Magnetic Resonance
Magnetic Resonance
Magnetic Resonance
Preprints
https://doi.org/10.5194/mr-2020-33
https://doi.org/10.5194/mr-2020-33

  03 Dec 2020

03 Dec 2020

Review status: a revised version of this preprint was accepted for the journal MR and is expected to appear here in due course.

Revisiting paramagnetic relaxation enhancements in slowly rotating systems: how long is the long range?

Giovanni Bellomo1,2,a, Enrico Ravera1,2, Vito Calderone1,2, Mauro Botta3, Marco Fragai1,2, Giacomo Parigi1,2, and Claudio Luchinat1,2 Giovanni Bellomo et al.
  • 1Magnetic Resonance Center (CERM) and Department of Chemistry, University of Florence, via Sacconi 6, Sesto Fiorentino, Italy
  • 2Consorzio Interuniversitario Risonanze Magnetiche di Metalloproteine (CIRMMP), Sesto Fiorentino, Italy
  • 3Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale “Amedeo Avogadro”, Viale TMichel 11, 15121, Alessandria, Italy
  • apresent address: Laboratory of Clinical Neurochemistry, Neurology Clinic, University of Perugia, Piazzale Lucio Severi 1/8, 06132 Perugia (PG), Italy

Abstract. Cross relaxation terms in paramagnetic systems that reorient rigidly with slow tumbling times can increase the effective longitudinal relaxation rates of protons of more than one order of magnitude. This is evaluated by simulating the time evolution of the nuclear magnetization using a complete relaxation matrix approach. The calculations show that the Solomon dependence of the relaxation rates on the metal-proton distance (as r−6) can be incorrect for protons farther than 15 Å from the metal, and thus can originate sizable errors in R1-derived distance restraints used, for instance, for protein structure determination. Furthermore, the chemical exchange of these protons with bulk water protons can enhance the relaxation rate of the solvent protons by far more than expected from the Solomon equation. Therefore, it may contribute significantly to the water proton relaxation rates measured at MRI magnetic fields in the presence of slow-rotating nanoparticles containing paramagnetic ions and a large number of exchangeable surface protons.

Giovanni Bellomo et al.

 
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Status: closed
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Giovanni Bellomo et al.

Giovanni Bellomo et al.

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Short summary
The efficiency of the MRI contrast agents can increase by exploiting magnetization transfer effects occurring in slow-rotating nanoparticles containing a paramagnetic metal ion and a large number of exchangeable surface protons. Occurrence of magnetization transfer should also be considered to determine accurate metal-proton distances, used for protein structure determination, from the experimental proton relaxation rates.