Ligand Control of 59Co Nuclear Spin Relaxation Thermometry.

Tyler M Ozvat,Anthony K Rappé,Joseph M Zadrozny,Spencer H Johnson

doi:10.3390/magnetochemistry6040058

Tyler M Ozvat, Anthony K Rappé + Show 2 more

Open Access

https://doi.org/10.3390/magnetochemistry6040058

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Abstract

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 59Co T1 (spin–lattice) and T2 (spin–spin) relaxation times in a set of Co(III) complexes: K3[Co(CN)6] (1); [Co(NH3)6]Cl3 (2); [Co(en)3]Cl3 (3), en = ethylenediamine); [Co(tn)3]Cl3 (4), tn = trimethylenediamine); [Co(tame)2]Cl3 (5), tame = triaminomethylethane); and [Co(dinosar)]Cl3 (6), dinosar = dinitrosarcophagine). Measurements indicate that 59Co T1 and T2 increase with temperature for 1–6 between 10 and 60 °C, with the greatest ΔT1/ΔT and ΔT2/ΔT temperature sensitivities found for 4 and 3, 5.3(3)%T1/°C and 6(1)%T2/°C, respectively. Temperature-dependent T2* (dephasing time) analyses were also made, revealing the highest ΔT2*/ΔT sensitivities in structures of greatest encapsulation, as high as 4.64%T2*/°C for 6. Calculations of the temperature-dependent quadrupolar coupling parameter, Δe2qQ/ΔT, enable insight into the origins of the relative ΔT1/ΔT values. These results suggest tunable quadrupolar coupling interactions as novel design principles for enhancing temperature sensitivity in nuclear spin-based probes.

Highlights

The control of nuclear spin properties by molecular design is an important capability for many applications, spanning from diagnostic bioimaging [1,2,3] to encoding and processing quantum information [4,5,6,7]
Calculations of the temperature-dependent quadrupolar coupling parameter, ∆e2 qQ/ ∆T, enable insight into the origins of the relative ∆T1 /∆T values. These results suggest tunable quadrupolar coupling interactions as novel design principles for enhancing temperature sensitivity in nuclear spin-based probes
The first temperature-dependent 59 Co nuclear spin property we investigated was the spin–lattice, or T1, relaxation time

Summary

Introduction

The control of nuclear spin properties by molecular design is an important capability for many applications, spanning from diagnostic bioimaging [1,2,3] to encoding and processing quantum information [4,5,6,7]. A more focused application is designing temperature dependence into nuclear spin properties toward molecular-level thermometry, an essential technique for next-generation treatments of cancer [8,9,10,11]. 59 Co nuclear spins are an extremely promising platform for detecting changes in temperature, owing to the extreme thermal sensitivity of the metal ion chemical shift [12]. We note that chemical shift is not the only temperature-dependent property of nuclear spins.

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