Enterobactin (ent) exhibits the largest association constant with Fe(III) of any siderophore. Correlated with its relatively higher Lewis acidity, Ti(IV) might bind tighter to ent than does Fe(III). Spectrophotometric titrations were utilized to determine the pH-dependent aqueous speciation of Ti-ent. Competition titrations at constant pH with disodium 4,5-dihydroxy-1,3-benzenedisulfonate (tiron) were employed to determine the association constant of Ti-ent. Taken together, these experiments suggest that Ti-ent is the metal/siderophore complex with the largest association constant known. The kinetics of Ti-ent formation was also probed by introducing ent to Ti(IV) complexes of citrate, deferrioxamine B, and human serum transferrin, and observing Ti-ent formation. Once bound to ent, Ti(IV) does not appear to exchange with any other ligand. This large apparent binding strength suggests that Ti(IV) might outcompete Fe(III) in the environment, interfering with Fe(III) transport and leading to possible incorporation of Ti(IV) into biological systems.

Investigation of the binding affinity and kinetics of the Ti(IV) enterobactin complex

254th National Meeting (2017)

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