Enterobactin is the classic catecholate-type siderophore made by bacteria like $\mathrm{E.\ coli}$ to capture iron(III) from the surroundings. Each statement can be checked against its known structure.
- It has three catechol moieties: True. Enterobactin is built from three units of 2,3-dihydroxybenzoic acid, so it carries three catechol (1,2-dihydroxybenzene) rings.
- It has a serine-trilactone backbone: True. The three catechol-bearing acid units are each attached to one serine, and the three serines link through ester bonds into a 9-membered macrocyclic triester, the trilactone ring that forms the core scaffold of the molecule.
- It binds with $\mathrm{Fe^{3+}}$ ion to form $\mathrm{[Fe(ent)]^{3-}}$ ion: True. The three catechol groups fully deprotonate and wrap around one $\mathrm{Fe^{3+}}$ centre using all six phenolate oxygens, giving an octahedral hexadentate complex. Three catecholate($2-$) ligands carry a total charge of $-6$, so with $\mathrm{Fe^{3+}}$ the complex charge works out to $-6+3=-3$, matching $\mathrm{[Fe(ent)]^{3-}}$.
- It has three hydroxamic acid groups: False. Hydroxamate donor groups belong to a separate family of siderophores, such as ferrioxamine; enterobactin uses catechol oxygens for iron binding, not hydroxamic acid groups.
So enterobactin is correctly described by its three catechol groups, its serine-trilactone ring, and the $\mathrm{[Fe(ent)]^{3-}}$ complex it forms; it does not contain hydroxamic acid groups.
Let's summarize:
- Three 2,3-dihydroxybenzoyl (catechol) units are attached to a cyclic tri-serine lactone core.
- The six catecholate oxygens give hexadentate, octahedral binding to $\mathrm{Fe^{3+}}$, forming $\mathrm{[Fe(ent)]^{3-}}$.
- Enterobactin has no hydroxamic acid groups; that feature belongs to a different siderophore class.
The correct options are (A), (B), and (C).