IRON(III) COORDINATION CHEMISTRY OF LINEAR DIHYDROXYSERINE COMPOUNDS DERIVED FROM ENTEROBACTIN

The solution thermodynamic stability and iron transport properties of the hydrolysis products of enterobactin are reported. Enterobactin, a tricatechol siderophore, is a cyclic trilactone that undergoes three stepwise hydrolysis reactions to form a linear trimer, then dimer, and finally the monomeric N-(2,3-dihydroxybenzoyl)serine. The protonation and ferric complex formation constants of the linear trimer and linear dimer have been determined. The enthalpies of formation of the linear trimer complex and ferric enterobactin have been measured by calorimetric titrations. The greater stability of the ferric enterobactin complex, compared with tricatechol ligand analogues, is about one-third enthalpic and two-thirds entropic in origin. The DELTA chirality of the ferric enterobactin is also maintained by the linear trimer complex. Assays of the mediation of iron uptake in Escherichia coli RW193 show that both the linear dimer and linear trimer are nearly as effective as enterobactin in mediating iron uptake in this organism.