Potassium complexes biology

Jagoda-Cwiklik B, Vacha R, Lund M, Srebro M, Jungwirth P. (2007) Ion pairing as a possible clue for discriminating between sodium and potassium in biological and other complex environments. /Phys Chem Bill 14077-14079. 

Cobalt compounds have been in use for centuries, notably as pigments ( cobalt blue ) in glass and porcelain (a double silicate of cobalt and potassium) the metal itself has been produced on an industrial scale only during the twentieth century. Cobalt is relatively uncommon but widely distributed it occurs biologically in vitamin B12 (a complex of cobalt(III) in which the cobalt is bonded octahedrally to nitrogen atoms and the carbon atom of a CN group). In its ores, it is usually in combination with sulphur or arsenic, and other metals, notably copper and silver, are often present. Extraction is carried out by a process essentially similar to that used for iron, but is complicate because of the need to remove arsenic and other metals. 

The complexation of sodium, potassium, and related cations by neutral multidentate molecules is, however, an uncommon phenomenon (30, 40), and stable stoichiometric complexes have been observed only in the last decade, and then only with biological material (3, 10—14, 30). This is one of the reasons why Pedersen (41) and Lehn (42, 43) recently studied macrocyclic polyethers (41) and macroheterobicyclic compounds (42, 43). Forming stable complexes in solution as well as in crystalline form with the salts of alkali and other metals, these ligands have aroused considerable interest (40, 44). 

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