Jean-Louis Seris

Efficient Oxidative Dechlorination and Aromatic Ring Cleavage of Chlorinated Phenols Catalyzed by Iron Sulfophthalocyanine

An efficient method has been developed for the catalytic oxidation of pollutants that are not easily degraded. The products of the hydrogen peroxide (H2O2) oxidation of 2,4,6,-trichlorophenol (TCP) catalyzed by the iron complex 2,9,16,23-tetrasulfophthalocyanine (FePcS) were observed to be chloromaleic, chlorofumaric, maleic, and fumaric acids from dechlorination and aromatic cycle cleavage, as well as additional products that resulted from oxidative coupling. Quantitative analysis of the TCP oxidation reaction revealed that up to two chloride ions were released per TCP molecule. This chemical system, consisting of an environmentally safe oxidant (H2O2) and an easily accessible catalyst (FePcS), can perform several key steps in the oxidative mineralization of TCP, a paradigm of recalcitrant pollutants.

Kinetics of the catalysis by the Alcaligenes eutrophus H16 hydrogenase of the electrochemical reduction of NAD

Abstract The regeneration of the pyridine coenzyme NADH is the key step in numerous enzymatic synthesis processes. This work deals with the kinetics of the catalysis by the Alcaligenes eutrophus H16 hydrogenase of the electrochemical reduction of NAD+ on a platinum electrode. In a classical way the enzyme catalyses the homogeneous reduction of NAD+ by dissolved hydrogen. The kinetics of this reaction has been determined. It follows a Michaelis-Menten law with inhibition by the substrate. On the other hand, the kinetics of the electrochemical reduction is of zero order with respect to the NAD+ concentration and clearly shows an adsorption step. The control experiments verify that the species obtained by electrochemical reduction is the enzymatically active form of NADH. Comparison of the features of the two catalysis reactions shows that the electrochemical reduction is a heterogeneous process quite different from the classical homogeneous one, where the enzyme catalyses the electronic transfer from the platinum electrode to NAD+.

Biomimetic oxidation studies. 10. Cyclohexane oxidation reactions with active site methane monooxygenase enzyme models and t-butyl hydroperoxide in aqueous micelles: Mechanistic insights and the role of t-butoxy radicals in the CH functionalization reaction

Abstract The oxidation of cyclohexane (CyH) in an aqueous micelle system with t -butyl hydroperoxide (TBHP) in the presence of biomimetic methane monooxygenase enzyme complexes, [Fe 2 O( η 1 -H 2 O)( η 1 -OAc)(TPA) 2 ] 3+ , 1 , [Fe 2 O( η 1 -H 2 O)( η 1 -OAc)(BPIA) 2 ] 3+ , 2 , and O 2 , was studied and found to provide cyclohexanol (CyOH), cyclohexanone (CyONE), and cyclohexyl- t -butyl peroxide (CyOO t -Bu). The mechanistic aspects of this oxidation reaction in aqueous micelles were studied and included the effects of the surfactant concentration, cetyltrimethylammonium hydrosulfate; concentration of CyH and TBHP; and a trapping reagent, CCl 4 . Several factors allowed us to conclude that a t -butoxy radical ( t -BuO) was generated from the favorable redox chemistry of the biomimetic complexes with TBHP, and was responsible for the free radical initiation process with CyH in the aqueous micelle system.

Synthesis of di-µ-oxo manganese(III/IV) complexes as functional models of L. Plantarum pseudo-catalase: influence of electronic and steric factors; catalysis and kinetics of hydrogen peroxide disproportionation

Di-µ-oxo dimanganese(III/IV) complexes are efficient catalysts for H2O2 disproportionation in neutral aqueous medium; the activity can be correlated to the electron density on the metal and the accessibility of the catalytic site.

Role of horseradish peroxidase in the catalytic hydroxylation of phenol

Abstract The reaction between phenol, dihydroxyfumaric acid and oxygen was studied in the presence of horseradish peroxidase. The use of a sensitive HPLC method enables detection of three products of hydroxylation: catechol, hydroquinone and 1,2,4-benzenetriol. Influence of various parameters indicates that the enzyme catalyses the autooxidation of DHF. The formation of compound III is a consequence of superoxide anion present in excess in the solution. However, this compound is not involved in the catalysis of formation of the .OH radicals.

Effect of Organic Acids on Reactions Catalyzed by Manganese Peroxidase from Phanerochaete chrysosporium

The effect of several organic acids on the oxidation of Mn(II) catalyzed by manganese peroxidase was studied. Reactivities of manganese peroxidase and chemically prepared Mn(III) organic acid complexes towards phenolic compounds were compared. If lactate appears to be the best complexant for manganese peroxidase activity, chemically prepared Mn(III)—lactate complex is a less effective oxidant towards phenolic compounds than other Mn(III)—complexes. Our results agree with the hypothesis that certain organic acids are involved in the catalytic cycle of manganese peroxidase. Malonate and lactate seem to be the most attractive complexants for practical applications of manganese peroxidase and were used in enzymatic treatment of hardwood kraft pulp. Bleaching of kraft pulp was studied and after alkaline extraction, a significant decrease of kappa number was measured. The bleaching was enhanced in lactate buffer.

Effect of linking allyl and aromatic chains to histidine 170 in horseradish peroxidase.

Histidine residues in horseradish peroxidase (HRP) were modified chemically with diethyl pyrocarbonate, 4,omega-dibromoacetophenone or diallylpyrocarbonate. Histidines were chosen as His-170, the fifth ligand of the heme iron atom, forms part of the active site of this enzyme. Good yields of hemoprotein were obtained in all cases. Analysis by HPLC of peptides obtained after tryptic digestion showed that His-170 of HRP was in fact modified. The specific activity remained satisfactory after chemical modification of the histidine residues, and so the active site of HRP can thus be altered without a dramatic loss of hemoprotein or peroxidase activity. This may open routes to the preparation of novel biocatalysts.

Use of thin layer spectroelectrochemistry in the study of NADH regeneration by means of an hydrogenase

Abstract Thin layer spectroelectrochemistry is used to show that it is possible to mediate the electrochemical reduction of NADH by means of an hydrogenase. This kind of cofactor regeneration is associated to three model reactions involving the reduction of pyruvate, acetoacetylCoA and ketoglutarate.

Chemical deglycosylation of Horseradish peroxidase and surglycosylation using a new glycosylating reagent: effects on catalytic activity and stability

Abstract Horseradish peroxidase (H.R.P.) is a glycoprotein widely used in immunoassay tests and is also of potential importance in some industrial processes. Its stability following treatment with periodate (a classical way to prepare H.R.P.-antibodies conjugates) was studied. This treatment resulted in a loss of specific activity which was shown not to be correlated with the removal of sugars. Our conclusion is that the sugar-chains on the native enzyme play no role in the catalytic activity as it is tested in vitro. The thermal stability and resistance to hydrogen peroxide (a substrate of H.R.P.) were found to be decreased by this chemical deglycosylation. On the other hand, a substituted anhydride derived from glucose was used to covalently graft more sugars onto the enzyme; fixing as few as 3 to 4 glucose residues (a sugar which is not present in the sugar-chains of the protein) dramatically increased its thermal stability. Thus, the half-life of the enzyme at 60° C was increased by a factor of 5 to 6. This result is of importance for the use of H.R.P. in industrial and biomedical analysis processes.

Differential pulse polarography for monitoring cell cultures

The differential pulse polarography has been used on samples taken from the medium during the culture of chinese hamster ovary cells with a view to producing the active principle of an anti-cancer drug.