Figure 14. Human angiotensin-1 converting enzyme (sACE-1) binding affinity of M-chelate-lisinopril complexes was inversely correlated with the size and negative charge of the species attached to the lysine side chain of lisinopril (17). Lisinopril and all M-chelate-lisinopril species (metal-bound and metal-free) are shown: lozenges = lisinopril; squares = NTA-lisinopril; triangles = GGH-lisinopril; circles = EDTA-lisinopril; inverted triangles = DOTA-lisinopril. Orange = Fe; pink = Co; cyan = Ni; blue = Cu; black = no metal. The charge of the modified lysine side chain of lisinopril is listed for each attachment; the charge for each Fe³⁺ complex was 1+ higher than for each corresponding M²⁺ complex.