TY - JOUR
T1 - Spin-crossover and high-spin iron(ii) complexes as chemical shift 19F magnetic resonance thermometers
AU - Thorarinsdottir, Agnes E.
AU - Gaudette, Alexandra I.
AU - Harris, T. David
N1 - Funding Information:
This research was funded by the Air Force Research Laboratory under agreement no. FA8650-15-5518, the Chemistry of Life Processes Institute, and Northwestern University. The U.S. Government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of AFRL or the U.S. Government. T.D.H. thanks the Alfred P. Sloan Foundation. We thank Mr K. Du and Ms L. Lilley for experimental assistance and helpful discussions, Dr J. Y. Lee for experimental assistance, Ms C. Stern for assistance with X-ray crystallography, and Prof T. Meade for generous donation of 19F NMR standards and fetal bovine serum.
Publisher Copyright:
© The Royal Society of Chemistry.
PY - 2017
Y1 - 2017
N2 - 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.
AB - 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.
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U2 - 10.1039/c6sc04287b
DO - 10.1039/c6sc04287b
M3 - Article
C2 - 28694955
AN - SCOPUS:85014067104
VL - 8
SP - 2448
EP - 2456
JO - Chemical Science
JF - Chemical Science
SN - 2041-6520
IS - 3
ER -