Editorial overview: Bioinorganic chemistry - ScholarWorks

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Editorial overview: Bioinorganic chemistry: Bioinorganic
catalysis for renewable energy
Mi Hee Lim and Yi Lu
Current Opinion in Chemical Biology 2015, 25:vii–viii
For a complete overview see the Issue
Available online 17th March 2015
http://dx.doi.org/10.1016/j.cbpa.2015.03.001
1367-5931/# 2015 Elsevier Ltd. All rights reserved.
Mi Hee Lim
Department of Chemistry, Ulan National
Institute of Science and Technology (UNIST),
50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan
689-798, Republic of Korea
e-mail: mhlim@unist.ac.kr
Mi Hee Lim is an Associate Professor in the
Department of Chemistry at the Ulsan
Institute of Science and Technology (UNIST),
Ulsan, Korea. She obtained her MSc degree
under Professor Wonwoo Nam at Ewha
Womans University, Seoul, Korea, and a PhD
degree under the supervision of Professor
Stephen J. Lippard at MIT. She was a TRDRP
postdoctoral fellow with Professor
Jacqueline K. Barton at Caltech. Her current
research focuses on elucidating the roles of
metals, proteins, and reactive oxygen
species in human neurodegenerative
diseases.
Yi Lu1,2
1
Department of Chemistry, University of
Illinois at Urbana-Champaign, 600 South
Mathews Ave., Urbana, IL 61801, United
States
2
Department of Biochemistry, University of
Illinois at Urbana-Champaign, 600 South
Mathews Ave., Urbana, IL 61801, United States
e-mail: yi-lu@illinois.edu
Yi Lu is Jay and Ann Schenck Professor in the
Department of Chemistry at the University of
Illinois at Urbana-Champaign. He received his
B.S. degree from Peking University, Ph.D.
degree from UCLA under Professor Joan S.
Valentine, and was a postdoctoral fellow in
Professor Harry B. Gray group at Caltech. His
research interests include (a) engineering
functional metalloproteins as catalysts in
renewable energy generation and
pharmaceuticals; (b) understanding
DNAzymes and their applications in
environmental monitoring and medical
diagnostics; and (c) directed assembly of
nanomaterials with controlled morphologies
and its applications in imaging and medicine.
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As the world population grows, with increased living standards, the consumption rate of fossil fuels and associated costs are dramatically rising. In
order to face and conquer this global energy challenge, efficient methods to
generate renewable energy are being sought after by a variety of research
groups in academia and industry. Among them, bioinorganic chemists have
been playing a prominent role because conversion of abundant resources,
such as dioxygen (O2), carbon dioxide (CO2), water, and solar light, into fuels
and other energy forms almost invariably requires metalloenzymes or bioinspired inorganic catalysts. In this issue of Current Opinion in Chemical
Biology, we present eight review articles that summarize recent progresses in
the field of renewable solar fuels and other energy-related catalysis in
bioinorganic chemistry.
A major focus in our search for sustainable energies is the transfer of solar
energy into chemical energy and the sustainable production of solar fuels,
such as hydrogen (H2) from water and carbon-based molecules from CO2
reduction. Despite much effort, metalloenzymes, such as the oxygen-evolving complex (OEC) in photosystem II (PSII), hydrogenase, carbon monoxide dehydrogenases (CODH), remain the most efficient catalysts for these
reactions, with minimal driving force or overpotential and using earthabundant metal ions. Therefore, understanding how native enzymes perform these reactions efficiently is the first step toward developing artificial
photosynthetic catalysts. While extensive attention has been paid to the role
of the primary coordination sphere in conferring enzymatic activity, Brudvig
and coworkers have reviewed experimental and computational findings of
the importance of non-covalent secondary shell residues and associated
hydrogen bonding network in controlling the water substrate exchange, Yz
electron transfer, equilibrium between the S2 isomers, formation of the S3
state, and proton and O2 release pathways in the OEC. They have shown
that these hydrogen-bond networks surrounding the OEC on the lumenal
side of the PSII protein serve to stabilize charged intermediates and regulate
the structure of the channels that allow transport of water, protons, and O2.
Additionally, the efficient interconversion of protons (H+) and electrons (e )
is required for H2 production, activation, and transfer reactions. The article
by Moore, Dahl, and Szymczak briefly illustrates the utility of the primary
and secondary coordination environments surrounding the active site of the
[Fe]-hydrogenase for the heterolysis of H2. The role of the 2-hydroxypyridine ligands, found in an iron cofactor of the [Fe]-hydrogenase, for handling
of H+/e equivalents in reductive and oxidative catalysis is discussed, along
with recent achievements in the homogeneous catalysts containing 2-hdyroxypryidine motifs.
Current Opinion in Chemical Biology 2015, 25:vii–viii
viii Bioinorganic chemistry
Along with fine control of the residues around the primary
coordination sphere within the same enzyme, the arrangement of different enzymes and their interactions
with their partners are also very important in efficient
energy conversion. Therefore, Bachmeier and Armstrong
reviewed four different strategies in assembly of hydrogenase or CODH with their light-harvesting partners, with
focus on insights gained from developing such artificial
photosynthesis systems for tight electronic integration
where both rates and efficiency are essential. Recent
efforts for the development of artificial photosynthesis,
including hybrids of natural and artificial components, are
well summarized by Fukuzumi. The article by Fukuzumi
also describes energy-efficient storage of H2 as a liquid or
solid form, which is needed for stationary and portable
H2-delivery infrastructure.
In another review article that nicely complements the
above articles, Utschig and coworkers have summarized
recent advances in designing biohybrid systems composed
of photosystem I (PSI) and different types of H2 catalysts,
including protein catalysts, such as hydrogenase, noble
metal catalysts, such as platinum-based nanomaterials, or
earth abundant molecular catalysts, such as cobaloxime.
Another innovative method includes encapsulation of a
molecular catalyst within a flavodoxin protein enabling
protein–protein interactions to control the reaction between the components in the biohybrid system. These
systems have resulted in practical O2 tolerant, earth abundant photo-generation of H2 by combining Nature’s optimized PSI light capture and conversion capabilities with
the creativity offered by synthetic chemistry.
Given the work in both understanding native enzymes
and synthesizing biomimetic complexes, it would be
interesting to compare the two systems. Ye, Neese and
coworkers have compared reaction mechanisms of the
Current Opinion in Chemical Biology 2015, 25:vii–viii
two-electron reduction of CO2 carried out by CODH and
formate dehydrogenase (FDH) with those by chemical
catalysts inspired by those enzymes. By summarizing the
similarities between the two classes of catalysts, they
offered important insights into future catalyst design,
such as the important roles of the metal-(h1-CO2) interaction and the subsequent proton-coupled electron transfer for the [NiFe] CODH activity, and of the hydride
transfer from metal-hybrids to the C-atom of CO2 to yield
formate or formic acid for the FDH functionality.
Moreover, the article by Ray, Heims, Schwalbe, and Nam
reports the recent advance in reactivity of high-valent
metal-oxo complexes related to energy conversion and
conservation processes. Particularly, the mechanistic
studies of biologically relevant metal-oxo cores, evidenced to be active intermediates during dioxygen reduction and water oxidation reactions, are focused in this
review.
In the last contribution, Lee and Karlin focus on how the
structures and nature of the metal active sites in copper
monooxygeneases can direct their reactivity toward substrates. In addition, recent efforts in the generation of
synthetic analogs containing single copper active sites are
described. Studies of copper–oxygen intermediates, proposed to be involved in reactivity of copper monooxygeneases, are also summarized. Association of electrons
and/or protons, upon formation of such intermediates, is
compared with that in aqueous O2-reduction, oxidase,
and monooxygenase processes.
We have enjoyed editing this edition of Current Opinion in
Chemical Biology and we thank all of the authors who have
contributed to this themed issue for their contributions
and hope that the readers of the issue will be as inspired
by the work as we have been.
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