UV-Vis spectroscopy.

Purified escherichelin was reconstituted to 1 mM in 50% ethanol (Sigma-Aldrich). For experiments to monitor metal binding, escherichelin was diluted to 100 μM in water and combined with an equimolar amount of FeCl₃ or CuSO₄ (Sigma-Aldrich). The samples were incubated at room temperature for 2 hours, and then a wavelength scan was collected from 200 to 800 nm on a UV-Vis spectrophotometer (Beckman Coulter; DU800). For each escherichelin-plus-metal scan, the instrument was blanked with a metal-only control. For escherichelin alone, the instrument was blanked with 5% ethanol.