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

Parahydrogen-relayed hyperpolarization is used for enhancing ¹³C and ¹⁵N benchtop NMR signals of key metabolites – urea, ammonium, glycine, glucose – and a drug precursor benzamide. After sample optimization, a 17,100-fold ¹⁵N NMR signal enhancement of [¹³C, ¹⁵N₂]-urea 1 T was reached. The presented method opens ways of enhancing NMR signals of various molecules for benchtop NMR spectroscopy.

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.

Zum Volltext