Construction of a Liquid-State NMR DNP Shuttle Spectrometer: First Experimental Results and Evaluation of Optimal Performance Characteristics

Abstract

First results from a liquid-state shuttle dynamic nuclear polarization (DNP) spectrometer are presented. The device polarizes a water sample at 9.7 GHz and 0.34 T in a commercial Bruker electron paramagnetic resonance (EPR) spectrometer and then transfers the sample via a homebuilt pneumatic shuttle device into the 600 MHz and 14.09 T nuclear magnetic resonance (NMR) spectrometer with a conventional NMR probe for detection. The shuttle transfer time is approximately 115 ms. Initial experiments measure the postshuttle proton magnetization compared with the Boltzmann magnetization at 14.09 T. The DNP enhancement factor at 0.34 T is reported for the nitroxide polarizer TEMPOL in water solution. Reduction of the magnetization during shuttling because of relaxation is quantified. Optimization of this apparatus is expected to bring the NMR enhancement factor for protons close to the theoretical enhancement maximum of #7.92.

Studies of Dynamic Nuclear Polarization with Nitroxides in Aqueous Solution

“…Alternatively, improved microwave resonance structures with higher conversion factors could lead to saturation factors close to 1 without requirement of higher microwave power. We are currently using the present nitroxide-water solution polarizer system to test and optimize DNP with a new shuttle spectrometer operating at 9 GHz EPR pumping frequency and at 600 MHz 1 H NMR frequency [16].…”

A magnetic tunnel to shelter hyperpolarized fluids

“…In field shuttling experiments, this low-field region has pertinently been referred to as "death valley." 10 The hyperpolarization is likely to perish in this hostile territory because various nuclear spin-lattice relaxation mechanisms may be exacerbated at low fields, including paramagnetic effects, scalar relaxation, etc.…”

Rapid-melt Dynamic Nuclear Polarization

“…In low field Overhauser DNP and high field NMR detection, the sample is polarized at a lower field under favorable conditions (discussed in 1.5.1) to attain high polarization and the NMR signal is acquired at a higher field either by shuttling [44] or flowing [45] the hyperpolarized sample to the higher field. 13 C enhancements for halogenated compounds were demonstrated in the late 1990's [45,46].…”

“…Han and co-workers demonstrated a continuous flow approach to polarize water in the fringe field of an MRI magnet for imaging [47]. In the sample shuttling approach, the sample is shuttled to higher magnetic field with pneumatic equipment [44].…”