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Hydrolysis Rate Constants (hydrolysis + rate_constant)

Distribution by Scientific Domains

Chemistry	83%

Selected Abstracts

Estimation of Carboxylic Acid Ester Hydrolysis Rate Constants

MOLECULAR INFORMATICS, Issue 9-10 2003
H. Hilal
Abstract SPARC chemical reactivity models were extended to calculate hydrolysis rate constants for carboxylic acid esters from molecular structure. The energy differences between the initial state and the transition state for a molecule of interest are factored into internal and external mechanistic perturbation components. The internal perturbations quantify the interactions of the appended perturber (P) with the reaction center (C). These internal perturbations are factored into SPARC's mechanistic components of electrostatic and resonance effects. External perturbations quantify the solute-solvent interactions and are factored into H-bonding, field stabilization and steric effects. These models have been tested using 1471 measured hydrolysis rate constants in water and mixed-solvent systems at different temperatures. The aggregate RMS deviation of the calculated versus observed values was 0.374,M,1s,1; close to the intralaboratory experimental error. [source]

KINETICS AND HYDROLYSIS PARAMETERS OF TOTAL FRUCTOOLIGOSACCHARIDES OF ONION BULBS: EFFECTS OF TEMPERATURE REGIMES AND CULTIVARS

JOURNAL OF FOOD BIOCHEMISTRY, Issue 1 2007
NOUREDDINE BENKEBLIA
ABSTRACT This work studied the percentage of hydrolysis, observed hydrolysis rate constant (kobs), half-life time (t1/2) and kinetics of degradation of the total fructooligosaccharides (FOS) of three different onion bulb cultivars (Yellow Spanish, Red Amposta and Tenshin) kept during 6 months under three temperature regimes, 10, 15 and 20C. The percentage of hydrolysis of FOS was higher at 20C than at 10C and ranged from 47 to 58% at 10C, from 63 to 68% at 15C and from 74 to 83% at 20C. The kobs ranged from 27 × 10,3 to 36 × 10,3/week at 10C and from 41 × 10,3/week to 47 × 10,3/week at 15C, while at 20C, it was high and was about kobs 56 × 10,3/week.. The t1/2 decreased when temperature increased, and varied from 19.5 to 26.0 weeks at 10C, from 14.6 to 16.8 weeks at 15C and from 9.4 to 12.3 weeks at 20C, indicating that high degree of polymerization (DP) FOS have shorter lives than low DP FOS. Linear regression and kinetics of hydrolysis have shown that FOS hydrolysis is higher at 20C, with a coefficient of regression ranging between 0.87 and 0.99. Apparently, FOS hydrolysis is temperature independent, and storage time had more effect on the higher DP FOS than on the lower DP FOS. [source]

Chemical Recycling and Kinetics of Aqueous Alkaline Depolymerization of Poly(Butylene Terephthalate) Waste

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2004
A.S. Goje
Abstract Depolymerization reactions of poly(butylene terephthalate) (PBT) waste in aqueous sodium hydroxide solution were carried out in a batch reactor at 80,140,°C at atmospheric pressure by varying PBT particle size in the range of 50,512.5,,m. Reaction time was also varied from 10,110,min to understand the influence of PBT particle size and reaction time on the batch reactor performance. Agitator speed, particle size of PBT and reaction time required were optimized. Disodium terephthalate (salt) and 1,4-butanediol (BD) remain in the liquid phase. BD was recovered by the salting-out method. Disodium terephthalate was separated by acidification to obtain solid terephthalic acid (TPA). The produced monomeric products (TPA and BD) and PBT were analyzed. The yields of TPA and BD were in agreement with PBT conversion. The depolymerization reaction rate was first order to PBT concentration as well as first order to sodium hydroxide concentration. The acid value of TPA changes with the reaction time as well as particle size of PBT. This indicates that PBT molecules get fragmented and hydrolyze simultaneously with aqueous sodium hydroxide to produce BD and disodium terephthalate. Activation energy, Arrhenius constant, equilibrium constant, Gibbs free energy, enthalpy and entropy were determined. The dependence of the hydrolysis rate constant on reaction temperature was correlated by the Arrhenius plot, which shows an activation energy of 25,kJ/mol and an Arrhenius constant of 438,L/min/cm2. [source]

Estimation of Carboxylic Acid Ester Hydrolysis Rate Constants

Simultaneous saccharification and co-fermentation of paper sludge to ethanol by Saccharomyces cerevisiae RWB222,Part I: Kinetic modeling and parameters

BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009
Jiayi Zhang
Abstract A kinetic model was developed to predict batch simultaneous saccharification and co-fermentation (SSCF) of paper sludge by the xylose-utilizing yeast Saccharomyces cerevisiae RWB222 and the commercial cellulase preparation Spezyme CP. The model accounts for cellulose and xylan enzymatic hydrolysis and competitive uptake of glucose and xylose. Experimental results show that glucan and xylan enzymatic hydrolysis are highly correlated, and that the low concentrations of xylose encountered during SSCF do not have a significant inhibitory effect on enzymatic hydrolysis. Ethanol is found to not only inhibit the specific growth rate, but also to accelerate cell death. Glucose and xylose uptake rates were found to be competitively inhibitory, but this did not have a large impact during SSCF because the sugar concentrations are low. The model was used to evaluate which constants had the greatest impact on ethanol titer for a fixed substrate loading, enzyme loading, and fermentation time. The cellulose adsorption capacity and cellulose hydrolysis rate constants were found to have the greatest impact among enzymatic hydrolysis related constants, and ethanol yield and maximum ethanol tolerance had the greatest impact among fermentation related constants. Biotechnol. Bioeng. 2009; 104: 920,931. © 2009 Wiley Periodicals, Inc. [source]