Open AccessEXAFS investigations of temperature-dependent structure in cobalt-59 molecular NMR thermometers
Author(s) -
Tyler M. Ozvat,
George E. Sterbinsky,
Anthony J. Campanella,
Anthony K. Rappé,
Joseph M. Zadrozny
Publication year - 2020
Publication title -
dalton transactions
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.98
H-Index - 184
eISSN - 1477-9234
pISSN - 1477-9226
DOI - 10.1039/d0dt01391a
Subject(s) - extended x ray absorption fine structure , ethylenediamine , cobalt , chemistry , nuclear magnetic resonance spectroscopy , aqueous solution , yield (engineering) , spectroscopy , crystallography , analytical chemistry (journal) , absorption spectroscopy , materials science , stereochemistry , inorganic chemistry , organic chemistry , physics , metallurgy , quantum mechanics
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 59Co NMR chemical shift. We apply this spectroscopic technique to five Co(iii) complexes: [Co(NH3)6]Cl3 (1), [Co(en)3]Cl3 (2) (en = ethylenediamine), [Co(tn)3]Cl3 (3) (tn = trimethylenediamine), [Co(tame)2]Cl3 (4) (tame = 1,1,1-tris(aminomethyl)ethane), and [Co(diNOsar)]Cl3 (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 Δr(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 59Co NMR thermometry in macrocyclic complexes.