Studies on nucleotide pyrophosphatase I. Partial purification and properties of a sheep liver enzyme that catalyzes the hydrolysis of dinucleotides

A partially purified sheep liver enzyme that hydrolyzed dinucleotides at the pyrophosphate bond was obtained by solubilizing the 18,000g sediment with n-butanol and fractionating the solubilized enzyme with acetone. The enzyme activity when measured using FAD as substrate, (FAD → FMN + AMP), was optimal at pH 9.7 and temperatures between 30 °–36 ° and at 60 °. The rate of release of FMN with time occurred with an initial lag of 30 sec, a linear increase for 1 min, and a subsequent irregular rate. In the presence of orthophosphate (Pi; 10 μImage ), FMN was released at an uniformly continuous and enhanced rate. 32Pi was not incorporated into the substrate or products. Sodium arsenate counteracted the effects of Pi. The apparent Km and Vmax were 0.133 mImage and 100 units; and 0.133 mImage and 200 units, in the absence and presence of Pi, respectively. The temperature optimum was 42 ° in the presence of Pi.Negative cooperative interactions observed at low concentrations of FAD were abolished by the addition of Pi. The inhibition by AMP was sigmoid and Pi abolished this sigmoidal response. The enzyme hydrolyzed in addition to FAD, NAD+ and NADP+. Nucleoside triphosphates were potent inhibitors of the enzyme activity. The partial inhibition of the enzyme by o-phenanthroline and by p-hydroxymercuribenzoate could be reversed by Fe2+ ions and by reduced glutathione, respectively.

Degradation Kinetics of Poly(HDDA-co-MMA)

1,6-hexanediol diacrylate (HDDA) and methyl methacrylate (MMA) were copolymerized in different weight ratios using UV light induced photo-polymerization to give poly(HDDA-co-MMA). Differential scanning calorimetry shows that copolymer was formed. The thermogravimetric and differential scanning calorimetric studies with different heating rates were carried out on these copolymers to understand the nature of degradation and to determine its kinetics. Different kinetic models were adopted to evaluate various parameters like the activation energy, the order, and the frequency factor. These analyses are important to study the binder removal from 3D-shaped ceramic objects made by techniques like Solid free form fabrication. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2444-2453, 2010.

Kinetics and the mechanism of interaction of the endoplasmic reticulum chaperone, calreticulin, with monoglucosylated (Glc(1)Man(9)GlcNAc(2)) substrate

Calreticulin is a lectin-like molecular chaperone of the endoplasmic reticulum in eukaryotes. Its interaction with N-glycosylated polypeptides is mediated by the glycan, Glc(1)Man(9)GlcNAc(2), present on the target glycoproteins. In this work, binding of monoglucosyl IgG (chicken) substrate to calreticulin has been studied using real time association kinetics of the interaction with the biosensor based on surface plasmon resonance (SPR). By SPR, accurate association and dissociation rate constants were determined, and these yielded a micromolar association constant. The nature of reaction was unaffected by immobilization of either of the reactants. The Scatchard analysis values for K-a agreed web crith the one obtained by the ratio k(1)/k(-1). The interaction was completely inhibited by free oligosaccharide, Glc(1)Man(9)GlcNAc(2), whereas Man(9)GlcNAc(2) did not bind to the calreticulin-substrate complex, attesting to the exquisite specificity of this interaction. The binding of calreticulin to IgG was used for the development of immunoassay and the relative affinity of the lectin-substrate association was indirectly measured. The values are in agreement with those obtained with SPR. Although the reactions are several orders of magnitude slower than the diffusion controlled processes, the data are qualitatively and quantitatively consistent with single-step bimolecular association and dissociation reaction. Analyses of the activation parameters indicate that reaction is enthalpically driven and does not involve a highly ordered transition state. Based on these data, the mechanism of its chaperone activity is briefly discussed.

Kinetics of two-stage crystallization in Metglas 2826A

Crystallization kinetics of MSI and MSII stages in Metglas 2826A has been investigated by quantitative transmission electron microscopy. The volume fraction of crystallization against time curve has been found to show a plateau in the lower temperature region of annealing. It has been found that the glass transition temperature, T g, has no effect on the sequence reversal of the crystallization reaction. It has been shown that the sequence reversal of transformation stages occurs due to the large difference in the activation energy of crystallization of MSI and MSII. In addition, the change in the morphology of the crystals obtained by annealing the amorphous alloy below and above the glass transition temperature, T g, is reported.

Effect of Nanostructuring and Ex situ Amorphous Carbon Coverage on the Lithium Storage and Insertion Kinetics in Anatase Titania

Implications of nanostructuring and conductive carbon interface on lithium insertion/removal capacity and insertion kinetics innanoparticles of anatase polymorph of titania is discussed here.Sol-gel synthesized nanoparticles of titania (particle size similar to 6 nm) were hydrothermally coated ex situ with a thin layer of amorphous carbon (layer thickness: 2-5 nm) and calcined at a temperature much higher than the sol-gel synthesis temperature. The carbon-titania composite particles (resulting size similar to 10 nm) displayed immensely superior cyclability and rate capability (higher current rates similar to 4 g(-1)) compared to unmodified calcined anatase titania. The conductive carbon interface around titania nanocrystal enhances the electronic conductivity and inhibits crystallite growth during electrochemical insertion/removal thus preventing detrimental kinetic effects observed in case of unmodified anatase titania. The carbon coating of the nanoparticles also stabilized the titania crystallographic structure via reduction in the accessibility of lithium ions to the trapping sites. This resulted in a decrease in the irreversible capacity observed in the case of nanoparticles without any carbon coating.

A novel fiber-coated strong base-type anion exchanger with superfast kinetics. Removal and recovery of silver thiosulfate from aqueous solutions

A commercial acrylic fiber with 92% (w/w) acrylonitrile content was partially hydrolyzed converting a fraction of the nitrile (-CN) groups to carboxylic acid (-COOH) groups, to coat the fiber with polyethylenimine (PEI) resin, which was then crosslinked with glutaraldehyde and further quaternized with ethyl chloroacetate to produce a novel strong-base anionic exchanger in the form of fiber. Designated as PAN(QPEI.XG)(Cl-), the fibrous sorbent was compared with a commercial bead-form resin Amberlite IRA-458(Cl-) in respect of sorption capacity, selectivity, and kinetics for removal of silver thiosulfate complexes from aqueous solutions. Though the saturation level of [Ag(S2O3)(2)](3-) on PAN(QPEI.XG)(Cl-) is considerably less than that on IRA-458(Cl-), the gel-coated fibrous sorbent exhibits, as compared to the bead-form sorbent, a significantly higher sorption selectivity for the silver thiosulfate complex in the presence of excess of other anions Such as S2O32-, SO42-, and Cl-, and a remarkably faster rate of both sorption and stripping. The initial uptake of the sorbate by the fibrous sorbent is nearly instantaneous, reaching up to similar to 80% of the saturation capacity within 10 s, as compared to only similar to 12% on the bead-form sorbent. The high initial rate of uptake fits a shell-core kinetic model for sorption on fiber of cylindrical geometry. With 4M HCl, the stripping of the sorbed silver complex from the fibrous sorbent is clean and nearly instantaneous, while, in contrast, a much slower rate of stripping on the bead-form sorbent leads to its fouling due to a slow decomposition of the silver thiosulfate complex in the acidic medium.

Kinetics of TiO2-catalyzed ultrasonic degradation of rhodamine dyes

The ultrasonic degradation of two dyes, Rhodamine B (C28H31ClN2O3) and Rhodamine Blue (C28H32N2O3), were studied in the absence of catalyst and in the presence of two catalysts (combustion-synthesized anatase TiO2 and commercial Degussa P-25 TiO2. The rate of degradation of catalyzed reaction was higher than that obtained with in the absence of the catalysts. Among the catalysts, combustion-synthesized anatase TiO2 degraded the dyes faster when compared to the degradation with commercial Degussa P-25 catalyst. A Langmuir-Hinshelwood kinetic model was developed and the kinetic rate parameters were determined. The effect of other operating parameters, such as initial concentration, pH, temperature, and power intensity, was also investigated. The degradation rate increased with decreasing pH, increasing temperature, and higher intensity.

Hydrolysis of Organophosphate Esters: Phosphotriesterase Activity of Metallo-beta-lactamase and Its Functional Mimics

The phosphotriesterase (PTE) activity of a series of binuclear and mononuclear zinc(II) complexes and metallo-beta-lactamase (m beta 1) from Bacillus cereus was studied. The binuclear complex 1, which exhibits good m beta 1 activity, shows poor PTE activity. In contrast,complex 2, a poor mimic of m beta 1, exhibits much higher activity than 1 The replacement of Cl- ligands by OH- is important for the high PTE activity of complex 2 because this complex does not show any catalytic activity in methanol. The natural enzyme m beta 1 from B. cereus is also found to be an inefficient catalyst in the hydrolysis of phosphotriesters. These observations indicate that the binding of beta-lactam substrates at the binuclear zinc(II) center is different from that of phosphotriesters. Furthermore, phosphodiesters, the products from the hydrolysis of triesters, significantly inhibit the PTE activity of m beta 1 and its functional mimics. Although the mononuclear complexes 3 and 4 exhibited significant m beta 1 activity, these complexes are found to be almost inactive in the hydrolysis of phosphotriesters. These observations indicate that the elimination of phosphodiesters from the reaction site is important for the PTE activity of zinc(II) complexes.

Kinetics of TiO2-catalyzed ultrasonic degradation of rhodamine dyes

The ultrasonic degradation of two dyes, Rhodamine B (C28H31ClN2O3) and Rhodamine Blue (C28H32N2O3), were studied in the absence of catalyst and in the presence of two catalysts (combustion-synthesized anatase TiO2 and commercial Degussa P-25 TiO2. The rate of degradation of catalyzed reaction was higher than that obtained with in the absence of the catalysts. Among the catalysts, combustion-synthesized anatase TiO2 degraded the dyes faster when compared to the degradation with commercial Degussa P-25 catalyst. A Langmuir-Hinshelwood kinetic model was developed and the kinetic rate parameters were determined. The effect of other operating parameters, such as initial concentration, pH, temperature, and power intensity, was also investigated. The degradation rate increased with decreasing pH, increasing temperature, and higher intensity.

Transfer of F- in the reaction of SF6- with SOF4: Implications for SOF4 production in corona discharges

The temperature (T) and electric field-to-gas pressure (E/P) dependences of the rate coefficientk for the reaction SF 6 � +SOF4rarrSOF 5 � +SF5 have been measured. ForT<270>k approaches a constant of 2.1×10�9 cm3/s, and for 433>T>270 K,k decreases withT according tok (cm3/s)=0.124 exp [�3.3 lnT(K)]. ForE/Pk has a constant value of about 2.5×10�10 cm3/s, and for 130 V/cm·torr>E/P>60 V/cm·torr, the rate is approximately given byk (cm3/s)sim7.0×10�10 exp (�0.022E/P). The measured rate coefficient is used to estimate the influence of this reaction on SOF4 production from negative, point-plane, glow-type corona discharges in gas mixtures containing SF6 and at least trace amounts of O2 and H2O. A chemical kinetics model of the ion-drift region in the discharge gap is used to fit experimental data on SOF4 yields assuming that the SF 6 � +SOF4 reaction is the predominant SOF4 loss mechanism. It is found that the contribution of this reaction to SOF4 destruction falls considerably below the estimated maximum effect assuming that SF 6 � is the predominant charge carrier which reacts only with SOF4. The results of this analysis suggest that SF 6 � is efficiently deactivated by other reactions, and the influence of SF 6 � +SOF4 on SOF4 production is not necessarily more significant than that of other slower secondary processes such as gas-phase hydrolysis