1
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Rogers CJ, Bogdanov A, Seal M, Thornton ME, Su XC, Natrajan LS, Goldfarb D, Bowen AM. Frequency swept pulses for the enhanced resolution of ENDOR spectra detecting on higher spin transitions of Gd(III). JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 351:107447. [PMID: 37119743 DOI: 10.1016/j.jmr.2023.107447] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Revised: 04/04/2023] [Accepted: 04/08/2023] [Indexed: 05/29/2023]
Abstract
Half-Integer High Spin (HIHS) systems with zero-field splitting (ZFS) parameters below 1 GHz are generally dominated by the spin |─1/2>→|+1/2 > central transition (CT). Accordingly, most pulsed Electron Paramagnetic Resonance (EPR) experiments are performed at this position for maximum sensitivity. However, in certain cases it can be desirable to detect higher spin transitions away from the CT in such systems. Here, we describe the use of frequency swept Wideband, Uniform Rate, Smooth Truncation (WURST) pulses for transferring spin population from the CT, and other transitions, of Gd(III) to the neighbouring higher spin transition |─3/2>→|─1/2 > at Q- and W-band frequencies. Specifically, we demonstrate this approach to enhance the sensitivity of 1H Mims Electron-Nuclear Double Resonance (ENDOR) measurements on two model Gd(III) aryl substituted 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) complexes, focusing on transitions other than the CT. We show that an enhancement factor greater than 2 is obtained for both complexes at Q- and W-band frequencies by the application of two polarising pulses prior to the ENDOR sequence. This is in agreement with simulations of the spin dynamics of the system during WURST pulse excitation. The technique demonstrated here should allow more sensitive experiments to be measured away from the CT at higher operating temperatures, and be combined with any relevant pulse sequence.
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Affiliation(s)
- Ciarán J Rogers
- Department of Chemistry, Photon Science Institute and the National Research Facility for Electron Paramagnetic Resonance, School of Natural Sciences, The University of Manchester, Manchester M13 9PL, UK
| | - Alexey Bogdanov
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Manas Seal
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Matthew E Thornton
- Department of Chemistry, Photon Science Institute and the National Research Facility for Electron Paramagnetic Resonance, School of Natural Sciences, The University of Manchester, Manchester M13 9PL, UK
| | - Xun-Cheng Su
- State Key Laboratory of Elemento-Organic Chemistry, Tianjin Key Laboratory of Biosensing and Molecular Recognition College of Chemistry, Nankai University, Tianjin 300071, China
| | - Louise S Natrajan
- Department of Chemistry, Photon Science Institute and the National Research Facility for Electron Paramagnetic Resonance, School of Natural Sciences, The University of Manchester, Manchester M13 9PL, UK
| | - Daniella Goldfarb
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 7610001, Israel.
| | - Alice M Bowen
- Department of Chemistry, Photon Science Institute and the National Research Facility for Electron Paramagnetic Resonance, School of Natural Sciences, The University of Manchester, Manchester M13 9PL, UK.
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2
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Salvadori E, Bruzzese PC, Giamello E, Chiesa M. Single Metal Atoms on Oxide Surfaces: Assessing the Chemical Bond through 17O Electron Paramagnetic Resonance. Acc Chem Res 2022; 55:3706-3715. [PMID: 36442497 PMCID: PMC9774661 DOI: 10.1021/acs.accounts.2c00606] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
ConspectusEven in the gas phase single atoms possess catalytic properties, which can be crucially enhanced and modulated by the chemical interaction with a solid support. This effect, known as electronic metal-support interaction, encompasses charge transfer, orbital overlap, coordination structure, etc., in other words, all the crucial features of the chemical bond. These very features are the object of this Account, with specific reference to open-shell (paramagnetic) single metal atoms or ions on oxide supports. Such atomically dispersed species are part of the emerging class of heterogeneous catalysts known as single-atom catalysts (SACs). In these materials, atomic dispersion ensures maximum atom utilization and uniform active sites, whereby the nature of the chemical interaction between the metal and the oxide surface modulates the catalytic activity of the metal active site by tuning the energy of the frontier orbitals. A comprehensive set of examples includes fourth period metal atoms and ions in zeolites on insulating (e.g., MgO) or reducible (e.g., TiO2) oxides and are among the most relevant catalysts for a wealth of key processes of industrial and environmental relevance, from the abatement of NOx to the selective oxidation of hydrocarbons and the conversion of methane to methanol.There exist several spectroscopic techniques able to inform on the geometric and electronic structure of isolated single metal ion sites, but either they yield information averaged over the bulk or they lack description of the intimate features of chemical bonding, which include covalency, ionicity, electron and spin delocalization. All of these can be recovered at once by measuring the magnetic interactions between open-shell metals and the surrounding nuclei with Electron Paramagnetic Resonance (EPR) spectroscopy. In the case of oxides, this entails the synthesis of 17O isotopically enriched materials. We have established 17O EPR as a unique source of information about the local binding environment around oxygen of magnetic atoms or ions on different oxidic supports to rationalize structure-property relationships. Here, we will describe strategies for 17O surface enrichments and approaches to monitor the state of charge and spin delocalization of atoms or ions from K to Zn dispersed on oxide surfaces characterized by different chemical properties (i.e., basicity or reducibility). Emphasis is placed on chemical insight at the atomic-scale level achieved by 17O EPR, which is a crucial step in understanding the structure-property relationships of single metal atom catalysts and in enabling efficient design of future materials for a range of end uses.
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Affiliation(s)
- Enrico Salvadori
- Department
of Chemistry and NIS Centre of Excellence, University of Turin, via Giuria 9, 10125 Torino, Italy
| | - Paolo Cleto Bruzzese
- Department
of Chemistry and NIS Centre of Excellence, University of Turin, via Giuria 9, 10125 Torino, Italy,Felix
Bloch Institute for Solid State Physics, Leipzig University, Linnéstr. 5, 04103 Leipzig, Germany
| | - Elio Giamello
- Department
of Chemistry and NIS Centre of Excellence, University of Turin, via Giuria 9, 10125 Torino, Italy
| | - Mario Chiesa
- Department
of Chemistry and NIS Centre of Excellence, University of Turin, via Giuria 9, 10125 Torino, Italy,E-mail:
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3
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Váradi B, Lihi N, Bunda S, Nagy A, Simon G, Kéri M, Papp G, Tircsó G, Esteban-Gómez D, Platas-Iglesias C, Kálmán FK. Physico-Chemical Characterization of a Highly Rigid Gd(III) Complex Formed with a Phenanthroline Derivative Ligand. Inorg Chem 2022; 61:13497-13509. [PMID: 35972786 DOI: 10.1021/acs.inorgchem.2c02050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The discovery of the nephrogenic systemic fibrosis (NSF) and its link with the in vivo dissociation of certain Gd(III)-based contrast agents (CAs) applied in the magnetic resonance imaging (MRI) induced a still growing research to replace the compromised agents with safer alternatives. In recent years, several ligands were designed to exploit the luminescence properties of the lanthanides, containing structurally constrained aromatic moieties, which may form rigid Gd(III) complexes. One of these ligands is (1,10-phenanthroline-2,9-diyl)bis(methyliminodiacetic acid) (H4FENTA) designed and synthesized to sensitize Eu(III) and Tb(III) luminescence. Our results show that the conditional stability of the [Gd(FENTA)]- chelate calculated for physiological pH (pGd = 19.7) is similar to those determined for [Gd(DTPA)]2- (pGd = 19.4) and [Gd(DOTA)]- (pGd = 20.1), routinely used in the clinical practice. The [Gd(FENTA)]- complex is remarkably inert with respect to its dissociation (t1/2 = 872 days at pH = 7 and 25 °C); furthermore, its relaxivity values determined at different field strengths and temperatures (e.g., r1p = 4.3 mM-1s-1at 60 MHz and 37 °C) are ca. one unit higher than those of [Gd(DTPA)]2- (r1p = 3.4 mM-1 s-1) and [Gd(DOTA)]- (r1p = 3.1 mM-1 s-1) under the same conditions. Moreover, significant improvement on the relaxivity was observed in the presence of serum proteins (r1p = 6.9 mM-1 s-1 at 60 MHz and 37 °C). The luminescence lifetimes recorded in H2O and D2O solutions indicate the presence of a water molecule (q = 1) in the inner sphere of the complex directly coordinated to the metal ion, possessing a relatively high water exchange rate (kex298 = 29(2) × 106 s-1). The acceleration of the water exchange can be explained by the steric compression around the water binding site due to the rigid structure of the complex, which was supported by DFT calculations. On the basis of these results, ligands containing a phenanthroline platform have great potential in the design of safer Gd(III) agents for MRI.
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Affiliation(s)
- Balázs Váradi
- Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary.,Doctoral School of Chemistry, Faculty of Science and Technology, University of Debrecen, Egyetem tér 1, Debrecen H-4032, Hungary
| | - Norbert Lihi
- ELKH-DE Mechanisms of Complex Homogeneous and Heterogeneous Chemical Reactions Research Group, Department of Inorganic and Analytical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary
| | - Szilvia Bunda
- Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary
| | - Antónia Nagy
- Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary
| | - Gréta Simon
- Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary
| | - Mónika Kéri
- Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary
| | - Gábor Papp
- Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary
| | - Gyula Tircsó
- Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary
| | - David Esteban-Gómez
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química, Facultade de Ciencias, Univer-sidade da Coruña, A Coruña, Galicia 15071, Spain
| | - Carlos Platas-Iglesias
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química, Facultade de Ciencias, Univer-sidade da Coruña, A Coruña, Galicia 15071, Spain
| | - Ferenc K Kálmán
- Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Debrecen H-4032, Hungary
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4
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Hecker F, Stubbe J, Bennati M. Detection of Water Molecules on the Radical Transfer Pathway of Ribonucleotide Reductase by 17O Electron-Nuclear Double Resonance Spectroscopy. J Am Chem Soc 2021; 143:7237-7241. [PMID: 33957040 PMCID: PMC8154519 DOI: 10.1021/jacs.1c01359] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Indexed: 12/19/2022]
Abstract
The role of water in biological proton-coupled electron transfer (PCET) is emerging as a key for understanding mechanistic details at atomic resolution. Here we demonstrate 17O high-frequency electron-nuclear double resonance (ENDOR) in conjunction with H217O-labeled protein buffer to establish the presence of ordered water molecules at three radical intermediates in an active enzyme complex, the α2β2 E. coli ribonucleotide reductase. Our data give unambiguous evidence that all three, individually trapped, intermediates are hyperfine coupled to one water molecule with Tyr-O···17O distances in the range 2.8-3.1 Å. The availability of this structural information will allow for quantitative models of PCET in this prototype enzyme. The results also provide a spectroscopic signature for water H-bonded to a tyrosyl radical.
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Affiliation(s)
- Fabian Hecker
- Max
Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - JoAnne Stubbe
- Department
of Chemistry, Massachusetts Institute of
Technology, Cambridge, Massachusetts 20139, United States
| | - Marina Bennati
- Max
Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
- Department
of Chemistry, Georg-August-University, 37077 Göttingen, Germany
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5
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Racow EE, Kreinbihl JJ, Cosby AG, Yang Y, Pandey A, Boros E, Johnson CJ. General Approach to Direct Measurement of the Hydration State of Coordination Complexes in the Gas Phase: Variable Temperature Mass Spectrometry. J Am Chem Soc 2019; 141:14650-14660. [DOI: 10.1021/jacs.9b05874] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Emily E. Racow
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11790, United States
| | - John J. Kreinbihl
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11790, United States
| | - Alexia G. Cosby
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11790, United States
| | - Yi Yang
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11790, United States
| | - Apurva Pandey
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11790, United States
| | - Eszter Boros
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11790, United States
| | - Christopher J. Johnson
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11790, United States
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6
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Sappidi P, Namsani S, Ali SM, Singh JK. Extraction of Gd 3+ and UO 22+ Ions Using Polystyrene Grafted Dibenzo Crown Ether (DB18C6) with Octanol and Nitrobenzene: A Molecular Dynamics Study. J Phys Chem B 2018; 122:1334-1344. [PMID: 29281280 DOI: 10.1021/acs.jpcb.7b11384] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Atomistic molecular dynamics (MD) simulations are performed in order to derive thermodynamic properties important to understand the extraction of gadolinium (Gd3+) and uranium dioxide (UO2) with dibenzo crown ether (DBCE) in nitrobenzene (NB) and octanol (OCT) solvents. The effect of polystyrene graft length, on DBCE, on the binding behavior of Gd3+ and UO22+ is investigated for the first time. Our simulation results demonstrate that the binding of Gd3+ and UO22+ onto the oxygens of crown ethers is favorable for polystyrene grafted crown ether in the organic solvents OCT and NB. The metal ion binding free energy (ΔGBinding) in different solvent environments is calculated using the thermodynamic integration (TI) method. ΔGBinding becomes more favorable in both solvents, NB and OCT, with an increase in the polystyrene monomer length. The metal ion transferability from an aqueous phase to an organic phase is estimated by calculating transfer free-energy calculations (ΔGTransfer). ΔGTransfer is significantly favorable for both Gd3+ and UO22+ for the transfer from the aqueous phase to the organic phase (i.e., NB and OCT) via ion-complexation to DBCE with an increase in polystyrene length. The partition coefficient (log P) values for Gd3+ and UO22+ show a 5-fold increase in separation capacity with polystyrene grafted DBCE. We corroborate the observed behavior by further analyzing the structural and dynamical properties of the ions in different phases.
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Affiliation(s)
- Praveenkumar Sappidi
- Computational Nano Science Laboratory, Department of Chemical Engineering, Indian Institute of Technology (IIT) Kanpur , Kanpur 208016, India
| | - Sadanandam Namsani
- Computational Nano Science Laboratory, Department of Chemical Engineering, Indian Institute of Technology (IIT) Kanpur , Kanpur 208016, India
| | - Sk Musharaf Ali
- Chemical Engineering Division, Bhabha Atomic Research Center , Mumbai 400085, India
| | - Jayant Kumar Singh
- Computational Nano Science Laboratory, Department of Chemical Engineering, Indian Institute of Technology (IIT) Kanpur , Kanpur 208016, India
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7
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Bombieri G, Artali R, Mason SA, McIntyre GJ, Mortillaro A, Aime S. Inner-sphere water and hydrogen bonds in lanthanide DOTAM complexes. A neutron diffraction study. Inorganica Chim Acta 2018. [DOI: 10.1016/j.ica.2017.09.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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8
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Collauto A, Feintuch A, Qi M, Godt A, Meade T, Goldfarb D. Gd(III) complexes as paramagnetic tags: Evaluation of the spin delocalization over the nuclei of the ligand. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 263:156-163. [PMID: 26802219 DOI: 10.1016/j.jmr.2015.12.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Revised: 12/28/2015] [Accepted: 12/30/2015] [Indexed: 05/15/2023]
Abstract
Complexes of the Gd(III) ion are currently being established as spin labels for distance determination in biomolecules by pulse dipolar spectroscopy. Because Gd(III) is an f ion, one expects electron spin density to be localized on the Gd(III) ion - an important feature for the mentioned application. Most of the complex ligands have nitrogens as Gd(III) coordinating atoms. Therefore, measurement of the (14)N hyperfine coupling gives access to information on the localization of the electron spin on the Gd(III) ion. We carried out W-band, 1D and 2D (14)N and (1)H ENDOR measurements on the Gd(III) complexes Gd-DOTA, Gd-538, Gd-595, and Gd-PyMTA that serve as spin labels for Gd-Gd distance measurements. The obtained (14)N spectra are particularly well resolved, revealing both the hyperfine and nuclear quadrupole splittings, which were assigned using 2D Mims ENDOR experiments. Additionally, the spectral contributions of the two different types of nitrogen atoms of Gd-PyMTA, the aliphatic N atom and the pyridine N atom, were distinguishable. The (14)N hyperfine interaction was found to have a very small isotropic hyperfine component of -0.25 to -0.37MHz. Furthermore, the anisotropic hyperfine interactions with the (14)N nuclei and with the non-exchangeable protons of the ligands are well described by the point-dipole approximation using distances derived from the crystal structures. We therefore conclude that the spin density is fully localized on the Gd(III) ion and that the spin density distribution over the nuclei of the ligands is rightfully ignored when analyzing distance measurements.
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Affiliation(s)
- A Collauto
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - A Feintuch
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - M Qi
- University Bielefeld, Faculty of Chemistry and Center for Molecular Materials, D-33615 Bielefeld, Germany
| | - A Godt
- University Bielefeld, Faculty of Chemistry and Center for Molecular Materials, D-33615 Bielefeld, Germany
| | - T Meade
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
| | - D Goldfarb
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
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9
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Rapatskiy L, Ames WM, Pérez-Navarro M, Savitsky A, Griese JJ, Weyhermüller T, Shafaat HS, Högbom M, Neese F, Pantazis DA, Cox N. Characterization of Oxygen Bridged Manganese Model Complexes Using Multifrequency 17O-Hyperfine EPR Spectroscopies and Density Functional Theory. J Phys Chem B 2015. [DOI: 10.1021/acs.jpcb.5b04614] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Leonid Rapatskiy
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
| | - William M. Ames
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
| | - Montserrat Pérez-Navarro
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
| | - Anton Savitsky
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
| | - Julia J. Griese
- Department
of Biochemistry and Biophysics, Stockholm University, Stockholm SE-106 91, Sweden
| | - Thomas Weyhermüller
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
| | - Hannah S. Shafaat
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
| | - Martin Högbom
- Department
of Biochemistry and Biophysics, Stockholm University, Stockholm SE-106 91, Sweden
| | - Frank Neese
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
| | - Dimitrios A. Pantazis
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
| | - Nicholas Cox
- Max-Planck Institute for Chemical Energy, Stiftstr. 34-36, Mülheim an der Ruhr, DE-45470 Germany
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10
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Abstract
This perspective outlines strategies towards the development of MR imaging probes that our lab has explored over the last 15 years. Namely, we discuss methods to enhance the signal generating capacity of MR probes and how to achieve tissue specificity through protein targeting or probe activation within the tissue microenvironment.
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Affiliation(s)
- Eszter Boros
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA
| | - Eric M Gale
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA
| | - Peter Caravan
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA
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11
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Elhabiri M, Abada S, Sy M, Nonat A, Choquet P, Esteban-Gómez D, Cassino C, Platas-Iglesias C, Botta M, Charbonnière LJ. Importance of Outer-Sphere and Aggregation Phenomena in the Relaxation Properties of Phosphonated Gadolinium Complexes with Potential Applications as MRI Contrast Agents. Chemistry 2015; 21:6535-46. [DOI: 10.1002/chem.201500155] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Indexed: 11/10/2022]
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12
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Fusaro L, Casella G, Bagno A. Direct Detection of17O in [Gd(DOTA)]−by NMR Spectroscopy. Chemistry 2014; 21:1955-60. [DOI: 10.1002/chem.201405092] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Indexed: 11/07/2022]
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13
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Shafaat HS, Griese JJ, Pantazis DA, Roos K, Andersson CS, Popović-Bijelić A, Gräslund A, Siegbahn PEM, Neese F, Lubitz W, Högbom M, Cox N. Electronic structural flexibility of heterobimetallic Mn/Fe cofactors: R2lox and R2c proteins. J Am Chem Soc 2014; 136:13399-409. [PMID: 25153930 DOI: 10.1021/ja507435t] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The electronic structure of the Mn/Fe cofactor identified in a new class of oxidases (R2lox) described by Andersson and Högbom [Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 5633] is reported. The R2lox protein is homologous to the small subunit of class Ic ribonucleotide reductase (R2c) but has a completely different in vivo function. Using multifrequency EPR and related pulse techniques, it is shown that the cofactor of R2lox represents an antiferromagnetically coupled Mn(III)/Fe(III) dimer linked by a μ-hydroxo/bis-μ-carboxylato bridging network. The Mn(III) ion is coordinated by a single water ligand. The R2lox cofactor is photoactive, converting into a second form (R2loxPhoto) upon visible illumination at cryogenic temperatures (77 K) that completely decays upon warming. This second, unstable form of the cofactor more closely resembles the Mn(III)/Fe(III) cofactor seen in R2c. It is shown that the two forms of the R2lox cofactor differ primarily in terms of the local site geometry and electronic state of the Mn(III) ion, as best evidenced by a reorientation of its unique (55)Mn hyperfine axis. Analysis of the metal hyperfine tensors in combination with density functional theory (DFT) calculations suggests that this change is triggered by deprotonation of the μ-hydroxo bridge. These results have important consequences for the mixed-metal R2c cofactor and the divergent chemistry R2lox and R2c perform.
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Affiliation(s)
- Hannah S Shafaat
- Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, Mülheim an der Ruhr D-45470, Germany
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14
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Lee T, Bang D, Park Y, Kim SH, Choi J, Park J, Kim D, Kim E, Suh JS, Huh YM, Haam S. Gadolinium-enriched polyaniline particles (GPAPs) for simultaneous diagnostic imaging and localized photothermal therapy of epithelial cancer. Adv Healthc Mater 2014; 3:1408-14. [PMID: 24550214 DOI: 10.1002/adhm.201300636] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Revised: 02/01/2014] [Indexed: 11/08/2022]
Abstract
By loading Gd(III) inside NIR-absorbing polyaniline nanostructures, a novel diagnostic and photothermal agent with enhanced MR sensitivity, targeting ability, and photothermal ability to treat epithelial cancer is developed.
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Affiliation(s)
- Taeksu Lee
- Department of Chemical and Biomolecular Engineering; Yonsei University; Seoul 120-749 Republic of Korea
| | - Doyeon Bang
- Department of Chemical and Biomolecular Engineering; Yonsei University; Seoul 120-749 Republic of Korea
- Active Polymer Center for Pattern Integration (APCPI), Yonsei University; Seoul 120-749 Republic of Korea
| | - Yeonji Park
- Department of Radiology; Yonsei University; Seoul 120-752 Republic of Korea
| | - Sun Hee Kim
- Korea Basic Science Institute (KBSI); Daejeon Republic of Korea
| | - Jihye Choi
- Department of Chemical and Biomolecular Engineering; Yonsei University; Seoul 120-749 Republic of Korea
| | - Joseph Park
- Department of Chemical and Biomolecular Engineering; Yonsei University; Seoul 120-749 Republic of Korea
| | - Donghun Kim
- Korea Basic Science Institute (KBSI); Daejeon Republic of Korea
| | - Eunkyoung Kim
- Department of Chemical and Biomolecular Engineering; Yonsei University; Seoul 120-749 Republic of Korea
- Active Polymer Center for Pattern Integration (APCPI), Yonsei University; Seoul 120-749 Republic of Korea
| | - Jin-Suck Suh
- Department of Radiology; Yonsei University; Seoul 120-752 Republic of Korea
| | - Yong-Min Huh
- Department of Radiology; Yonsei University; Seoul 120-752 Republic of Korea
| | - Seungjoo Haam
- Department of Chemical and Biomolecular Engineering; Yonsei University; Seoul 120-749 Republic of Korea
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15
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Esteban-Gómez D, Cassino C, Botta M, Platas-Iglesias C. 17O and 1H relaxometric and DFT study of hyperfine coupling constants in [Mn(H2O)6]2+. RSC Adv 2014. [DOI: 10.1039/c3ra45721d] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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16
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Rapatskiy L, Cox N, Savitsky A, Ames WM, Sander J, Nowaczyk MM, Rögner M, Boussac A, Neese F, Messinger J, Lubitz W. Detection of the Water-Binding Sites of the Oxygen-Evolving Complex of Photosystem II Using W-Band 17O Electron–Electron Double Resonance-Detected NMR Spectroscopy. J Am Chem Soc 2012; 134:16619-34. [DOI: 10.1021/ja3053267] [Citation(s) in RCA: 224] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Leonid Rapatskiy
- Max-Planck-Institut für
Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim
an der Ruhr, Germany
| | - Nicholas Cox
- Max-Planck-Institut für
Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim
an der Ruhr, Germany
| | - Anton Savitsky
- Max-Planck-Institut für
Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim
an der Ruhr, Germany
| | - William M. Ames
- Max-Planck-Institut für
Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim
an der Ruhr, Germany
| | - Julia Sander
- Plant
Biochemistry, Ruhr University Bochum, Universitätsstrasse
150, D-44780 Bochum, Germany
| | - Marc. M. Nowaczyk
- Plant
Biochemistry, Ruhr University Bochum, Universitätsstrasse
150, D-44780 Bochum, Germany
| | - Matthias Rögner
- Plant
Biochemistry, Ruhr University Bochum, Universitätsstrasse
150, D-44780 Bochum, Germany
| | - Alain Boussac
- iBiTec-S, URA UMR 8221, CEA Saclay,
91191 Gif-sur-Yvette, France
| | - Frank Neese
- Max-Planck-Institut für
Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim
an der Ruhr, Germany
| | - Johannes Messinger
- Department of Chemistry, Chemical
Biological Centre (KBC), Umeå University, S-90187 Umeå, Sweden
| | - Wolfgang Lubitz
- Max-Planck-Institut für
Chemische Energiekonversion, Stiftstrasse 34-36, D-45470 Mülheim
an der Ruhr, Germany
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17
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Esteban-Gómez D, de Blas A, Rodríguez-Blas T, Helm L, Platas-Iglesias C. Hyperfine Coupling Constants on Inner-Sphere Water Molecules of GdIII-Based MRI Contrast Agents. Chemphyschem 2012; 13:3640-50. [DOI: 10.1002/cphc.201200417] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Indexed: 01/02/2023]
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18
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Bonnet CS, Tóth É. Magnetic Resonance Imaging Contrast Agents. Supramol Chem 2012. [DOI: 10.1002/9780470661345.smc104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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19
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Tircsó G, Kálmán FK, Pál R, Bányai I, Varga TR, Király R, Lázár I, Québatte L, Merbach AE, Tóth É, Brücher E. Lanthanide Complexes Formed with the Tri- and Tetraacetate Derivatives of Bis(aminomethyl)phosphinic Acid: Equilibrium, Kinetic and NMR Spectroscopic Studies. Eur J Inorg Chem 2012. [DOI: 10.1002/ejic.201101299] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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20
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Klein EL, Raitsimring AM, Astashkin AV, Rajapakshe A, Johnson-Winters K, Arnold AR, Potapov A, Goldfarb D, Enemark JH. Identity of the exchangeable sulfur-containing ligand at the Mo(V) center of R160Q human sulfite oxidase. Inorg Chem 2012; 51:1408-18. [PMID: 22225516 DOI: 10.1021/ic201643t] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In our previous study of the fatal R160Q mutant of human sulfite oxidase (hSO) at low pH (Astashkin et al. J. Am. Chem. Soc.2008, 130, 8471-8480), a new Mo(V) species, denoted "species 1", was observed at low pH values. Species 1 was ascribed to a six-coordinate Mo(V) center with an exchangeable terminal oxo ligand and an equatorial sulfate group on the basis of pulsed EPR spectroscopy and (33)S and (17)O labeling. Here we report new results for species 1 of R160Q, based on substitution of the sulfur-containing ligand by a phosphate group, pulsed EPR spectroscopy in K(a)- and W-bands, and extensive density functional theory (DFT) calculations applied to large, more realistic molecular models of the enzyme active site. The combined results unambiguously show that species 1 has an equatorial sulfite as the only exchangeable ligand. The two types of (17)O signals that are observed arise from the coordinated and remote oxygen atoms of the sulfite ligand. A typical five-coordinate Mo(V) site is compatible with the observed and calculated EPR parameters.
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Affiliation(s)
- Eric L Klein
- Department of Chemistry and Biochemistry, 1306 East University Boulevard, University of Arizona, Tucson, Arizona 85721-0041, United States
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21
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Maurelli S, Livraghi S, Chiesa M, Giamello E, Van Doorslaer S, Di Valentin C, Pacchioni G. Hydration Structure of the Ti(III) Cation as Revealed by Pulse EPR and DFT Studies: New Insights into a Textbook Case. Inorg Chem 2011; 50:2385-94. [DOI: 10.1021/ic1021802] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Sara Maurelli
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
| | - Stefano Livraghi
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
| | - Mario Chiesa
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
| | - Elio Giamello
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
| | - Sabine Van Doorslaer
- University of Antwerp, Department of Physics, Universiteitsplein 1, B-2610 Wilrijk-Antwerp, Belgium
| | - Cristiana Di Valentin
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53-20125, Milano, Italy
| | - Gianfranco Pacchioni
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53-20125, Milano, Italy
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22
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Enemark JH, Raitsimring AM, Astashkin AV, Klein EL. Implications for the mechanism of sulfite oxidizing enzymes from pulsed EPR spectroscopy and DFT calculations for "difficult" nuclei. Faraday Discuss 2011; 148:249-67; discussion 299-314. [PMID: 21322488 PMCID: PMC3079391 DOI: 10.1039/c004404k] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The catalytic mechanisms of sulfite oxidizing enzymes (SOEs) have been investigated by multi-frequency pulsed EPR measurements of "difficult" magnetic nuclei (35.37Cl, 33S, 17O) associated with the Mo(v) center. Extensive DFT calculations have been used to relate the experimental magnetic resonance parameters of these nuclei to specific active site structures. This combined spectroscopic and computational approach has provided new insights concerning the structure/function relationships of the active sites of SOEs, including: (i) the exchange of oxo ligands; (ii) the nature of the blocked forms; and (iii) the role of Cl- in low pH forms.
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Affiliation(s)
- John H Enemark
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721-0041, USA.
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23
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Nagarajan V, Hovav Y, Feintuch A, Vega S, Goldfarb D. EPR detected polarization transfer between Gd3+ and protons at low temperature and 3.3 T: the first step of dynamic nuclear polarization. J Chem Phys 2010; 132:214504. [PMID: 20528028 DOI: 10.1063/1.3428665] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Electron-electron double resonance pulsed electron paramagnetic resonance (EPR) at 95 GHz (3.3 T) is used to follow the dynamics of the electron spin polarization during the first stages of dynamic nuclear polarization in solids. The experiments were performed on a frozen solution of Gd(+3) (S=7/2) in water/glycerol. Focusing on the central vector -1/2 --> vector +1/2 transition we measured the polarization transfer from the Gd(3+) electron spin to the adjacent (1)H protons. The dependence of the echo detected EPR signal on the length of the microwave irradiation at the EPR "forbidden" transition corresponding to an electron and a proton spin flip is measured for different powers, showing dynamics on the microsecond to millisecond time scales. A theoretical model based on the spin density matrix formalism is suggested to account for this dynamics. The central transition of the Gd(3+) ion is considered as an effective S = 1/2 system and is coupled to (1)H (I = 1/2) nuclei. Simulations based on a single electron-single nucleus four level system are shown to deviate from the experimental results and an alternative approach taking into account the more realistic multinuclei picture is shown to agree qualitatively with the experiments.
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Terrier C, Vitorge P, Gaigeot MP, Spezia R, Vuilleumier R. Density functional theory based molecular dynamics study of hydration and electronic properties of aqueous La3+. J Chem Phys 2010; 133:044509. [DOI: 10.1063/1.3460813] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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25
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Regueiro-Figueroa M, Esteban-Gómez D, de Blas A, Rodríguez-Blas T, Platas-Iglesias C. Structure and Dynamics of Lanthanide(III) Complexes with an N-Alkylated do3a Ligand (H3do3a = 1,4,7,10-Tetraazacyclododecane-1,4,7-triacetic Acid): A Combined Experimental and DFT Study. Eur J Inorg Chem 2010. [DOI: 10.1002/ejic.201000334] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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26
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Henig J, Tóth É, Engelmann J, Gottschalk S, Mayer HA. Macrocyclic Gd3+ Chelates Attached to a Silsesquioxane Core as Potential Magnetic Resonance Imaging Contrast Agents: Synthesis, Physicochemical Characterization, and Stability Studies. Inorg Chem 2010; 49:6124-38. [DOI: 10.1021/ic1007395] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jörg Henig
- Institut für Anorganische Chemie, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Éva Tóth
- Le Centre de Biophysique Moléculaire, CNRS, Rue Charles Sadron, 45071 Orléans, France
| | - Jörn Engelmann
- Hochfeld-Magnetresonanz-Zentrum, Max-Planck-Institut für Biologische Kybernetik, Spemannstrasse 41, 72076 Tübingen, Germany
| | - Sven Gottschalk
- Hochfeld-Magnetresonanz-Zentrum, Max-Planck-Institut für Biologische Kybernetik, Spemannstrasse 41, 72076 Tübingen, Germany
| | - Hermann A. Mayer
- Institut für Anorganische Chemie, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
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HIGH-RESOLUTION EPR SPECTROSCOPY OF MO ENZYMES. SULFITE OXIDASES: STRUCTURAL AND FUNCTIONAL IMPLICATIONS. BIOLOGICAL MAGNETIC RESONANCE 2010; 29:121-168. [PMID: 21283528 PMCID: PMC3030814 DOI: 10.1007/978-1-4419-1139-1_6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Sulfite oxidases (SOs) are physiologically vital Mo-containing enzymes that occur in animals, plants, and bacteria and which catalyze the oxidation of sulfite to sulfate, the terminal reaction in the oxidative degradation of sulfur-containing compounds. X-ray structure determinations of SOs from several species show nearly identical coordination structures of the molybdenum active center, and a common catalytic mechanism has been proposed that involves the generation of a transient paramagnetic Mo(V) state through a series of coupled electron-proton transfer steps. This chapter describes the use of pulsed electron-nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) spectroscopic techniques to obtain information about the structure of this Mo(V) species from the hyperfine interactions (hfi) and nuclear quadrupole interactions (nqi) of nearby magnetic nuclei. Variable frequency instrumentation is essential to optimize the experimental conditions for measuring the couplings of different types of nuclei (e.g., (1)H, (2)H, (31)P, and (17)O). The theoretical background necessary for understanding the ESEEM and ENDOR spectra of the Mo(V) centers of SOs is outlined, and examples of the use of advanced pulsed EPR methods (RP-ESEEM, HYSCORE, integrated four-pulse ESEEM) for structure determination are presented. The analysis of variable-frequency pulsed EPR data from SOs is aided by parallel studies of model compounds that contain key functional groups or that are isotopically labeled and thus provide benchmark data for enzymes. Enormous progress has been made on the use of high-resolution variable-frequency pulsed EPR methods to investigate the structures and mechanisms of SOs during the past ~15 years, and the future is bright for the continued development and application of this technology to SOs, other molybdenum enzymes, and other problems in metallobiochemistry.
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28
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Astashkin AV, Klein EL, Ganyushin D, Johnson-Winters K, Neese F, Kappler U, Enemark JH. Exchangeable oxygens in the vicinity of the molybdenum center of the high-pH form of sulfite oxidase and sulfite dehydrogenase. Phys Chem Chem Phys 2009; 11:6733-42. [PMID: 19639147 PMCID: PMC2789977 DOI: 10.1039/b907029j] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The electron spin echo envelope modulation (ESEEM) investigation of the high-pH (hpH) form of sulfite oxidase (SO) and sulfite dehydrogenase (SDH) prepared in buffer enriched with H(2)(17)O reveals the presence of three types of exchangeable oxygen atoms at the molybdenum center. Two of these oxygen atoms belong to the equatorial OH ligand and the axial oxo ligand, and are characterized by (17)O hyperfine interaction (hfi) constants of about 37 MHz and 6 MHz, respectively. The third oxygen has an isotropic hfi constant of 3-4 MHz and likely belongs to a hydroxyl moiety hydrogen-bonded to the equatorial OH ligand. This exchangeable oxygen atom is not observed in the ESEEM spectra of the Y236F mutant of SDH, where the active site tyrosine has been replaced by phenylalanine.
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Affiliation(s)
- Andrei V. Astashkin
- Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA; Fax: +1 (1)520 6218407; Tel: +1 (1)520 6219968
| | - Eric L. Klein
- Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA; Fax: +1 (1)520 6218407; Tel: +1 (1)520 6219968
| | - Dmitry Ganyushin
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstrasse 12, 53115 Bonn, Germany; Fax: +49 (0)228 739064; Tel: +49 28 732351
| | - Kayunta Johnson-Winters
- Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA; Fax: +1 (1)520 6218407; Tel: +1 (1)520 6219968
| | - Frank Neese
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstrasse 12, 53115 Bonn, Germany; Fax: +49 (0)228 739064; Tel: +49 28 732351
| | - Ulrike Kappler
- Centre for Metals in Biology, University of Queensland, St. Lucia, Queensland 4072, Australia; Fax: +61 (07)3365 4620; Tel: +61 (07)3365 2978
| | - John H. Enemark
- Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA; Fax: +1 (1)520 6218407; Tel: +1 (1)520 6219968
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Pálinkás Z, Roca-Sabio A, Mato-Iglesias M, Esteban-Gómez D, Platas-Iglesias C, de Blas A, Rodríguez-Blas T, Tóth É. Stability, Water Exchange, and Anion Binding Studies on Lanthanide(III) Complexes with a Macrocyclic Ligand Based on 1,7-Diaza-12-crown-4: Extremely Fast Water Exchange on the Gd3+ Complex. Inorg Chem 2009; 48:8878-89. [DOI: 10.1021/ic9011197] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Zoltán Pálinkás
- Centre de Biophysique Moléculaire, CNRS, rue Charles Sadron, 45071 Orléans, Cedex 2, France
| | - Adrián Roca-Sabio
- Departamento de Química Fundamental, Universidade da Coruña, Campus da Zapateira, Alejandro de la Sota 1, 15008 A Coruña, Spain
| | - Marta Mato-Iglesias
- Departamento de Química Fundamental, Universidade da Coruña, Campus da Zapateira, Alejandro de la Sota 1, 15008 A Coruña, Spain
| | - David Esteban-Gómez
- Departamento de Química Fundamental, Universidade da Coruña, Campus da Zapateira, Alejandro de la Sota 1, 15008 A Coruña, Spain
| | - Carlos Platas-Iglesias
- Departamento de Química Fundamental, Universidade da Coruña, Campus da Zapateira, Alejandro de la Sota 1, 15008 A Coruña, Spain
| | - Andrés de Blas
- Departamento de Química Fundamental, Universidade da Coruña, Campus da Zapateira, Alejandro de la Sota 1, 15008 A Coruña, Spain
| | - Teresa Rodríguez-Blas
- Departamento de Química Fundamental, Universidade da Coruña, Campus da Zapateira, Alejandro de la Sota 1, 15008 A Coruña, Spain
| | - Éva Tóth
- Centre de Biophysique Moléculaire, CNRS, rue Charles Sadron, 45071 Orléans, Cedex 2, France
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Xiao W, Xia QQ, Zhang YF, Ning LX, Cui ZF. Density Functional Study on Structures and Relative Stability of Gd(H2O)n3+(n= 8,9). CHINESE J CHEM PHYS 2009. [DOI: 10.1088/1674-0068/22/04/395-400] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Caravan P. Protein-targeted gadolinium-based magnetic resonance imaging (MRI) contrast agents: design and mechanism of action. Acc Chem Res 2009; 42:851-62. [PMID: 19222207 DOI: 10.1021/ar800220p] [Citation(s) in RCA: 288] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Magnetic resonance imaging (MRI) is a powerful medical diagnostic technique: it can penetrate deep into tissue, provide excellent soft tissue contrast with sub-millimeter resolution, and does not employ ionizing radiation. Targeted contrast agents provide an additional layer of molecular specificity to the wealth of anatomical and functional information already attainable by MRI. However, the major challenge for molecular MR imaging is sensitivity: micromolar concentrations of Gd(III) are required to cause a detectable signal change, which makes detecting proteins by MRI a challenge. Protein-targeted MRI contrast agents are bifunctional molecules comprising a protein-targeting moiety and typically one or more gadolinium chelates for detection by MRI. The ability of the contrast agent to enhance the MR image is termed relaxivity, and it depends upon many molecular factors, including protein binding itself. As in other imaging modalities, protein binding provides the pharmacokinetic effect of concentrating the agent at the region of interest. Unique to MRI, protein binding provides the pharmacodynamic effect of increasing the relaxivity of the contrast agent, thereby increasing the MR signal. In designing new agents, optimization of both the targeting function and the relaxivity is critical. In this Account, we focus on optimization of the relaxivity of targeted agents. Relaxivity depends upon speciation, chemical structure, and dynamic processes, such as water exchange kinetics and rotational tumbling rates. We describe mechanistic studies that relate these factors to the observed relaxivities and use these findings as the basis of rational design of improved agents. In addition to traditional biochemical methods to characterize ligand-protein interactions, the presence of the metal ion enables more obscure biophysical techniques, such as relaxometry and electron nuclear double resonance, to be used to elucidate the mechanism of relaxivity differences. As a case study, we explore the mechanism of action of the serum-albumin-targeted angiography agent MS-325 and closely related compounds and show how small changes in the metal chelate can impact relaxivity. We found that, while protein binding generally improves relaxivity by slowing the tumbling rate of the complex, in some cases, the protein itself can also negatively affect hydration of the metal complex and/or inner-sphere water exchange. Drawing on these findings, we designed next-generation agents targeting albumin, fibrin, or collagen and incorporating up to four gadolinium chelates. Through judicious molecular design, we show that high-relaxivity complexes with high target affinity can be realized.
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Affiliation(s)
- Peter Caravan
- A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, 149 Thirteenth Street, Suite 2301, Charlestown, Massachusetts 02129
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Caravan P, Farrar CT, Frullano L, Uppal R. Influence of molecular parameters and increasing magnetic field strength on relaxivity of gadolinium- and manganese-based T1 contrast agents. CONTRAST MEDIA & MOLECULAR IMAGING 2009; 4:89-100. [PMID: 19177472 DOI: 10.1002/cmmi.267] [Citation(s) in RCA: 377] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Simulations were performed to understand the relative contributions of molecular parameters to longitudinal (r(1)) and transverse (r(2)) relaxivity as a function of applied field, and to obtain theoretical relaxivity maxima over a range of fields to appreciate what relaxivities can be achieved experimentally. The field-dependent relaxivities of a panel of gadolinium and manganese complexes with different molecular parameters, water exchange rates, rotational correlation times, hydration state, etc. were measured to confirm that measured relaxivities were consistent with theory. The design tenets previously stressed for optimizing r(1) at low fields (very slow rotational motion; chelate immobilized by protein binding; optimized water exchange rate) do not apply at higher fields. At 1.5 T and higher fields, an intermediate rotational correlation time is desired (0.5-4 ns), while water exchange rate is not as critical to achieving a high r(1). For targeted applications it is recommended to tether a multimer of metal chelates to a protein-targeting group via a long flexible linker to decouple the slow motion of the protein from the water(s) bound to the metal ions. Per ion relaxivities of 80, 45, and 18 mM(-1) s(-1) at 1.5, 3 and 9.4 T, respectively, are feasible for Gd(3+) and Mn(2+) complexes.
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Affiliation(s)
- Peter Caravan
- A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Department of Radiology, Harvard Medical School, 149 Thirteenth St, Charlestown, MA 02129, USA.
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Structures and reaction pathways of the molybdenum centres of sulfite-oxidizing enzymes by pulsed EPR spectroscopy. Biochem Soc Trans 2009; 36:1129-33. [PMID: 19021510 DOI: 10.1042/bst0361129] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
SOEs (sulfite-oxidizing enzymes) are physiologically vital and occur in all forms of life. During the catalytic cycle, the five-co-ordinate square pyramidal oxo-molybdenum active site passes through the Mo(V) state, and intimate details of the structure can be obtained from variable frequency pulsed EPR spectroscopy through the hyperfine and nuclear quadrupole interactions of nearby magnetic nuclei. By employing variable spectrometer operational frequencies, it is possible to optimize the measurement conditions for difficult quadrupolar nuclei of interest (e.g. (17)O, (33)S, (35)Cl and (37)Cl) and to simplify the interpretation of the spectra. Isotopically labelled model Mo(V) compounds provide further insight into the electronic and geometric structures and chemical reactions of the enzymes. Recently, blocked forms of SOEs having co-ordinated sulfate, the reaction product, were detected using (33)S (I=3/2) labelling. This blocking of product release is a possible contributor to fatal human sulfite oxidase deficiency in young children.
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Kaminker I, Potapov A, Feintuch A, Vega S, Goldfarb D. Population transfer for signal enhancement in pulsed EPR experiments on half integer high spin systems. Phys Chem Chem Phys 2009; 11:6799-806. [DOI: 10.1039/b906177k] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kubíček V, Hamplová A, Maribé L, Mameri S, Ziessel R, Tóth É, Charbonnière L. Relaxation and luminescence studies on hydrated bipyridyl- and terpyridyl-based lanthanide complexes. Dalton Trans 2009:9466-74. [DOI: 10.1039/b913084e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Livramento JB, Helm L, Sour A, O'Neil C, Merbach AE, Tóth É. A benzene-core trinuclear GdIIIcomplex: towards the optimization of relaxivity for MRI contrast agent applications at high magnetic field. Dalton Trans 2008:1195-202. [DOI: 10.1039/b717390c] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Yazyev OV, Helm L. Nuclear Spin Relaxation Parameters of MRI Contrast Agents – Insight from Quantum Mechanical Calculations. Eur J Inorg Chem 2007. [DOI: 10.1002/ejic.200701013] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Oleg V. Yazyev
- Institut de Théorie des Phénomènes Physiques, Ecole Polytechnique Fédérale de Lausanne, and Institut Romand de Recherche Numérique en Physique des Matériaux (IRRMA), EPFL‐PPH, 1015 Lausanne, Switzerland, Fax: +41‐21‐693‐9875
| | - Lothar Helm
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, EPFL‐BCH, 1015 Lausanne, Switzerland, Fax: +41‐21‐693‐9875
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39
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Yazyev OV, Helm L. Gadolinium (III) ion in liquid water: Structure, dynamics, and magnetic interactions from first principles. J Chem Phys 2007; 127:084506. [PMID: 17764268 DOI: 10.1063/1.2759919] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We applied first principles molecular dynamics (MD) technique to study structure, dynamics, and magnetic interactions of the Gd(3+) aqua ion dissolved in liquid water, a prototypical system for Gd-based complexes used as contrast agents for magnetic resonance imaging. The first coordination sphere contains eight water molecules with an average Gd-O distance of 2.37 A and an average geometric arrangement close to a square antiprism. The mean tilt angle of the electric dipole vector of these water molecules is theta=145 degrees . In our picosecond time scale simulation we observe no exchange event from the first coordination sphere but only fast "wagging" motions. The second coordination sphere is well pronounced though water molecules in this sphere are subjected to large amplitude dynamic motions. The isotropic hyperfine coupling constants for the inner sphere water molecules [A(iso)((17)O(I))=0.65+/-0.03 MHz, A(iso)((1)H(I))=0.085+/-0.005 MHz] are in good agreement with experimental data and with an earlier study using classical MD. Second sphere Fermi contact hyperfine coupling constants calculated are more than one order of magnitude smaller and of opposite sign as those of the first coordination sphere. The effect of spin polarization induced by the paramagnetic Gd(3+) ion on the dipolar hyperfine interaction was found to be sizable only for the (17)O nuclei of inner sphere water molecules and has a screening character.
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Affiliation(s)
- Oleg V Yazyev
- Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
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Raitsimring AM, Astashkin AV, Baute D, Goldfarb D, Poluektov OG, Lowe MP, Zech SG, Caravan P. Determination of the hydration number of gadolinium(III) complexes by high-field pulsed 17O ENDOR spectroscopy. Chemphyschem 2007; 7:1590-7. [PMID: 16810729 DOI: 10.1002/cphc.200600138] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Pulsed 17O Mims electron-nuclear double resonance (ENDOR) spectroscopy at the W band (95 GHz) and D band (130 GHz) is used for the direct determination of the water coordination number (q) of gadolinium-based magnetic resonance imaging (MRI) contrast agents. Spectra of metal complexes in frozen aqueous solutions at approximately physiological concentrations can be obtained either in the presence or absence of protein targets. This method is an improvement over the 1H ENDOR method described previously, which involved the difference ENDOR spectrum of exchangeable protons from spectra taken in H2O and D2O. In addition to exchangeable water protons, the 1H ENDOR method is also sensitive to other exchangeable protons, and it is shown here that this method can overestimate hydration numbers for complexes with exchangeable protons at GdH distances similar to that of the coordinated water, for example, from NH groups. The 17O method does not suffer from this limitation. 17O ENDOR spectroscopy is applied to Gd(III) complexes containing zero, one, or two inner-sphere water molecules. In addition, 13C and 1H ENDOR studies were performed to assess the extent of methanol coordination, since methanol is used to produce a glass in these experiments. Under the experimental conditions used for the hydration number determination (30 mol % methanol), fewer than 15 % of the coordination sites were found to be occupied by methanol.
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Tyeklar Z, Dunham SU, Midelfort K, Scott DM, Sajiki H, Ong K, Lauffer RB, Caravan P, McMurry TJ. Structural, Kinetic, and Thermodynamic Characterization of the Interconverting Isomers of MS-325, a Gadolinium(III)-Based Magnetic Resonance Angiography Contrast Agent. Inorg Chem 2007; 46:6621-31. [PMID: 17625838 DOI: 10.1021/ic7006843] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The amphiphilic gadolinium complex MS-325 ((trisodium-{(2-(R)-[(4,4-diphenylcyclohexyl) phosphonooxymethyl] diethylenetriaminepentaacetato) (aquo)gadolinium(III)}) is a contrast agent for magnetic resonance angiography (MRA). MS-325 comprises a GdDTPA core with an appended phosphodiester moiety linked to a diphenylcyclohexyl group to facilitate noncovalent binding to serum albumin and extension of the plasma half-life in vivo. The chiral DTPA ligand (R) was derived from L-serine, and upon complexation with gadolinium, forms two interconvertible diastereomers, denoted herein as isomers A and B. X-ray crystallography of the tris(ethylenediamine)cobalt(III) salt derivative of isomer A revealed a structure in the polar acentric space group P32. The structure consisted of three independent molecules of the gadolinium complex in the asymmetric unit along with three Delta-[Co(en)3]3+ cations, and it represents an unusual example of spontaneous Pasteur resolution of the cobalt cation. The geometry of the coordination core was best described as a distorted trigonal prism, and the final R factor was 5.6%. The configuration of the chiral central nitrogen of the DTPA core was S. The Gd-water (2.47-2.48 A), the Gd-acetate oxygens (2.34-2.42 A), and the Gd-N bond distances (central N, 2.59-2.63 A; terminal N, 2.74-2.80 A) were similar to other reported GdDTPA structures. The structurally characterized single crystal was one of two interconvertable diastereomers (isomers A and B) that equilibrated to a ratio of 1.81 to 1 at pH 7.4 and were separable at elevated pH by ion-exchange chromatography. The rate of isomerization was highly pH dependent: k1 = (1.45 +/- 0.08) x 102[H+] + (4.16 +/- 0.30) x 105[H+]2; k-1 = (2.57 +/- 0.17) x 102[H+] + (7.54 +/- 0.60) x 105[H+]2.
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42
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Zech SG, Sun WC, Jacques V, Caravan P, Astashkin AV, Raitsimring AM. Probing the water coordination of protein-targeted MRI contrast agents by pulsed ENDOR spectroscopy. Chemphyschem 2007; 6:2570-7. [PMID: 16294353 DOI: 10.1002/cphc.200500250] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A novel methodology based on electron-nuclear double resonance (ENDOR) spectroscopy is used for the direct determination of the water coordination number (q) of gadolinium-based magnetic resonance imaging (MRI) contrast agents. Proton ENDOR spectra can be obtained at approximately physiological concentrations for metal complexes in frozen aqueous solutions either in the presence or absence of protein targets. It is shown that, depending on the structure of the co-ligand, the water hydration number of a complex in aqueous solution can be significantly different to when the complex is noncovalently bound to a protein. From the ENDOR spectra of the exchangeable protons, precise information on the metal-proton distance can be derived as well. These essential parameters directly correlate with the efficacy of MRI contrast agents and should therefore aid the development of novel, highly efficient compounds targeted to various proteins.
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Affiliation(s)
- Stephan G Zech
- EPIX Pharmaceuticals, Inc., 67 Rogers Street, Cambridge, MA 02142, USA.
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Costa J, Balogh E, Turcry V, Tripier R, Le Baccon M, Chuburu F, Handel H, Helm L, Tóth E, Merbach AE. Unexpected Aggregation of Neutral, Xylene-Cored Dinuclear GdIII Chelates in Aqueous Solution. Chemistry 2006; 12:6841-51. [PMID: 16770815 DOI: 10.1002/chem.200501335] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have synthesized ditopic ligands L(1), L(2), and L(3) that contain two DO3A(3-) metal-chelating units with a xylene core as a noncoordinating linker (DO3A(3-) = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate; L(1) = 1,4-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzene; L(2) = 1,3-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzene; L(3) = 3,5-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzoic acid). Aqueous solutions of the dinuclear Gd(III) complexes formed with the three ligands have been investigated in a variable-temperature, multiple-field (17)O NMR and (1)H relaxivity study. The (17)O longitudinal relaxation rates measured for the [Gd(2)L(1-3)(H2O)(2)] complexes show strong field dependence (2.35-9.4 T), which unambiguously proves the presence of slowly tumbling entities in solution. The proton relaxivities of the complexes, which are unexpectedly high for their molecular weight, and in particular the relaxivity peaks observed at 40-50 MHz also constitute experimental evidences of slow rotational motion. This was explained in terms of self-aggregation related to hydrophobic interactions, pi stacking between the aromatic linkers, or possible hydrogen bonding between the chelates. The longitudinal (17)O relaxation rates of the [Gd(2)L(1-3)(H2O)(2)] complexes have been analysed with the Lipari-Szabo approach, leading to local rotational correlation times tau(1)(298) of 150-250 ps and global rotational correlation times tau(g)(298) of 1.6-3.4 ns (c(Gd): 20-50 mM), where tau(1)(298) is attributed to local motions of the Gd segments, while tau(g)(298) describes the overall motion of the aggregates. The aggregates can be partially disrupted by phosphate addition; however, at high concentrations phosphate interferes in the first coordination sphere by replacing the coordinated water. In contrast to the parent [Gd(DO3A)(H2O)(1.9)], which presents a hydration equilibrium between mono- and dihydrated species, a hydration number of q = 1 was established for the [Ln(2)L(1-3)(H2O)(2)] chelates by (17)O chemical shift measurements on Ln = Gd and UV/Vis spectrophotometry for Ln = Eu. The exchange rate of the coordinated water is higher for [Gd(2)L(1-3)(H2O)(2)] complexes k(ex)(298) = 7.5-12.0 x 10(6) s(-1)) than for [Gd(DOTA)(H2O)](-). The proton relaxivity of the [Gd(2)L(1-3)(H2O)(2)] complexes strongly decreases with increasing pH. This is related to the deprotonation of the inner-sphere water, which has also been characterized by pH potentiometry. The protonation constants determined for this process are logK(OH) = 9.50 and 10.37 for [Gd(2)L(1)(H2O)(2)] and [Gd(2)L(3)(H2O)(2)], respectively.
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Affiliation(s)
- Jérôme Costa
- Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire de Chimie Inorganique et Bioinorganique, EPFL-BCH, 1015 Lausanne, Switzerland
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Yazyev OV, Helm L. O17 nuclear quadrupole coupling constants of water bound to a metal ion: A gadolinium(III) case study. J Chem Phys 2006; 125:054503. [PMID: 16942222 DOI: 10.1063/1.2217950] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Rotational correlation times of metal ion aqua complexes can be determined from 17O NMR relaxation rates if the quadrupole coupling constant of the bound water oxygen-17 nucleus is known. The rotational correlation time is an important parameter for the efficiency of Gd3+ complexes as magnetic resonance imaging contrast agents. Using a combination of density functional theory with classical and Car-Parrinello molecular dynamics simulations we performed a computational study of the 17O quadrupole coupling constants in model aqua ions and the [Gd(DOTA)(H2O)]- complex used in clinical diagnostics. For the inner sphere water molecule in the [Gd(DOTA)(H2O)]- complex the determined quadrupole coupling parameter chi square root of (1 + eta2/3) of 8.7 MHz is very similar to that of the liquid water (9.0 MHz). Very close values were also predicted for the the homoleptic aqua ions of Gd3+ and Ca2+. We conclude that the 17O quadrupole coupling parameters of water molecules coordinated to closed shell and lanthanide metal ions are similar to water molecules in the liquid state.
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Affiliation(s)
- Oleg V Yazyev
- Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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45
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Enemark JH, Astashkin AV, Raitsimring AM. Investigation of the coordination structures of the molybdenum(v) sites of sulfite oxidizing enzymes by pulsed EPR spectroscopy. Dalton Trans 2006:3501-14. [PMID: 16855750 DOI: 10.1039/b602919a] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Sulfite oxidizing enzymes (SOEs) are physiologically vital and occur in all forms of life. During the catalytic cycle the five-coordinate square-pyramidal oxo-molybdenum active site passes through the Mo(v) state, and intimate details of the structure can be obtained from pulsed EPR spectroscopy through the hyperfine interactions (hfi) and nuclear quadrupole interactions (nqi) of nearby magnetic nuclei (e.g., (1)H, (2)H, (17)O, (31)P) of the ligands. By employing spectrometer operational frequencies ranging from approximately 4 to approximately 32 GHz, it is possible to make the nuclear Zeeman interaction significantly greater than the hfi and nqi, and thereby simplify the interpretations of the spectra. The SOEs exhibit three general types of Mo(v) structures which differ in the number of nearby exchangeable protons (one, two or zero). The observed structure depends upon the organism, pH, anions in the medium, and method of reduction. One type of structure has a single exchangeable Mo-OH proton approximately in the equatorial plane and a large isotropic hfi (e.g., low pH form of chicken SOE, low pH form of plant SOE reduced by Ti(iii)); the second type has two exchangeable protons with distributed orientations out of the equatorial plane and very small (or zero) isotropic hfi (e.g., high pH form of chicken SOE, high pH form of plant SOE reduced by sulfite); the third type has no nearby exchangeable protons and a coordinated oxyanion (e.g., phosphate inhibited chicken SOE, low pH form of plant SOE reduced by sulfite). An additional structural conclusion is that the orientation angle of any exchangeable equatorial ligand (OH, OH(2), PO(4)(3-)) is not uniquely fixed, but is distributed around its central value by up to +/-20 degrees (depending on pH, the type of the ligand and the type of enzyme). An unexpected finding was that the axial oxo group of SOEs exchanges with (17)O in solutions enriched in H(2)(17)O. The first determination of oxo (17)O nqi parameters for a well-characterized model compound, [Mo(17)O(SPh)(4)](-), clearly demonstrated that (17)O nqi parameters can distinguish between oxo and OH(2) ligands.
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Affiliation(s)
- John H Enemark
- Department of Chemistry, Univesity of Arizona, 1306 E. University Blvd, Tucson, AZ 85721, USA.
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Bennati M, Hertel MM, Fritscher J, Prisner TF, Weiden N, Hofweber R, Spörner M, Horn G, Kalbitzer HR. High-frequency 94 GHz ENDOR characterization of the metal binding site in wild-type Ras x GDP and its oncogenic mutant G12V in frozen solution. Biochemistry 2006; 45:42-50. [PMID: 16388579 DOI: 10.1021/bi051156k] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The guanine nucleotide binding protein Ras plays a central role as molecular switch in cellular signal transduction. Ras cycles between a GDP-bound "off" state and a GTP-bound "on" state. Specific oncogenic mutations in the Ras protein are found in up to 30% of all human tumors. Previous 31P NMR studies had demonstrated that in liquid solution different conformational states in the GDP-bound as well as in the GTP-bound form coexist. High-field EPR spectroscopy of the GDP complexes in solution displayed differences in the ligand sphere of the wild-type complex as compared to its oncogenic mutant Ras(G12V). Only three water ligands were found in the former with respect to four in the G12V mutant [Rohrer, M. et al. (2001) Biochemistry 40, 1884-1889]. These differences were not detected in previous X-ray structures in the crystalline state. In this paper, we employ high-frequency electron nuclear double resonance (ENDOR) spectroscopy to probe the ligand sphere of the metal ion in the GDP-bound state. This technique in combination with selective isotope labeling has enabled us to detect the resonances of nuclei in the first ligand sphere of the ion with high spectral resolution. We have observed the 17O ENDOR spectra of the water ligands, and we have accurately determined the 17O hyperfine coupling with a(iso) = -0.276 mT, supporting the results of previous line shape analysis in solution. Further, the distinct resonances of the alpha-, beta-, and gamma-phosphorus of the bound nucleotides are illustrated in the 31P ENDOR spectra, and their hyperfine tensors lead to distances in agreement with the X-ray structures. Finally, 13C ENDOR spectra of uniformly 13C-labeled Ras(wt) x GDP and Ras(G12V) x GDP complexes as well as of the Ras(wt) x GppNHp and the selectively 1,4-13C-Asp labeled Ras(wt) x GDP complexes have revealed that in frozen solution only one amino acid is ligated to the ion in the GDP state, whereas two are bound in the GppNHp complex. Our results suggest that a second conformational state of the protein, if correlated with a different ligand sphere of the Mn2+ ion, is not populated in the GDP form of Ras at low temperatures in frozen solution.
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Affiliation(s)
- M Bennati
- Institute of Physical and Theoretical Chemistry and Center for Biomolecular Magnetic Resonance, J. W. Goethe University of Frankfurt, D-60439 Frankfurt, Germany.
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Astashkin AV, Neese F, Raitsimring AM, Cooney JJA, Bultman E, Enemark JH. Pulsed EPR investigations of systems modeling molybdenum enzymes: hyperfine and quadrupole parameters of oxo-17O in [Mo 17O(SPh)4]-. J Am Chem Soc 2006; 127:16713-22. [PMID: 16305262 DOI: 10.1021/ja055472y] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ka band ESEEM spectroscopy was used to determine the hyperfine (hfi) and nuclear quadrupole (nqi) interaction parameters for the oxo-17O ligand in [Mo 17O(SPh)4]-, a spectroscopic model of the oxo-Mo(V) centers of enzymes. The isotropic hfi constant of 6.5 MHz found for the oxo-17O is much smaller than the values of approximately 20-40 MHz typical for the 17O nucleus of an equatorial OH(2) ligand in molybdenum enzymes. The 17O nqi parameter (e2qQ/h = 1.45 MHz, eta approximately = 0) is the first to be obtained for an oxo group in a metal complex. The parameters of the oxo-17O ligand, as well as other magnetic resonance parameters of [Mo 17O(SPh)4]- predicted by quasi-relativistic DFT calculations, were in good agreement with those obtained in experiment. From the electronic structure of the complex revealed by DFT, it follows that the SOMO is almost entirely molybdenum d(xy) and sulfur p, while the spin density on the oxo-17O is negative, determined by spin polarization mechanisms. The results of this work will enable direct experimental identification of the oxo ligand in a variety of chemical and biological systems.
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Affiliation(s)
- Andrei V Astashkin
- Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA.
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Livramento JB, Sour A, Borel A, Merbach AE, Tóth E. A Starburst-Shaped Heterometallic Compound Incorporating Six Densely Packed Gd3+ Ions. Chemistry 2006; 12:989-1003. [PMID: 16311990 DOI: 10.1002/chem.200500969] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The heterotritopic ligand [bpy(DTTA)2]8- has two diethylenediamine-tetraacetate units for selective lanthanide(III) coordination and one bipyridine function for selective Fe(II) coordination. In aqueous solution and in the presence of these metals, the ligand is capable of self-assembly to form a rigid supramolecular metallostar structure, [Fe[Gd2bpy(DTTA)2(H2O)4]3]4-. We report here the physicochemical characterization of the dinuclear complex [Gd2bpy(DTTA)2(H2O)4]2- and the metallostar [Fe[Gd2bpy(DTTA)2(H2O)4]3]4- with regard to potential MRI contrast agent applications. A combination of pH potentiometry and 1H NMR spectroscopy has been used to determine protonation constants for the ligand [bpy(DTTA)2]8- and for the complexes [Fe[bpy(DTTA)2]3]22- and [Y2bpy(DTTA)2]2-. In addition, stability constants have been measured for the dinuclear chelates [M2bpy(DTTA)2]n- formed with M = Gd3+ and Zn2+ (log K(GdL) = 18.2; log K(ZnL) = 18.0; log K(ZnHL) = 3.4). A multiple field, variable-temperature 17O NMR and proton relaxivity study on [Gd2bpy(DTTA)2(H2O)4]2- and [Fe[Gd2bpy(DTTA)2(H2O)4]3](4-) yielded the parameters for water exchange and the rotational dynamics. The 17O chemical shifts are indicative of bishydration of the lanthanide ion. The exchange rates of the two inner-sphere water molecules are very similar in the dinuclear [Gd2bpy(DTTA)2(H2O)(4)]2- and in the metallostar (k(ex)298 = 8.1 +/- 0.3 x 10(6) and 7.4 +/- 0.2 x 10(6) s(-1), respectively), and are comparable to k(ex)298 for similar Gd(III) poly(amino carboxylates). The rotational dynamics of the metallostar has been described by means of the Lipari-Szabo approach, which involves separating global and local motions. The difference between the local and global rotational correlation times, tau(lO)298 = 190 +/- 15 ps and tau(gO)298 = 930 +/- 50 ps, respectively, shows that the metallostar is not completely rigid. However, the relatively high value of S2 = 0.60 +/- 0.04, describing the restriction of the local motions with regard to the global one, points to a limited flexibility compared with previously reported macromolecules such as dendrimers. As a result of the two inner-sphere water molecules, with their near-optimal exchange rate, and the limited flexibility, the metallostar has a remarkable molar proton relaxivity, particularly at high magnetic fields (r1 = 33.2 and 16.4 mM(-1) s(-1) at 60 and 200 MHz, respectively, at 25 degrees C). It packs six efficiently relaxing Gd(III) ions into a small molecular space, which leads, to the best of our knowledge, to the highest relaxivity per molecular mass ever reported for a Gd(III) complex. The [bpy(DTTA)2]8- ligand is also a prime candidate as a terminal ligand for constructing larger sized, Fe(II) (or Ru(II))-based metallostars or metallodendrimers loaded with Gd(III) on the surface.
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Affiliation(s)
- João Bruno Livramento
- Laboratoire de Chimie Inorganique et Bioinorganique, Ecole Polytechnique Fédérale de Lausanne, EPFL-BCH, 1015 Lausanne, Switzerland
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Goldfarb D. High field ENDOR as a characterization tool for functional sites in microporous materials. Phys Chem Chem Phys 2006; 8:2325-43. [PMID: 16710481 DOI: 10.1039/b601513c] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The determination of the details of the spatial and electronic structure of functional sites (centers) in any system, be it in materials chemistry or in biology, is the first step towards understanding their function. When such sites happen to be paramagnetic in any point of their activity cycle, the tool box offered by a variety of high resolution electron paramagnetic resonance (EPR) spectroscopic techniques becomes very attractive for their characterization. This tool box has been considerably expanded by the developments in high field (HF) EPR in general, and HF electron nuclear double resonance (ENDOR), in particular. These have led to numerous new applications in the fields of biology, physics, chemistry and materials sciences. This overview focuses specifically on recent applications of pulsed HF ENDOR spectroscopy to microporous materials, such as zeotype materials, presenting the new opportunities it offers. First, a brief description of the theoretical basis required for the analysis of the HF ENDOR spectrum is given, followed by a description of the pulsed techniques used to record spectra and assign the signals, along with a brief presentation of the required instrumentation. Next, specific applications are given, including transition metal ions and complexes exchanged into zeolite cages, transition metal substitution into frameworks of zeolites, aluminophosphate molecular sieves, and silicious mesoporous materials, the interaction of NO with Lewis sites in zeolite cages and trapped S. We end with a discussion of the advantages and the shortcomings of the method and conclude with a future outlook.
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Affiliation(s)
- Daniella Goldfarb
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel.
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50
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Yazyev OV, Helm L, Malkin VG, Malkina OL. Quantum Chemical Investigation of Hyperfine Coupling Constants on First Coordination Sphere Water Molecule of Gadolinium(III) Aqua Complexes. J Phys Chem A 2005; 109:10997-1005. [PMID: 16331943 DOI: 10.1021/jp053825+] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Hyperfine interactions (HFI) on the nuclei of the first coordination sphere water molecules in a model [Gd(H(2)O)(8)](3+) aqua complex and in the magnetic resonance imaging contrast agent [Gd(DOTA)(H(2)O)](-) were studied theoretically. Density functional theory (DFT) calculations combined with classical molecular dynamics (MD) simulations have been used in order to take into account dynamic effects in aqueous solution. DFT relativistic calculations show a strong spin-polarization of the first coordination sphere water molecules. This spin-polarization leads to a positive (17)O isotropic hyperfine coupling constant (A(iso)((17)O) = 0.58 +/- 0.11 MHz) and to a significant increase of the effective distance (r(eff)(Gd-O) = 2.72 +/- 0.06 A) of dipolar interaction compared to the mean internuclear distance (r(Gd-O) = 2.56 +/- 0.06 A) obtained from the MD trajectory of [Gd(DOTA)(H(2)O)](-) in aqueous solution. The point-dipole model for anisotropic hyperfine interaction overestimates therefore the longitudinal relaxation rate of the (17)O nucleus by approximately 45%. The (1)H isotropic hyperfine coupling constant of the bound water molecule is predicted to be very small (A(iso)((1)H) = 0.03 +/- 0.02 MHz), and the point-dipole approximation for first coordination sphere water protons holds. The calculated hyperfine parameters are in good agreement with available experimental data.
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Affiliation(s)
- Oleg V Yazyev
- Laboratoire de Chimie Inorganique et Bioinorganique, Ecole Polytechnique Fédérale de Lausanne, EPFL-BCH, CH-1015 Lausanne, Switzerland
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