No abstract

No abstract

The oxidation reaction of chlorinated anilines by two manganese oxides, birnessite and pyrolusite, and by iron oxide has been investigated. The oxidation ability of the oxides was in the order birnessite . pyrolusite > iron oxide. Birnessite removed 100% of chloroanilines in 30 min, whereas pyrolusite and iron oxide removed from 5 to 96% of chloroanilines in 72 h. The differences in the reactivity of chloroanilines depended on the number and the position of chloro substituents on the aromatic ring. The activity of the oxides was maximal at pH 4.0 and decreased as the pH increased. The reaction kinetics in each of the systems investigated was adequately described by a secondorder rate expression. A free-radical mechanism for the oxidative coupling reaction of chlorinated anilines was suggested. Chloroazobenzene and chlorohydroxydiphenylamine dimers were detected among the oxidation products. The results obtained suggested that the oxidative mechanism occurred through a head-to-head and head-to-tail coupling of chloroanilino radicals.

Gelatine gels originate from water in oil microemulsions in which the ternary system consists of isooctane/ sulfosuccinic acid bis [2-ethyl hexyl] ester/water; the solubilization of gelatin in the water pool of these microemulsions transforms them into viscous gels in which it is possible to cosolubilize various reactive molecules. These gels were used to immobilize two phenoloxidases, a laccase from Trametes versicolor and a tyrosinase from mushroom. The best balance between gel retention and catalytic activity was reached at a gelatine concentration of 2.5% (w/v) in the case of tyrosinase, while laccase immobilization was independent of gelatine concentration. Both enzymes kept the same optimum pH as the corresponding soluble controls, while a partial loss of activity was observed when they were immobilized. Immobilized enzymes showed an increased stability when incubated for several days at 4 degrees C with a very low release from the gels in the incubation solutions. The immobilization of tyrosinase and of laccase enhanced stability to thermal inactivation. Furthermore, gel-entrapped tyrosinase was almost completely preserved from proteolysis: more than 80% of the activity was maintained, while only 25% of the soluble control activity was detected after the same proteolytic treatments. A column packed with gel-immobilized tyrosinase was used to demonstrate that enzymes immobilized with this technique may be reused several times in the same reaction without loosing their efficiency. Finally, gel-entrapped tyrosinase and laccase were capable of removing naturally occurring and xeno-biotic aromatic compounds from aqueous suspensions with different degrees of efficiency. (c) 1995 John Wiley & Sons, Inc.