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Heidinger L, Perez K, Spatzal T, Einsle O, Weber S, Rees DC, Schleicher E. Analysis of early intermediate states of the nitrogenase reaction by regularization of EPR spectra. Nat Commun 2024; 15:4041. [PMID: 38740794 DOI: 10.1038/s41467-024-48271-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Accepted: 04/25/2024] [Indexed: 05/16/2024] Open
Abstract
Due to the complexity of the catalytic FeMo cofactor site in nitrogenases that mediates the reduction of molecular nitrogen to ammonium, mechanistic details of this reaction remain under debate. In this study, selenium- and sulfur-incorporated FeMo cofactors of the catalytic MoFe protein component from Azotobacter vinelandii are prepared under turnover conditions and investigated by using different EPR methods. Complex signal patterns are observed in the continuous wave EPR spectra of selenium-incorporated samples, which are analyzed by Tikhonov regularization, a method that has not yet been applied to high spin systems of transition metal cofactors, and by an already established grid-of-error approach. Both methods yield similar probability distributions that reveal the presence of at least four other species with different electronic structures in addition to the ground state E0. Two of these species were preliminary assigned to hydrogenated E2 states. In addition, advanced pulsed-EPR experiments are utilized to verify the incorporation of sulfur and selenium into the FeMo cofactor, and to assign hyperfine couplings of 33S and 77Se that directly couple to the FeMo cluster. With this analysis, we report selenium incorporation under turnover conditions as a straightforward approach to stabilize and analyze early intermediate states of the FeMo cofactor.
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Affiliation(s)
- Lorenz Heidinger
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Kathryn Perez
- Howard Hughes Medical Institute (HHMI), California Institute of Technology, Division of Chemistry and Chemical Engineering, Pasadena, CA, USA
| | - Thomas Spatzal
- Howard Hughes Medical Institute (HHMI), California Institute of Technology, Division of Chemistry and Chemical Engineering, Pasadena, CA, USA
| | - Oliver Einsle
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Stefan Weber
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Douglas C Rees
- Howard Hughes Medical Institute (HHMI), California Institute of Technology, Division of Chemistry and Chemical Engineering, Pasadena, CA, USA.
| | - Erik Schleicher
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.
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Cineus R, Abozeid SM, Sokolow GE, Spernyak JA, Morrow JR. Fe(III) T1 MRI Probes Containing Phenolate or Hydroxypyridine-Appended Triamine Chelates and a Coordination Site for Bound Water. Inorg Chem 2023; 62:16513-16522. [PMID: 37748050 DOI: 10.1021/acs.inorgchem.3c02344] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/27/2023]
Abstract
Fe(III) complexes containing a triamine framework and phenolate or hydroxypyridine donors are characterized and studied as T1 MRI probes. In contrast to most Fe(III) MRI probes of linear chelates reported to date, the ligands reported here are pentadentate to give six-coordinate complexes with a coordination site for inner-sphere water. The crystal structure of the complex containing unsubstituted phenolate donors, Fe(L1)Cl, shows a six-coordinate iron center and contains a chloride ligand that is displaced in water. Two additional derivatives are sufficiently water-soluble for study as MRI probes, including a complex with a hydroxypyridine group, Fe(L2), and a hydroxybenzoic acid group, Fe(L3). The pH potentiometric titrations give protonation constants of 7.2 and 7.5 for Fe(L2) and Fe(L3), respectively, which are assigned to deprotonation of the bound water. Changes in the electronic absorbance spectra of the complexes as a function of pH are consistent with the deprotonation of phenol pendants at acidic pH values. However, the inner-sphere water ligand of Fe(L2) and Fe(L3) does not exchange rapidly on the NMR timescale at pH 6.0 or 7.4, as shown by variable-temperature 17O NMR spectroscopy. The pH-dependent proton relaxivity profiles show a maximum in relaxivity at a near-neutral pH, suggesting that exchange of the protons of the bound water is an important contribution. Competitive binding studies with ethylenediaminetetraacetic acid (EDTA) show effective stability constants for Fe(L2) and Fe(L3) at pH 7.4 with log K values of 21.1 and 20.5, respectively. These two complexes are kinetically inert in carbonate phosphate buffer at 37 °C for several hours but transfer iron to transferrin. Fe(L2) and Fe(L3) show enhanced contrast in T1-weighted imaging analyses in BALB/c mice. These studies show that Fe(L2) clears through mixed renal and hepatobiliary routes, while Fe(L3) has a similar pharmacokinetic clearance profile to a macrocyclic Gd(III) contrast agent.
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Affiliation(s)
- Roy Cineus
- Department of Chemistry, University at Buffalo, The State University of New York Amherst, New York 14260, United States
| | - Samira M Abozeid
- Department of Chemistry, Faculty of Science, Mansoura University, El-Gomhoria Street, 35516 Mansoura, Egypt
| | - Gregory E Sokolow
- Department of Chemistry, University at Buffalo, The State University of New York Amherst, New York 14260, United States
| | - Joseph A Spernyak
- Department of Cell Stress Biology, Roswell Park Comprehensive Cancer Center, Buffalo, New York 14263, United States
| | - Janet R Morrow
- Department of Chemistry, University at Buffalo, The State University of New York Amherst, New York 14260, United States
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Zhang N, Guo Q, Ye W, Feng R, Yuan H. Temperature Fluctuations Compensation with Multi-Frequency Synchronous Manipulation for a NV Magnetometer in Fiber-Optic Scheme. SENSORS (BASEL, SWITZERLAND) 2022; 22:5218. [PMID: 35890898 PMCID: PMC9320826 DOI: 10.3390/s22145218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 07/09/2022] [Accepted: 07/10/2022] [Indexed: 06/15/2023]
Abstract
Nitrogen-vacancy (NV) centers in diamonds play a large role in advanced quantum sensing with solid-state spins for potential miniaturized and portable application scenarios. With the temperature sensitivity of NV centers, the temperature fluctuations caused by the unknown environment and the system itself will mix with the magnetic field measurement. In this research, the temperature-sensitive characteristics of different diamonds, alongside the temperature noise generated by a measurement system, were tested and analyzed with a homemade NV magnetometer in a fiber-optic scheme. In this work, a multi-frequency synchronous manipulation method for resonating with the NV centers in all axial directions was proposed to compensate for the temperature fluctuations in a fibered NV magnetic field sensing scheme. The symmetrical features of the resonance lines of the NV centers, the common-mode fluctuations including temperature fluctuations, underwent effective compensation and elimination. The fluorescence change was reduced to 1.0% by multi-frequency synchronous manipulation from 5.5% of the single-frequency manipulation within a ±2 °C temperature range. Additionally, the multi-frequency synchronous manipulation improved the fluorescence contrast and the magnetic field measurement SNR through an omnidirectional manipulation scheme. It was very important to compensate for the temperature fluctuations, caused by both internal and external factors, to make use of the NV magnetometer in fiber-optic schemes' practicality. This work will promote the rapid development and widespread applications of quantum sensing based on various systems and principles.
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Affiliation(s)
- Ning Zhang
- Research Center for Quantum Sensing, Intelligent Perception Research Institute, Zhejiang Lab, Hangzhou 310000, China;
| | - Qiang Guo
- Research Center for Quantum Sensing, Intelligent Perception Research Institute, Zhejiang Lab, Hangzhou 310000, China;
| | - Wen Ye
- Division of Mechanics and Acoustic Metrology, National Institute of Metrology, Beijing 100029, China;
| | - Rui Feng
- The School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing 100191, China;
- Hangzhou Innovation Institute, Beihang University, Hangzhou 310000, China
| | - Heng Yuan
- The School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing 100191, China;
- Hangzhou Innovation Institute, Beihang University, Hangzhou 310000, China
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4
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Gompa TP, Greer SM, Rice NT, Jiang N, Telser J, Ozarowski A, Stein BW, La Pierre HS. High-Frequency and -Field Electron Paramagnetic Resonance Spectroscopic Analysis of Metal-Ligand Covalency in a 4f 7 Valence Series (Eu 2+, Gd 3+, and Tb 4+). Inorg Chem 2021; 60:9064-9073. [PMID: 34106710 DOI: 10.1021/acs.inorgchem.1c01062] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The recent isolation of molecular tetravalent lanthanide complexes has enabled renewed exploration of the effect of oxidation state on the single-ion properties of the lanthanide ions. Despite the isotropic nature of the 8S ground state in a tetravalent terbium complex, [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4], preliminary X-band electron paramagnetic resonance (EPR) measurements on tetravalent terbium complexes show rich spectra with broad resonances. The complexity of these spectra highlights the limits of conventional X-band EPR for even qualitative determination of zero-field splitting (ZFS) in these complexes. Therefore, we report the synthesis and characterization of a novel valence series of 4f7 molecular complexes spanning three oxidation states (Eu2+, Gd3+, and Tb4+) featuring a weak-field imidophosphorane ligand system, and employ high-frequency and -field electron paramagnetic resonance (HFEPR) to obtain quantitative values for ZFS across this valence series. The series was designed to minimize deviation in the first coordination sphere from the pseudotetrahedral geometry in order to directly interrogate the role of metal identity and charge on the complexes' electronic structures. These HFEPR studies are supported by crystallographic analysis and quantum-chemical calculations to assess the relative covalent interactions in each member of this valence series and the effect of the oxidation state on the splitting of the ground state and first excited state.
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Affiliation(s)
| | - Samuel M Greer
- Los Alamos National Laboratory (LANL), Los Alamos, New Mexico 87545, United States
| | | | | | - Joshua Telser
- Department of Biological, Physical and Health Sciences, Roosevelt University, Chicago, Illinois 60605, United States
| | - Andrew Ozarowski
- National High Magnetic Field Laboratory (NHMFL), Florida State University, Tallahassee, Florida 32310, United States
| | - Benjamin W Stein
- Los Alamos National Laboratory (LANL), Los Alamos, New Mexico 87545, United States
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Azarkh M, Gast P, Mason AB, Groenen EJJ, Mathies G. Analysis of the EPR spectra of transferrin: the importance of a zero-field-splitting distribution and 4 th-order terms. Phys Chem Chem Phys 2019; 21:16937-16948. [PMID: 31339131 DOI: 10.1039/c9cp02626f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Multi-frequency EPR spectroscopy can provide high-level structural information on high-spin Fe3+ sites in proteins and enzymes. Unfortunately, analysis of the EPR spectra of these spin systems is hindered by the presence of broad distributions in the zero-field-splitting (ZFS) parameters, which reflect conformational heterogeneity of the iron sites. We present the analysis of EPR spectra of high-spin Fe3+ bound to human serum transferrin. We apply a method termed the grid-of-errors to extract the distributions of the individual ZFS parameters from EPR spectra recorded in the high-field limit at a microwave frequency of 275 GHz. Study of a series of transferrin variants shows that the ZFS distributions are as characteristic of the structure of a high-spin Fe3+ site as the ZFS parameters themselves. Simulations based on the extracted ZFS distributions reproduce spectra recorded at 34 GHz (Q band) and 9.7 GHz (X band), including subtle variations that were previously difficult to quantify. The X-band spectrum of transferrin shows a characteristic double peak, which has puzzled researchers for decades. We show that the double peak is uniquely related to the term B4-3O4-3(S) in the spin Hamiltonian. Our method is generally applicable in the analysis of spectra that arise from a broad distribution of parameters.
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Affiliation(s)
- Mykhailo Azarkh
- Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany.
| | - Peter Gast
- Department of Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, PO Box 9504, 2300 RA Leiden, The Netherlands
| | - Anne B Mason
- Department of Biochemistry, University of Vermont College of Medicine, Burlington, VT 05405, USA
| | - Edgar J J Groenen
- Department of Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, PO Box 9504, 2300 RA Leiden, The Netherlands
| | - Guinevere Mathies
- Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany.
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Clayton JA, Keller K, Qi M, Wegner J, Koch V, Hintz H, Godt A, Han S, Jeschke G, Sherwin MS, Yulikov M. Quantitative analysis of zero-field splitting parameter distributions in Gd(iii) complexes. Phys Chem Chem Phys 2018; 20:10470-10492. [PMID: 29617015 DOI: 10.1039/c7cp08507a] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The magnetic properties of paramagnetic species with spin S > 1/2 are parameterized by the familiar g tensor as well as "zero-field splitting" (ZFS) terms that break the degeneracy between spin states even in the absence of a magnetic field. In this work, we determine the mean values and distributions of the ZFS parameters D and E for six Gd(iii) complexes (S = 7/2) and critically discuss the accuracy of such determination. EPR spectra of the Gd(iii) complexes were recorded in glassy frozen solutions at 10 K or below at Q-band (∼34 GHz), W-band (∼94 GHz) and G-band (240 GHz) frequencies, and simulated with two widely used models for the form of the distributions of the ZFS parameters D and E. We find that the form of the distribution of the ZFS parameter D is bimodal, consisting roughly of two Gaussians centered at D and -D with unequal amplitudes. The extracted values of D (σD) for the six complexes are, in MHz: Gd-NO3Pic, 485 ± 20 (155 ± 37); Gd-DOTA/Gd-maleimide-DOTA, -714 ± 43 (328 ± 99); iodo-(Gd-PyMTA)/MOMethynyl-(Gd-PyMTA), 1213 ± 60 (418 ± 141); Gd-TAHA, 1361 ± 69 (457 ± 178); iodo-Gd-PCTA-[12], 1861 ± 135 (467 ± 292); and Gd-PyDTTA, 1830 ± 105 (390 ± 242). The sign of D was adjusted based on the Gaussian component with larger amplitude. We relate the extracted P(D) distributions to the structure of the individual Gd(iii) complexes by fitting them to a model that superposes the contribution to the D tensor from each coordinating atom of the ligand. Using this model, we predict D, σD, and E values for several additional Gd(iii) complexes that were not measured in this work. The results of this paper may be useful as benchmarks for the verification of quantum chemical calculations of ZFS parameters, and point the way to designing Gd(iii) complexes for particular applications and estimating their magnetic properties a priori.
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Affiliation(s)
- Jessica A Clayton
- University of California, Santa Barbara, Department of Physics, Santa Barbara, CA, USA.
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Nohr D, Franz S, Rodriguez R, Paulus B, Essen LO, Weber S, Schleicher E. Extended Electron-Transfer in Animal Cryptochromes Mediated by a Tetrad of Aromatic Amino Acids. Biophys J 2017; 111:301-311. [PMID: 27463133 DOI: 10.1016/j.bpj.2016.06.009] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Revised: 05/24/2016] [Accepted: 06/10/2016] [Indexed: 02/06/2023] Open
Abstract
The cryptochrome/photolyase protein family possesses a conserved triad of tryptophans that may act as a molecular wire to transport electrons from the protein surface to the FAD cofactor for activation and/or signaling-state formation. Members from the animal (and animal-like) cryptochrome subclade use this process in a light-induced fashion in a number of exciting responses, such as the (re-)setting of circadian rhythms or magnetoreception; however, electron-transfer pathways have not been explored in detail yet. Therefore, we present an in-depth time-resolved optical and electron-paramagnetic resonance spectroscopic study of two cryptochromes from Chlamydomonas reinhardtii and Drosophila melanogaster. The results do not only reveal the existence of a fourth, more distant aromatic amino acid that serves as a terminal electron donor in both proteins, but also show that a tyrosine is able to fulfill this very role in Chlamydomonas reinhardtii cryptochrome. Additionally, exchange of the respective fourth aromatic amino acid to redox-inactive phenylalanines still leads to light-induced radical pair formation; however, the lifetimes of these species are drastically reduced from the ms- to the μs-range. The results presented in this study open up a new chapter, to our knowledge, in the diversity of electron-transfer pathways in cryptochromes. Moreover, they could explain unique functions of animal cryptochromes, in particular their potential roles in magnetoreception because magnetic-field effects of light-induced radical pairs strongly depend on distance and orientation parameters.
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Affiliation(s)
- Daniel Nohr
- Institute of Physical Chemistry, University of Freiburg, Freiburg, Germany
| | | | - Ryan Rodriguez
- Institute of Physical Chemistry, University of Freiburg, Freiburg, Germany
| | - Bernd Paulus
- Institute of Physical Chemistry, University of Freiburg, Freiburg, Germany
| | | | - Stefan Weber
- Institute of Physical Chemistry, University of Freiburg, Freiburg, Germany
| | - Erik Schleicher
- Institute of Physical Chemistry, University of Freiburg, Freiburg, Germany.
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