The enzyme laccase oxidises phenolic groups of lignin but not the non-phenolic ones. Redox mediators activate laccase towards the non-phenolic groups, particularly the benzyl alcohols. The oxidation step is performed by the oxidised form of the mediator, generated on its interaction with laccase. The oxidised mediator can follow an electron transfer, a radical hydrogen atom transfer or an ionic mechanism in the oxidation of the non-phenolic subunits. Support for these conclusions is provided by (i) investigating the product pattern with suitable probe substrates, (ii) measuring the intramolecular kinetic isotope effect. Determination of electrochemical properties and bond dissociation energies via semiempirical calculations enabled us to rationalise the origin of the different mechanistic behaviour of the mediators. Finally, a comparison of different laccase-mediator-systems (LMS), when applied to the delignification of wood pulp, indicates violuric acid as the most efficient mediator, in an oxidation that is selectively directed towards lignin only.
Catalytic efficiency of some mediators in laccase-catalyzed alcohol oxidation / A. M., Barreca; B., Sjogren; M., Fabbrini; Galli, Carlo; Gentili, Patrizia. - In: BIOCATALYSIS AND BIOTRANSFORMATION. - ISSN 1024-2422. - 22:2(2004), pp. 105-112. (Intervento presentato al convegno Joint Symposium on Engineering the Co-Factor Interface/Novel Enzymes - Frontiers in Discovery and Improvement tenutosi a Basel, SWITZERLAND nel AUG 24-29, 2003) [10.1080/10242420410001692750].
Catalytic efficiency of some mediators in laccase-catalyzed alcohol oxidation
GALLI, Carlo;GENTILI, Patrizia
2004
Abstract
The enzyme laccase oxidises phenolic groups of lignin but not the non-phenolic ones. Redox mediators activate laccase towards the non-phenolic groups, particularly the benzyl alcohols. The oxidation step is performed by the oxidised form of the mediator, generated on its interaction with laccase. The oxidised mediator can follow an electron transfer, a radical hydrogen atom transfer or an ionic mechanism in the oxidation of the non-phenolic subunits. Support for these conclusions is provided by (i) investigating the product pattern with suitable probe substrates, (ii) measuring the intramolecular kinetic isotope effect. Determination of electrochemical properties and bond dissociation energies via semiempirical calculations enabled us to rationalise the origin of the different mechanistic behaviour of the mediators. Finally, a comparison of different laccase-mediator-systems (LMS), when applied to the delignification of wood pulp, indicates violuric acid as the most efficient mediator, in an oxidation that is selectively directed towards lignin only.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
