Asymmetry-enhanced Co NMR thermometry in Co(iii) complexes.

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 Co NMR investigations of four air-stable Co(iii) complexes: Co(accp) (1), Co(bzac) (2), Co(Bu-acac) (3), and Co(acac) (4) (accp = 2-acetylcyclopentanonate; bzac = benzoylacetonate; Bu-acac = 2,2,6,6-tetramethyl-3,5-heptanedionate and acac = acetylacetonate).

Record Chemical-Shift Temperature Sensitivity in a Series of Trinuclear Cobalt Complexes.

Designing spins that exhibit long-lived coherence and strong temperature sensitivity is central to designing effective molecular thermometers and a fundamental challenge in the chemistry/quantum-information space. Herein, we provide a new pathway to both properties in the same molecule by designing a nuclear spin, which possesses a robust spin coherence, to mimic the strong temperature sensitivity of an electronic spin. This design strategy is demonstrated in the group of trinuclear Co(III) spin-crossover compounds [(CpCo(OP(OR)))Co](SbCl) where Cp = cyclopentadienyl and R = Me (), Et (), -Pr (), and -Bu ().

Ligand design of zero-field splitting in trigonal prismatic Ni(II) cage complexes.

Complexes of encapsulated metal ions are promising potential metal-based electron paramagnetic resonance imaging (EPRI) agents due to zero-field splitting. Herein, we synthesize and magnetically characterize a series of five new Ni(II) complexes based on a clathrochelate ligand to provide a new design strategy for zero-field splitting in an encaged environment. UV-Vis and X-ray single-crystal diffraction experiments demonstrate slight physical and electronic structure changes as a function of the differing substituents.

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

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 Co chemical shift thermometry. Exposure of [Co(en)] (; en = ethylenediamine) and [Co(diNOsar)] (; diNOsar = dinitrosarcophagine) to mixtures of HO and DO produces distributions of [Co(en)]- ( = 0-12) and [Co(diNOsar)]- ( = 0-6) isotopomers all resolvable by Co NMR.

Ligand Control of Co Nuclear Spin Relaxation Thermometry.

Studying the correlation between temperature-driven molecular structure and nuclear spin dynamics is essential to understanding fundamental design principles for thermometric nuclear magnetic resonance spin-based probes. Herein, we study the impact of progressively encapsulating ligands on temperature-dependent Co (spin-lattice) and (spin-spin) relaxation times in a set of Co(III) complexes: K[Co(CN)] (); [Co(NH)]Cl (); [Co(en)]Cl (), en = ethylenediamine); [Co(tn)]Cl (), tn = trimethylenediamine); [Co(tame)]Cl (), tame = triaminomethylethane); and [Co(dinosar)]Cl (), dinosar = dinitrosarcophagine). Measurements indicate that Co and increase with temperature for - between 10 and 60 °C, with the greatest Δ /Δ and Δ /Δ temperature sensitivities found for and , 5.

EXAFS investigations of temperature-dependent structure in cobalt-59 molecular NMR thermometers.

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).

Influence of ligand encapsulation on cobalt-59 chemical-shift thermometry.

Thermometry magnetic resonance imaging (MRI) would provide a powerful noninvasive window into physiological temperature management. Cobalt-59 nuclear spins demonstrate exceptional temperature dependence of their NMR chemical shifts, yet the insight to control this dependence molecular design is lacking. We present the first systematic evidence that encapsulation of this spin system amplifies the temperature sensitivity.