Rates of iron chelation and exchange between ELT and DFX in vitro. The rates of ferric–chelate complex formation from preformed ferric–citrate complexes (iron: citrate 10:100 µM) are shown with either (A) ELT (30 µM), monitored at 614 nm, which forms a secondary peak of ELT-Fe complex, or (B) DFX (30 µM), monitored at 556 nm, secondary peak for DFX-iron complex. The top horizontal line represents 100% iron complex formation of ELT or DFX (10 µM iron[III]). The lower horizontal lines represent the absorbances of the iron-free ligands (30 µM). It can be seen that ELT binds iron from ferric citrate complexes faster than DFX. The 50% effect is achieved at about 180 min for ELT, but later at around 300 min for DFX. The 100% effect is achieved by ELT at about 12 hours, whereas DFX takes approximately 33 hours. (C) The rates of ferric–DFX complex formation (300 µM of DFX) from either preformed ferric–citrate (iron:citrate 10:100 µM) or from ferric–ELT (10 µM, 1:2) is shown. It can be seen that DFX binds iron from preformed complexes of ELT faster than from ferric–citrate complexes (D). Rate of CP40 ferric complex formation is shown at 200 µM IBE CP40 from preformed 10 µM FeELT₂. The reaction is completed at approximately 200 minutes. (E) The effect of excess ELT ratio to iron on the rate of DFX chelation from preformed iron(III):ELT complexes (ratios 1:1, 1:2, 1:3, and 1:10) and 3.33, 6.66, 10, 33.3 µM ELT, respectively) are shown. Iron complexes of DFX form more rapidly and most completely when the ratio is 1:2 and 1:3 than with ratios of 1:1. A 10-fold excess of iron-free ELT to iron retards the rate of iron donation to DFX.