Search results for "kinetics"

Characteristics of the polymer transport in ratchet systems

2010

Molecules with complex internal structure in time-dependent periodic potentials are studied by using short Rubinstein-Duke model polymers as an example. We extend our earlier work on transport in stochastically varying potentials to cover also deterministic potential switching mechanisms, energetic efficiency and non-uniform charge distributions. We also use currents in the non-equilibrium steady state to identify the dominating mechanisms that lead to polymer transportation and analyze the evolution of the macroscopic state (e.g., total and head-to-head lengths) of the polymers. Several numerical methods are used to solve the master equations and nonlinear optimization problems. The domina…

Structural, energetic and kinetic database of catalytic reactions: Benzyl alcohol to benzaldehyde oxidation on MnOx clusters

2021

Abstract Data here reported are connected with the research article “Benzyl Alcohol to Benzaldehyde Oxidation on MnO x Clusters: Unraveling Atomistic Features” Gueci et al. [1] . This work described and discussed structural and energetic results, calculated by Density Functional Theory (DFT). In order to get kinetic information, DFT results were refined by an original approach, which will be shortly described in the following article. The crossed analysis of experimental and computational energetic and kinetic data allowed to (i) reconstruct the complicated lattice that connects the primary and secondary mechanisms of the reaction and (ii) identify alternative process pathways capable of by…

Heterogeneous kinetics: from solid–gas reaction to solid–liquid dissolution

2002

Abstract The extension of the formal kinetics of solid–gas reactions to solid–liquid dissolution is investigated theoretically. The work is based on modelling the dissolution of a solid in a closed system by a stoichiometrically simple chemical reaction A solid ⇄A liquid proceeding up to either an equilibrium state if the solid phase is initially in excess or exhaustion in the reverse situation. The initial amount of solid compared to the capacity of the liquid phase appears as a major factor of complexity. First, the rate equation is formulated in terms of the intensive variables without any assumption about the mechanism and the rate-limiting step. The resulting equations are compared to …

Water capillary absorption in porous media in different wettability conditions studied by Quantitative MRI and X-ray CT

2007

X-ray computed tomography (CT) and magnetic resonance imaging (MRI) have been successfully applied to study both the capillary properties of several samples of Lecce stone and the performances of treatments used for protection and conservation of historical stone artifacts. The presence of water inside the sample may be visualized by both MRI and X-ray CT. For the treated samples, the different dynamics of water absorption gives indirectly the efficacy of the polymer in the rock.

Xanthine oxidase catalyzes the oxidation of retinol.

2007

In mammals, xanthine oxidase (E.C. 1.17.3.2) catalyzes the hydroxylation of a wide variety of heterocyclic substrates such as purines, pyrimidines, and pterins, in addition to aldehydes [1] as all-trans-retinaldehyde [2-5]. Here, we show that buttermilk xanthine oxidase was capable to oxidizing all-trans-retinol (t-ROL) to all-trans-retinaldehyde (t-RAL) that was successively oxidized to all-trans-retinoic acid (t-RA). A rise in the enzyme activity, when t-ROL-CRBP complex was assayed, with respect to the free t-ROL, was observed. Furthermore, treatment of the enzyme with Na2S and glutathione resulted in a significant increment in catalytic activity toward t-ROL and t-RAL, due to the recons…

The effect of excipients on the stability and phase transition rate of xylazine hydrochloride and zopiclone

2015

The compatibility of thermodynamically unstable polymorph of two active pharmaceutical compounds (xylazine hydrochloride form X and zopiclone form C) with different excipients was investigated. The effects of the excipient and its amount in the sample on the thermal properties and possible chemical interactions were studied. The most commonly used excipients in the pharmaceutical industry - calcium carbonate, lactose hydrate, cellulose, magnesium stearate hydrate and calcium stearate hydrate were selected for this study. The dependence of the phase transition rate from an unstable to a more stable polymorph on the excipients and their amounts in the initial sample was analysed at 80°C, and …

Hydration and dehydration kinetics of xylazine hydrochloride

2009

From the experiments where mixture of xylazine hydrochloride hydrate H and anhydrous X were held at constant conditions, the stable form of xylazine hydrochloride can be found out. To determine equilibrium relative humidity, the unstable form of xylazine hydrochloride was inserted in thermostated humidity chamber and its weight was recorded by weighing the sample outside the chamber. The kinetic model and the rate constant for each condition were determined. The rate constants give information regarding the speed of the process at every experimentally used relative humidity. Thus using the data in coordinates k – p for each temperature it is possible to determine the water vapor pressure of…

An Interfacial Thermodynamic Model for the Oxidation Kinetics of a Metal: Epitaxial Stress Effects

2004

Mechanical Stresses: Inhibitor of Catalyst of High Temperature Oxidation?

2001

Oxidation of metals is a complex reaction in which mechanical and chemical phenomena occur. A dynamic and macroscopic model is developed in order to simulate oxidation kinetics of a metal. It includes the stress/diffusion coupling in the bulk and the interfacial phenomena at metal/oxide interface. Its application to the Zr/ZrO 2 system shows the important role of stress field distribution in oxide on kinetic behavior. According to the sign of stress gradient in the oxide scale, the oxidation rate can speed up or slow down. The calculated kinetic curves could he fitted using a k p .t 1/n law where n and kp vary all over the process, like for the experimental kinetic curves.

The paradoxical cyanide-stimulated respiration of Zymomonas mobilis: cyanide sensitivity of alcohol dehydrogenase (ADH II)

2003

The respiratory inhibitor cyanide stimulates growth of the ethanologenic bacteriumZymomonas mobilis, perhaps by diverting reducing equivalents from respiration to ethanol synthesis, thereby minimizing accumulation of toxic acetaldehyde. This study sought to identify cyanide-sensitive components of respiration. In aerobically grown, permeabilizedZ. mobiliscells, addition of 200 μM cyanide caused gradual inhibition of ADH II, the iron-containing alcohol dehydrogenase isoenzyme, which, in aerobic cultures, might be oxidizing ethanol and supplying NADH to the respiratory chain. In membrane preparations, NADH oxidase was inhibited more rapidly, but to a lesser extent, than ADH II. The time-cours…