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Siderophores

المؤلف:  Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong

المصدر:  Shriver and Atkins Inorganic Chemistry ,5th E

الجزء والصفحة:  ص735-736

2025-10-22

503

Siderophores

Siderophores are small polydentate ligands that have a very high affinity for Fe (III). They are secreted from many bacterial cells into the external medium, where they sequester Fe to give a soluble complex that re-enters the organism at a specific receptor. Once inside the cell, the Fe is released.

Figure 27.11 The biological Fe cycle showing how Fe is taken up from the external medium and guarded carefully in its travels through organisms.

Aside from citrate (the Fe (III) citrate complex is the simplest Fe transport species in biology) there are two main types of siderophore. The first type is based on phenolate or catecholate ligands, and is exemplified by enterobactin (17), for which the value of the as sociation constant for Fe (III) is 1052, an affinity so great that enterobactin enables bacteria to erode steel bridges. The second type of siderophore is based on hydroxamate ligands and is exemplified by ferrichrome (18), a cyclic hexapeptide consisting of three glycine and three N-hydroxyl-l-ornithines. All Fe (III) siderophore complexes are octahedral and high spin. Because the donor atoms are hard O or N atoms and negatively charged, they have a relatively low affinity for Fe (II). Synthetic siderophores are proving to be very useful agents for the control of ‘iron overload’, a serious condition affecting large populations of the world, particularly South-East Asia (Section 27.17).