To identify the pigment NMR signals, we compared three types of cartilage: heavily For further analysis of HGA and its derivatives in those samples, we recorded a series of HETCOR experiments with different CP contact times (Fig. and Fig. ). Increasing CP contact time led to an increase of the number of signals observed, with signals from more distal 1 H and C pairs emerging (Supplementary Fig. ). ), but not on the synthetic pigment. Only where HGA-derived pigment and pigmented AKU cartilage show signals in the same chemical shift range, which we also present as an overlay (50 μs, Supplementary Fig. ). B. EPR spectra of two aqueous solutions of the synthetic HGA-derived pigment. Sample 1 was recovered from the solidstate NMR rotor on which DNP enhancement was attempted, on which a room temperature X-band EPR continuous-wave spectrum was acquired. Sample 2 did not have other radical species added.