Since most of the retrieved ligands contained a phosphate group, also most of the identified chelating groups contained phosphate or another phosphorus-containing group (40%, Table , complete list in S3 in the Supporting Information). Among the ten most frequent chelating groups for the three metal ions, a third contained a phosphate group (S4 in the Supporting Information). Those groups were mostly found in chelating groups derived from Mg 2+ ligands (68%), followed by groups derived from Mn 2+ ligands (35%) while phosphate groups were less prevalent among chelating groups derived from Zn 2+ ligands (19%). Accordingly, also 8 out the 10 most common metal-chelating groups found for Mg 2+ ligands contained phosphate groups while the common chelating groups were more diverse for the other two ions (Figure ). Besides the large number of phosphorus-containing groups, there were other similarities among the extracted metal-chelating groups. This was mainly caused by the chelating pattern (Figure ) which could in addition result in different allowed substi tution points in substructure searches. To visualize the relationship between the extracted groups, a hierarchical tree was built ba sed on substructure matching (Figure , file S5 in Supporting Information). This resulted in 58 groups at the highest level (roots), and 20 of those represented at least 20 different substructures (Table ). The maximum depth of the tree was 14 nodes.