Siderophores thermodynamic stability

The identity of the hard donor group and how it is incorporated in a molecular structure has a bearing on the affinity of a siderophore for iron(III). An analysis of siderophore structure and its relationship to iron(III) binding affinity as expressed by the thermodynamic stability constant is useful in understanding structure/function relationships and in the design of siderophore mimics for specific applications. 

As mentioned previously, siderophores must selectively bind iron tightly in order to solubilize the metal ion and prevent hydrolysis, as well as effectively compete with other chelators in the system. The following discussion will address in more detail the effect of siderophore structure on the thermodynamics of iron binding, as well as different methods for measuring and comparing iron-siderophore complex stability. The redox potentials of the ferri-siderophore complexes will also be addressed, as ferri-siderophore reduction may be important in the iron uptake process in biological systems. 

Thermodynamic Stability Constants for Iron(III)-Siderophore Complexes,... 

Despite the considerable structural variation found in the siderophores, their common feature is to form six-coordinate octahedral complexes with ferric ion of great thermodynamic stability. The ligating groups usually contain the oxygen atoms of hydroxamate (a) or catecholate (b) anions. 

Many siderophores are three-armed podands that contain hydroxamates or catechol moieties which bind to the metal ion. Siderophore iron(iii) complexes are high-spin and are highly thermodynamically stable. The highest stability constant for a natural siderophore is for enterobactin (2.43), whose affinity for iron(iii) is 10 M h The iron(iii) ion is totally enveloped by the catechol arms in a six-coordinate geometry (2.43). Artificial, macrobicyclic siderophores have achieved binding constants of up to... 

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