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271.
272.
The vesicle system consisting of 80 mol% dipalmitoylphosphatidylethanolamine (DPPE) and 20 mol% dipalmitoylphosphatidylglycerol (DPPG) undergoes to structural changes caused by various concentrations of Salmonella minnesota R595 lipopolysaccharide (LPS). The phenomenon was investigated by methods applying small- and wide-angle X-ray scattering (SAXS and WAXS), calorimetry (DSC) and freeze-fracture. In the low LPS concentration regime (investigated at 0.02 LPS/DPPE–DPPG molar ratio) a phase separation was observed. Two kind of domains are formed which are rich and poor in DPPE and in these domains cubic and lamellar structures are present, respectively. Increasing the LPS concentration up to 0.1 LPS/DPPE–DPPG molar ratio the phase separation is more expressed and the temperature domains of the phase transitions are more different. Increasing the temperature chain melting of the lamellar phase occurs first and destruction of the cubic phase is observed later. At high LPS concentration (equimolar ratio of LPS/DPPE–DPPG), where this amphiphilic molecule cannot be considered any more a guest molecule, the cubic structure dominates the phase behaviour of the LPS molecules. 相似文献
273.
Illanes A Wilson L Caballero E Fernández-Lafuente R Guisán JM 《Applied biochemistry and biotechnology》2006,133(3):189-202
Crosslinked enzyme aggregates (CLEAs) of a partially purified penicillin acylase from a recombinant Escherichia coli strain have been produced as a novel type of biocatalysts well endowed to perform in organic media. Different protein precipitants
were studied and glutaraldehyde was used as the crosslinking agent. Precipitation curves were obtained for all precipitants
to determine the concentrations at which all the protein precipitated out of the solution. The effect of the glutaraldehyde-to-protein
ratio was studied with respect to process recovery and the specific activity and stability of the biocatalyst. Recovery of
penicillin acylase activity was moderately high, about 50%; major losses of enzyme activity were produced at the precipitation
step. Specific activities of all CLEAs were very high, which is one of the advantages of using nonsupported biocatalysts.
Ammonium sulfate and tert-butyl alcohol were the best precipitants at a glutaraldehyde-protein mass ratio of 2 and were selected to perform the kinetically
controlled synthesis of ampicillin in 60% (v/v) ethylene glycol medium. At comparable conversion yields, volumetric and specific
antibiotic productivity were much higher for CLEAs than for carrier-bound penicillin acylases. 相似文献
274.
A continuously operating hydride-generation system has been developed for determination of volatile hydride-forming elements such as arsenic and selenium by d.c. plasma atomic-emission spectrometry. Arsenic and selenium are converted into their hydrides by reduction with sodium borohydride. The hydrides evolved are stripped from the liquid phase in a gas/liquid separator and are continuously fed into the d.c. plasma by a small argon stream. Under optimized operating conditions the detection limits (3s) obtained for arsenic and selenium are 0.3 and 0.5, mug/l., respectively. The precision at the 5 mu/l. level is better than 4% r.s.d. The measurement time, including sample introduction and three replicate measurements with 5-sec integration per sample is about 1 min. The effects of well known interferents such as copper and nickel have been investigated. For minimizing their interference continuous addition of 1, 10-phenanthroline as masking agent has been found useful. The method has been tested by its use for analysing NBS standard reference materials. 相似文献
275.
The use of bulky ligands in the rhodium-catalyzed reaction of aldehydes 7 (R1 = Ph) and 18 with 1-octyne increased the selectivity for ketones 13 and 20, to the detriment of ketones 12 and 19. Bulky phosphines reduced the hydroacylation reaction rate, leading to competition from the addition of the benzoic acid co-catalyst to the alkynes. This competing reaction can be suppressed by using the clay Montmorillonite K 10 (MK-10) as the co-catalyst instead of benzoic acid. 相似文献
276.
This paper presents size exclusion chromatography data with on-line coupling to UV and inductively coupled plasma mass spectrometry (ICP-MS) of water soluble metal-binding compounds present in zinc, copper, chromium and iodine enriched yeast nutritional supplements. Molecular weight estimates of the extracted metal-containing compounds are given and are shown to vary substantially from 1.2 kDa to larger than 668 kDa. Seven proteins suspected of containing chromium were identified from one of the chromium-containing fractions. Four of these identified proteins are known to form complexes with other metal ions. The metal chromatographic profiles of zinc, copper and chromium-enriched yeasts were compared to their respective native metal profiles in non-enriched yeast samples. The chromium profiles are shown to be markedly different while those of zinc and copper are qualitatively similar. Only iodide ions or weakly bound, non-aromatic, low molecular weight ( 1.2 kDa) iodine species were observed in the iodine-enriched yeast samples. 相似文献
277.
Molecularly imprinted capillary electrochromatography for selective determination of thiabendazole in citrus samples 总被引:3,自引:0,他引:3
In this work, the suitability of the combination of molecular imprinting and capillary electrochromatography (MIP-CEC) to be used as powerful tool in environmental or food analysis has been for the first time studied and successfully demonstrated. A molecularly imprinted monolith (MIM) has been synthesised and evaluated as stationary phase for the selective determination of the fungicide thiabendazole (TBZ) in citrus samples by non-aqueous capillary electrochromatography. The influence of the mobile phase composition, the voltage of the power supply and the separation temperature on the recognition of TBZ by the imprinted polymer has been evaluated, and the imprint effect in the MIM was clearly demonstrated. Once optimum recognition conditions were established, other variables affecting mechanical properties and chromatographic performance of MIM were adjusted using computational approach. The high selectivity achieved by the MIP-CEC developed procedure allowed unambiguous detection and quantification of TBZ in citrus samples by direct injection of the crude sample extracts, without any previous clean-up, in less than 6 min. The developed method was properly validated and the calculated detection limits were below the established maximum residue limits (MRLs), clearly demonstrating the suitability of the method to be used for the control of the selected fungicide. 相似文献
278.
Gabriela HuelgasLynne K. LaRochelle Lucrecia RivasYekaterina Luchinina Rubén A. ToscanoPatrick J. Carroll Patrick J. WalshCecilia Anaya de Parrodi 《Tetrahedron》2011,67(24):4467-4474
The catalytic asymmetric addition of alkyl groups to ketones has received considerable attention. Outlined herein is the synthesis of two new ligands based on the C2-symmetric 11,12-diamino-9,10-dihydro-9,10-ethanoanthracene. The scope of the new ligands has been evaluated in the catalytic asymmetric addition of diethylzinc to a variety of ketones. Enantioselectivities as high as 99% have been achieved. The structures of two of these ligands have been determined by X-ray crystallography and are compared with related structures. Additionally, the structure of a titanium complex bound to a bis(sulfonamide) diol ligand is reported. 相似文献
279.
Production waste of primary lithium batteries constitutes a considerable secondary lithium feedstock. Although the recycling of lithium batteries is a widely studied field of research, the metallic residues of non-rechargeable lithium battery production are disposed of as waste without further recycling. The risks of handling metallic Li on a large scale typically prevent the metal from being recycled. A way out of this situation is to handle Li in an aqueous solution, from where it can be isolated as Li2CO3. However, the challenge in hydrometallurgical treatment lies in the high energy release during dissolution and generation of H2. To reduce these process-related risks, the Li sheet metal punching residues underwent oxidative thermal treatment from 300 to 400 °C prior to dissolution in water. Converting Li metal to Li2O in this initial process step results in an energy release reduction of ∼70 %. The optimal oxidation conditions have been determined by experimental design varying three factors: temperature, Li metal sheet thickness, and residence time. With 96.9±2.6 % almost the entire Li amount is converted to Li2O, after 2.5 h treatment at 400 °C for a Li sheet thickness of 1.99 mm. Final precipitation with CO2 yields 85.5±3.0 % Li2CO3. Using pure Li sheets, the product Li2CO3 is obtained in battery-grade quality (>99.5 %). Non-precipitated Li is recirculated into the process on the stage of dissolving Li2O, thus avoiding loss of material. 相似文献
280.
Leonardo I. Farfan-Cabrera Mariana Franco-Morgado Armando Gonzlez-Snchez Jos Prez-Gonzlez Benjamín M. Marín-Santibez 《Molecules (Basel, Switzerland)》2022,27(4)
Lubricants are materials able to reduce friction and/or wear of any type of moving surfaces facilitating smooth operations, maintaining reliable machine functions, and reducing risks of failures while contributing to energy savings. At present, most worldwide used lubricants are derived from crude oil. However, production, usage and disposal of these lubricants have significant impact on environment and health. Hence, there is a growing pressure to reduce demand of this sort of lubricants, which has fostered development and use of green lubricants, as vegetable oil-based lubricants (biolubricants). Despite the ecological benefits of producing/using biolubricants, availability of the required raw materials and agricultural land to create a reliable chain supply is still far from being established. Recently, biomass from some microalgae species has attracted attention due to their capacity to produce high-value lipids/oils for potential lubricants production. Thus, this multidisciplinary work reviews the main chemical-physical characteristics of lubricants and the main attempts and progress on microalgae biomass production for developing oils with pertinent lubricating properties. In addition, potential microalgae strains and chemical modifications to their oils to produce lubricants for different industrial applications are identified. Finally, a guide for microalgae oil selection based on its chemical composition for specific lubricant applications is provided. 相似文献