Jean-Louis Burgot

Validation of a new method using the reactivity of electrogenerated superoxide radical in the antioxidant capacity determination of flavonoids

This article lays out a new method to measure the antioxidant capacity of some flavonoids. The methodology developed is based on the kinetics of the reaction of the antioxidant substrate with the superoxide radical (O(2)(*-)). A cyclic voltammetric technique was used to generate O(2)(*-) by reduction of molecular oxygen in aprotic media. In the same experiment the consumption of the radical was directly measured by the anodic current decay of the superoxide radical oxidation in the presence of increasing concentrations of antioxidant substrate. The method was statistically validated on flavonoid monomers and on the standard antioxidants: trolox, ascorbic acid and phloroglucinol. The linear correlations between the anodic current of O(2)(*-) and the substrate concentration allowed the determination of antioxidant index values expressed by the substrate concentration needed to consume 30% (AI(30)) and 50% (AI(50)) of O(2)(*-) in given conditions of oxygen concentration and scanning rate. The fidelity of the method was examined intraday and interlaboratories.

Selective indirect electroreduction of 5-(nitrophenyl)-1,2-dithiole-3-thiones

Abstract Indirect electrolysis of 5-(o-, m- and p-nitrophenyl)-1,2-dithiole-3-thiones in toluene is performed by phase transfer reaction with a titanium complex (C5H5)2Ti+ in aqueous sulfuric acid. Nitro groups are selectively reduced to amino groups without reduction of the dithiolethione ring and the resulting oxidized form of the complex is reduced at a porous graphite felt cathode by continuous recycling of the aqueous solution.

log P Estimation of 1,2-Dithiole-3-thiones and 1,2-Dithiole-3-ones: A Comparison of Experimental and Calculative Approaches

PurposeTo estimate experimental log P values of formerly described 5-formyl- and 5-acyl-dithiole-3-thiones (DTT) and -dithiole-3-ones (DTO) and to check the validity of five log P calculation programs via experimental log P for a database of 68 DTT and DTO.MethodsExperimental log P values were measured by means of octanol/water partitioning; for determining solute concentrations in water, RP-HPLC with spectrophotometric detection was used. For calculating log P, the fragmental methods ACD/log P, CLOGP, and KOWWIN, the atom-based approach XLOGP, and the whole-molecule approach QLOGP were applied.ResultsQuality of calculations significantly differs depending on the subset under consideration. For database compounds 01–48, comprising alkyl and aryl substitution in 4- and 5-position, the fragmental methods ACD/log P, CLOGP, and KOWWIN perform significantly better than the atom-based approach XLOGP and the whole-molecule method QLOGP. For database compounds 49–68, comprising formyl and acyl substitution in 4- and 5-position, superiority of the whole-molecule method QLOGP over the substructure-based approaches is observed. The strong underestimation of log P for compounds 49–68 probably indicates hidden physicochemical phenomena resulting from the juxtaposition of the acyl and dithiole moieties.ConclusionsAll calculation methods included in this study need a thorough refinement to adequately cope with particular solvation behavior suspected to prevail in formyl- or acyl-DTT and DTO, which represent a chemical class of high pharmacological interest.

Cathodic behaviour of some 5-nitrophenyl-1,2-dithiole-3-thiones and 5-nitrophenyl-1,2-dithiole-3-ones

Abstract The electrochemical behaviour of 5-(nitrophenyl)-1,2-dithiole-3-thiones and 5-(nitrophenyl)-1,2-dithiole-3-ones was studied by cyclic voltammetry in DMF. The standard reduction potentials of 5-( p -nitrophenyl)-dithiolethione and 5-( p -nitrophenyl)-dithiolone entered into a linear correlation involving standard reduction potentials of substituted nitrobenzenes and known electronic constants of several substituents. This correlation allowed the determination of the electronic effects of [3-thioxo-1,2-dithiole]-5-yl and [3-oxo-1,2-diothiole]-5-yl groups which were, respectively, σ p − =1.14 and σ p − =0.86, comparable with those of nitro or cyano substituents.

Existence of two basic sites in triazolo-1,4-diazepines: determination of two pKa values for a model compound in water

By a UV/VIS spectrophotometric study in the pH range –1.6 to 10.1 and by a polarographic study of a water soluble model compound, the occurrence of two basic sites in water has been ascertained for triazolo-1,4-diazepines. The pKa values found for this model were –0.24 and +1.81. Owing to the overlapping of the two pKa values, microforms exist simultaneously. Corresponding ionization microconstant values have been tentatively assigned.

Principe de l'estimation par titrimétrie thermométrique de l'enthalpie et de l'entropie de transfert eau/n-octanol de solutes très lipophiles

Abstract Titrimetric thermometry allows estimation of the enthalpy of transfer of very lipophilic solutes from water to n-octanol. Combining these values with those of the corresponding transfer coefficients obtained independently gives an estimation of the entropy of transfer. A number of examples are given.

On the preparation of 3-(5-Formyl-3-thioxo-3H-[1,2]dithiol-4-yl)-propionic acid

3-(5-Formyl-3-thioxo-3H-[1,2]dithiol-4-yl)propionic acid has been obtained from 3-[5-(hydroxyiminomethyl)-3-thioxo-3H-[1,2]dithiol-4-yl]propionic acid under standard conditions. Conversely, for the hydroxyimino derivative the general procedure failed and so it has been prepared by the action, in a basic medium, of isoamyl nitrite on 3-(5-methyl-3-thioxo-3H-[1,2]dithiol-4-yl)propionic acid ethyl ester.

New tautomerism suggested by pKa determinations

The UV/VIS spectrophotometric pKa determination of (E)- and (Z)-5-(1-hydroxyiminomethyl)-4-methyl-1,2-dithiole-3-thione is described; for each isomer, the pKa value was obtained by a non-linear least-squares methodology. This methodology was used to take into account some unusual experimental difficulties (very low solubility in water and E→Z isomerization). The pKaZ value (5.13) strongly suggests that the resonant basic Z form is chiefly a thiolate form of a heteropentalene. Spectrophotometric results were confirmed by 13C NMR spectroscopy. A new type of tautomerism is suggested to explain the results.

The Notion of Activity in Chemistry

Definitions and properties of some thermodynamic systems and of some quantities in relation with the notion of activity are recalled in this chapter. The properties of thermodynamic systems and of their states, and the notions of extensive and intensive properties, of transformations, equilibria, state functions, and reversible or irreversible processes are also mentioned. Especially, emphasis is given on the different expressions of the composition of a solution and on the pathways between them.

pKa Values of the Opened Form of a Thieno-1,2,4-triazolo-1,4-diazepine in Water

The pK a values of the freely water-soluble opened form of a thieno-1,2,4-triazolo-1,4-diazepine, namely 2-(3-amino- methyl-5-methyl-1,2,4-triazolo)-3-(2-chlorobenzoyl)- [2,3-c]thienopiperidine, were determined. pH measurements were made in the range 1 < pH < 10. Two of the three pK a values found in this range significantly overlapped; they quantify the ionization of both the aminomethyl residue and the piperidino moiety of the molecule. The third corresponds exclusively to the ionization of the triazolo nucleus. The pK a value of the thienophenone was obtained by UV spectrophotometry using acidity functions. All results were extracted from experimental data by a curve-fitting method.