Pro-oxidant activity of vitamin C in drinking water ... - Ã bo Akademi

Review of the literatureREVIEW OF THE LITERATURE1. Vitamin C – ascorbic acid - ascorbateVitamin C is a weak acid and a highly water-soluble molecule. Ascorbic acid (C 6H 8O 6) isthe trivial name for vitamin C, while the chemical name, very seldom used in the literature,is 2-oxo-L-threo-hexono-1,4-lactone-2,3-enediol or 2-(1,2-dihydroxyethyl)-4,5-dihydroxyfuran-3-one(IUPAC). Biologically it is the L-enantiomer of ascorbic acid that is active,while the D-enantiomer shows much lower biological activity. 12 Ascorbic acid is the acidicform of vitamin C having two ionizable –OH groups, with pKa values of 4.25 and 11.8. Atphysiological pH, the mono-anion is favoured and therefore ascorbic acid is usuallyreferred to as ascorbate (salt) in the literature (Figure 1).HOHOOOHOOpKa 1 = 4.25 HOO pKa 2 = 11.8HOHOOOHO OH_O OH_O_OAscorbic acid Ascorbate Ascorbate dianionFigure 1. Forms of vitamin C at various pH1.1. Vitamin C deficiency and scurvyThe history of vitamin C is largely the history of the human disease scurvy, one of the firstnutritional deficiency diseases recorded. 13-16 The symptoms of scurvy were marked byanaemia, weakness, spongy gums, oedema, often with open sores in the mouth, andloosening of the teeth, bleeding in the mucous membranes, and hard bumps in the musclesof the legs. In 1566, the Dutch physician Ronsseus instructed sailors to consume oranges toprevent scurvy. In 1639, John Woodall, a leading physician in England, recommendedlemon juice to treat scurvy. Later a Scottish naval surgeon, James Lind, conducted acontrolled trial adding oranges and lemons to the sailors’ diet. The positive observed effectof lemons and oranges on scurvy in Lind’s trial led to the increased usage of lemons andoranges in the diet of sailors on Captain James Cook’s second voyage around the world.However, it was not until 1795 that all sailors in England were ordered to ingest lemon7