The MS 2 spectra show that the suite of ligands produced by P. tricornutum are structurally related (Table ). Major fragment ions m/z 422 and 269 observed in the MS 2 spectrum of metal-free ligand G are also observed in the MS 2 spectra of metal-free ligands D, F, H, and J. While the MS 2 spectrum of metal-free ligand E does not contain m/z 422 or 269, it does contain m/z 420 and 267 indicating an additional unsaturation. Given these similarities, it is likely that the tetrapyrrole ligands B-J share the same parent structure but differ in the number, type, and arrangement of functional group substitutions (Fig. ). The other two ligands detected, A and K, are likely tripyrroles as the same fragmentation pathways are observed (loss of methoxycarbonyl, H2O, CO, pyrrole ring, decarboxylation). Interestingly, the tripyrroles were present as both the metal-free and Cu-bound ligands, indicating that the ligands produced by P. tricornutum are tri-dentate ligands, which is consistent with metal-bound complexes of chlorophyll catabolites.