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Low pH Conditions (low + ph_condition)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Kinetics and simulations of reaction between safranine- O and acidic bromate and role of bromide therein

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2002
S. B. Jonnalagadda
Safranine- O, a dye of the phenazinium class, was found to exhibit intricate kinetics during its reaction with bromate at low pH conditions. Under conditions of excess concentrations of acid and bromate, safranine- O (SA+) initially depleted very slowly (k = (3.9 ± 0.3) × 10,4 M,3 s,1) but after an induction time, the reaction occurred swiftly. Bromide exhibited a dual role in the reaction mechanism, both as an autocatalyst and as an inhibitor. The added bromide increased the initial rate of depletion of SA+, but delayed the transition to rapid reaction. The overall stiochiometric reaction was found to be 6SA+ + 4 BrO3, = 6SP + 3N2O + 3H2O + 6H+ + 4Br,, where SP is 3-amino-7-oxo-2,8-dimethyl-5-phenylphenazine. The fast kinetics of the reaction between aqueous bromine and safranine- O (k = (2.2 ± 0.1) × 103 M,1 s,1) are also reported in this paper A 17-step mechanism, consistent with the overall reaction dynamics and supported by simulations, is proposed and the role of various bromo and oxybromo species is also discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 542,549, 2002 [source]

Bacterial enteritis and the development of the larval digestive tract in olive flounder, Paralichthys olivaceus (Temminck & Schlegel)

JOURNAL OF FISH DISEASES, Issue 9 2004
D-H Kim
Abstract Three bacterial isolates obtained from diseased olive flounder larvae, Paralichthys olivaceus, were identified as Vibrio ichthyoenteri based on the results of phenotypic characterization and 16S rRNA gene sequencing studies. Bacterial enteritis was reproduced in 16 and 22 days post-hatch (dph) larvae by administering brine shrimp nauplii, Artemia salina, dosed with the environmental isolates and reference strains of V. ichthyoenteri. To investigate the effect of the disease on development of the stomach, a pepsin activity assay and reverse transcription-polymerase chain reaction (RT-PCR) analysis of the expression of the pepsinogen gene were performed. Expression of olive flounder pepsinogen was detected from 30-dph larvae and the increased level of pepsin activity coincided with reduced susceptibility to the disease. Growth rates of V. ichthyoenteri, V. anguillarum and Edwardsiella tarda were tested in artificial stomach conditions using HCl and porcine pepsin. All the strains of V. ichthyoenteri were inhibited by low pH conditions which corresponded with an increase in pepsin levels. This suggests that differentiation of the stomach in olive flounder larvae and juveniles, an essential physiological development, also provides the host with a non-immunological defence mechanism. [source]

Development of Industrial-Medium-Required Elimination of the 2,3-Butanediol Fermentation Pathway To Maintain Ethanol Yield in an Ethanologenic Strain of Klebsiellaoxytoca,

BIOTECHNOLOGY PROGRESS, Issue 5 2005
Brent E. Wood
Fermentation efficiency and nutrient costs are both significant factors in process economics for the microbial conversion of cellulosic biomass to commodity chemicals such as ethanol. In this study, we have developed a more industrial medium (OUM1) composed of 0.5% corn steep liquor (dry weight basis) supplemented with mineral salts (0.2%), urea (0.06%), and glucose (9%). Although the growth of strain P2 was vigorous in this medium, approximately 14% of substrate carbon was diverted into 2,3-butanediol and acetoin under the low pH conditions needed for optimal cellulase activity during simultaneous saccharification. Deleting the central region of the budAB genes encoding ,-acetolactate synthase and ,-acetolactate decarboxylase eliminated the butanediol and acetoin coproducts and increased ethanol yields by 12%. In OUM1 medium at pH 5.2, strain BW21 produced over 4% ethanol in 48 h (0.47 g ethanol per g glucose). Average productivity (48 h), ethanol titer, and ethanol yield for BW21 in OUM1 medium (pH 5.2) exceeded that of the parent (strain P2) in rich laboratory medium (Luria broth). [source]

Noncovalent Modulation of pH-Dependent Reactivity of a Mn,Salen Cofactor in Myoglobin with Hydrogen Peroxide

CHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2009
Jun-Long Zhang Dr.
Abstract To demonstrate protein modulation of metal-cofactor reactivity through noncovalent interactions, pH-dependent sulfoxidation and 2,2,-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) oxidation reactivity of a designed myoglobin (Mb) containing non-native Mn,salen complex (1) was investigated using H2O2 as the oxidant. Incorporation of 1 inside the Mb resulted in an increase in the turnover numbers through exclusion of water from the metal complex and prevention of Mn,salen dimer formation. Interestingly, the presence of protein in itself is not enough to confer the increase activity as mutation of the distal His64 in Mb to Phe to remove hydrogen-bonding interactions resulted in no increase in the turnover numbers, while mutation His64 to Arg, another residue with ability to hydrogen-bond interactions, resulted in an increase in reactivity. These results strongly suggest that the distal ligand His64, through its hydrogen-bonding interaction, plays important roles in enhancing and fine-tuning reactivity of the Mn,salen complex. Nonlinear least-squares fitting of rate versus pH plots demonstrates that 1,Mb(H64X) (X=H, R and F) and the control Mn,salen 1 exhibit pKa values varying from pH,6.4 to 8.3, and that the lower pKa of the distal ligand in 1,Mb(H64X), the higher the reactivity it achieves. Moreover, in addition to the pKa at high pH, 1,Mb displays another pKa at low pH, with pKa of 5.0±0.08. A comparison of the effect of different pH on sulfoxidation and ABTS oxidation indicates that, while the intermediate produced at low pH conditions could only perform sulfoxidation, the intermediate at high pH could oxidize both sulfoxides and ABTS. Such a fine-control of reactivity through hydrogen-bonding interactions by the distal ligand to bind, orient and activate H2O2 is very important for designing artificial enzymes with dramatic different and tunable reactivity from catalysts without protein scaffolds. [source]