A large number of biologically relevant species are negatively charged, the- fore it is not surprising that nature has developed sophisticated receptors to recognise, detect and transformanions. For example, complex receptors such as phosphate- and sulphate-binding proteins are employed by living cells to selectively recognise these two geometrically analogous anions. In addition to their roles in biological systems, some anions also have important en- ronmental impacts. For example, cyanide, pertechnetate and chromates pose serious health problems if present in water supplies. Because of...