Question

Bacteria and plants that live in soils will sometimes produce biogenic siderophores which are small organic compounds that act as ligands to complex metals.  It can be difficult for bacteria and plants to move around and find nutrients on their own sometimes, so they rely on siderophores to do the job for them.  They produce the siderophores, release them when water passes by, and the siderophores complex metal nutrients like iron, and the bacteria or plants can then suck up the iron-siderophore complex to receive its nutrient.  

One such siderophore is called desferrioxamine B (note, your tables mis-label this as “desferri-ferrioxamine B”).  You can call it DFOB.

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It can easily wrap around iron when iron is dissolved in the form of Fe²⁺ and Fe³⁺.  Your job now is to identify all the possible Fe²⁺ and Fe³⁺ complexes with DFOB.  So, write a list of all the possible Fe²⁺ and Fe³⁺ complexes with DFOB, and write all the equilibrium equations (and their stability constants) for these complexes.  

Answer 1

Siderophores (Greek: "iron carrier") are small, high-affinity iron-chelating compounds secreted by microorganisms such as bacteria, fungi and grasses. Siderophores are amongst the strongest soluble Fe 3+ binding agents known.There are three main kinds of siderophores known as hydroxamate, catecholate and carboxylate. Such siderphores , how do they regulate soil fertility and plant nutrition via changes in soil biology , is the central theme of whole discussion.

Bacterial pathogens acquire the iron they need for survival and growth in a host by using siderophores. The structures of siderophores are specialized for binding ferric ion with high affinity. Siderophore structures are also specialized to specifically interact with the proteins that mediate siderophore function. These proteins include the bacterial proteins involved in siderophore uptake and utilization, as well as host proteins that inhibit bacterial iron acquisition by intercepting siderophores. The interactions between siderophores and iron underlie biological function. The fundamental coordination chemistry of catecholate and hydroxamate siderophores affects protein interactions during siderophore uptake and host defense.
Siderophores carry iron into a bacterial cell through specific transport systems. Once inside the cell, the iron must be removed from the siderophore. Bacteria that use ferric enterobactin remove the iron by hydrolyzing the backbone with an esterase followed by reduction of the ferric ion. Hydrolysis is necessary because the high stability of intact ferric enterobactin prevents biological reduction and iron release. V. cholerae had been reported to use ferric enterobactin, but it does not have an esterase to hydrolyze the backbone.
Uptake of ferric siderophores relies on specific cell membrane receptors. Many
siderophore receptors recognize the apo-siderophores as well as the ferric complexes. Binding apo-siderophores does not directly deliver iron to the bacteria, but it plays a role in the uptake mechanism. YxeB transports the siderophores using a Gram-positive siderophore-shuttle in which metal exchange between a ferric siderophore and the bound apo-siderophore is facilitated by the receptor. Metal exchange is not required for uptake, but the siderophore-shuttle is faster than transport without metal exchange. Metal exchange, iron release, and the sterics and electronics of the metal center are coordination chemistry principles that influence the interactions between siderophores and proteins. Proteins usher siderophores through the biological functions of removing iron from the host, passing through the bacterial membrane, and releasing iron to the cell. Therefore, siderophores act as the intermediaries between ferric ion and the biology of bacterial iron uptake