Two Rate Constant Kinetic Model for the Chromium(III)-EDTA Complexation Reaction by Numerical Simulations

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.

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Central Composite Design, Kinetic Model, Thermodynamics, and Chemical Composition of Pomelo (Citrus Maxima (Burm.) Merr.) Essential Oil Extraction by Steam Distillation

Processes ◽

10.3390/pr9112075 ◽

2021 ◽

Vol 9 (11) ◽

pp. 2075

Author(s):

Tan Phat Dao ◽

Thanh Viet Nguyen ◽

Thi Yen Nhi Tran ◽

Xuan Tien Le ◽

Ton Nu Thuy An ◽

...

Keyword(s):

Activation Energy ◽

Kinetic Model ◽

Essential Oil ◽

Rate Constant ◽

Flow Rate ◽

Steam Distillation ◽

Extraction Process ◽

Oil Extraction ◽

Extraction Time ◽

Pomelo Peel

Pomelo peel-derived essential oils have been gaining popularity due to greater demand for stress relief therapy or hair care therapy. In this study, we first performed optimization of parameters in the pomelo essential oil extraction process on a pilot scale to gain better insights for application in larger scale production. Then extraction kinetics, activation energy, thermodynamics, and essential oil quality during the extraction process were investigated during the steam distillation process. Three experimental conditions including material mass, steam flow rate, and extraction time were taken into consideration in response surface methodology (RSM) optimization. The optimal conditions were found as follows: sample weight of 422 g for one distillation batch, steam flow rate of 2.16 mL/min and extraction time of 106 min with the coefficient of determination R2 of 0.9812. The nonlinear kinetics demonstrated the compatibility of the kinetic model with simultaneous washing and unhindered diffusion with a washing rate constant of 0.1515 min−1 and a diffusion rate constant of 0.0236 min−1. The activation energy of the washing and diffusion process was 167.43 kJ.mol−1 and 96.25 kJ.mol−1, respectively. The thermodynamic value obtained at the ΔG° value was −35.02 kJ.mol−1. The quality of pomelo peel essential oil obtained by steam distillation was characterized by its high limonene content (96.996%), determined by GC-MS.

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Connecting charge transfer kinetics to device parameters of a narrow-bandgap polymer-based solar cell

Physical Chemistry Chemical Physics ◽

10.1039/c6cp04688f ◽

2016 ◽

Vol 18 (38) ◽

pp. 26550-26561 ◽

Cited By ~ 4

Author(s):

Jongwoo Song ◽

Younah Lee ◽

Boa Jin ◽

Jongdeok An ◽

Hyunmin Park ◽

...

Keyword(s):

Charge Transfer ◽

Solar Cell ◽

Kinetic Model ◽

Rate Constant ◽

Transfer Rate ◽

Polymer Solar Cell ◽

Transfer Rate Constant ◽

Charge Transfer Rate ◽

Narrow Bandgap

The spectroscopic charge transfer rate constant was compared with the PV properties of a polymer solar cell using a kinetic model.

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A CFD-kinetic model for the flotation rate constant, Part II: Model validation

Minerals Engineering ◽

10.1016/j.mineng.2014.05.014 ◽

2014 ◽

Vol 69 ◽

pp. 205-213 ◽

Cited By ~ 15

Author(s):

M. Karimi ◽

G. Akdogan ◽

S.M. Bradshaw

Keyword(s):

Kinetic Model ◽

Model Validation ◽

Rate Constant ◽

Flotation Rate ◽

Constant Part

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Predicting overall survival (OS) and overall response (OR) following durvalumab treatment in patients with multiple cancer types using a hybrid modeling strategy.

Journal of Clinical Oncology ◽

10.1200/jco.2020.38.15_suppl.e15161 ◽

2020 ◽

Vol 38 (15_suppl) ◽

pp. e15161-e15161

Author(s):

Ting Chen ◽

Yanan Zheng ◽

Lorin Roskos ◽

Donald E Mager

Keyword(s):

Kinetic Model ◽

Kinetic Parameters ◽

Rate Constant ◽

Tumor Size ◽

Hybrid Modeling ◽

Tumor Growth Rate ◽

Growth Rate Constant ◽

Model Parameters ◽

Cancer Types ◽

Modeling Strategy

e15161 Background: This study aimed to predict OS/OR and identify key predictors in patients with diverse cancer types treated with durvalumab, a PD-L1 targeting monoclonal antibody, using a hybrid modeling strategy that combines population pharmacodynamic (PD) modeling and machine learning (ML) algorithms. Methods: Individual longitudinal tumor size measurements and OS/OR data were available for 855 patients who received durvalumab therapy (10 mg/kg Q2W or 20 mg/kg Q4W; NCT01693562). Nine cancer types included non-small cell lung cancer (NSCLC), bladder cancer (BC), microsatellite instability-high (MSI-H) cancer, hepatocellular carcinoma (HCC), squamous cell carcinoma of the head and neck (SCCHN), gastroesophageal cancer (GEC), ovarian cancer (OC), pancreatic adenocarcinoma (PDAC) and triple-negative breast cancer (TNBC). A tumor kinetic model was developed to characterize diverse temporal profiles using a population-based modeling approach. Individual estimated tumor kinetic model parameters and patient demographic/physiological factors were used as inputs for predicting OS/OR using several ML approaches. Results: The final tumor kinetic model with liver metastasis (LM), neutrophil/lymphocyte ratio (NLR), tumor size at baseline (TBSL) and cancer types as covariates characterized the temporal tumor size data well. HCC and MSI-H cancer have the slowest tumor growth rate constant (kg), while GEC, SCCHN and TNBC have the fastest kg. BC, NSCLC and OC have the highest tumor killing rate constant. The most important predictors of OS identified by ML approach were tumor kinetic parameters (kg, fraction of drug-sensitive cells, time-delay in immune response), along with baseline disease factors, including hemoglobin (HGBBL), albumin (ALB), and NLR. Decision tree-based algorithms showed the best performance in predicting OR with accuracy above 90%. In addition to tumor kinetic parameters, PD-L1 expression on tumor cells (TC) and ALB were the most important predictors of OR. Conclusions: A combined population PD/ML approach showed good predictions of OS/OR in patients with different cancer types treated with durvalumab. LM, NLR,TBSL and cancer types were found to be important factors for tumor kinetics. In addition to tumor kinetic parameters, HGBBL, ALB, and NLR were found to be important predictors of OS, and TC and ALB were found to be important predictors of OR. These findings could provide a guidance on patient selection in future clinical trials.

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SCALING BEHAVIOUR OF A MULTIPLY CONNECTED FLUCTUATING INTERFACE IN TWO DIMENSIONS

Fractals ◽

10.1142/s0218348x03001884 ◽

2003 ◽

Vol 11 (supp01) ◽

pp. 227-232

Author(s):

AYŞE ERZAN ◽

HÜSEY.IN KAYA ◽

ALKAN KABAKÇIOĞLU

Keyword(s):

Kinetic Model ◽

Numerical Simulations ◽

Average Velocity ◽

Two Dimensions ◽

Scaling Exponents ◽

Multiply Connected ◽

Fractal Set ◽

Scaling Behaviour ◽

Infinite String

We consider a one-parameter kinetic model for a fluctuating interface which can be thought of as an infinite string decorated with infinitely many closed strings. Numerical simulations show that a number of scaling exponents describing this string system may be related to the Kardar-Parisi-Zhang exponents. However, as the average velocity of the infinite string is taken to zero, and the string system becomes an isotropic fractal set, we also find new exponents which cannot be reduced to previously known ones.

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DYNAMICS OF NEUROMUSCULAR TRANSMISSION REPRODUCED BY CALCIUM-DEPENDENT SERIAL TRANSITIONS IN THE VESICLE FUSION COMPLEX

10.1101/2021.09.15.460525 ◽

2021 ◽

Author(s):

Alejandro Martínez-Valencia ◽

Guillermo Ramírez-Santiago ◽

Francisco F. De-Miguel

Keyword(s):

Experimental Data ◽

Kinetic Model ◽

Electrical Activity ◽

Rate Constant ◽

Rate Constants ◽

Resting State ◽

Neuromuscular Transmission ◽

Spontaneous Release ◽

Calcium Dependent ◽

Vesicle Pool

Neuromuscular transmission, from spontaneous release to facilitation and depression was accurately reproduced by a mechanistic kinetic model of sequential maturation transitions in the molecular fusion complex. The model incorporates three predictions. First, sequential calcium-dependent forward transitions take vesicles from docked to pre-primed to primed states, followed by fusion. Second, pre-priming and priming are reversible. Third, fusion and recycling are unidirectional. The model was fed with experimental data from previous studies while the backward (β) and recycling (ρ) rate constant values were fitted. Classical experiments were successfully reproduced when every forward (α) rate constant had the same value, and both backward rate constants were 50-100 times larger. Such disproportion originated an abruptly decreasing gradient of resting vesicles from docked to primed states. Simulations also predict that: i. Spontaneous release reflects primed to fusion spontaneous transitions. ii. Calcium elevations synchronize the series of forward transitions that lead to fusion. iii Facilitation reflects a transient increase of priming following calcium-dependent transitions. iv. Backward transitions and recycling restore the resting state. v. Depression reflects backward transitions and slow recycling after intense release. Such finely-tuned kinetics offers a mechanism for collective non-linear transitional adaptations of a homogeneous vesicle pool to an ever-changing pattern of electrical activity.

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Kinetics and Mechanism of Acid-Catalyzed Decomposition of 1,3-Bis(4-methylphenyl)triazene in Hexane-Organic Acid Medium

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19960355 ◽

1996 ◽

Vol 61 (3) ◽

pp. 355-363 ◽

Cited By ~ 2

Author(s):

Miroslav Ludwig ◽

Miriam Kabíčková

Keyword(s):

Kinetic Model ◽

Organic Acid ◽

Acid Medium ◽

Rate Constant ◽

Fourth Order ◽

Kinetics And Mechanism ◽

Acid Catalyzed ◽

Kinetics Of

The kinetics of acid-catalyzed decomposition of 1,3-bis(4-methylphenyl)triazene have been studied in mixtures of hexane and organic acid of various ratios using acetic, isovaleric, and pivalic acids as the catalysts. In all the cases, a monotonously increasing dependence of the observed rate constant upon mol fraction of the acid has been found. The results obtained are discussed with the help of the classic third- and fourth-order functions by Margules and the respective kinetic model. The main catalyzing particle appears to be the dimer of the respective acid, the reaction probably going via a complex formed by two molecules of acid and one molecule of the triazene.

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Transport of a dilute active suspension in pressure-driven channel flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.372 ◽

2015 ◽

Vol 777 ◽

pp. 482-522 ◽

Cited By ~ 50

Author(s):

Barath Ezhilan ◽

David Saintillan

Keyword(s):

Distribution Function ◽

Kinetic Model ◽

Numerical Simulations ◽

Persistence Length ◽

Conservation Equation ◽

Depletion Layer ◽

Hydrodynamic Interactions ◽

Kinematic Effect ◽

Flow Limit ◽

Pressure Driven

Confined suspensions of active particles show peculiar dynamics characterized by wall accumulation, as well as upstream swimming, centreline depletion and shear trapping when a pressure-driven flow is imposed. We use theory and numerical simulations to investigate the effects of confinement and non-uniform shear on the dynamics of a dilute suspension of Brownian active swimmers by incorporating a detailed treatment of boundary conditions within a simple kinetic model where the configuration of the suspension is described using a conservation equation for the probability distribution function of particle positions and orientations, and where particle–particle and particle–wall hydrodynamic interactions are neglected. Based on this model, we first investigate the effects of confinement in the absence of flow, in which case the dynamics is governed by a swimming Péclet number, or ratio of the persistence length of particle trajectories over the channel width, and a second swimmer-specific parameter whose inverse measures the strength of propulsion. In the limit of weak and strong propulsion, asymptotic expressions for the full distribution function are derived. For finite propulsion, analytical expressions for the concentration and polarization profiles are also obtained using a truncated moment expansion of the distribution function. In agreement with experimental observations, the existence of a concentration/polarization boundary layer in wide channels is reported and characterized, suggesting that wall accumulation in active suspensions is primarily a kinematic effect that does not require hydrodynamic interactions. Next, we show that application of a pressure-driven Poiseuille flow leads to net upstream swimming of the particles relative to the flow, and an analytical expression for the mean upstream velocity is derived in the weak-flow limit. In stronger imposed flows, we also predict the formation of a depletion layer near the channel centreline, due to cross-streamline migration of the swimming particles towards high-shear regions where they become trapped, and an asymptotic analysis in the strong-flow limit is used to obtain a scale for the depletion layer thickness and to rationalize the non-monotonic dependence of the intensity of depletion upon flow rate. Our theoretical predictions are all shown to be in excellent agreement with finite-volume numerical simulations of the kinetic model, and are also supported by recent experiments on bacterial suspensions in microfluidic devices.

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Kinetics of rouleaux formation using TV image analyzer. II. Rat erythrocytes

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1983.245.2.h259 ◽

1983 ◽

Vol 245 (2) ◽

pp. H259-H264 ◽

Cited By ~ 3

Author(s):

T. Shiga ◽

K. Imaizumi ◽

N. Maeda ◽

K. Kon

Keyword(s):

Kinetic Model ◽

Rate Constant ◽

Three Dimensional ◽

Erythrocyte Aggregation ◽

Image Analyzer ◽

One Dimensional ◽

Specific Pathogen ◽

Time Courses ◽

Kinetics Of ◽

Rouleaux Formation

With the use of a rheoscope combined with a TV image analyzer, the kinetics of specific pathogen-free rat erythrocyte aggregation was studied. Under certain conditions (gamma 7.5 s-1, hematocrit 0.36%, in own plasma, at 25 degrees C) one-dimensional aggregates (rouleaux) were formed without the development of three-dimensional aggregates, perhaps because of very low concentration of gamma-globulin. The observed phenomena could be explained by 1) the erythrocyte sedimentation and 2) the rouleaux formation. The time courses, of the biphasic change in erythrocyte count and of the increments in total area and in the area/count, were successfully simulated by a kinetic model of linear polymerization, assuming a sedimentation rate constant and an association rate constant. Further, a Poissonlike distribution of the length of rouleaux was shown, as predicted theoretically on the basis of the same kinetic model.

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