Heterogeneous ¹H and ¹³C Parahydrogen‐Induced Polarization of Acetate and Pyruvate Esters

Abstract

Magnetic resonance imaging of [1‐13C]hyperpolarized carboxylates (most notably, [1‐13C]pyruvate) allows one to visualize abnormal metabolism in tumors and other pathologies. Herein, we investigate the efficiency of 1H and 13C hyperpolarization of acetate and pyruvate esters with ethyl, propyl and allyl alcoholic moieties using heterogeneous hydrogenation of corresponding vinyl, allyl and propargyl precursors in isotopically unlabeled and 1‐13C‐enriched forms with parahydrogen over Rh/TiO2 catalysts in methanol‐d4 and in D2O. The maximum obtained 1H polarization was 0.6±0.2 % (for propyl acetate in CD3OD), while the highest 13C polarization was 0.10±0.03 % (for ethyl acetate in CD3OD). Hyperpolarization of acetate esters surpassed that of pyruvates, while esters with a triple carbon‐carbon bond in unsaturated alcoholic moiety were less efficient as parahydrogen‐induced polarization precursors than esters with a double bond. Among the compounds studied, the maximum 1H and 13C NMR signal intensities were observed for propyl acetate. Ethyl acetate yielded slightly less intense NMR signals which were dramatically greater than those of other esters under study.

Mechanisms of Methylenecyclobutane Hydrogenation over Supported Metal Catalysts Studied by Parahydrogen‐Induced Polarization Technique

“…Similar results were obtained in PASADENA experiment – except that here PHIP effects were weaker (Figure S7). The observation of lower polarization levels in case of Rh/TiO 2 catalyst with 13.4 wt.% Rh loading compared to 1 wt.% Rh loading is in agreement with previous results [57,58] …”

“…The observation of lower polarization levels in case of Rh/TiO 2 catalyst with 13.4 wt.% Rh loading compared to 1 wt.% Rh loading is in agreement with previous results. [57,58] Pt/TiO 2 Catalyst 0.8 wt.% Pt/TiO 2 catalyst showed lower activity in methylenecyclobutane hydrogenation than Rh/TiO 2 catalysts (Figure 2c). At 150-350 °C methylcyclobutane 3 was the major product with ca.…”

Nanomaterials for hyperpolarized nuclear magnetic resonance and magnetic resonance imaging

“…Lately, the capacity of metal‐supported nanocatalysts for PHIP in aqueous solutions has been further investigated, showing the potential for the polarization of pyruvate and acetate in PHIP‐SAH approaches using their ethyl‐, propyl‐, and allyl esters respectively. In this study, polarization levels of up to 0.3% could be achieved (Salnikov, Chukanov, et al, 2021). An extraordinary step towards the production of catalyst‐free solutions of hyperpolarized substrates was the introduction of an automated continuous flow setup (Figure 8).…”