Natural ligand donor sites

A range of coordination complexes of has been prepared in which the vanadyl group is absent, a number of these compounds being synthesized as part of an effort to understand the nature of biological vanadium sites, such as amavadin," which contains an octadentate, hydroxyiminodipropionate ligand bound to vanadium A number of model complexes of this type have been prepared and discussion of this area can be found in the article Vanadium in Biology Further discussion in this section follows the main ligand donor atom to vanadium. 

Some compounds extend from a purine site into an adjacent hydrophobic region, which is not thought to be used by natural ligands and is often known as the selectivity pocket (Figure 4.3). This is an allosteric site, because it is not used by substrates of the enzyme. The selectivity pocket is so named because it is not well conserved and inhibitor selectivity often correlates with the identity of a gatekeeper residue at the entrance to the pocket, occurring 3 residues before the main-chain NH donor in the purine site. Most compounds that use... 

If the physical scale of the ligands introduces complexities which were not of concern to Werner, the nature of the donor sites on these intermediate scale ligands adds no complexities. Structures 1, 2, and 3 could stand as representatives of the vast majority of the complexing sites for metal ions, (M), with many O and a few N donor atoms. Sulfide sites and simple halide ions are the other donors of lesser importance. Consequently, we need to anticipate nothing in the bonding of the ligand to the metal that was not exhibited in the complexes known to Alfred Werner. This soil/water system chemistry is the chemistry of classical complexes, mainly between metal ions and hard base ligands. 

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