Abstract
The potential utility of paramagnetic transition metal complexes as chemical shift 19F magnetic resonance (MR) thermometers is demonstrated. Further, spin-crossover FeII complexes are shown to provide much higher temperature sensitivity than do the high-spin analogues, owing to the variation of spin state with temperature in the former complexes. This approach is illustrated through a series of FeII complexes supported by symmetrically and asymmetrically substituted 1,4,7-triazacyclononane ligand scaffolds bearing 3-fluoro-2-picolyl derivatives as pendent groups (Lx). Variable-temperature magnetic susceptibility measurements, in conjunction with UV-vis and NMR data, show thermally-induced spin-crossover for [Fe(L1)]2+ in H2O, with T1/2 = 52(1) °C. Conversely, [Fe(L2)]2+ remains high-spin in the temperature range 4-61 °C. Variable-temperature 19F NMR spectra reveal the chemical shifts of the complexes to exhibit a linear temperature dependence, with the two peaks of the spin-crossover complex providing temperature sensitivities of +0.52(1) and +0.45(1) ppm per °C in H2O. These values represent more than two-fold higher sensitivity than that afforded by the high-spin analogue, and ca. 40-fold higher sensitivity than diamagnetic perfluorocarbon-based thermometers. Finally, these complexes exhibit excellent stability in a physiological environment, as evidenced by 19F NMR spectra collected in fetal bovine serum.
Original language | English (US) |
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Pages (from-to) | 2448-2456 |
Number of pages | 9 |
Journal | Chemical Science |
Volume | 8 |
Issue number | 3 |
DOIs | |
State | Published - 2017 |
ASJC Scopus subject areas
- Chemistry(all)
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CCDC 1505471: Experimental Crystal Structure Determination
Thorarinsdottir, A. E. (Creator), Gaudette, A. I. (Creator) & Harris, T. D. (Creator), Cambridge Crystallographic Data Centre, 2017
DOI: 10.5517/ccdc.csd.cc1mjkl9, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/ccdc.csd.cc1mjkl9&sid=DataCite
Dataset
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CCDC 1505534: Experimental Crystal Structure Determination
Thorarinsdottir, A. E. (Creator), Gaudette, A. I. (Creator) & Harris, T. D. (Creator), Cambridge Crystallographic Data Centre, 2017
DOI: 10.5517/ccdc.csd.cc1mjmmd, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/ccdc.csd.cc1mjmmd&sid=DataCite
Dataset
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CCDC 1505472: Experimental Crystal Structure Determination
Thorarinsdottir, A. E. (Creator), Gaudette, A. I. (Creator) & Harris, T. D. (Creator), Cambridge Crystallographic Data Centre, 2017
DOI: 10.5517/ccdc.csd.cc1mjkmb, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/ccdc.csd.cc1mjkmb&sid=DataCite
Dataset