Coordination entity, attributes

The coordination entity or complex has come to be recognized as the unifying concept of coordination chemistry. The traditional coordination entity has each of the following attributes a central (metal) atom, a number of ligands, a coordination number, and a polyhedral structure. The coordination polyhedron often occupies center stage as the basis for structural understanding. 

The really unique reaction of the lipoate centre in ct-keto acid metabolism is the oxidative thioester formation from a thiamine-coordinated active aldehyde . Thiol transacetylase and dithiol-disulphide oxidation reduction roles are well-known attributes of other biological thiols. Unfortunately mechanistic studies on this reductive acylation of a cyclic disulphide have so far received little attention. Proposals that a lipoic acid-thiamine pyrophosphate compound was the functional entity in a-keto acid oxidation have been completely abandoned, but data supporting this concept remain unexplained. Investigations in this area might have some relevance for the reductive acylation process. 

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