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To immobilize Pseudomonas delafieldii R-8 cells in magnetic polyvinyl alcohol (PVA) beads for biodesulfurization.Magnetic PVA beads were prepared by a freezing-thawing technique under liquid nitrogen. The beads have distinct super-paramagnetic properties and their saturation magnetization is 8.02 emu g(-1). The desulfurization rate of the immobilized cells could reach 40.2 mmol kg(-1) h(-1). Desulfurization patterns of dibenzothiophene in model oil with the immobilized and free cells were represented by the Michaelis-Menten equation. The Michaelis constant for both immobilized and free cells was 1.3 mmol l(-1).The cells immobilized in magnetic PVA beads could be stably stored and be repeatedly used over 12 times for biodesulfurization. The immobilized cells could be easily separated by magnetic field.Magnetic PVA beads are easy to prepare. The immobilization process in the paper is to increase the efficiency of cells and to decrease the cost of operations.

The desulfurization kinetics of Nocardia globerula R-9 was investigated initially in a model system consisting of dibenzothiophene (DBT) dissolved in dodecane. The ability to desulfurize straight-run diesel oil by resting cells of this strain was also evaluated. The course of desulfurization of DBT in dodecane could be represented by the Michaelis-Menten equation. The desulfurization of DBT and 4,6-dimethyl dibenzothiophene (4,6-DMDBT) in a mixture of the two proceeded simultaneously without preference for either of them. The sulfur content of the straight-run diesel oil could be reduced from 1807 to 741 mg dm(-3) by treatment with resting cells of this strain, at a mean rate of 5.1 mmol sulfur kg(-1) h(-1). This showed that Nocardia globerula R-9 could be a potential bacterium for reducing the sulfur content of petroleum products. (C) 2003 Society of Chemical Industry.

This paper reports our investigations on the secondary structure of lysozyme in aqueous solution with D2O and comparing systems emulsified with ionic and non-ionic amphiphiles, respectively. The opposite effect of concentration of surfactants on the lysozyme aqueous system was studied and the activity of lysozyme by the turbidimetric assay with different kinds of surfactant was compared. The effect of different surfactants on emulsification volume formed was observed and discussed. The different interactive patterns between lysozyme and ionic and non-ionic surfactants, such as sodium dodecyl sulfate (SDS), cetyl trimethyl ammonium bromide (CTAB) and Triton-X100 (Isooctoylphenoxypolyethoxy ethanol), respectively, was studied with FTIR. A simple relationship between the secondary structure and denaturation of protein is given for the emulsification of lysozyme in aqueous solutions. It is important for understanding the stabilization and avoiding the emulsions in the extraction process that the interactions between the proteins and surfactants which leads to the formation of such complexes are characterized. The utility of surfactants as a de-emulsifying agent for the commercial process to extract penicillin G from the filtrate of fermentation broth was consistent with these results. (C) 1998 Elsevier Science S.A. All rights reserved.

The desulfurization of dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and their mixture by lyophilized cells ofPseudomonas delafieldii R-8 was studied in the presence of dodecane. The desulfurization rate for 4,6-DMDBT was found to be about 40% in comparison with that for DBT. The desulfurization process for DBT and 4,6-DMDBT proceeded simultaneously without preference for either one. The desulfurization rate for each compound was decreased when they were mixed together. The extent of desulfurization of 4,6-DMDBT was increased with the increase of cell concentration and the decrease of the volume ratio of oil-to-water used. The specific desulfurization rate for 4,6-DMDBT could be reached to 10.4 mmol sulfur kg−1 (cell) h−1 [approximately 0.33 mg sulfur g−1 (cell) h−1].Pseudomonas delafieldii R-8 showed high desulfurization capability for straight-run diesel oil (containing 1,807 mg/L of sulfur). About 1,000 mg/L of sulfur in diesel oil was removed by resting cells of this strain in 24 h of reaction. The specific desulfurization rate was 8.75 mmol sulfur kg−1 (cell) h−1.

The kinetics of base catalyzed racemization of ibuprofen enantiomers has been studied in DMSO-water mixed medium. The dynamic equilibrium rate of keto-enol tautomerism leading to racemization of ibuprofen enantiomers, is proportional to the concentrations of base catalyst and substrate. A kinetic model capable of predicting the time course of racemization, under different base and substrate concentrations, is established and experimentally verified.

It has been found in the present study that Re(VII) can be quantitatively separated from Mo(VI) in alkaline solutions by synergistic extraction with primary amine and neutral phosphorus esters. The mechanism of synergistic extraction was studied. Results of extraction with combinations of different donor and acceptor solvents indicated that during extraction hydrogen bonds were formed between perrhenic acid and active hydrogen atoms of primary amines as well as between the acid and active phosphoryl oxygen of neutral phosphorus esters. The composition of the synergistic extraction adduct was studied and its structure was also proposed. This newly found extraction system is important to the extraction and separation of Re(VII) and also to the studies of mechanism of synergistic extraction.