Transition metals, anion-binding group

Transition Metals as Anion-Binding Groups and/or Structural Components 79... 

The polyhedral boranes and carboranes discussed above may be regarded as boron clusters in which the single external orbital of each vertex atom helps to bind an external hydrogen or other monovalent atom or group. Post-transition main group elements are known to form clusters without external ligands bound to the vertex atoms. Such species are called bare metal clusters for convenience. Anionic bare metal clusters were first observed by Zintl and co-workers in the 1930s [2-5], The first evidence for anionic clusters of post-transition metals such as tin, lead, antimony, and bismuth was obtained by potentiometric titrations with alkali metals in liquid ammonia. Consequently, such anionic post-transition metal clusters are often called Zintl phases. 

There is a great deal of information available on the surface binding of transition metals to cell walls. Such cell walls possess many charged groups, such as peptidoglycan, which can contribute carboxylate groups, and teichoic acids, which provide anionic clusters due to the... 

Many metal ions, especially those of transition metals, have an affinity for groups that donate electron pairs. This results in the formation of a complex in which the metal ion binds to anions, H20, NH3, or other species, because these species have unshared pairs... 

The carriers for magnesium in bacterial membranes are more likely to have one nitrogen base, probably imidazole, and two anion groups, e.g., phosphate or carboxylate. Steric restrictions could be built in, as in chlorophyll. The nitrogen base would imply that the carrier would bind transition metals such as cobalt, nickel, and manganese (II) which could make excellent probes. Certain bacteria can be loaded with transition metals and perhaps the mechanism of loading utilizes the magnesium carrier. 

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