Iron -siderophore complexes natural siderophores

There are a variety of factors concerning siderophore architecture that can contribute to the stability of iron-siderophore complexes. The overall architecture for natural multidentate siderophores can be any one of a number of different types linear,... 

Table 12 Stability constants for iron(III) complexes of natural and model siderophores.

A linear bis(catecholamide), analogue of the naturally occurring siderophore (40), has been synthesized by the azolide method and its complexation with molybdenum investigated.51 Thermodynamic and kinetic studies on the flexible ligand (41), able to form a homochiral Fe2(41)3 dinuclear iron(II) complex, were undertaken for a better understanding of the self-assembling processes.52... 

Stmcture activity studies with the cyclic hexapeptide siderophores demonstrate that modification of the amino acid sequence in the cyclic peptide does not appreciably influence the ability of the resulting siderophore to transport iron. However, the nature of the hydroxamate acyl substituent has a major influence, the presence of one or more trans anhydromevalonic acid residues severely inhibits the process. Furthermore, the chiral nature of the iron complex has a dominant influence, the cyclic hexapeptide siderophore receptor with a marked preference for the A complex. 

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... 

Henry M, Jolivet JP, Livage J (1991) Aqueous Chemistry of Metal Cations Hydrolysis, Condensation and Complexation. 77 153-206 Hider RC (1984) Siderophores Mediated Absorption of Iron. 57 25-88 Hill HAO, Rdder A, Williams RJP (1970) The Chemical Nature and Reactivity of Cytochrome P-450. 8 123-151... 

Siderophores are iron-complexing compounds of low molecular weight that are synthesized by bacteria and fungi, and serve to deliver iron to the microbes. Because of their exclusive affinity and specificity for Fe3+, natural siderophores and synthetic derivatives have been exploited in the treatment of human iron-overload diseases. The most successfully used example is Desferal , which is the methane sulfonate derivative of iron-free ferrioxamine B, a linear trihydroxamate (Figure 3.2). Ferrioxamine was isolated in 1958 from the culture supernatant of Streptomyces... 

Many microorganisms, when in iron-depleted conditions, are able to mobilize environmental iron by secreting low-molecular weight, high-affinity ironchelating compounds called siderophores, as well as cell-surface receptors for the ferric-siderophore complex and other proteins necessary for their uptake. Over the last three decades we have learned a lot about the chemical nature of these... 

Table V shows redox potentials (Ey2) for ferric complexes of a series of natural and synthetic siderophores. The first coordination shell of the complex formed between iron and siderophore...

In some cases, exudates enable the plankton to control their environment. For example, diatoms release compounds, called oxyUpins, that induce natural abortions and growth reduction in the zooplankton that are their primary predators. Other exudates complex with trace metals, serving to reduce the bioavailability of toxics, such as copper, and enhance the bioavailability of micronutrients, such as iron. Examples of iron-binding extracellular DOM are the siderophores (Figure 5.11). 

Kinetic and equilibrium data are available for complex formation between iron(III) and 4-Me0C6H4C(S)N(0 )H, a system studied in relation to the possibility that some natural siderophores may bind iron through a thiohydroxamate moiety. The Fe " " complex of this... 

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