Isotopomeric Elucidation of the Mechanism of Temperature Sensitivity in 59Co NMR Molecular Thermometers

• Published in: Inorganic chemistry Vol. 61; no. 2; pp. 778 - 785
• Main Authors: Ozvat, Tyler M, Rappé, Anthony K, Zadrozny, Joseph M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17-01-2022
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.1c03326

Understanding the mechanisms governing temperature-dependent magnetic resonance properties is essential for enabling thermometry via magnetic resonance imaging. Herein we harness a new molecular design strategy for thermometrythat of effective mass engineering via deuteration in the first coordination shellto reveal the mechanistic origin of 59Co chemical shift thermometry. Exposure of [Co­(en)3]3+ (1; en = ethylenediamine) and [Co­(diNOsar)]3+ (2; diNOsar = dinitrosarcophagine) to mixtures of H2O and D2O produces distributions of [Co­(en)3]3+-d n (n = 0–12) and [Co­(diNOsar)]3+-d n (n = 0–6) isotopomers all resolvable by 59Co NMR. Variable-temperature 59Co NMR analyses reveal a temperature dependence of the 59Co chemical shift, Δδ/ΔT, on deuteration of the N-donor atoms. For 1, deuteration amplifies Δδ/ΔT by 0.07 ppm/°C. Increasing degrees of deuteration yield an opposing influence on 2, diminishing Δδ/ΔT by −0.07 ppm/°C. Solution-phase Raman spectroscopy in the low-frequency 200–600 cm–1 regime reveals a red shift of Raman-active Co–N6 vibrational modes by deuteration. Analysis of the normal vibrational modes shows that Raman modes produce the largest variation in 59Co δ. Finally, partition function analysis of the Raman-active modes shows that increased populations of Raman modes predict greater Δδ/ΔT, representing new experimental insight into the thermometry mechanism.