Shuttle DNP spectrometer with a two-center magnet

Abstract

A DNP set-up is described where a liquid sample is hyperpolarized by the electron-nucleus Overhauser effect in a field of 0.34 T and transferred to a field of 14.09 T for NMR detection. In contrast to a previous set-up, using two dedicated magnets for polarization and detection, a dedicated ferroshim system was inserted into the bore of a 14.09 T shielded cryomagnet to provide a homogeneous low-field region in the stray field above the magnetic center. After polarization in the low-field the sample is transferred to the high-field magnetic center within 40 ms by a pneumatic shuttle system. In our set-up a standard high-resolution inverse ¹H/¹³C selective probe was used for NMR detection and a homebuilt EPR cavity, operating in the TM₁₁₀ mode was used for polarisation. First experimental data are presented. We observed a maximum proton Overhauser enhancement of up to ε^HF = −3.7 in the high-field position for a 5 mM 4-Oxo-TEMPO-D,¹⁵N (TEMPONE)/H₂O sample. While this reproduces the DNP enhancement observed also in the old set-up, with the new set-up we observe enhancement on larger molecules that were impossible to enhance in the old set-up. Therefore, we can demonstrate for the first time Overhauser enhanced high resolution proton spectra of glucose and 2,2-dimethyl-2-silapentane-5-sulfonic acid sodium salt (DSS) in D₂O, where the high resolution spectrum was acquired in the high-field position after polarizing the sample in the low-field.