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Isotope‐Effect Profiles in the Oxidative N ‐Demethylation of N,N ‐Dimethylanilines Catalysed by Lignin Peroxidase and a Chemical Model
Author(s) -
Baciocchi Enrico,
Gerini M. Francesca,
Lanzalunga Osvaldo,
Lapi Andrea,
Lo Piparo Maria Grazia,
Mancinelli Simona
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200106)2001:12<2305::aid-ejoc2305>3.0.co;2-e
Subject(s) - chemistry , deprotonation , aniline , demethylation , medicinal chemistry , peroxidase , radical ion , kinetic isotope effect , electron transfer , lignin , ring (chemistry) , photochemistry , stereochemistry , organic chemistry , enzyme , ion , biochemistry , gene expression , physics , deuterium , quantum mechanics , dna methylation , gene
Lignin peroxidase catalyses the oxidative N ‐demethylation of ring‐substituted N,N ‐dimethylanilines by an electron‐transfer mechanism whereby an anilinium radical cation is formed which is then deprotonated by the enzyme. Information on the nature of the basic centre which deprotonates the radical cation has been obtained by determining the KDIE profile (plot of k H / k D vs. the p K a of the aniline radical cations) for a number of ring‐substituted N,N ‐bis(dideuteriomethyl)anilines. From the bell‐shaped curve it has been estimated that the p K a of the proton‐abstracting base is about 7. Interestingly, almost the same value has been obtained when the same type of study has been carried out using a water‐soluble model compound: 5,10,15,20‐tetraphenyl‐21 H ,23 H ‐porphine‐ p , p ′, p ′′, p ′′′‐tetrasulfonic acid iron(III) chloride. This is a strong indication that the radical cation is deprotonated by the same species in the enzymatic and in the chemical reactions. It is suggested that this species is the reduced iron‐oxo complex.