On N-acetylcysteine. Part I. Experimental and theoretical approaches of the N-acetylcysteine/H2O2complexation

1994 ◽  
Vol 72 (10) ◽  
pp. 2094-2101 ◽  
Author(s):  
Jlil Arroub ◽  
Jacqueline Bergès ◽  
Zohreh Abedinzadeh ◽  
Jacqueline Langlet ◽  
Monique Gardès-Albert
Keyword(s):  
Hydrogen Peroxide ◽  
Complex Formation ◽  
Solvent Effect ◽  
Equilibrium Constant ◽  
Thermodynamic Equilibrium ◽  
Continuum Model ◽  
Theoretical Calculations ◽  
Thermodynamic Equilibrium Constant ◽  
Theoretical Approaches ◽  
Biphasic Process

The complexation of N-acetylcysteine (RSH) with hydrogen peroxide has been studied experimentally and theoretically. Experimentally we have measured the evolution of RSH, H2O2, and RSSR (N-acetylcystine) as a function of time. Surprisingly, H2O2 decays by a biphasic process, which is not the case for RSH and RSSR. In the first stage of the kinetics, H2O2 disappears without oxidizing the thiol function of RSH. By analogy with glutathione (GSH), the formation of a complex between RSH and H2O2 has been proposed. The thermodynamic equilibrium constant of complex formation has been determined. Theoretical calculations were performed within the SIBFA method to pinpoint the sites of complexation in isolated and hydrated states. A mixed "discrete–continuum" model was used to evaluate the solvent effect. The two stable complexes found in isolated state have different behaviour under the influence of the solvent. Comparison with complexed GSH is discussed.

The equilibrium constant of the reaction Cr2O72- + H2O ↔ 2HCrO,4- at 15° to 45°

1968 ◽  
Vol 21 (6) ◽  
pp. 1445 ◽  
Author(s):  
HG Linge ◽  
AL Jones
Keyword(s):  
Acid Solution ◽  
Equilibrium Constant ◽  
Thermodynamic Equilibrium ◽  
Thermodynamic Equilibrium Constant

The equilibrium Cr2O2-7,+H2O + 2HcrO4 has been studied in acid solution spectrophotometrically. Values have been obtained for the thermodynamic equilibrium constant at 15°, 25°, 35°, and 45°.

Thermodynamic Equilibrium Constant of a Molecular Charge Transfer Complex

1968 ◽  
pp. 276-279
Author(s):  
J.M. WILSON ◽  
R.J. NEWCOMBE ◽  
A.R. DENARO ◽  
R.M.W. RICKETT
Keyword(s):  
Charge Transfer ◽  
Equilibrium Constant ◽  
Thermodynamic Equilibrium ◽  
Charge Transfer Complex ◽  
Thermodynamic Equilibrium Constant ◽  
Molecular Charge

Theoretical Study of Solvent Effect on π-EDA Complexation I. SCF and DFT Calculations Within Polarized Continuum Model on TCNE-Benzene Complex

2003 ◽  
Vol 68 (12) ◽  
pp. 2355-2376 ◽  
Author(s):  
Ondrej Kyseľ ◽  
György Juhász ◽  
Pavel Mach
Keyword(s):  
Complex Formation ◽  
Gibbs Energy ◽  
Solvent Effect ◽  
Gas Phase ◽  
Continuum Model ◽  
Solvent Polarity ◽  
Polar Solvents ◽  
Complexation Constant ◽  
Polarized Continuum Model ◽  
Eda Complex

SCF, MP2, DFT(B3LYP) and the polarizable continuum model (PCM) were used to study geometry, charge distribution and energetics of the π-EDA complex formation between tetracyanoethene (TCNE) and benzene both in gas phase and in various polar solvents (cyclohexane, dichloromethane and water). MP2/6-31G*, MP2/6-31+G*, MP2/6-31G*(0.25) calculations have shown that geometry of the complex is planparallel with interplane distance of 3.05 × 10-10 m on the MP2/6-31G* level and the complexation energy is equal to -6.8 to -8.95 kcal/mol, while dominant contributions to the complexation energy come from intermolecular correlation and energy. The PCM continuum model of polar solvents describes well both the Gibbs energy of solvation of individual solutes and the difference between the complex and its constituents and also agrees with the experimental finding that the polar solvent effect decreases the complexation constant of the π-EDA complex formation by a factor of 2-4 when chloroform is replaced by more polar dichloromethane, and by a factor of 9, when tetrachlormethane is replaced by dichloromethane. It seems that the solvation Gibbs energy of the π-EDA complex formation always prefers stability of solvated constituents to that of the solvated complex. The electrostatic polarization Gibbs energy of solvation is responsible for the tendency of complexation constants to decrease with increasing solvent polarity; however, non-electrostatic terms contribute as well. While the enthalpy of complexation between benzene and TCNE in gas phase is about -10.0 kcal/mol due to the negative complexation entropy ∆(∆S) = -22.56 cal/mol K, the ∆G of complexation is -3.8 kcal/mol. The solvation part of the complexation Gibbs energy in dichloromethane is +5.14 kcal/mol (PCM-SCF/6-31G* calculation) so that complexation constant K = 0.1 dm3/mol in this solvent was found.

Thermodynamic equilibrium constant of isobutane-isobutylene-hydrogen system

1973 ◽  
Vol 18 (2) ◽  
pp. 152-154 ◽  
Author(s):  
John Happel ◽  
Reiji Mezaki
Keyword(s):  
Equilibrium Constant ◽  
Thermodynamic Equilibrium ◽  
Thermodynamic Equilibrium Constant ◽  
Hydrogen System

Thermodynamic equilibrium constant of ethyl alcohol-acetaldehyde-hydrogen system

1974 ◽  
Vol 19 (2) ◽  
pp. 110-112 ◽  
Author(s):  
John Happel ◽  
James C. Chao ◽  
Reiji Mezaki
Keyword(s):  
Equilibrium Constant ◽  
Ethyl Alcohol ◽  
Thermodynamic Equilibrium ◽  
Thermodynamic Equilibrium Constant ◽  
Hydrogen System
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