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Debord J.,Service de Pharmacologie Toxicologie | Harel M.,French National Center for Scientific Research | Bollinger J.-C.,CNRS Research Group on Water, Soil and Environment | Dantoine T.,Service de Gerontologie Clinique
Analytical Methods | Year: 2010

We describe a method for determining the pseudo-first order rate constant of a chemical reaction by flow microcalorimetry operating in the flow-through mode. The impulse response of the instrument was described by a Gamma distribution and the equation of the thermogram was computed analytically. The resulting equation was fitted to the data by simulated annealing. The method was applied to an enzyme reaction following Michaelis-Menten kinetics by means of a new empirical equation relating the apparent rate constant to the kinetic parameters Vmax and Km. The method was exemplified by a kinetic study of horse serum butyrylcholinesterase. © 2010 The Royal Society of Chemistry.

Hamidouche S.,Blida University | Bouras O.,Blida University | Zermane F.,Blida University | Cheknane B.,Blida University | And 6 more authors.
Chemical Engineering Journal | Year: 2015

New generations of hydrophobic composite geomaterials intended to sorb certain hazardous wastes are assembled by mixing surfactant-modified aluminum-pillared montmorillonite (Al-SMPM) with activated carbon (AC). The sorption of 4-nitrophenol (4NP) and 2-nitrophenol (2NP) on these sorbents was studied in both single and binary component systems from aqueous solutions using batch tests. Results showed the efficiency of these composite sorbents relative to the two phenolic compounds, with a dominant contribution from Al-SMPM. In single-component systems, sorption isotherms of 4NP and 2NP as a function of pH were analyzed with the Freundlich equation, whose statistical interpretation was also developed. Sorption capacities sharply decreased when the solution pH value was raised from 3 to 9. In binary-component systems, the fit between measured and predicted simultaneous sorption capacities of both 4NP and 2NP indicated that the Sheindorf-Rebhun-Sheintuch model, an extended Freundlich model, is fully applicable. The 2NP favorably influences the sorption of 4NP. The synergistic effect between these two nitrophenol compounds has been confirmed by the higher competition coefficients, which increase with increasing pH. A number of hypotheses, based on the Abraham's solvation parameters model, have been advanced to discuss this mechanism. © 2015 Elsevier B.V..

Cadkova E.,Czech University of Life Sciences | Cadkova E.,Czech Geological Survey | Komarek M.,Czech University of Life Sciences | Debord J.,Service de Pharmacologie Toxicologie | And 3 more authors.
Journal of Solution Chemistry | Year: 2013

We determined the acidity constants of tebuconazole and penconazole, two fungicides from the group of 1,2,4-triazoles. Potentiometric titrations were performed in a 20 % (v/v) acetonitrile/water mixture at 25 C and at a fixed ionic strength (KNO3, 0.1 mol·dm-3). The pK a values (representing thermodynamic constants) were determined to be 5.0 ± 0.1 and 5.2 ± 0.1 for tebuconazole and penconazole, respectively. These values could be used in pure water solutions to consider the protonated or deprotonated forms when studying the field behavior of these fungicides. Molecular modeling calculations allowed identifying the N4 atom as the protonation site. © 2013 Springer Science+Business Media New York.

Debord J.,Service de Pharmacologie Toxicologie | Harel M.,French National Center for Scientific Research | Harel M.,University of Limoges | Cheknane B.,Blida University | And 2 more authors.
RSC Advances | Year: 2016

The classical energy distribution introduced by Sips to account for the Langmuir-Freundlich adsorption isotherm is extended to the case when the exponent α of the isotherm is higher than 1. The mean free energy of desorption E0 is estimated from the apparent dissociation constant K by the classical formula E0 = -RTlK. The dispersion of the energy values, which reflects the heterogeneity of the adsorbing sites, is estimated from the exponent α. The dispersion decreases when the exponent increases. Comparisons are made with the Gaussian approximation and the condensation approximation. The Sips distribution is also applied to activation energies, resulting in a Mittag-Leffler kinetic equation, as used in 'fractal kinetic' studies. The adsorption of the dye Basic Yellow 28 onto a surfactant-modified aluminium-pillared clay is studied as an example. © 2016 The Royal Society of Chemistry.

Debord J.,Service de Pharmacologie Toxicologie | Bollinger J.-C.,CNRS Research Group on Water, Soil and Environment | Bordas F.,CNRS Research Group on Water, Soil and Environment | Harel M.,French National Center for Scientific Research | Dantoine T.,Service de Gerontologie Clinique
Thermochimica Acta | Year: 2013

The inhibition of horse serum butyrylcholinesterase (EC by sodium arsenite (NaAsO2) and zinc chloride (ZnCl2) was studied at 37 C in a TRIS buffer, pH 7.5, with a flow microcalorimeter operating in the mixing mode. The dose-response curves were analyzed with the Hill equation, as deduced from the "fractal kinetic" model of Savageau by considering an exponential distribution of reaction rate constants. The C50 values were in the millimolar range and zinc chloride was a better inhibitor than sodium arsenite. This was confirmed by the values of the apparent rate constants. The Hill exponent, interpreted as a fractional reaction order, was also higher for zinc chloride. According to the statistical interpretation, the heterogeneity of binding reactions was slightly higher for Zn, in agreement with a speciation study which showed the existence of several Zn species in solution, with the free Zn2+ ion accounting for about 10% of the total. © 2013 Elsevier B.V. All rights reserved.

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