Biological systems chelate complexes

Moi, M.K., Meares, C.F., McCall, M.J., Cole, W.C., and DeNardo, S.J. (1985) Copper chelates as probes of biological systems stable copper complexes with a macrocyclic bifunctional chelating agent. Anal. Biochem. 148, 249-253. 

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. 

Another factor that can possibly affect the redox potential in biological systems is the presence of secondary chelating agents that can participate in coupled equilibria (3). When other chelators are present, coupled equilibria involving iron-siderophore redox occur and a secondary ligand will cause the siderophore complex effective redox potential to shift. The decrease in stability of the iron-siderophore complex upon reduction results in a more facile release of the iron. Upon release, the iron(II) is available for complexation by the secondary ligand, which results in a corresponding shift in the redox equilibrium toward production of iron(II). In cases where iron(II) is stabilized by the secondary chelators, there is a shift in the redox potential to more positive values, as shown in Eqs. (42)—(45). 

Unfortunately, the iron complexes of both chelators desferal and LI are able to catalyze the formation of oxygen radicals [394,395]. Cragg et al. [395] also showed that LI exposure markedly enhanced free radical-mediated DNA damage in iron-loaded liver cells. It has been suggested that the prooxidantrantioxidant ratio of LI activity depends on the composition of complexes formed a 1 3 Fe/Ll is supposed to be inactive in the production of free radicals while the generation of radicals is possible at lower Fe/Ll ratios [395], But it should be noted that in real biological systems there is always equilibrium between iron-chelator complexes of different composition. 

There are many examples of the analytical use of 1,10-phenanthroline and its derivatives in biological systems by virtue of their chelating properties. Uses that depend solely on these properties are outside the scope of this review. The biological effects of metal complexes of 1,10-phenanthroline are also excluded. These have been reviewed.394... 

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