¹³C and ¹⁵N Benchtop NMR Detection of Metabolites via Relayed Hyperpolarization**

Abstract

Parahydrogen‐based nuclear spin hyperpolarization allows various magnetic‐resonance applications, and it is particularly attractive because of its technical simplicity, low cost, and ability to quickly (in seconds) produce large volumes of hyperpolarized material. Although many parahydrogen‐based techniques have emerged, some of them remain unexplored due to the lack of careful optimization studies. In this work, we investigate and optimize a novel parahydrogen‐induced polarization (PHIP) technique that relies on proton exchange referred to below as PHIP‐relay. An INEPT (insensitive nuclei enhanced by polarization transfer) sequence is employed to transfer polarization from hyperpolarized protons to heteronuclei ( 15 ${^{15} }$ N and 13 ${^{13} }$ C) and nuclear signals are detected using benchtop NMR spectrometers (1 T and 1.4 T, respectively). We demonstrate the applicability of the PHIP‐relay technique for hyperpolarization of a wide range of biochemicals by examining such key metabolites as urea, ammonium, glucose, amino acid glycine, and a drug precursor benzamide. By optimizing chemical and NMR parameters of the PHIP‐relay, we achieve a 17,100‐fold enhancement of 15 ${^{15} }$ N signal of [ 13 ${^{13} }$ C, 15 ${^{15} }$ N 2 ${_2 }$ ]‐urea compared to the thermal signal measured at 1 T. We also show that repeated measurements with shorter exposure to parahydrogen provide a higher effective signal‐to‐noise ratio compared to longer parahydrogen bubbling.

Cryogen‐free 400‐MHz nuclear magnetic resonance spectrometer as a versatile tool for pharmaceutical process analytical technology

“…The study concluded that low‐field benchtop NMRs are not that useful for structure elucidation of complex unknown materials because of their low resolution compared with high‐field NMR spectrometers. In addition, research has been ongoing in low‐field benchtop NMRs to improve their sensitivity for low‐sensitive nuclides through hyperpolarization 70–74 . Poor resolution issues in low‐field NMR can sometimes be ameliorated with chemometrics for structural analysis of molecules with low‐to‐medium complexity.…”