Anions are ubiquitous in the Natural world. Chloride anions are present in large quantities in the oceans; nitrate and sulfate are present in acid rain; and carbonates in biomineralised materials. Anthropogenic anions including pertechnetate, a radioactive product of nuclear fuel reprocessing, and phosphate and nitrates from agriculture and other human activities, constitute major pollution hazards. Anions are also critical to the maintenance of life. Indeed, without exaggeration, the recognition, transport or transformation of anions is involved at some level in almost every conceivable biochemical operation. It is essential in the formation of the majority of enzyme–substrate and enzyme–cofactor complexes as well as in the interaction between proteins and RNA or DNA. ATP, phosphocreatine and other high-energy anionic phosphate derivatives, power processes as diverse and important as biosynthesis, molecular transport and muscle contraction while serving as the energy currency for a host of enzymatic transformations. Anion channels and carriers are involved in the transport of small anions such chloride, phosphate and sulfate and thus serve to regulate the flux of key metabolites into and out of cells while maintaining osmotic balance.
