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Link to original content: https://pubmed.ncbi.nlm.nih.gov/29326984
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. 2018 Jan 5;4(1):eaao6250.
doi: 10.1126/sciadv.aao6250. eCollection 2018 Jan.

Using para hydrogen to hyperpolarize amines, amides, carboxylic acids, alcohols, phosphates, and carbonates

Wissam Iali  1 , Peter J Rayner  1 , Simon B Duckett  1
Affiliations

Using para hydrogen to hyperpolarize amines, amides, carboxylic acids, alcohols, phosphates, and carbonates

Wissam Iali et al. Sci Adv. .

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 parahydrogen 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.

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Figures

Scheme 1
Scheme 1. (A) Hyperpolarization via SABRE and (B) hyperpolarization via SABRE-RELAY.
SABRE is used to hyperpolarize the transfer agent NH2R, where R is H or CH2Ph or CH2CH2Ph (etc.), which relays polarization to the analyte (HR″, route A), and R″ is amide, carboxyl, phosphate, or alkoxide (etc.). This process involves both proton exchange and spin-spin interactions and may be mediated by an intermediary HOR′, where R′ is H or suitable scaffold (route B). Center: Reaction scheme shows the formation of SABRE active 2-NH3, which leads to NH3.
Fig. 1
Fig. 1. Hyperpolarization of NH3 under SABRE.
(A) Thermally polarized control 1H NMR spectrum showing peaks for 2-NH3, NH3, and H2 at 298 K in dichloromethane-d2, ×128 vertical expansion relative to (B). (B) Corresponding single-scan 1H NMR spectrum in the presence of p-H2, with the hyperpolarized responses for H2O, NH3(free), Ir-NH3(equatorial), and Ir-NH3(axial) of 2-NH3 indicated.
Fig. 2
Fig. 2. Single-scan NMR spectra of 15.3 mM pentanol (CH3CH2CH2CH2CH2OH, color-coded structure shown) in dichloromethane-d2 solution resulting from the action of NH3, 2-NH3, and p-H2.
(A) Upper 1H NMR spectrum in the thermally polarized control, ×8 vertical expansion, relative to lower SABRE-RELAY spectrum. (B) Single-scan SABRE-RELAY 1H-13C refocused INEPT NMR spectrum (see fig. S8B for the corresponding thermal control trace).
Fig. 3
Fig. 3. Single-scan SABRE-RELAY NMR spectra recorded in dichloromethane-d2 with NH3 and 2-NH3 in the presence of p-H2.
(A) Sodium adenosine 5′-triphosphate, 1H-31P refocused INEPT spectrum (OH transfer) and (B) sodium 13C–labeled pyruvate, 13C NMR spectrum. Single-scan SABRE-RELAY NMR spectra recorded with PEA and 2-PEA in the presence of p-H2 for (C) 15N-13C–labeled urea, 13C NMR spectrum, 25 mM concentration, and (D) 15N-13C–labeled urea, 15N NMR spectrum, 25 mM concentration. The corresponding thermally polarized spectra are detailed in figs. S29A, S18A, S23A, and S23C and yield no signal.
Fig. 4
Fig. 4. Hyperpolarization of benzylamine (BnNH2) under SABRE.
(A) 1H NMR spectrum of hyperpolarized BnNH2 achieved via 2-BnNH2 (top right) under SABRE in dichloromethane-d2 solution after transfer at 60 G (see fig. S32A for the corresponding thermally equilibrated NMR spectrum). The enhanced signals are color-coded; NH2 (blue), CH2 (light green), and Ph (orange) for the bound equatorial BnNH2 ligand of 2-BnNH2, NH2 and CH2 of the free material, and H2O. (B) Corresponding 15N NMR spectrum recorded using 15N-labeled BnNH2 after transfer in a μ-metal shield showing the free (left) and equatorial ligand (right) responses.
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