Scalable dissolution-dynamic nuclear polarization with rapid transfer of a polarized solid

Abstract

In dissolution-dynamic nuclear polarization, nuclear spins are hyperpolarized at cryogenic temperatures using radicals and microwave irradiation. The hyperpolarized solid is dissolved with hot solvent and the solution is transferred to a secondary magnet where strongly enhanced magnetic resonance signals are observed. Here we present a method for transferring the hyperpolarized solid. A bullet containing the frozen, hyperpolarized sample is ejected using pressurized helium gas, and shot into a receiving structure in the secondary magnet, where the bullet is retained and the polarized solid is dissolved rapidly. The transfer takes approximately 70 ms. A solenoid, wound along the entire transfer path ensures adiabatic transfer and limits radical-induced low-field relaxation. The method is fast and scalable towards small volumes suitable for high-resolution nuclear magnetic resonance spectroscopy while maintaining high concentrations of the target molecule. Polarization levels of approximately 30% have been observed for 1- 13 C-labelled pyruvic acid in solution.

Transport of hyperpolarized samples in dissolution-DNP experiments

“…Alternatively, the sample can be shuttled to the NMR spectrometer as a solid pellet and dissolved near or in the spectrometer. 15 In both cases, regardless whether one transfers a solid or a liquid, it is advantageous to maintain a non-vanishing ''guiding'' magnetic field during the transfer to prevent losses of polarization during the transfer.…”

A Low‐Temperature Broadband NMR Probe for Multinuclear Cross‐Polarization

“…In addition, 13 C and 17 O signals were also detected with cross polarization from 1 H. Unlike common designs of D-DNP probes, most of the RF circuit is immersed in superfluid liquid helium. This apparatus was used to detect NMR spectra of 1 H, 23 Na, 13 C, 2 H, and 17 O with direct polarization.…”

“…There are several radio frequency (RF) designs that have been used in different D-DNP probes, ranging from internally doubly tuned and matched solenoids, [7] externally doubly tuned and matched saddle coils, [11] to locally quasi-distributed doubly tuned and matched Alderman-Grant coils. [13] The tuning and matching circuits include home-built and commercial capacitors that are immersed in superfluid helium at temperatures down to 1.2 K. Care must be taken to avoid oscillations of the superfluid helium in the cryostat. Unlike most conventional setups that have at least a few capacitors outside the polarizer for the fine adjustment of tuning and matching, in our case, the complete RF circuit is immersed in the low-temperature cryostat inside the polarizer.…”

“…NMR spectra of various nuclei with and without DNP at 4 K and 6.7 T. a)1 H spectra at 285.3 MHz with detection of the free induction decay after a 90°pulse of 3 μs. c)13 C spectra at 71.7 MHz with a single adiabatic cross-polarization from 1 H that consists of an adiabatic sweep of 800 μs, a central interval of 200 μs without frequency sweep, and another adiabatic sweep of 800 μs followed by a 90°pulse of 5 μs and detection. c)13 C spectra at 71.7 MHz with a single adiabatic cross-polarization from 1 H that consists of an adiabatic sweep of 800 μs, a central interval of 200 μs without frequency sweep, and another adiabatic sweep of 800 μs followed by a 90°pulse of 5 μs and detection.…”

Use of dissolved hyperpolarized species in NMR: Practical considerations

“…5.5 T, which limits the loss of spin polarization due to T 1 relaxation. The liquid state enhancement factor obtained for [1-13 C ]acetate were comparable to those reported for other13 C -labelled compounds with long T 1 time constants using two separate magnets and pneumatic shuttling.Recently, Meier et al proposed the 'Bullet-DNP' method [33]. It consists in ejecting a bullet containing the frozen, hyperpolarized sample with pressurized helium gas, shooting it into a receiving structure in the NMR magnet, where the bullet is retained and the polarized solid is rapidly dissolved(Figure 3).…”