Fig. 3. 1D 1H NMR confirms direct zinc binding to yersiniabactin.

1D ¹H NMR spectra of Ybt dissolved in CD₃CN (top trace, 0 equivalents of Zn, red trace) as increasing zinc is titrated into the solution (0.5 equiv., gray trace), (1.0 equiv., blue trace). The loss of intensity of the NH and OH signals arises from the coordination of zinc by the corresponding N and O atoms; the signals that shift correspond to protons whose electronic environment changes due to binding of the Zn²⁺ ion. Only partial binding is observed because Ybt is in rapid equilibrium between two tautomers at C10 in addition to hydrolysis that occurs at C10 ⁴⁹.