Fig. 3. Optimization of rapid PHIP.

¹³C hyperpolarization P_13C of HEP (blue dots) as a function of temperature T (a), parahydrogen pressure p_pH2 (b, T = 90 °C), concentration of catalyst c_cat (c, c_HEA = 80 mM), precursor c_HEA (d), and hydrogenation time t_h (e, c_HEA = 5 mM). In (d), the payload (c_HEA ∙ P_13C; normalized; red circles) is also shown with errors calculated from errors of P_13C(c_HEA) using Gaussian error propagation. Fitted curves correspond to a mono-exponential saturation function (d; R² = 0.98) and the hydrogenation kinetics model from the main text (e; R² = 0.7). Unless stated otherwise, parameters were T = 80 °C, p_pH2 = 15 bar, c_cat = 2 mM, c_HEA = 20 mM, t_h = 5 s, and the mean and standard error of N = 3 experiments is reported; P_13C was quantified assuming hydrogenation of the full amount of precursor was completed. Data is reported in Supplementary Table 3. Data in (c) and (e) were published before but add to the matter at hand^36,56.