Although ATP concentration is expected to be highest, therefore easiest to detect, in the RBC extract, not ATP signals were detected (Figure , black vs dark pink signals). At the same time, the signals of the nh-PHIP hyperpolarized hydride chemical shift reference compound, nicotinamide (naturally present in RBC extract), overlapped perfectly. When RBC extract NMR was spiked 0.1 mM ATP, signals appeared in a slightly different region (Figure , orange signals) compared to the ATP standard. This could suggest that the RBC extract either does not contain ATP (black vs orange spectrum). However, considerable amount of ATP was observed in the RBC extract by regular 1 H NMR (See SI), suggesting that ATP is present but is unable to form a complex with the nh-PHIP catalyst (Scheme 1). One of the most likely reasons for this is that in a physiological environment polyanionic ATP forms complexes with divalent metal ions, mainly with Mg 2+ . Therefore the positively charged active nh-PHIP catalyst complex ([(IMes)(H)2(mtz)3] + ) would not be able to form a complex with the ATP-Mg.