Intermolecular nuclear relaxation in paramagnetic solutions: from free radicals to rare earths |
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| Institution: | 1. Laboratoire de spectrométrie physique, CNRS-UMR 5588, université Joseph-Fourier, BP 87, 38402, Saint-Martin-d’Hères cedex, France;2. Laboratoire de reconnaissance ionique, service de chimie inorganique et biologique (UMR 5046), département de recherche fondamentale sur la matière condensée, CEA-Grenoble, 17, rue des Martyrs, 38054 Grenoble cedex 9, France;1. Department of Biology, University Federico II, via Cintia, 80126 Napoli, Italy;2. Department of Science and Technologies, University of Naples Parthenope, 80143 Napoli, Italy;1. Constantine the Philosopher University, 949 74 Nitra, Slovakia;2. Research Institute of Animal Production, 951 41 Lužianky, Slovakia;3. Faculty Hospital Nitra, 949 01 Nitra, Slovakia;4. King Saud University, Department of Zoology, College of Science, Riyadh 11451, Saudi Arabia;5. Institute of Animal Reproduction and Food Research, 10-748 Olsztyn, Poland;1. Constantine the Philosopher University, 949 74 Nitra, Slovak Republic;2. Research Institute for Animal Production in Nitra, 951 41 Lužianky, Slovak Republic;3. Institute of Animal Reproduction and Food Research, 10-718 Olsztyn-Kortowo, Poland;4. King Saud University, P. O. Box 2455, 11451 Riyadh, Saudi Arabia;1. Laboratory of Food and Molecular Biochemistry, National Institute of Applied Sciences and Technology (INSAT), University of Carthage, Zone Urbaine Nord, 1080 Tunis, Tunisia;2. Faculty of Sciences of Bizerte, University of Carthage, Tunis, Tunisia;3. Faculty of Sciences of Tunis, University of Tunis El Manar, Tunis, Tunisia;4. College of Sciences and Humanities of Dawadmi, Shaqra University, Shaqra, Kingdom of Saudi Arabia;5. ISAJC, Bir El Bey, University of Tunis, Tunis, Tunisia |
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| Abstract: | The principles of the intermolecular relaxation of a nuclear spin by its fluctuating magnetic dipolar interactions with the electronic spins of the paramagnetic surrounding species in solution are briefly recalled. It is shown that a very high dynamic nuclear polarization (DNP) of solvent protons is obtained by saturating allowed transitions of free radicals with a hyperfine structure, and that this effect can be used in efficient Earth field magnetometers. Recent work on trivalent lanthanide Ln3+ aqua complexes in heavy water solutions is discussed, including paramagnetic shift and relaxation rate measurements of the 1H NMR lines of probe solutes. This allows a determination of the effective electronic magnetic moments of the various Ln3+ ions in these complexes, and an estimation of their longitudinal and transverse electronic relaxation times T1e and T2e. Particular attention is given to Gd(III) hydrated chelates which can serve as contrast agents in magnetic resonance imaging (MRI). The full experimental electronic paramagnetic resonance (EPR) spectra of these complexes can be interpreted within the Redfield relaxation theory. Monte-Carlo simulations are used to explore situations beyond the validity of the Redfield approximation. For each Gd(III) complex, the EPR study leads to an accurate prediction of T1e, which can be also derived from an independent relaxation dispersion study of the protons of the probe solutes. |
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