Angewandte Chemie International Edition
10.1002/anie.202003032
COMMUNICATION
Selective electroenzymatic oxyfunctionalization by alkane
monooxygenase in a biofuel cell
[a]
[a]
[a]
[a]
[a]
Mengwei Yuan, Sofiene Abdellaoui, Hui Chen, Matthew J. Kummer, Christian A. Malapit, Chun
[b]
[a]
You and Shelley D. Minteer*
Abstract: Aliphatic synthetic intermediates with high added value are
generally produced from alkane sources (e.g., petroleum) by inert
carbon-hydrogen (C-H) bond activation using classical chemical
methods (high temperature, rare metals). As an alternative approach
for these reactions, alkane monooxygenase from Pseudomonas
putida (alkB) is able to catalyze the difficult terminal
oxyfunctionalization of alkanes selectively and under mild conditions.
Here, we report an electrosynthetic system using an alkB biocathode
which produces alcohols, epoxides, and sulfoxides through
bioelectrochemical hydroxylation, epoxidation, sulfoxidation, and
demethylation. The capacity of the alkB binding pocket to protect
internal functional groups, a lucrative capability, is also demonstrated.
By coupling our alkB biocathode with a hydrogenase bioanode and
monooxygenase (alkB) from Pseudomonas putida GPO1, an
integral membrane, nonheme, diiron enzyme, has uniquely high
selectivity for the oxidation of terminal carbons of gasoline-range
alkanes (C5-C12) and aromatic compounds; therefore, it has
been identified as an attractive enzyme for petroleum-derived
chemical conversions. Natively, alkB belongs to a system
comprised of nine proteins coded by
a
gene cluster
alkBFGHJKLST which enables P. putida to assimilate alkanes as
a carbon source. The crucial first step of this pathway, the
conversion of alkanes to fatty alcohols, involves three proteins:
the monooxygenase alkB, a soluble electron transfer protein
called rubredoxin (alkG), and a soluble NADH rubredoxin
reductase (alkT). AlkG is reduced by alkT using NADH as an
electron donor, and the reduced alkG transfers electrons to the
diiron cofactor of alkB, forming a high-valent iron-oxo species
2
using H as a clean fuel source, we have developed and characterized
a series of enzymatic fuel cells capable of oxyfunctionalization while
simultaneously producing electricity.
2
upon complexation with O . This complex enables the catalytic
hydrogen extraction from an alkane yielding a radical alkane
intermediate and an iron hydroxide, which is subsequently
attacked by the radical to generate an alcohol by the following
reaction:[7]
Petroleum, the combustion of which accounts for 45% of all
carbon dioxide emissions in the U.S., will find increasing utility as
a source of chemical synthons while its use in other sectors is
being replaced by renewable energy sources.[1] As the petroleum
industry carries out this transition, it is of critical importance to
improve sustainability and minimize the negative environmental
impact of petroleum chemical conversions which currently involve
the use of high temperatures (200-600℃), rare metals, and
organic solvents.[2] Such conditions are required due to the
inertness of carbon-hydrogen (C-H) bonds in alkane compounds,
a major component of petroleum. In addition to these conventional
methods being energy-consuming, alkane chemical conversions
typically have poor selectivity.[3] Particularly, the selective
activation of the terminal position of alkanes is a class of reactions
+
+
C
n
H
2n+2 +O
2
+ NADH + H = C
n 2
H2n+1OH + H O + NAD n=5-12
Furthermore, alkB catalyzes other terminal-position
reactions including the epoxidation of olefins, sulfoxidation of
thioethers, and demethylation of branched methyl ethers.[8] These
reactions are lucrative for the synthesis of many building blocks
widely used in fine chemical and pharmaceutical industries, such
as: 1,2-epoxyoctane, a highly reactive intermediate in organic
synthesis; cyclohexanol, a molecule further converted to nylon; 2-
phenylethanol, used in the synthesis of flavor additives or
fragrances; and 1-alkanols, used in cosmetics, food, industrial
solvents, and detergents.[6, 9] Despite the versatile activity of alkB,
a primary constraint for its use in such chemical conversions is
the continuous and costly consumption of NADH; it is therefore
with
a particular interest in the production of commodity
[
4]
chemicals. Internal sites are more readily functionalized due to
their weaker bond dissociation energies (BDE: 94.6 kcal/mol vs.
1
04 kcal/mol for n-decane), leading to the generation of unwanted
preferable to replace this cofactor with
electrochemical system.[7a]
a
mediated
by-products.[
5]
The design of more efficient synthesis routes with high
Finally, enzymatic fuel cells (EFCs) are devices using redox
enzymes to catalyze different reactions under ambient conditions
and are highly desirable alternatives for chemical production with
the spontaneous generation of power.[10] Our group has
demonstrated that the combination of a hydrogenase anode with
cathodes containing nitrogenase or aldehyde deformylating
oxygenase can be used to produce ammonia or alkanes,
regioselectivity, clean oxidants (i.e.,O
2
), aqueous media, and mild
conditions is achievable through the use of biocatalysts.[ Alkane
6]
[
a]
b]
M. Yuan, Dr. S. Abdellaoui, Dr. H. Chen, M. Kummer, Dr. C.
Malapit, Prof. S. D. Minteer: Department of Chemistry, University
of Utah, 315 S 1400 E, Salt Lake City, UT 84112, USA
Dr. S. Abdellaoui (Current Address)
Université de Reims Champagne-Ardenne, INRAE, FARE
Laboratory, 51100, Reims, France
respectively, oxidizing H
2
as a clean fuel while generating
electricity.[11]
In this work, we present a biocathode in a series of EFCs
capable of four types of oxyfunctionalization. Toluidine blue O
*
E-mail: minteer@chem.utah.edu
[
Dr. Y. Chun
(
TBO) serves as an electrochemical mediator continuously
Tianjin Institute of Industrial Biotechnology, Chinese Academy of
Sciences, 32 West 7th Avenue, Tianjin Airport Economic Area,
Tianjin, 300308 China.
Supporting information for this article is given via a link at the end
of the document.
supplying electrons to an alkB/alkG biocathode, thereby replacing
both NADH and alkT. Further, C-H bond activation is
demonstrated with varied substrates. Octane, cyclohexane, and
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