%0 Journal Article
%A Bietti, Massimo
%A Baciocchi, Enrico
%A Steenken, Steen
%D 1998
%T Lifetime, Reduction Potential and Base-Induced Fragmentation of the Veratryl Alcohol
Radical Cation in Aqueous Solution. Pulse Radiolysis Studies on a Ligninase “Mediator”
%U https://acs.figshare.com/articles/journal_contribution/Lifetime_Reduction_Potential_and_Base-Induced_Fragmentation_of_the_Veratryl_Alcohol_Radical_Cation_in_Aqueous_Solution_Pulse_Radiolysis_Studies_on_a_Ligninase_Mediator_/3726900
%R 10.1021/jp9812482.s002
%2 https://acs.figshare.com/ndownloader/files/5818614
%K benzylic position
%K veratryl alcohol methy l e
%K Pulse Radiolysis Studies
%K OH
%K product analysis results
%K deprotonation
%K Veratryl Alcohol Radical Cation
%K proton loss
%K pH
%K CH
%K lignin
%K fragmentation
%K cation
%K 1.36
%K VA
%X The radical cation of veratryl alcohol (3,4-dimethoxybenzyl alcohol), VA•+, was produced in aqueous solution,
mainly by oxidation with the radiation chemically generated SO4•- or Tl2+. By electron-transfer equilibration
with thioanisole as a redox standard, the reduction potential of VA•+ was determined to be 1.36 ± 0.01
V/NHE. On the basis of product analysis results, the radical cation undergoes a C−H deprotonation reaction
from the side chain, leading to an α-hydroxybenzyl-type radical, with k = (17 ± 1) s-1 at pH ≤ 5, as determined
by time-resolved conductance. The α-hydroxybenzyl-type radical was also produced by reduction of veratryl
aldehyde with the hydrated electron, and the pKa value of this radical was determined to be 10.0. The
deprotonation of VA•+ is enhanced by bases such as OH-, with the rate constant being 1.3 × 109 M-1 s-1.
In contrast, the corresponding rate constant for reaction of OH- with the radical cation of veratryl alcohol
methyl ether, whose reduction potential is also 1.36 V/NHE, is only 2 × 107 M -1 s-1. With the veratryl
alcohol derivative, 3,4-(MeO)2C6H3CH(OH)CMe3, the radical cation undergoes both a proton loss from the
benzylic position and a Cα−Cβ fragmentation with the ratio, at pH ≤ 5, of ca. 1:2. The decay of the radical
cation is strongly enhanced by OH- (k = 8.3 × 109 M-1 s-1), with the base induction favoring the C−C
fragmentation relative to the proton loss from the benzylic position. The possible bearing of these results
with respect to the role of VA in the lignin peroxidase-catalyzed decomposition of lignin is discussed.
%I ACS Publications