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pH. However (ph + however)
Selected AbstractsComparison of methanol and acetonitrile as solvents for the separation of sertindole and its major metabolites by capillary zone electrophoresisELECTROPHORESIS, Issue 17 2005Xavier Subirats Abstract Sertindole (1-[2-[4-[5-chloro-1-(4-fluorophenyl)-1H -indol-3-yl]-1-piperidinyl]ethyl]-2-imidazolidinone), an atypical antipsychotic drug, was separated by capillary electrophoresis from its two main metabolites norsertindole and dehydrosertindole. The low solubility of the analytes in water (octanol-water partition coefficient is about 105) is overcome by the use of methanol (MeOH) and acetonitrile (ACN) as solvents for the background electrolyte (BGE). Mobilities were measured in BGEs with defined pH in a broad range. It was found that in MeOH the mobility of the analytes is mainly governed by acid,base equilibria, whereas in ACN other reactions like ion pairing and homoconjugation play a pronounced role and lead to a complex pattern of the mobility as function of the pH. However, separation can be obtained in less than 10,min in both solvent systems. [source] Thermodynamic Analysis of Energy Transfer in Acidogenic CulturesENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2008J.-R. Bastidas-Oyanedel Abstract A global thermodynamic analysis, normally used for pure cultures, has been performed for steady-state data sets from acidogenic mixed cultures. This analysis is a combination of two different thermodynamic approaches, based on tabulated standard Gibbs energy of formation, global stoichiometry and medium compositions. It takes into account the energy transfer efficiency, ,, together with the Gibbs free energy dissipation, ,Go, analysis of the different data. The objective is to describe these systems thermodynamically without any heat measurement. The results show that , is influenced by environmental conditions, where increasing hydraulic retention time increases its value all cases. The pH effect on , is related to metabolic shifts and osmoregulation. Within the environmental conditions analyzed, , ranges from 0.23 for a hydraulic retention time of 20,h and pH,4, to 0.42 for a hydraulic retention time of 8,h and a pH ranging from 7,8.5. The estimated values of ,Go are comparable to standard Gibbs energy of dissipation reported in the literature. For the data sets analyzed, ,Go ranges from ,1210,kJ/molx, corresponding to a stirring velocity of 300,rpm, pH,6 and a hydraulic retention time of 6,h, to ,20744,kJ/molx for pH,4 and a hydraulic retention time of 20,h. For average conclusions, the combined approach based on standard Gibbs energy of formation and global stoichiometry, used in this thermodynamic analysis, allows for the estimation of Gibbs energy dissipation values from the extracellular medium compositions in acidogenic mixed cultures. Such estimated values are comparable to the standard Gibbs energy dissipation values reported in the literature. It is demonstrated that , is affected by the environmental conditions, i.e., stirring velocity, hydraulic retention time and pH. However, a relationship that relates this parameter to environmental conditions was not found and will be the focus of further research. [source] Water-extractability, free ion activity, and pH explain cadmium sorption and toxicity to Folsomia candida (Collembola) in seven soil-pH combinationsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2004Cornelis A. M. van Gestel Abstract Toxicity of cadmium to Folsomia candida was determined in soils at different pHs (3.5, 5.0, and 6.5). The Langmuir sorption constant (KL), based on pore-water or water-extractable concentrations, showed a pH-related increase of cadmium sorption that was most pronounced when using free Cd2+ ion activities ({Cd2+}s). Two-species Langmuir isotherms that used total cadmium concentration ([Cd]) or {Cd2+} and pH in the water-extractable fractions gave the best description of cadmium sorption on all soils together. Cadmium concentrations causing 50% reduction of growth and reproduction (median effective concentrations [EC50s]) differed by a factor of 4.5 to 20 when based on total soil concentrations and increased with increasing pH. However, when based on water-extractable or pore-water [Cd] or {Cd2+}, EC50s decreased with increasing pH, but differences between soils were still a factor of 4.5 to 32. The EC50s differed by less than a factor of 2.2 when based on body [Cd] in the surviving animals. Two-species Langmuir isotherms were used to relate body [Cd] in survivors to {Cd2+}, corrected for pH in water-extractable or pore-water fractions. An excellent description of effects on growth and reproduction was found when related to the body concentrations predicted in this way; the difference in EC50s between soils was reduced to a factor <2. This demonstrates that F. candida is mainly exposed to cadmium through the soil solution, and suggests that principles of a biotic ligand model approach may be applicable for this soil organism. [source] Factorial design analysis of the catalytic activity of di-imine copper(II) complexes in the decomposition of hydrogen peroxideINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2001W. A. Alves Factorial design analysis was applied to the study of the catalytic activity of di-imine copper(II) complexes, in the decomposition of hydrogen peroxide. The studied complexes show a tridentate imine ligand (apip), derived from 2-acetylpyridine and 2-(2-aminoethyl)pyridine, and a hydroxo or an imidazole group at the fourth coordination site of the copper ion. The factorial design models for both [Cu(apip)imH]2+ and [Cu(apip)OH]+ were similar. Increasing the peroxide concentration from 3.2 × 10,3 to 8.1 × 10,3 mol L,1 resulted in increased oxygen formation. Increasing the pH from 7 to 11 also increased oxygen formation and had an effect about twice as large as the peroxide one. Both complexes also had an important interaction effect between peroxide concentration and pH. However, increasing the catalyst concentration led to a decrease in total oxygen formation. The obtained results were corroborated by further data, achieved by using the usual univariate method, and helped to elucidate equilibrium steps occurring in the studied systems. In very alkaline solutions, the studied [Cu(apip)imH]2+ complex can form the corresponding dinuclear species, [Cu2(apip)2im]3+. While the mononuclear complex proved to be an efficient catalyst in hydrogen peroxide decomposition, the corresponding dinuclear compound seemed to be able to coordinate with the dioxygen molecule, inhibiting its observed release. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 472,479, 2001 [source] Synergistic effect of enterocin AS-48 in combination with outer membrane permeabilizing treatments against Escherichia coli O157:H7JOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2005S. Ananou Abstract Aims:, To determine the effects of outer membrane (OM) permeabilizing agents on the antimicrobial activity of enterocin AS-48 against Escherichia coli O157:H7 CECT 4783 strain in buffer and apple juice. Methods and Results:, We determined the influence of pH, EDTA, sodium tripolyphosphate (STPP) and heat on E. coli O157:H7 CECT 4783 sensitivity to enterocin AS-48 in buffer and in apple juice. Enterocin AS-48 was not active against intact cells of E. coli O157:H7 CECT 4783 at neutral pH. However, cells sublethally injured by OM permeabilizing agents (EDTA, STPP, pH 5, pH 8·6 and heat) became sensitive to AS-48, decreasing the amount of bacteriocin required for inhibition of E. coli O157:H7 CECT 4783. Conclusions:, The results presented indicate that enterocin AS-48 could potentially be applied with a considerably wider range of protective agents, such as OM permeabilizing agents, with increased efficacy in inhibiting E. coli O157:H7. Significance and Impact of the Study:, Results from this study support the potential use of enterocin AS-48 to control E. coli O157:H7 in combination with other hurdles. [source] FUNCTIONALITY COMPARISON BETWEEN DERIVATIZED WHEY PROTEINS AND A PREGELATINIZED STARCHJOURNAL OF TEXTURE STUDIES, Issue 4 2002H. M. HUDSON ABSTRACT A process has been patented to produce stabilizing ingredients from whey proteins which are applicable over a wide range of typical food conditions and do not require heat or the addition of salts to induce thickening functionality. Once reconstituted in deionized water, solutions were evaluated and compared with water holding performance and rheological attributes of a pregelatinized cornstarch. Rotational viscometry was performed at pH values between 3 and 8, temperatures between 5 and 90C, and shear rates between 1 and 100 s,1. Derivatized whey protein powders and pregelatinized starch displayed pseudo-plastic behavior under shear at all temperatures tested. During temperature ramps from 5 to 90C, derivatized whey protein flow properties were essentially unchanged by varying pH. However, viscosity after the temperature increase was higher than initial values, possibly due to additional protein denaturation and hydrophobic interactions. Derivatized powders were stable and retained desired functionality over a wide range of food processing and preparation conditions and may therefore possess applicability to many products currently utilizing modified starches or hydrocolloids to texturize. [source] RhIII - and IrIII -Catalyzed Asymmetric Transfer Hydrogenation of Ketones in WaterCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2008Xiaofeng Wu Dr. Abstract Asymmetric transfer hydrogenation (ATH) of ketones by formate in neat water is shown to be viable with Rh-TsDPEN and Ir-TsDPEN catalysts, derived in situ from [Cp*MCl2]2 (M=Rh, Ir) and TsDPEN. A variety of ketones were reduced, including nonfunctionalized aryl ketones, heteroaryl ketones, ketoesters, and unsaturated ketones. In comparison with Ir-TsDPEN and the related RuII catalyst, the RhIII catalyst is most efficient in water, affording enantioselectivities of up to 99,% ee at substrate/catalyst (S/C) ratios of 100,1000 even without working under an inert atmosphere. The aqueous phase reduction is shown to be highly pH-dependent; the optimum pH windows for TOF greater than 50,mol,mol,1,h,1 for Rh- and Ir-TsDPEN are 5.5,10.0 and 6.5,8.5, respectively. Outside the pH window, the reduction becomes slow or stagnant depending on the pH. However, the enantioselectivities erode only under acidic conditions. At a higher S/C ratio, the aqueous ATH by Rh-TsDPEN is shown to be product- as well as byproduct-inhibited; the product inhibition appears to stem at least partly from the reaction being reversible. The aqueous phase reduction is simple, efficient and environmentally benign, thus presenting a viable alternative for asymmetric reduction. [source] | |||||||||||||