A new method to determine active enzyme distribution, effective diffusivity, rate constant for main reaction and rate constant for deactivation

1987 ◽  
Vol 29 (5) ◽  
pp. 545-551 ◽  
Author(s):  
D. D. Do ◽  
Md. M. Hossain
Keyword(s):  
Rate Constant ◽  
Effective Diffusivity ◽  
Active Enzyme ◽  
New Method ◽  
Main Reaction ◽  
Enzyme Distribution

scholarly journals A Novel Stoichio-Kinetic Model for the DPPH• Assay: The Importance of the Side Reaction and Application to Complex Mixtures

Antioxidants ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1019
Author(s):  
Lucrezia Angeli ◽  
Sebastian Imperiale ◽  
Yubin Ding ◽  
Matteo Scampicchio ◽  
Ksenia Morozova
Keyword(s):  
Antioxidant Activity ◽  
Kinetic Model ◽  
Rate Constant ◽  
High Resolution Mass Spectrometry ◽  
Sinapic Acid ◽  
Side Reaction ◽  
Main Reaction ◽  
Dpph Assay ◽  
Best Fitting ◽  
The Common

The 2,2-diphenyl-1-picrylhydrazyl (DPPH•) assay is widely used to determine the antioxidant activity of food products and extracts. However, the common DPPH• protocol uses a two-point measurement and does not give information about the kinetics of the reaction. A novel stoichio-kinetic model applied in this study monitors the consumption of DPPH• by common antioxidants following the second order reaction. The fitting of such decay yields the rate constant k1, which describes the main reaction between antioxidants and DPPH•, and the rate constant k2, which is attributed to a slower side reaction considering the products generated between the transient radicals (AO•) and another molecule of DPPH•. The model was first applied to antioxidant standards. Sinapic acid, Trolox and ascorbic and chlorogenic acids did not show any side reaction. Instead gallic, ferulic and caffeic acids achieved the best fitting with k2. The products of the side reaction for these compounds were confirmed and identified with high-resolution mass spectrometry. Finally, the kinetic model was applied to evaluate the antioxidant activity of eight herbal extracts. This study suggests a new kinetic approach to standardize the common DPPH• assay for the determination of antioxidant activity.

Photochemical reaction kinetics and mechanism of bisphenol A with K2S2O8 in aqueous solution: a laser flash photolysis study

2021 ◽  
Vol 99 (1) ◽  
pp. 43-50
Author(s):  
Yongchao Zhu ◽  
Mengyu Zhu ◽  
Jingjing Xie ◽  
Yadong Hu ◽  
Ying Liu ◽  
...  
Keyword(s):  
Bisphenol A ◽  
Rate Constant ◽  
Photochemical Reaction ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Phenoxyl Radical ◽  
Laser Flash ◽  
Kinetics And Mechanism ◽  
Main Reaction ◽  
Specific Rate

The photochemical reaction kinetics and mechanism of bisphenol A (BPA) with potassium persulfate (K2S2O8) were investigated by using 266 nm laser flash photolysis and gas chromatography mass spectrum (GC-MS) technique. Sulfate radical (SO4•−), generated upon K2S2O8 photolysis, reacted with BPA with the overall rate constant of (1.61 ± 0.15) × 109 L mol−1 s−1, and two main reaction mechanisms were involved. One was addition channel to generate BPA–SO4•− adduct with a specific second-order rate constant of (1.09 ± 0.15) × 109 L mol−1 s−1. Molecular oxygen was involved in the decay of the BPA–SO4•− adduct with a rate constant of (1.28 ± 0.14) × 108 L mol−1 s−1. Another channel was the formation of BPA’s phenoxyl radical, likely derived from a deprotonation of the cation radical (BPA•+) generated from single electron transfer reactions. The specific rate constant of BPA’s phenoxyl radical formation was determined to be (6.16 ± 0.08) × 108 L mol−1 s−1. The overall rate constant was in line with the sum of aforementioned two specific rate constants for two main reaction channels. By comparing these rate constants, it was indicated that SO4•− addition channel accounted for ∼65% (1.09/1.61) to the overall reaction, and phenoxyl radical formation accounted for only ∼35% (0.62/1.61). The transformation products of BPA were identified by using GC-MS including 4-isopropylphenol, 4-isopropenylphenol, and 2,4-di-tert-butylphenol, and the reaction mechanism was proposed. These results may provide microscopic kinetics and mechanism information on BPA degradation using SO4•−-based advanced oxidation processes.

scholarly journals Kinetic and Mass Transfer for the Extraction of Peanut Oil Using Soxhlet Extraction

2018 ◽  
Vol 3 (2) ◽  
pp. 75-87
Author(s):  
Faraliana binti Md Dan ◽  
◽  
Nazlina binti Zulbadli ◽  
Keyword(s):  
Mass Transfer ◽  
Optimum Condition ◽  
Rate Constant ◽  
Mass Transfer Rate ◽  
Effective Diffusivity ◽  
Soxhlet Extraction ◽  
Extraction Process ◽  
Peanut Oil ◽  
Solvent Ratio ◽  
Solid Ratio

This project focused on the extraction of peanut oil by using Soxhlet extraction. The main objective of this research is to determine the optimum condition for the Soxhlet extraction process in order to produce the highest extraction yields. Apart from that, this research is also to study about the mass transfer rate and kinetic to obtain the suitable diffusion coefficient and rate constant based on Fick’s law and kinetic studies. The experiments were conducted with few manipulated variables which are particle sizes, solvent to solid ratio and extraction contact time. The optimum condition for the peanut oil extraction was found at 0.6 mm of particle size, 15:1 solid to solvent ratio with an extraction time of 8 hours. Besides, the calculated effective diffusivity is 4.3258 x 10-14 m2/s. The extraction rate constant, k was found increase when the ratio of solvent to solid ratio increase due to higher amount of solvent facilitates the extraction process.

scholarly journals Mathematical Modelling of Water Absorption Kinetics Using Empirical and Phenomenological Models for Millets

2019 ◽  
Vol 8 (6) ◽  
pp. 1016-1021 ◽  
Keyword(s):  
Activation Energy ◽  
Water Absorption ◽  
Pearl Millet ◽  
Rate Constant ◽  
Finger Millet ◽  
Effective Diffusivity ◽  
Process Time ◽  
Absorption Kinetics ◽  
Experimental Conditions ◽  
Sigmoidal Model

Steeping is one of the major pre-treatment which can reduce anti-nutritional factors without losing dietary fibre and polyphenols unlike in dehulling. In the current study water absorption characteristics of pearl millet and finger millet during steeping at temperature 10°C, 20°C, 30°C, 40°C and 50°C were calculated. Two empirical and one phenomenological model were used to simulate water absorption kinetics. Both the Peleg model and Omoto model were found adequately capable to predict water uptake of pearl millet and finger millet under the designed experimental conditions with regression coefficient more than 0.96. Due to comparatively high variation in grain volume during the hydration process and longer process time, sigmoidal model cannot be utilized for calculation of effective diffusivity and activation energy. Peleg’s rate constant shows an inverse relationship with steeping temperature. The activation energy was calculated by substituting effective diffusivity with reciprocal of Peleg’s rate constant in Arrhenius equation and was found 25.97 kJ/mol and 32.36 kJ/mol respectively for pearl millet and finger millet.

scholarly journals Anharmonic effect of the rate constant of the reactions of CH3SCH2OO system in high-temperature combustion

2017 ◽  
Vol 95 (10) ◽  
pp. 1064-1072 ◽  
Author(s):  
Yu Hao ◽  
Xinxiang Pan ◽  
Liguo Song ◽  
Yang Ding ◽  
Wenwen Xia ◽  
...  
Keyword(s):  
High Temperature ◽  
Total Energy ◽  
Rate Constant ◽  
Rate Constants ◽  
Transition States ◽  
Main Reaction ◽  
Anharmonic Effect ◽  
Barrier Heights ◽  
Temperature Combustion ◽  
High Temperature Combustion

The study mainly focuses on the anharmonic effect of the reactions of CH3SCH2OO system. The geometries of the reactants and the transition states are optimized with Gaussian 09. The barrier heights are calculated with the energy of the reactants and the transition states. The RRKM theory is utilized to calculate the anharmonic and harmonic rate constants of the reactions. The anharmonic effect of these reactions can be clearly demonstrated by our results. Generally speaking, in the study, for most reactions, the rate constants increase with the temperature in the canonical case and the total energy in the microcanonical case, and the anharmonic effect of these reactions is significant and should not be neglected in high-temperature combustion. In CH3SCH2OO system, CH3SCH2OO → CH2SCH2OOH → CH2S + CH2O + OH is the main reaction channel. After a series of calculations, the anharmonic effect is remarkable, especially in high-temperature combustion. By analyzing other meaningful reactions that followed that channel above, the anharmonic effect of these reactions is generally obvious enough, especially for those reactions whose barrier heights are relatively low.

scholarly journals Cost analysis of drying process by studying its kinetic parameters: A new study in Mexican chillies

2020 ◽  
Vol 38 (No. 6) ◽  
pp. 375-387
Author(s):  
José Carrera-Escobedo ◽  
Oscar Cruz-Domínguez ◽  
César Guzmán-Valdivia ◽  
Víctor Carrera-Escobedo ◽  
Mario García-Ruiz ◽  
...  
Keyword(s):  
Weibull Distribution ◽  
Kinetic Parameters ◽  
Effective Diffusivity ◽  
Drying Kinetics ◽  
New Method ◽  
Effect Of Temperature ◽  
Drying Process ◽  
Kinetics Parameters ◽  
Drying Time ◽  
The Cost

The drying process of vegetables is a widely used technique for food conservation. However, this process can be expensive, and the cost highly depends on the ventilation, drying temperature and drying characteristics of the chillies. The contribution of this new study was to obtain the drying kinetics parameters of two different types of Mexican Capsicum annuum (Puya and Mulato) and model it at different temperatures with two different ventilation levels. The aim of this study is to provide a method to analyse the cost of the drying process by studying its drying kinetics parameters. The experimental results were fitted to Weibull distribution and Newton’s model, obtaining an adequate numerical fit at different drying temperatures. The Weibull distribution demonstrates to be a better fit than Newton’s model. Drying kinetics parameters were also studied by a diffusive model with effective diffusivity. The effect of temperature on the diffusivity was described by the Arrhenius equation with activation energy of 49.7 kJ mol−1 for Puya and 24.1 kJ mol−1 for Mulato. The ventilation effect on chilli drying kinetics parameters was qualitatively assessed. As expected, the ventilation effect improved the drying rate and reduced the drying time, and consequently the cost of the drying process was reduced. In addition, a new method is presented to evaluate the cost of the drying process considering the kinetic parameters obtained. This new method allows evaluating the cost of the drying process in a simple way and with little experimental work. Consequently, it is possible to greatly reduce the cost of the drying process.

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