Question

Enterobactin is a hexadentate catecholate ligand secreted by pathogenic bacteria (E. Coli). Its job is to appropriate your body's iron for use by the bacteria. It has an iron affinity ~26 orders of magnitude higher than that of EDTA. HO OH HTTP OH NH HO он HO TOH enterobactin EDTA a. What thermodynamic quantity gives rise to the chelate effect? b. Based on your answer in a, explain why rigid ligands with preorganized geometries for metal chelation are observed to exhibit a large chelate effect? c. Given that enterobactin only binds iron with its six catechol oxygens, explain why the iron affinity for enterobactin is so much higher. (Hint: Think about the two quantities which contribute toward AG, think about the stereocenters of enterobactin)

Answer 1

1. Standard Entropy is the thermodynamic quantity that gives rise to the chelate effect. EDTA is a versatile chelating agent, which can form chelate with the transition- metal ions and other main group ions. It deactivates enzyme by removing the metal ions and stabilising them. Metal ions remain in the solution but activity is highly reduced. The coordination bond between chelating ligand and metal ion makes the chelation effect. Stability constant is important for formation of complex in a solution, it is the measure nof stength of interaction between two reagents that form complex.
2. With increase in the amount of disorder, the tendency to form also increases due to increased entrophy and partially by enthalphy.
3. Enterobactin have larger concentration of N and O, thus they can readily dissosciate their protons and can serve as oxygen donors to bound with the Fe.