Metal Transport Agents

Certain secondary metabolites act as metal transport agents. One group is composed of the siderophores (also known as sideramines) which function in uptake, transport, and solubilization of iron. Siderophores are complex molecules which solubilize ferric ion which has a solubility of only 10 18 mo 1/1 at pH 7.4 

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Oxic Diagenesis Metals remobilized from sediments lying in the oxic zone. Remobilization likely occurs in anoxic microzones adjacent to nodules. Bioturbation is an important metal transport agent. Some nodules now found in oxic sediments were likely formed during times when the redox boundary was closer to the seafloor. 10-50 Todorokite (high Cu and Ni content) 32% 5-10 15-20... 

Iron transport agents may belong to the protein or non-protein class. In the former group are found the animal proteins transferrin (25), lactoferrin (26) and conalbumin (27). The low molecular weight iron carrying compounds from microorganisms, the siderochromes, may occur with or without a bound metal ion. Typically, severe repression of biosynthesis of these substances can be expected to set in at an iron concentration of ca. 2 x 10-5 g atoms/liter (28). Most, but not all, of these substances can be described as phenolates or hydroxamates (4). 

The Van Arkel process can also be used to prepare actinide metals if the starting compound reacts easily with the transporting agent (I2). The thorium and protactinium carbides react with I2 to give volatile iodides above 350°C these are unstable above 1200°C and decompose into the actinide metals and iodine. Attempts to prepare other actinides, such as U and Pu, through the process were not successful, because from Th to Pu along the actinide series, the vapour pressure of the iodide decreases and the thermal stability increases. 

The van Arkel-De Boer process is widely used to refine metals. A transporting agent such as Ij reacts with the metal (M) to be refined to form a volatile iodide. This iodide is then decomposed at a higher temperature into the refined metal and I2, which becomes available again to react with the impure metal, thus sustaining the process ... 

The iodine vapours act as transporting agent in this modified version of the van Arkel procedure ". By replacing the resistance heated dissociation wire by an induction heated metal sphere (W or Th, respectively) large samples of Th or Pa crystals can be... 

Therefore, and to avoid possible reactions with the quartz wall, it was attempted to combine synthesis and crystal growth of actinide pnictides in a modified van Arkel process Actinide metal or carbide - the latter obtained by carboreduction of the oxide - are heated in the presence of the pnictogen and of the transporting agent at the... 

Paramagnetic metal chelating agent in NMRI Transport across the blood brain barrier... 

D. van der Hehn and G. Winkelmann, Hydroxamates and Polycarboxylates as iron Transport Agents (Siderophores) in Fimgi, in Metal Ions in Fimgi , eds. G. Winkelmann and... 

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