Engineering topics
Publications and source records attributed to Jones, Anne K..
Histidine coordination of the distal [4Fe–4S] cluster in [FeFe]-hydrogenase was demonstrated to tune the cluster spin-states, spin-pairing and surrounding molecular orbitals to enable more facile electron transfer compared to cysteine coordination.
Hydrogenases show a wide range of catalytic rates and biases in reversible hydrogen gas oxidation catalysis. The interactions of the iron-sulfur-containing catalytic site with the local protein environment are thought to contribute to differences in catalytic reactivity, but this has not been demonstrated. The microbe Clostridium pasteurianum produces three [FeFe]-hydrogenases that differ in 'catalytic bias' by exerting a disproportionate rate acceleration in one direction or the other that spans a remarkable 6 orders of magnitude. The combination of high-resolution structural work, biochemical analyses, and computational modeling indicates that protein secondary interactions directly influence the relative stabilization/destabilization of different oxidation states of the active site metal cluster. This selective stabilization or destabilization of oxidation states can preferentially promote hydrogen oxidation or proton reduction and represents a simple yet elegant model by which a protein catalytic site can confer catalytic bias.
Electron bifurcation, or the coupling of exergonic and endergonic oxidation-reduction reactions, was discovered by Peter Mitchell and provides an elegant mechanism to rationalize and understand the logic that underpins the Q cycle of the respiratory chain. Thought to be a unique reaction of respiratory complex III for nearly 40 years, about a decade ago Wolfgang Buckel and Rudolf Thauer discovered that flavin-based electron bifurcation is also an important component of anaerobic microbial metabolism. Their discovery spawned a surge of research activity, providing a basis to understand flavin-based bifurcation, forging fundamental parallels with Mitchell's Q cycle and leading to the proposal of metal-based bifurcating enzymes. New insights into the mechanism of electron bifurcation provide a foundation to establish the unifying principles and essential elements of this fascinating biochemical phenomenon.
Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. Here, a key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.
[FeFe]- and [NiFe]-hydrogenases are two classes of enzymes that couple the reversible reduction of protons to the production of hydrogen gas. While these enzymes have unique taxonomic distributions and differences in their structure, function, maturation, and evolutionary history, they nevertheless share important similarities and may both be of critical importance for photobiological hydrogen production. Here, the structural and functional diversity of both types of hydrogenases are discussed in light of their phylogenetic and metabolic contexts. Overviews of the mechanisms of hydrogen activation at the respective active sites are given and provide insight into the role of the surrounding protein coordination sphere in catalysis and tuning reactivity. The distinct maturation pathways of both the [FeFe]- and [NiFe]-hydrogenases are described, revealing unique processes for assembling diatomic carbon monoxide and cyanide ligands onto Fe atoms, a key feature of the active sites that facilitates hydrogen activation during turnover conditions. Finally, a discussion of bifurcating [FeFe]- and [NiFe]-hydrogenases sheds light on this recently characterized group of enzymes that may hold a profound advantage at energetically efficient hydrogen production.
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To probe the influence of redox non‐innocent ligands on a well‐known class of [FeFe]‐hydrogenase models, three new asymmetrically disubstituted diiron complexes of the general formula (µ‐SRS)[Fe(CO) 3 ][Fe(CO)(N‐N)] {SRS = propane‐1,3‐dithiolate (pdt) or benzene‐1,2‐dithiolate (bdt), and N‐N = 2,2′‐bipyridine (bipy) or 2,2′‐bipyrimidine (bpym)} have been synthesized from their parent hexacarbonyls and characterized. The new complexes, (µ‐pdt)Fe 2 (CO) 4 (κ 2 ‐bpym) ( 2 ), (µ‐bdt)Fe 2 (CO) 4 (κ 2 ‐bipy) ( 3 ), and (µ‐bdt)Fe 2 (CO) 4 (κ 2 ‐bpym) ( 4 ), were fully characterized by spectroscopic and electrochemical techniques, and the results are compared to those of a related complex, (µ‐pdt)Fe 2 (CO) 4 (κ 2 ‐bipy) ( 1 ). The crystal structures of 2 – 4 show that, in each complex, the two iron units are in an eclipsed orientation, and the N‐N ligand lies in the basal plane. IR spectra and electrochemical analyses indicate that electron density at the iron centers decreases in the order 1 > 2 > 3 > 4 . Furthermore, compound 2 undergoes a ligand‐centered reduction at the same potential that the hexacarbonyl precursor undergoes its first reduction. However, unlike the 2,2′‐bipy derivatives 1 and 3 , the 2,2′‐bpym complexes 2 and 4 are not effective catalysts for electrochemical proton reduction from acetic acid.
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