Üngör Ö, Sanchez S, Ozvat TM, Zadrozny JM. Asymmetry-enhanced
59Co NMR thermometry in Co(iii) complexes.
Inorg Chem Front 2023;
10:7064-7072. [PMID:
38021440 PMCID:
PMC10660387 DOI:
10.1039/d3qi01641b]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Accepted: 10/20/2023] [Indexed: 12/01/2023]
Abstract
Design strategies for molecular thermometers by magnetic resonance are essential for enabling new noninvasive means of temperature mapping for disease diagnoses and treatments. Herein we demonstrate a new design strategy for thermometry based on chemical control of the vibrational partition function. To do so, we performed variable-temperature 59Co NMR investigations of four air-stable Co(iii) complexes: Co(accp)3 (1), Co(bzac)3 (2), Co(tBu2-acac)3 (3), and Co(acac)3 (4) (accp = 2-acetylcyclopentanonate; bzac = benzoylacetonate; tBu2-acac = 2,2,6,6-tetramethyl-3,5-heptanedionate and acac = acetylacetonate). We discovered 59Co chemical shift temperature sensitivity (Δδ/ΔT) values of 3.50(2), 3.39(3), 1.63(3), and 2.83(1) ppm °C-1 for 1-4, respectively, at 100 mM concentration. The values observed for 1 and 2 are new records for sensitivity for low-spin Co(iii) complexes. We propose that the observed heightened sensitivities for 1 and 2 are intimately tied to the asymmetry of the accp and bzac ligands versus the acac and tBu2-acac ligands, which enables a larger number of low-energy Raman-active vibrational modes to contribute to the observed Δδ/ΔT values.
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