Simon J George

Simon J George

PhD, University of East Anglia, 1986

About

112
Publications
8,442
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4,598
Citations
Introduction
Metals in Biology, Biological Chemistry. Time-Resolved Infra-red Spectroscopy, X-ray Spectroscopy including EXAFS, Reaction Kinetics. Examples of Current Projects: - Small molecule (N2, H2, O2, CO, CO2, NO) activation in biology - Lanthanide chemistry in human tissue - Maturation of complex metal cofactors such as the H-cluster of [FeFe] Hydrogenase. Specialist in the application of IR spectroscopy to biological systems.
Additional affiliations
January 2010 - present
University of California, Davis
December 2002 - December 2009
Lawrence Berkeley National Laboratory
April 1994 - December 2002
John Innes Centre
Education
October 1982 - September 1985
University of East Anglia
Field of study
  • Chemistry
October 1979 - June 1982
King's College London
Field of study
  • Chemistry

Publications

Publications (112)
Article
CO-bound forms of nitrogenase are N2-reduction inhibited and likely intermediates in Fischer-Tropsch chemistry. Visible-light photolysis at 7 K was used to interrogate all three known CO-related EPR-active forms as exhibited by the α-H195Q variant of Azotobacter vinelandii nitrogenase MoFe protein. The hi(5)-CO EPR signal converted to the hi-CO EPR...
Article
Oxygen K -edge X-ray absorption spectroscopy is used routinely to study a range of solid materials. However, liquid samples are studied less frequently at the oxygen K -edge due to the combined challenges of high-vacuum conditions and oxygen contamination of window materials. A modular sample holder design with a twist-seal sample containment syste...
Article
Recent improvements in both X-ray detectors and readout speeds have led to a substantial increase in the volume of X-ray fluorescence data being produced at synchrotron facilities. This in turn results in increased challenges associated with processing and fitting such data, both temporally and computationally. Herein an abridging approach is descr...
Article
Full-text available
Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful technique that gives element-specific information about the structure of molecules. The development of a laboratory EXAFS spectrometer capable of measuring transmission spectra would be a significant advance as the technique is currently only available at synchrotron radiat...
Article
Full-text available
Organic sulfoxides, a group of compounds containing the sulfinyl SO group, are widespread in nature, important in health and disease, and used in a variety of applications in the pharmaceutical industry. We have examined the sulfur K-edge X-ray absorption near-edge spectra of a range of different sulfoxides and find that their spectra are remarkabl...
Article
Full-text available
Mo and Fe K-edge EXAFS analysis of NifQ shows the presence of a [MoFe3S4] cluster and a second independent Mo environment that includes Mo-O bonds and Mo-S bonds. Both environments are relevant to FeMo-co biosynthesis and may represent different stages of Mo biochemical transformations catalyzed by NifQ.
Article
Direct reactions of MRI contrast agent K2[Gd(DTPA)(H2O)]•5H2O (1) (H5DTPA = diethylenetriaminpentaacetic acid) with dipotassium hydrogen phosphate (K2HPO4) or phosphite (K2HPO3) result in the isolations of well-defined Gd-DTPA phosphite K6[Gd2(DTPA)2(HPO3)]•7H2O (2), or phosphate K6[Gd2(DTPA)2(HPO4)]•10H2O (3) respectively, where their lanthanum an...
Article
The properties of CO-inhibited Azotobacter vinelandii (Av) Mo-nitrogenase (N2ase) have been examined by the combined application of nuclear resonance vibrational spectroscopy (NRVS), extended x-ray absorption fine structure (EXAFS), and density functional theory (DFT). Dramatic changes in the NRVS are seen under high-CO conditions, especially in a...
Article
Full-text available
Three iron-sulfur proteins--HydE, HydF, and HydG--play a key role in the synthesis of the [2Fe](H) component of the catalytic H-cluster of FeFe hydrogenase. The radical S-adenosyl-L-methionine enzyme HydG lyses free tyrosine to produce p-cresol and the CO and CN(-) ligands of the [2Fe](H) cluster. Here, we applied stopped-flow Fourier transform inf...
Article
The biosynthesis of Fe-S clusters in Bacillus subtilis and other Gram-positive bacteria is catalyzed by the SufCDSUB system. The first step in this pathway involves the sulfur mobilization from the free amino acid cysteine to a sulfur acceptor protein SufU via a PLP-dependent cysteine desulfurase SufS. In this reaction scheme, the formation of an e...
Conference Paper
[FeFe] hydrogenases rapidly produce H2, which has stimulated interest in their application for renewable energy technologies. In addition, their catalytic iron center termed the H-cluster has inspired the design of many synthetic catalysts, albeit few with ability to evolve H2, and a better understanding of how the H-cluster is made could further t...
Article
The radical S-adenosylmethionine (SAM) enzyme HydG lyses free l-tyrosine to produce CO and CN− for the assembly of the catalytic H cluster of FeFe hydrogenase. We used electron paramagnetic resonance spectroscopy to detect and characterize HydG reaction intermediates generated with a set of 2H, 13C, and 15N nuclear spin-labeled tyrosine substrates....
Article
Azotobacter vinelandii nitrogenase Fe protein (Av2) provides a rare opportunity to investigate a [4Fe-4S] cluster at three oxidation levels in the same environment. Here, we report the structural and vibrational changes of this cluster upon reduction using a combination of NRVS and EXAFS spectroscopies with DFT calculations. Key to this work is the...
Article
The [FeFe] hydrogenase from Clostridium pasteurianum (CpI) harbors four [FeS] clusters that facilitate electron transfer to the H-cluster, a ligand-coordinated six-iron prosthetic group that catalyzes the redox interconversion of protons and H(2). Here, we have used (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the iron centers...
Article
Full-text available
We have applied 57Fe nuclear resonance vibrational spectroscopy (NRVS) for the first time to study the dynamics of Fe centers in Iron-sulfur protein crystals, including oxidized wild type rubredoxin crystals from Pyrococcus furiosus, and the MoFe protein of nitrogenase from Azotobacter vinelandii. Thanks to the NRVS selection rule, selectively prob...
Article
Full-text available
The present paper describes general principles of redox catalysis and redox regulation in two diverse systems. The first is microbial metabolism of CO by the Wood-Ljungdahl pathway, which involves the conversion of CO or H2/CO2 into acetyl-CoA, which then serves as a source of ATP and cell carbon. The focus is on two enzymes that make and utilize C...
Article
Full-text available
We have used EXAFS and NRVS spectroscopies to examine the structural changes in the FeMo-cofactor active site of the α-70(Ala) variant of Azotobacter vinelandii nitrogenase on binding and reduction of propargyl alcohol (PA). The Mo K-edge near-edge and EXAFS spectra are very similar in the presence and absence of PA, suggesting PA does not bind at...
Data
Shewanella oneidensis HydF protein sequence based on recombinant expression of the S. oneidensis hydEF open reading frame in Escherichia coli. The underlined peptide sequence corresponds to the residues added to the N-terminus of the previously published S. oneidensis HydF peptide sequence (Accession # AAN56901). The amino acids highlighted in blac...
Article
Full-text available
[FeFe] hydrogenases are promising catalysts for producing hydrogen as a sustainable fuel and chemical feedstock, and they also serve as paradigms for biomimetic hydrogen-evolving compounds. Hydrogen formation is catalyzed by the H-cluster, a unique iron-based cofactor requiring three carbon monoxide (CO) and two cyanide (CN⁻) ligands as well as a d...
Article
Organic bulk-heterojunction solar cells are being developed as a low-cost alternative to inorganic photovoltaics. A key step to producing high-efficiency bulk-heterojunction devices is film curing using either heat or a solvent atmosphere. All of the literature examining the curing process have assumed that improvement of the bulk-heterojunction mo...
Article
Fourier-transform infrared-spectroscopy (FT-IR) was used to study the photochemistry of CO-inhibited Azotobacter vinelandii Mo nitrogenase using visible light at cryogenic temperatures. The FT-IR difference spectrum of photolyzed hi-CO at 4 K comprises negative bands at 1973 cm–1 and 1679 cm–1 together with positive bands at 1711 cm–1, 2135 and 212...
Article
Revealing kinetics: For the α-70 residue of MoFe nitrogenase in Azotobacter vinelandii the impact of substitution on the CO coordination to the enzyme's active center was studied by using stopped-flow IR spectroscopy. The results suggest that in all cases the CO ligand binds to the Fe 2-3-6-7 face of the FeMo-cofactor (see picture).
Article
We have studied both the atomic and electronic structures of nitrogenase Mo-Fe proteins using EXAFS and L-edge spectroscopy. The Mo and Fe K-edge EXAFS data show not only 2.37, 2.70, 2.29, and 2.63 Å first shell Mo-S, Mo-Fe, Fe-S, and Fe-Fe distances, but also 3.8, 4.3 and 5.1 Å second shell Fe-Fe, Fe-S, and Mo-Fe interactions. These observed dista...
Article
Full-text available
The realization of hydrogenase-based technologies for renewable H(2) production is presently limited by the need for scalable and high-yielding methods to supply active hydrogenases and their required maturases. In this report, we describe an improved Escherichia coli-based expression system capable of producing 8-30 mg of purified, active [FeFe] h...
Article
Full-text available
Background Nephrogenic systemic fibrosis (NSF) is an incurable, debilitating disease found exclusively in patients with decreased kidney function and comprises a fibrosing disorder of the skin and systemic tissues. The disease is associated with exposure to gadolinium (Gd)-based contrast agents (GBCA) used in magnetic resonance imaging (MRI). Tissu...
Article
Biosynthesis of the unusual organometallic H-cluster at the active site of the [FeFe]-hydrogenase requires three accessory proteins, two of which are radical AdoMet enzymes (HydE, HydG) and one of which is a GTPase (HydF). We demonstrate here that HydG catalyzes the synthesis of CO using tyrosine as a substrate. CO production was detected by using...
Article
Full-text available
The organometallic H cluster at the active site of [FeFe]-hydrogenase consists of a 2Fe subcluster coordinated by cyanide, carbon monoxide, and a nonprotein dithiolate bridged to a [4Fe-4S] cluster via a cysteinate ligand. Biosynthesis of this cluster requires three accessory proteins, two of which (HydE and HydG) are radical S-adenosylmethionine e...
Article
Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to mediate magnetic exchange interactions between the ions. Among them are star-shaped molecules in which antiferromagnetic couplings between the central and peripheral atoms are predominantly present. Those configurations lead to an appreciable spin moment i...
Conference Paper
Polyethylenedioxythiophene Polystyrenesulphonate (PEDOT:PSS) is a highly conducting transparent polymer mixture that is used as a hole carrying electrode for nearly all organic optoelectronic devices, including OLED's and solar cells. Despite numerous electrical and morphological studies, the mechanism for charge injection and extraction from PEDOT...
Article
The molybdenum nitrogenase is responsible for most biological nitrogen fixation, a prokaryotic metabolic process that determines the global biogeochemical cycles of nitrogen and carbon. Here we describe the trafficking of molybdenum for nitrogen fixation in the model diazotrophic bacterium Azotobacter vinelandii. The genes and proteins involved in...
Article
We have surveyed the chemical utility of the near-edge structure of molybdenum X-ray absorption edges from the hard X-ray K-edge at 20,000eV down to the soft X-ray M(4,5)-edges at approximately 230eV. We compared, for each edge, the spectra of two tetrahedral anions, MoO(4)(2-) and MoS(4)(2-). We used three criteria for assessing near-edge structur...
Article
We report a comprehensive study of the electronic and magnetic properties of a star-shaped molecule comprising a MnII4O6 core. One feature of this compound is weak magnetic coupling constants compared to other similar polyoxo compounds. This leads to complicated low-lying magnetic states in which the ground state is not well separated from the uppe...
Article
NifB-co, an Fe-S cluster produced by the enzyme NifB, is an intermediate on the biosynthetic pathway to the iron molybdenum cofactor (FeMo-co) of nitrogenase. We have used Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy together with (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the structure of NifB-co w...
Article
Under intense soft X-ray irradiation, we have observed time-dependent changes in the soft X-ray spectra of virtually all the Fe coordination complexes that we have examined, indicating chemical transformation of the compound under study. Each compound, with oxidation states ranging from Fe(IV) to Fe(0), has been studied with either Fe L-edge spectr...
Article
Full-text available
Cyclic voltammetry readily visualizes the redox properties of many proteins. Net electron exchange between the protein and an electrode produces an electrical current that simultaneously quantitates and characterizes the underlying redox event(s). However, no direct information regarding the molecular origin, or consequences, of electron transfer i...
Article
We have built a 36-pixel superconducting tunnel junction X-ray spectrometer for chemical analysis of dilute samples in the soft X-ray band. It offers an energy resolution of ∼10–20eV FWHM below 1keV, a solid angle coverage of ∼10−3, and can be operated at total rates of up to ∼106counts/s. Here, we describe the spectrometer performance in speciatio...
Article
Full-text available
Cytochromes cd(1) are dimeric bacterial nitrite reductases, which contain two hemes per monomer. On reduction of both hemes, the distal ligand of heme d(1) dissociates, creating a vacant coordination site accessible to substrate. Heme c, which transfers electrons from donor proteins into the active site, has histidine/methionine ligands except in t...
Article
The NifEN protein complex serves as a molecular scaffold where some of the steps for the assembly of the iron-molybdenum cofactor (FeMo-co) of nitrogenase take place. Purified NifEN protein contains multiple metal-sulfur clusters, where the exact types, structures, or functions are still unclear. Recently, Mo that is suitable for in vitro FeMo-co b...
Article
Methyl-coenzyme M reductase (MCR) catalyzes the final step in methane biosynthesis by methanogenic archaea and contains a redox-active nickel tetrahydrocorphin, coenzyme F430, at its active site. Spectroscopic and computational methods have been used to study a novel form of the coenzyme, called F330, which is obtained by reducing F430 with sodium...
Article
Nitrogenase catalyzes a reaction critical for life, the reduction of N(2) to 2NH(3), yet we still know relatively little about its catalytic mechanism. We have used the synchrotron technique of (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the dynamics of the Fe-S clusters in this enzyme. The catalytic site FeMo-cofactor exhibit...
Article
We have built a 36-pixel high-resolution superconducting tunnel junction (STJ) soft X-ray spectrometer for chemical analysis of dilute metals by fluorescence-detected X-ray absorption spectroscopy (XAS) at the Advanced Light Source synchrotron. Soft X-ray absorption edges are preferred over traditional hard X-ray spectroscopy at the K-edges, since...
Article
Full-text available
Protein film voltammetry of Paracoccus pantotrophus respiratory nitrate reductase (NarGH) and Synechococcus elongatus assimilatory nitrate reductase (NarB) shows that reductive activation of these enzymes may be required before steady state catalysis is observed. For NarGH complementary spectroscopic studies suggest a structural context for the act...
Article
We have used (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the Fe(S(cys))(4) site in reduced and oxidized rubredoxin (Rd) from Pyrococcus furiosus (Pf). The oxidized form has also been investigated by resonance Raman spectroscopy. In the oxidized Rd NRVS, strong asymmetric Fe-S stretching modes are observed between 355 and 375 c...
Article
Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) is a bifunctional enzyme which enables archaea and bacteria to grow autotrophically on CO and hydrogen/carbon dioxide using the Wood-Ljundahl pathway. CO produced from reduction of carbon dioxide by CODH is transferred to the active site of ACS through an intramolecular tunnel, where it c...
Article
Full-text available
[NEt(4)][FeCl(4)], [P(C(6)H(5))(4)][FeCl(4)], and [NEt(4)](2)[Fe(2)S(2)Cl(4)] have been examined using (57)Fe nuclear resonance vibrational spectroscopy (NRVS). These complexes serve as simple models for Fe-S clusters in metalloproteins. The (57)Fe partial vibrational density of states (PVDOS) spectra were interpreted by computation of the normal m...
Article
High-resolution molybdenum K-edge X-ray emission spectroscopy (XES) was used to characterize the K beta(4) and K beta' ' valence-to-core transition bands in the oxo-Mo compounds K(2)MoO(4), MoO(S(2)CNEt(2))(2), and MoO(2)(S(2)CNEt(2))(2). The K beta(4) and K beta' ' emission bands are attributed to transitions to the Mo 1s core hole from molecular...
Article
The Ni-Fe site in the active membrane-bound [NiFe]-hydrogenase from Allochromatium vinosum can exist in three different redox states. In the most oxidized state (Ni(a)-S) the nickel is divalent. The most reduced state (Ni(a)-SR) likewise has Ni(2+), while the intermediate state (Ni(a)-C) has Ni(3+). The transitions between these states have been st...
Article
The reaction between hydrogen and the [NiFe]-hydrogenase from Allochromatium vinosum in its inactive form has been studied by stopped-flow infrared spectroscopy. The data, for the first time, clearly show that at room temperature enzyme in the unready state, either oxidized or reduced, does not react with hydrogen. Enzyme in the ready state reacts...
Article
Full-text available
X-ray magnetic circular dichroism (XMCD) spectroscopy is a powerful emerging technique that measures difference in absorption of left- and right-circularly polarized X-rays by a magnetized sample, often at cryogenic temperatures. It is already well established in magnetic materials science, and it is likely to become a significant tool for the inor...
Article
The hydroxylase component (MMOH) of soluble methane monooxygenase from Methylococcus capsulatus (Bath) was reduced to the diiron(II) form and then allowed to react with dioxygen to generate the diiron(IV) intermediate Q in the first phase of a double-mixing stopped-flow experiment. CD3NO2 was then introduced in the second phase of the experiment, w...
Article
Full-text available
Cytochrome c ' (cyt c ') is found in the periplasmic space of denitrifying bacteria where it is thought to mediate the transfer of NO between the nitrogen-cycle enzymes dissimilatory nitrite reductase and nitric oxide reductase. It contains a 5-coordinate (5c) His-ligated haem that shares spectroscopic and ligand-binding properties with the haem gr...
Article
This paper describes the kinetics and intimate mechanisms associated with cyanation of [2Fe3S] assemblies to give species structurally related to the subsite of all-iron hydrogenase. Stopped-flow FTIR spectroscopy has enabled the quantitation of the dynamics of five well-defined steps that experimentally illustrate the role of bridging carbonyls in...
Article
Iron(I) in biology?: one-electron oxidation of an (Fe(I)-Fe(I)) carbonyl cyanide precursor bearing a proximal thioether group leads to an (Fe(I)-Fe(II)) bridging carbonyl transient with spectral features similar to the di-iron sub-site of the CO inhibited paramagnetic centre of all-iron hydrogenase.
Article
The 5-coordinate ferrous heme of Alcaligenes xylosoxidans cytochrome c' reacts with NO to form a 6-coordinate nitrosyl intermediate (lambdaSoret at 415 nm) which subsequently converts to a 5-coordinate nitrosyl end product (lambdaSoret at 395 nm) in a rate-determining step. Stopped-flow measurements at pH 8.9, 25 degrees C, yield a rate constant fo...
Chapter
The proceedings include the Johanna Döbereiner memorial lecture, a note on the discovery in 1965 of inorganic nitrogen complexes, the keynote address, and 68 papers in 15 sections (each mostly introduced by an overview): Chemistry and biochemistry of nitrogenase; Bacterial genomics; Plant genomics; Signal transduction; Developmental biology; Signal...
Article
Full-text available
Cytochrome cd(1) is a respiratory enzyme that catalyzes the physiological one-electron reduction of nitrite to nitric oxide. The enzyme is a dimer, each monomer containing one c-type cytochrome center and one active site d(1) heme. We present stopped-flow Fourier transform infrared data showing the formation of a stable ferric heme d(1)-NO complex...