EXAFS investigations of temperature-dependent structure in cobalt-59 molecular NMR thermometers

Cobalt-59 nuclei are known for extremely thermally sensitive chemical shifts ( δ ), which in the long term could yield novel magnetic resonance thermometers for bioimaging applications. In this manuscript, we apply extended X-ray absorption fine structure (EXAFS) spectroscopy for the first time to p...

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Published in:Dalton transactions : an international journal of inorganic chemistry 2020-11, Vol.49 (45), p.1638-16385
Main Authors: Ozvat, Tyler M, Sterbinsky, George E, Campanella, Anthony J, Rappé, Anthony K, Zadrozny, Joseph M
Format: Article
Language:English
Subjects:
Ammonia
Atomic structure
Chemical equilibrium
Coordination compounds
Ethane
Ethylenediamine
Fine structure
Medical imaging
Molecular structure
NMR
Nuclear magnetic resonance
Temperature dependence
Thermometers
X ray absorption
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Summary:Cobalt-59 nuclei are known for extremely thermally sensitive chemical shifts ( δ ), which in the long term could yield novel magnetic resonance thermometers for bioimaging applications. In this manuscript, we apply extended X-ray absorption fine structure (EXAFS) spectroscopy for the first time to probe the exact variations in physical structure that produce the exceptional thermal sensitivity of the 59 Co NMR chemical shift. We apply this spectroscopic technique to five Co( iii ) complexes: [Co(NH 3 ) 6 ]Cl 3 ( 1 ), [Co(en) 3 ]Cl 3 ( 2 ) (en = ethylenediamine), [Co(tn) 3 ]Cl 3 ( 3 ) (tn = trimethylenediamine), [Co(tame) 2 ]Cl 3 ( 4 ) (tame = 1,1,1-tris(aminomethyl)ethane), and [Co(diNOsar)]Cl 3 ( 5 ) (diNOsar = dinitrosarcophagine). The solution-phase EXAFS data reveal increasing Co-N bond distances for these aqueous complexes over a ∼50 °C temperature window, expanding by Δ r (Co-N) = 0.0256(6) Å, 0.0020(5) Å, 0.0084(5) Å, 0.0006(5) Å, and 0.0075(6) Å for 1-5 , respectively. Computational analyses of the structural changes reveal that increased connectivity between the donor atoms encourages complex structural variations. These results imply that rich temperature-dependent structural variations define 59 Co NMR thermometry in macrocyclic complexes. EXAFS spectroscopy was used to study the temperature-dependent molecular structures of a series of cobalt-59 NMR thermometers.
ISSN:1477-9226
1477-9234
DOI:10.1039/d0dt01391a