The use of appropriate low molecular-weight compounds (viz. mediators) in combination with fungal laccase enables this enzyme to catalyse the oxidation of ‘non-natural’ non-phenolic substrates, such as benzyl alcohols, according to the reaction scheme outlined below (Scheme 1). The mediator needs to be easily oxidised by laccase to the Medox status: the structure of the latter is then crucial for the mechanism of the ensuing non-enzymatic oxidation of the substrate. 1-Hydroxybenzotriazole (HBT) and N-hydroxyphthalimide (HPI) are two N–OH compounds that are known to mediate the activity of laccase, driving it towards non-phenolic substrates, and the relative efficiency of these mediators has been recently evaluated. Consensus has been reached upon the preliminary monoelectronic oxidation of these N–OH mediators by laccase to the corresponding N-oxyl radical (N–O•) forms, through the fleeting intervention of their radical cations, HPT•+ or HPI•+, respectively. Two different hypotheses have been proposed to explain the subsequent oxidation of the substrate. Either these N–O• radicals perform a one-electron oxidation (ET) of the substrate to a radical cation, or they abstract a H-atom from the substrate (HAT), converting it into a radical. The end-products of oxidation would be formed from either one of these two short-lived intermediates of the substrate. We favour the HAT mechanism on the basis of evidence previously described, but wanted to address this key issue once more.

Radical or electron transfer mechanism of oxidation with some laccase/mediator systems / M., Fabbrini; Galli, Carlo; Gentili, Patrizia. - In: JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC. - ISSN 1381-1177. - 18:(2002), pp. 169-171. [10.1016/S1381-1177(02)00082-6]

Radical or electron transfer mechanism of oxidation with some laccase/mediator systems

GALLI, Carlo;GENTILI, Patrizia
2002

Abstract

The use of appropriate low molecular-weight compounds (viz. mediators) in combination with fungal laccase enables this enzyme to catalyse the oxidation of ‘non-natural’ non-phenolic substrates, such as benzyl alcohols, according to the reaction scheme outlined below (Scheme 1). The mediator needs to be easily oxidised by laccase to the Medox status: the structure of the latter is then crucial for the mechanism of the ensuing non-enzymatic oxidation of the substrate. 1-Hydroxybenzotriazole (HBT) and N-hydroxyphthalimide (HPI) are two N–OH compounds that are known to mediate the activity of laccase, driving it towards non-phenolic substrates, and the relative efficiency of these mediators has been recently evaluated. Consensus has been reached upon the preliminary monoelectronic oxidation of these N–OH mediators by laccase to the corresponding N-oxyl radical (N–O•) forms, through the fleeting intervention of their radical cations, HPT•+ or HPI•+, respectively. Two different hypotheses have been proposed to explain the subsequent oxidation of the substrate. Either these N–O• radicals perform a one-electron oxidation (ET) of the substrate to a radical cation, or they abstract a H-atom from the substrate (HAT), converting it into a radical. The end-products of oxidation would be formed from either one of these two short-lived intermediates of the substrate. We favour the HAT mechanism on the basis of evidence previously described, but wanted to address this key issue once more.
2002
01 Pubblicazione su rivista::01a Articolo in rivista
Radical or electron transfer mechanism of oxidation with some laccase/mediator systems / M., Fabbrini; Galli, Carlo; Gentili, Patrizia. - In: JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC. - ISSN 1381-1177. - 18:(2002), pp. 169-171. [10.1016/S1381-1177(02)00082-6]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/256129
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