Temperature-Controlled Molecular Depolarization Gates in Nuclear Magnetic Resonance

Abstract

The potential of nuclear magnetic resonance (NMR) to yield spectroscopic and imaging (MRI) information based on molecule-specific signals is often impeded by its intrinsic low detection sensitivity. Amplifying the available magnetization has been the focus of many studies, leading to various hyperpolarization (hp) techniques, such as hp noble gases, parahydrogen-induced polarization transfer, or dynamic nuclear polarization. Exploiting chemical exchange of nuclei of a hyperpolarized reservoir in combination with a mechanism of gated transfer onto the molecule of interest would provide optimized, controlled utilization of the hyperpolarization, thus avoiding polarization losses during transfer reactions. As exchange rates depend on the ambient temperature, the amplification achieved by transferring information from a low-concentration target pool onto the high-concentration reservoir pool can be tuned. Herein, we demonstrate the implementation of this concept using molecular cages to host hp xenon, and apply this approach to noninvasive molecular temperature sensing.