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Hagen WR. Broadband EPR Spectroscopy of the Triplet State: Multi-Frequency Analysis of Copper Acetate Monohydrate. Int J Mol Sci 2023; 24:14793. [PMID: 37834243 PMCID: PMC10572876 DOI: 10.3390/ijms241914793] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2023] [Revised: 09/28/2023] [Accepted: 09/28/2023] [Indexed: 10/15/2023] Open
Abstract
Electron paramagnetic resonance spectroscopy is a long-standing method for the exploration of electronic structures of transition ion complexes. The difficulty of its analysis varies considerably, not only with the nature of the spin system, but more so with the relative magnitudes of the magnetic interactions to which the spin is subject, where particularly challenging cases ensue when two interactions are of comparable magnitude. A case in point is the triplet system S = 1 of coordination complexes with two unpaired electrons when the electronic Zeeman interaction and the electronic zero-field interaction are similar in strength. This situation occurs in the X-band spectra of the thermally excited triplet state of dinuclear copper(II) complexes, exemplified by copper acetate monohydrate. In this study, applicability of the recently developed low-frequency broadband EPR spectrometer to S = 1 systems is investigated on the analysis of multi-frequency, 0.5-16 GHz, data from [Cu(CH3COO)2H2O]2. Global fitting affords the spin Hamiltonian parameters gz = 2.365 ± 0.008; gy = 2.055 ± 0.010; gx = 2.077 ± 0.005; Az = 64 gauss; D = 0.335 ± 0.002 cm-1; E = 0.0105 ± 0.0003 cm-1. The latter two define zero-field absorptions at ca. 630, 7730, and 10,360 MHz, which show up in the spectra as one half of a sharpened symmetrical line. Overall, the EPR line shape is Lorentzian, reflecting spin-lattice relaxation, which is a combination of an unusual, essentially temperature-independent, inverted Orbach process via the S = 0 ground state, and a Raman process proportional to T2. Other broadening mechanisms are limited to at best minor contributions from a distribution in E values, and from dipolar interaction with neighboring copper pairs. Monitoring of a first-order double-quantum transition between 8 and 35 GHz shows a previously unnoticed very complex line shape behavior, which should be the subject of future research.
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Affiliation(s)
- Wilfred R Hagen
- Department of Biotechnology, Delft University of Technology, Building 58, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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Hagen WR, Louro RO. A Comparative Multi-Frequency EPR Study of Dipolar Interaction in Tetra-Heme Cytochromes. Int J Mol Sci 2023; 24:12713. [PMID: 37628894 PMCID: PMC10454114 DOI: 10.3390/ijms241612713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 08/04/2023] [Accepted: 08/09/2023] [Indexed: 08/27/2023] Open
Abstract
Distances between Fe ions in multiheme cytochromes are sufficiently short to make the intramolecular dipole-dipole interaction between hemes probable. In the analysis of EPR data from cytochromes, this interaction has thus far been ignored under the assumption that spectra are the simple sum of non-interacting components. Here, we use a recently developed low-frequency broadband EPR spectrometer to establish the extent of dipolar interaction in the example cytochromes, characterize its spectral signatures, and identify present limitations in the analysis. Broadband EPR spectra of Shewanella oneidensis MR-1 small tetraheme cytochrome (STC) have been collected over the frequency range of 0.45 to 13.11 GHz, and they have been compared to similar data from Desulfovibrio vulgaris Hildenborough cytochrome c3. The two cases are representative examples of two very different heme topologies and corresponding electron-transfer properties in tetraheme proteins. While in cytochrome c3, the six Fe-Fe distances can be sorted into two well-separated groups, those in STC are diffuse. Since the onset of dipolar interaction between Fe-Fe pairs is already observed in the X-band, the g values are determined in the simulation of the 13.11 GHz spectrum. Low-frequency spectra are analyzed with the inclusion of dipolar interaction based on available structural data on mutual distances and orientations between all hemes. In this procedure, all 24 possible assignments of individual heme spectra to heme topologies are sampled. The 24 configurations can be reduced to a few, but inspection falls short of a unique assignment, due to a remaining lack of understanding of the fine details of these complex spectra. In general, the EPR analysis suggests the four-heme system in c3 to be more rigid than that in STC, which is proposed to be related to different physiological roles in electron transfer.
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Affiliation(s)
- Wilfred R. Hagen
- Department of Biotechnology, Delft University of Technology, Building 58, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Ricardo O. Louro
- Instituto de Tecnologia Química e Biológica António Xavier (ITQB-NOVA), Universidade Nova de Lisboa, 2780-157 Oeiras, Portugal
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Hagen WR. Conversion of a Single-Frequency X-Band EPR Spectrometer into a Broadband Multi-Frequency 0.1-18 GHz Instrument for Analysis of Complex Molecular Spin Hamiltonians. Molecules 2023; 28:5281. [PMID: 37446944 DOI: 10.3390/molecules28135281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 07/01/2023] [Accepted: 07/05/2023] [Indexed: 07/15/2023] Open
Abstract
A broadband EPR spectrometer is an instrument that can be tuned to many microwave frequencies over several octaves. Its purpose is the collection of multi-frequency data, whose global analysis affords interpretation of complex spectra by means of deconvolution of frequency-dependent and frequency-independent interaction terms. Such spectra are commonly encountered, for example, from transition-metal complexes and metalloproteins. In a series of previous papers, I have described the development of broadband EPR spectrometers around a vector network analyzer. The present study reports on my endeavor to start from an existing X-band spectrometer and to reversibly re-build it into a broadband machine, in a quest to drastically reduce design effort, building costs, and operational complexity, thus bringing broadband EPR within easy reach of a wide range of researchers.
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Affiliation(s)
- Wilfred R Hagen
- Department of Biotechnology, Delft University of Technology, Building 58, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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Telser J. Linewidth, field, and frequency in electron paramagnetic resonance (EPR) spectroscopy. J Biol Inorg Chem 2022; 27:605-609. [DOI: 10.1007/s00775-022-01961-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 08/31/2022] [Indexed: 10/14/2022]
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Trindade IB, Coelho A, Cantini F, Piccioli M, Louro RO. NMR of paramagnetic metalloproteins in solution: Ubi venire, quo vadis? J Inorg Biochem 2022; 234:111871. [DOI: 10.1016/j.jinorgbio.2022.111871] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 05/16/2022] [Accepted: 05/19/2022] [Indexed: 10/18/2022]
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Bayaraa T, Gaete J, Sutiono S, Kurz J, Lonhienne T, Harmer JR, Bernhardt PV, Sieber V, Guddat L, Schenk G. Dihydroxy‐Acid Dehydratases From Pathogenic Bacteria: Emerging Drug Targets to Combat Antibiotic Resistance. Chemistry 2022; 28:e202200927. [PMID: 35535733 PMCID: PMC9543379 DOI: 10.1002/chem.202200927] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Indexed: 11/30/2022]
Abstract
There is an urgent global need for the development of novel therapeutics to combat the rise of various antibiotic‐resistant superbugs. Enzymes of the branched‐chain amino acid (BCAA) biosynthesis pathway are an attractive target for novel anti‐microbial drug development. Dihydroxy‐acid dehydratase (DHAD) is the third enzyme in the BCAA biosynthesis pathway. It relies on an Fe−S cluster for catalytic activity and has recently also gained attention as a catalyst in cell‐free enzyme cascades. Two types of Fe−S clusters have been identified in DHADs, i.e. [2Fe−2S] and [4Fe−4S], with the latter being more prone to degradation in the presence of oxygen. Here, we characterise two DHADs from bacterial human pathogens, Staphylococcus aureus and Campylobacter jejuni (SaDHAD and CjDHAD). Purified SaDHAD and CjDHAD are virtually inactive, but activity could be reversibly reconstituted in vitro (up to ∼19,000‐fold increase with kcat as high as ∼6.7 s−1). Inductively‐coupled plasma‐optical emission spectroscopy (ICP‐OES) measurements are consistent with the presence of [4Fe−4S] clusters in both enzymes. N‐isopropyloxalyl hydroxamate (IpOHA) and aspterric acid are both potent inhibitors for both SaDHAD (Ki=7.8 and 51.6 μM, respectively) and CjDHAD (Ki=32.9 and 35.1 μM, respectively). These compounds thus present suitable starting points for the development of novel anti‐microbial chemotherapeutics.
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Affiliation(s)
- Tenuun Bayaraa
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 Australia
| | - Jose Gaete
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 Australia
| | - Samuel Sutiono
- Chair of Chemistry of Biogenic resources Campus Straubing for Biotechnology and Sustainability Technical University of Munich Schulgasse 16 94315 Straubing Germany
| | - Julia Kurz
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 Australia
| | - Thierry Lonhienne
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 Australia
| | - Jeffrey R. Harmer
- Centre for Advanced Imaging The University of Queensland Brisbane 4072 Australia
| | - Paul V. Bernhardt
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 Australia
| | - Volker Sieber
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 Australia
- Chair of Chemistry of Biogenic resources Campus Straubing for Biotechnology and Sustainability Technical University of Munich Schulgasse 16 94315 Straubing Germany
| | - Luke Guddat
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 Australia
| | - Gerhard Schenk
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 Australia
- Sustainable Minerals Institute The University of Queensland Brisbane 4072 Australia
- Australian Institute for Bioengineering and Nanotechnology The University of Queensland Brisbane 4072 Australia
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Haak J, Krüger J, Abrosimov NV, Helling C, Schulz S, Cutsail Iii GE. X-Band Parallel-Mode and Multifrequency Electron Paramagnetic Resonance Spectroscopy of S = 1/2 Bismuth Centers. Inorg Chem 2022; 61:11173-11181. [PMID: 35834368 PMCID: PMC9326968 DOI: 10.1021/acs.inorgchem.2c01141] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The recent successes in the isolation and characterization of several bismuth radicals inspire the development of new spectroscopic approaches for the in-depth analysis of their electronic structure. Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for the characterization of main group radicals. However, the large electron-nuclear hyperfine interactions of Bi (209Bi, I = 9/2) have presented difficult challenges to fully interpret the spectral properties for some of these radicals. Parallel-mode EPR (B1∥B0) is almost exclusively employed for the study of S > 1/2 systems but becomes feasible for S = 1/2 systems with large hyperfine couplings, offering a distinct EPR spectroscopic approach. Herein, we demonstrate the application of conventional X-band parallel-mode EPR for S = 1/2, I = 9/2 spin systems: Bi-doped crystalline silicon (Si:Bi) and the molecular Bi radicals [L(X)Ga]2Bi• (X = Cl or I) and [L(Cl)GaBi(MecAAC)]•+ (L = HC[MeCN(2,6-iPr2C6H3)]2). In combination with multifrequency perpendicular-mode EPR (X-, Q-, and W-band frequencies), we were able to fully refine both the anisotropic g- and A-tensors of these molecular radicals. The parallel-mode EPR experiments demonstrated and discussed here have the potential to enable the characterization of other S = 1/2 systems with large hyperfine couplings, which is often challenging by conventional perpendicular-mode EPR techniques. Considerations pertaining to the choice of microwave frequency are discussed for relevant spin-systems.
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Affiliation(s)
- Julia Haak
- Max Planck Institute for Chemical Energy Conversion (CEC), Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany.,Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany
| | - Julia Krüger
- Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany.,Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany
| | - Nikolay V Abrosimov
- Leibniz-Institut für Kristallzüchtung, Max-Born Strasse 2, 12489 Berlin, Germany
| | - Christoph Helling
- Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany.,Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany
| | - Stephan Schulz
- Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany.,Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany
| | - George E Cutsail Iii
- Max Planck Institute for Chemical Energy Conversion (CEC), Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany.,Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany
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Hagen WR. Low-frequency EPR of ferrimyoglobin fluoride and ferrimyoglobin cyanide: a case study on the applicability of broadband analysis to high-spin hemoproteins and to HALS hemoproteins. J Biol Inorg Chem 2022; 27:497-507. [PMID: 35802192 PMCID: PMC9399021 DOI: 10.1007/s00775-022-01948-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Accepted: 06/04/2022] [Indexed: 11/29/2022]
Abstract
An EPR spectrometer has been developed that can be tuned to many frequencies in the range of ca 0.1–15 GHz. Applicability has been tested on ferrimyoglobin fluoride (MbF) and ferrimyoglobin cyanide (MbCN). MbF has a high-spin (S = 5/2) spectrum with 19F superhyperfine splitting that is only resolved in X-band along the heme normal. Low-frequency EPR also resolves the splitting in the heme plane. Measurement of linewidth as a function of frequency provides the basis for an analysis of inhomogeneous broadening in terms of g-strain, zero-field distribution, unresolved superhyperfine splittings and dipolar interaction. Rhombicity in the g tensor is found to be absent. MbCN (S = 1/2) has a highly anisotropic low spin (HALS) spectrum for which gx cannot be determined unequivocally in X-band. Low-frequency EPR allows for measurement of the complete spectrum and determination of the g-tensor.
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Affiliation(s)
- Wilfred R Hagen
- Department of Biotechnology, Delft University of Technology, Delft, The Netherlands.
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Orr-Ewing AJ, Crawford TD, Zanni MT, Hartland G, Shea JE. A Venue for Advances in Experimental and Theoretical Methods in Physical Chemistry. J Phys Chem A 2022; 126:177-179. [PMID: 35045707 DOI: 10.1021/acs.jpca.1c10457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Andrew J Orr-Ewing
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K
| | - T Daniel Crawford
- Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States.,Molecular Sciences Software Institute, 1880 Pratt Drive, Suite 1100, Blacksburg, Virginia 24060, United States
| | - Martin T Zanni
- Department of Chemistry, University of Wisconsin─Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Gregory Hartland
- University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Joan-Emma Shea
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United States.,Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106, United States
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