Using <i>para</i>hydrogen to hyperpolarize amines, amides, carboxylic acids, alcohols, phosphates, and carbonates.

Abstract

Hyperpolarization turns weak nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) responses into strong signals, so normally impractical measurements are possible. We use <i>para</i>hydrogen to rapidly hyperpolarize appropriate ¹H, ¹³C, ¹⁵N, and ³¹P responses of analytes (such as NH₃) and important amines (such as phenylethylamine), amides (such as acetamide, urea, and methacrylamide), alcohols spanning methanol through octanol and glucose, the sodium salts of carboxylic acids (such as acetic acid and pyruvic acid), sodium phosphate, disodium adenosine 5'-triphosphate, and sodium hydrogen carbonate. The associated signal gains are used to demonstrate that it is possible to collect informative single-shot NMR spectra of these analytes in seconds at the micromole level in a 9.4-T observation field. To achieve these wide-ranging signal gains, we first use the signal amplification by reversible exchange (SABRE) process to hyperpolarize an amine or ammonia and then use their exchangeable NH protons to relay polarization into the analyte without changing its identity. We found that the ¹H signal gains reach as high as 650-fold per proton, whereas for ¹³C, the corresponding signal gains achieved in a ¹H-¹³C refocused insensitive nuclei enhanced by polarization transfer (INEPT) experiment exceed 570-fold and those in a direct-detected ¹³C measurement exceed 400-fold. Thirty-one examples are described to demonstrate the applicability of this technique.