Optimizing the Reaction Conditions for the Formation of Fumarate via Trans-Hydrogenation

Abstract

Parahydrogen-induced polarization is a hyperpolarization method for enhancing nuclear magnetic resonance signals by chemical reactions/interactions involving the para spin isomer of hydrogen gas. This method has allowed for biomolecules to be hyperpolarized to such a level that they can be used for real time in vivo metabolic imaging. One particularly promising example is fumarate, which can be rapidly and efficiently hyperpolarized at low cost by hydrogenating an acetylene dicarboxylate precursor molecule using parahydrogen. The reaction is relatively slow compared to the timescale on which the hyperpolarization relaxes back to thermal equilibrium, and an undesirable 2nd hydrogenation step can convert the fumarate into succinate. To date, the hydrogenation chemistry has not been thoroughly investigated, so previous work has been inconsistent in the chosen reaction conditions in the search for ever-higher reaction rate and yield. In this work we investigate the solution preparation protocols and the reaction conditions on the rate and yield of fumarate formation. We report conditions to reproducibly yield over 100 mM fumarate on a short timescale, and discuss aspects of the protocol that hinder the formation of fumarate or lead to irreproducible results. We also provide experimental procedures and recommendations for performing reproducible kinetics experiments in which hydrogen gas is repeatedly bubbled into an aqueous solution, overcoming challenges related to the viscosity and surface tension of the water.

Advancing homogeneous catalysis for parahydrogen-derived hyperpolarisation and its NMR applications

“…182 It has since been reported that this has been increased to 30–45% by optimisation of the equipment, reaction conditions, and purification procedure (precipitation as a solid before redissolving). 183,184 The great benefit of this approach is that it is highly compatible with biological imaging studies as it can produce aqueous solutions of hyperpolarised fumarate without contaminant side products or toxic catalyst. 107,183 Production and injection of PHIP-hyperpolarised [1- 13 C]-fumarate into mice containing acetaminophen-induced hepatitis has allowed fumarate biochemistry to be examined in vivo using 2D chemical shift imaging at 1.5 T (Fig.…”

Direct Production of a Hyperpolarized Metabolite on a Microfluidic Chip

“…It is been reported that sodium sulfite improves the selectivity of the trans hydrogenation reaction, although the mechanism of its action is not yet known. 33 , 60 …”

Recent advances in the application of parahydrogen in catalysis and biochemistry

“…In the next step, the dependence of the fumarate production on temperature, pH, and sodium sulfite concentration was determined. Employing these optimized conditions, proton enhancement factors of 3500 at 500 MHz, corresponding to polarizations of P ( 1 H) = 28%, were obtained (for details see Wienands et al 78 ).…”

“…Budker and coworkers have proposed parahydrogen based ultralow-eld NMR techniques as part of the cosmic axion spin precession experiment (CAS-PEr), 68 an NMR-based dark-matter search to probe the axionfermion "wind" coupling. 69 Both PHIP and SABRE have a high application potential in the eld of hyperpolarized MRI, 63,[70][71][72][73][74][75][76][77][78] where hyperpolarized substances, such as hydroxyethyl propionate, fumarate or succinate, were employed as contrast agents (see e.g. the reviews by Hövener et al, 79 Reineri et al 80 and Aime et al 81 ).…”

“…Influence of (b) sodium sulfite concentration and (c) pH on the formation of fumarate; the inset plots show the maximal fumarate concentration reached and the time it took to reach the maximum. For details see Wienands et al78…”