Fig. 2.

(A) The polarization and concentration of fumarate formed for different durations of parahydrogen bubbling, under the experimental conditions described in the text. (B) Molar polarization of [1-¹³C]fumarate, i.e., the product of concentration and polarization. We do not account for non–¹³C-enriched material being used in these experiments, so the true values are ∼45$\times$ lower. (C) The ¹³C NMR spectra of a purified hyperpolarized fumarate solution (at natural ¹³C abundance) and a standard solution of 500 mM [1-¹³C]fumarate with thermal equilibrium spin polarization. Both spectra were acquired using one transient, and are shown with 0.3-Hz line broadening. (D) ¹³C $T_1$ data for the control and purified samples. Each data point shows the integral of the [1-¹³C]fumarate resonance in the corresponding spectrum. The ¹³C signal intensity in both datasets is normalized to 1 for the first data point, and the dotted lines are monoexponential decays of the form ${\text{e}}^{-t/T_1-t/T_{\text{P}}}$, fit to the data using the stated $T_1$ values and $T_{\text{P}}$ = 327 s to account for magnetization lost due to successive pulses as described in the text.