Fig. 2: Ethyl pyruvate (EP) hyperpolarized at 0.55 T.
a Conversion of the hyperpolarized anti-phase EP-d6 spectrum (a-2) into an in-phase spectrum (a-3) boosted the SNR about six times. b Experimental (red circles) and simulated (dashed line) 1H polarization achieved by the out-of-phase spin order transfer sequence with 3 refocusing elements (45o-OPE(3)) as a function of refocusing interval τ. The spectrum for the highest polarization at τ = 10 ms (arrow) is shown in a-3. Note that individual OPE-45 (red indicators) and longitudinal 45o-CPMG experiments (blue indicators) yielded very similar results (see Fig. 3 for details on 45o-CPMG SOT). The in-phase spectrum (a-3) was easier to analyze and less affected by the field inhomogeneity than the PASADENA spectrum (a-2). The estimated polarization of each proton was 14.4% (Supplementary Fig. 4), about one third of the theoretical maximum of 50% for a two-spin system65. Note that a new 300 μL sample injection was required for each red data point on (b). Note that spectrum of neat (~13.5 M), thermally polarized acetone-h6, acquired with a 90° excitation and acquisition sequence (90°-FID), showed a much lower amplitude as the signal of 50 mM hyperpolarized EP-d6. Spectra a-2,3 were obtained after bubbling 5 bar, 92% pH2 for 45 s through the sample containing [Rh] = 3 mM, [vinyl pyruvate-d6] = 50 mM using 45o-FID (a-2) or 45o-OPE(3) with τ = 9 ms (a-3). The simulated net polarization of EP-d6 (b) was multiplied by exp(-τ/60 ms) to accommodate signal decay phenomenologically (black dashed line).
