patients with tuberculous meningitis

A simple high-performance liquid chromatographic assay for the simultaneous determination of pyrazinamide and rifampicin in serum from patients with tuberculous meningitis is presented. The drugs and internal standard, p-acetamidobenzoic acid, were extracted from the acidified sample containing 2% ascorbic acid at pH 4.2 into dichloromethane-diethyl ether (2:3). The solvent extract was evaporated to dryness with the aid of nitrogen and the residue redissolved in methanol (75 microliters). The concentrate was analysed by a liquid chromatograph using a reversed-phase 30-microns C8 pre-column linked to a 5-microns C8 analytical column with a gradient solvent programme, which delivered 6% to 48% (v/v) acetonitrile in phosphate buffer (10 mM potassium dihydrogenphosphate, pH 3.5) in 10 min at 1.5 ml/min. The eluate was detected at 215 nm. Twelve patients with tuberculous meningitis were given daily chemotherapy, and their serum samples were assayed for pyrazinamide and rifampicin.     

A highly enantioselective synthesis of cyclic alpha-amino acids involving a one-pot,single catalyst,tandem hydrogenation-hydroformylation sequence

Tandem enantioselective hydrogenation followed by a hydroformylation-cyclisation sequence leading to cyclic alpha-amino acids with ee's > 95% can be achieved in a single pot, one catalyst system by successive reactions of prochiral dienamide esters with H2 followed by H2/CO using Rh(I)-DuPHOS.