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Constant pH (constant + ph)
Selected AbstractsPhosphate regulates uranium(VI) toxicity to Lemna gibba L. G3ENVIRONMENTAL TOXICOLOGY, Issue 1 2007Martin Mkandawire Abstract The influence of phosphate on the toxicity of uranium to Lemna gibba G3 was tested in semicontinuous culture with synthetic mine water developed as an analogue of surface water of two abandoned uranium mining and ore processing sites in Saxony, Germany. Six concentrations of uranium were investigated under five different supply regimes of PO43, at constant pH (7.0 ± 0.5) and alkalinity (7.0 ± 1.6 mg L,1 total CO32,). The results showed significant inhibition of specific growth rates in cultures exposed to the highest uranium concentrations (3500 and 7000 ,g U L,1) at lowest PO43, supply of 0.01 mg L,1. An increase of phosphate concentration from 0.01 to 8.0 mg L,1 resulted in an increase of EC50 from 0.9 ± 0.2 to 7.4 ± 1.9 mg L,1 (significant with Student's t test, P > 0.05). The accumulation of uranium in L. gibba increased exponentially with the increase in uranium concentration in cultures with 0.01 and 0.14 mg PO43, L,1. Accumulation also increased significantly when PO43, supply was increased from 0.14 to 1.36 mg PO43, L,1 for all uranium concentrations. However, as the supply of PO43, gradually increased from 1.36 to 8.0 mg PO43, L,1, uranium bioaccumulation increased slightly but insignificantly before leveling off. Uranium speciation modeling with PhreeqC geochemical code predicted increases in the proportions of uranyl phosphate species when PO43, concentrations increase in the media. Most of these uranyl phosphate species have a high probability of precipitation [saturation indices (SI) > 0.93]. Therefore, the alleviation of uranium toxicity to L. gibba with phosphates is due to interactions among components of the media, mainly uranyl and phosphate which results in precipitation. Consequently, bioavailable fractions of uranium to L. gibba are reduced. This might explain lack of consistent EC50 values for uranium to most aquatic organisms. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 9,16, 2007. [source] Kinetics and mechanism for the formation of o -carboxy(N -methyl)-benzohydroxamic acid in the cleavage of ethyl N -[o -(N -methyl- N -hydroxycarbamoyl)-benzoyl]carbamate in N -methylhydroxylamine, acetate, and phosphate buffersINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2003M. Niyaz Khan The rate of cleavage of ethyl N -[o -(N -methyl- N -hydroxycarbamoyl)benzoyl]- carbamate (ENMBC) in the buffer solutions containing N -methylhydroxylamine, acetate + N -methylhydroxylamine, and phosphate + N -methylhydroxylamine followed an irreversible consecutive reaction path: ENMBC where A and B represent N -hydroxyl group cyclized product of ENMBC and o -(N -methyl- N -hydroxycarbamoyl)benzoic acid, respectively. Both rate constants k1 obs and k2 obs showed the presence of buffer catalysis, but buffer catalysis turned out to be weak in the presence N -methylhydroxylamine buffer, while it was strong in the presence of acetate and phosphate ones. Buffer-independent rate constants k10 and k20 increased linearly with the increase in aOH with definite intercepts. The values of molar absorption coefficient of A, obtained under varying total buffer concentrations at a constant pH, showed the presence of a fast equilibrium: A + CH3NHOH , C, where C represents N -[o -(N -methyl- N -hydroxycarbamoyl)methyl]benzohydroxamic acid. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 427,437, 2003 [source] Kinetic evidence for the occurrence of kinetically detectable intermediates in the cleavage of N -ethoxycarbonylphthalimide under N -methylhydroxylamine buffersINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2002M. Niyaz Khan The kinetics of the aqueous cleavage of N -ethoxycarbonylphthalimide (NCPH) in CH3NHOH buffers of different pH reveals that the cleavage follows the general irreversible consecutive reaction path NCPH ENMBC AB, where ENMBC, A, and B represent ethyl N -[o -(N -methyl- N -hydroxycarbamoyl)benzoyl]carbamate, N -hydroxyl group cyclized product of ENMBC, and o -(N -methyl- N -hydroxycarbamoyl)benzoic acid, respectively. The rate constant k1 obs at a constant pH, obeys the relationship k1 obs = kw + knapp [Am]T + kb[Am]T2, where [Am]T is the total concentration of CH3NHOH buffer and kw is first-order rate constant for pH-independent hydrolysis of NCPH. Buffer-dependent rate constant kb shows the presence of both general base and general acid catalysis. Both the rate constants k2 obs and k3 obs are independent of [Am]T (within the [Am]T range of present study) at a constant pH and increase linearly with the increase in aOH with definite intercepts. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 95,103, 2002 [source] Bacterial synthesis of poly(hydroxybutyrate- co-hydroxyvalerate) using carbohydrate-rich mahua (Madhuca sp.) flowersJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2007P.K. Anil Kumar Abstract Aims:, The objective of the present work was to utilize an unrefined natural substrate namely mahua (Madhuca sp.) flowers, as a carbon source for the production of bacterial polyhydroxyalkanoate (PHA) copolymer by Bacillus sp-256. Methods and Results:, In the present work, three bacterial strains were tested for PHA production on mahua flower extract (to impart 20 g l,1 sugar) amongst which, Bacillus sp-256 produced higher concentration of PHA in its biomass (51%) compared with Rhizobium meliloti (31%) or Sphingomonas sp (22%). Biosynthesis of poly(hydroxybutyrate-co-hydroxyvalerate) , P(HB-co-HV) , of 90 : 10 mol% by Bacillus sp-256 was observed by gas chromatographic analysis of the polymer. Major component of the flower is sugars (57% on dry weight basis) and additionally it also contains proteins, vitamins, organic acids and essential oils. The bacterium utilized malic acid present in the substrate as a co-carbon source for the copolymer production. The flowers could be used in the form of aqueous extract or as whole flowers. PHA content of biomass (%) and yield (g l,1) in a 3·0-l stirred tank fermentor after 30 h of fermentation under constant pH (7) and dissolved oxygen content (40%) were 54% and 2·7 g l,1, respectively. Corresponding yields for control fermentation with sucrose as carbon source were 52% and 2·5 g l,1. The polymer was characterized by proton NMR. Conclusions:, Utilization of mahua flowers, a natural substrate for bacterial fermentation aimed at PHA production, had additional advantage, as the sugars and organic acids present in the flowers were metabolized by Bacillus sp-256 to synthesize P(HB-co-HV) copolymer. Significance and Impact of the Study:, Literature reports on utilization of suitable cheaper natural substrate for PHA copolymer production is scanty. Mahua flowers used in the present experiment is a cheaper carbon substrate compared with several commercial substrates and it is rich in main carbon as well as co-carbon sources that can be utilized by bacteria for PHA copolymer production. [source] Factor analysis of spectroelectrochemical reduction of FAD reveals the pKa of the reduced state and the reduction pathwayJOURNAL OF CHEMOMETRICS, Issue 12 2007Edmund R. Malinowski Abstract The free flavin adenine dinucleotide (FAD) cofactor is known to exhibit a pH-dependent midpoint potential involving a simultaneous two-electron transfer step (n,=,2). Uv-vis spectroelectrochemical reductions of FAD at constant pH, ranging from 5 to 9, were recorded and analyzed by factor analysis. Principal factor analysis was used to determine the number of species present at each pH. The results indicate that only two composite forms of FAD are present: the oxidized and the reduced forms. Window factor analysis was used to extract the concentration profiles of the controlling species. The oxidized form was found to be a single pH-independent species, whereas the reduced form consists of two species. The pH-dependent spectroscopic changes of reduced FAD were best modeled by a single proton transfer step involving two different ionization states with an apparent pKa,=,6.3. This value compares favorably with those obtained from NMR and from midpoint potential measurements. At pH 6, the reduction of FAD was found to be first order, whereas at pH 9 the reduction is zero order; these observations are explained in terms of the reaction pathway involving xanthine oxidase, its substrate, and the pH. Copyright © 2007 John Wiley & Sons, Ltd. [source] Characterization and rheological properties of model alkali-soluble rheology modifiers synthesized by reversible addition,fragmentation chain-transfer polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2003E. Sprong Abstract Model alkali-soluble rheology modifiers of different molar masses were synthesized by the reversible addition,fragmentation chain-transfer polymerization of methyl methacrylate, methacrylic acid, and two different associative macromonomers. The polymerization kinetics showed good living character including well-controlled molar mass, molar mass linearly increasing with conversion, and the ability to chain-extend by forming an AB block copolymer. The steady-shear and dynamic properties of a core-shell emulsion, thickened with the different model alkali-soluble rheology modifiers, were measured at constant pH and temperature. The steady-shear data for latex solutions with conventional rheology modifiers exhibited the expected thickening, whereas the associative rheology modifiers showed contrasting rheology behavior. The dynamic measurements revealed that the latex solutions thickened with the conventional rheology modifiers exhibit solid-like (dominant G,) behavior as compared with the associative rheology modifiers that give the latex solution a liquid-like (dominant G,) character. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 223,235, 2003 [source] Chilling induces a decrease in pyrophosphate-dependent H+ -accumulation associated with a ,pHvac -stat in mung bean, a chill-sensitive plantPLANT CELL & ENVIRONMENT, Issue 3 2008YUKIO KAWAMURA ABSTRACT Chilling leads to cytoplasmic acidification in chill-sensitive plants. A possible explanation for this observation is that a ,pH-stat between the cytosol and vacuole (,pHvac -stat) is perturbed by chilling. To understand the nature of this ,pHvac -stat, the effect of temperature, between 20 and 0 °C, on pyrophosphate (PPi)- or ATP-dependent acidification of vacuolar vesicles, isolated from mung bean hypocotyls, was determined. Over the temperature range investigated, the H+ -influx mediated by PPase was balanced with the H+ -efflux, which was PPi-dependently suppressed, and consequently a constant pH in vesicles (pHin) of ca. 5 was maintained against temperature changes. However, the ,pHin driven by ATP decreased as the temperature dropped. Thus, the PPi-dependent H+ -accumulation may function as an essential factor to form a ,pHvac -stat against temperature changes. Next, to study the chilling sensitivity of PPi-dependent H+ -accumulation, vacuolar vesicles were isolated from control seedlings or from seedlings chilled at 0 °C for 1 d. Chilling treatment resulted in a decrease in the H+ -accumulation rate and in the steady-state ,pHin formed by PPi, the causes of which were enhanced by PPi-dependent H+ -efflux and reduced by H+ -influx driven by PPase. Together, the results suggest that the decrease of PPi-dependent H+ -accumulation associated with the ,pHvac -stat could result in cytoplasmic acidification. [source] Development of a novel HPLC-MS/MS method for the determination of aconitine and its application to in vitro and rat microdialysis samplesBIOMEDICAL CHROMATOGRAPHY, Issue 7 2009Quan-long Zhang Abstract A sensitive and selective LC-MS/MS method was developed and validated for the determination of aconitine in microdialysate and rat plasma. Extraction of plasma sample was conducted by use of 1% trichloracetic acid and acetonitrile solution with 10 ng/mL internal standard (propafenone) spiked. Microdialysates were analyzed without sample purification. After sample preparation, 2 µL were injected and separated with an isocratic mobile phase consisting of acetonitrile:0.1% formic acid (60:40, v/v) at a flow rate of 0.3 mL/min. The Agilent G6410A triple quadrupole LC/MS system was operated under the multiple-reaction monitoring mode (MRM) using the electrospray ionization technique in positive mode. Overall, the assay exhibited good precision and accuracy. The diffusion properties of aconitine investigated in in vitro microdialysis experiments revealed unfavourable concentration dependence avertable by keeping a constant pH 5.77 using isotonic phosphate buffer solution as perfusate. The mean relative recoveries were 48.23% [coefficient of variation (CV 4.47%)] and 55.38% (CV 2.89%) for retrodialysis and recovery experiments, respectively. The in vivo recovery of aconitine was 34.48% (CV 3.05%) and was stable over the 6 h study period. Following characterization of aconitine both in vitro and in vivo microdialysis, the developed setting is suitable for application in pharmacokinetics and pharmacodynamics studies. Copyright © 2009 John Wiley & Sons, Ltd. [source] Simultaneous Saccharification and Co-Fermentation of Crystalline Cellulose and Sugar Cane Bagasse Hemicellulose Hydrolysate to Lactate by a Thermotolerant Acidophilic Bacillus sp.BIOTECHNOLOGY PROGRESS, Issue 5 2005Milind A. Patel Polylactides produced from renewable feedstocks, such as corn starch, are being developed as alternatives to plastics derived from petroleum. In addition to corn, other less expensive biomass resources can be readily converted to component sugars (glucose, xylose, etc.) by enzyme and/or chemical treatment for fermentation to optically pure lactic acid to reduce the cost of lactic acid. Lactic acid bacteria used by the industry lack the ability to ferment pentoses (hemicellulose-derived xylose and arabinose), and their growth and fermentation optima also differ from the optimal conditions for the activity of fungal cellulases required for depolymerization of cellulose. To reduce the overall cost of simultaneous saccharification and fermentation (SSF) of cellulose, we have isolated bacterial biocatalysts that can grow and ferment all sugars in the biomass at conditions that are also optimal for fungal cellulases. SSF of Solka Floc cellulose by one such isolate, Bacillus sp. strain 36D1, yielded l(+)-lactic acid at an optical purity higher than 95% with cellulase (Spezyme CE; Genencor International) added at about 10 FPU/g cellulose, with a product yield of about 90% of the expected maximum. Volumetric productivity of SSF to lactic acid was optimal between culture pH values of 4.5 and 5.5 at 50 °C. At a constant pH of 5.0, volumetric productivity of lactic acid was maximal at 55 °C. Strain 36D1 also co-fermented cellulose-derived glucose and sugar cane bagasse hemicellulose-derived xylose simultaneously (SSCF). In a batch SSCF of 40% acid-treated hemicellulose hydrolysate (over-limed) and 20 g/L Solka Floc cellulose, strain 36D1 produced about 35 g/L lactic acid in about 144 h with 15 FPU of Spezyme CE/g cellulose. The maximum volumetric productivity of lactic acid in this SSCF was 6.7 mmol/L (h). Cellulose-derived lactic acid contributed to about 30% of this total lactic acid. These results show that Bacillus sp. strain 36D1 is well-suited for simultaneous saccharification and co-fermentation of all of the biomass-derived sugars to lactic acid. [source] | |||||||||||||