Chemical of the Week 8 – L-Ascorbic Acid

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Most parents have spent an appreciable amount of time trying to get their little angels to eat some fruit or veg. At the back of their minds, lingering behind the five a day, is the dread that their child could be the first in their nursery to have scurvy! Oh the shame! An extreme lack of vitamin C for long periods of time can cause scurvy. Symptoms of scurvy include skin that bruises easily, bleeding gums, joint pain and poor wound healing and if untreated can be fatal. Enter the molecule (R)-3,4-dihydroxy-5-((S)-1,2-dihydroxyethyl)furan-2(5H)-one – enough of this chemical and their little protégées will be well on the road to health and success!

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IUPAC, the organisation that names chemicals, definitely had their work cut out with that name, have you guessed what it is yet? It is vitamin C – which incidentally is more frequently referred to as L-ascorbic acid by scientists. L-Ascorbic acid is actually derived from Latin to mean ‘no scurvy’ and don’t ignore the L. The D/L prefix (although outdated) infers that this molecule has chirality. The D molecule is not found in nature and does not have any significant physiological activity. The beady eyed reader may have noticed that ascorbic acid actually has two chiral centres which results in two sets of enantiomers in total. If you look back to the IUPAC name the letters R and S indicate the arrangement of the prioritised atoms/groups around each chiral centre (R right and S left). Vitamin C (L-ascorbic acid) is very important because it is used in the production of collagen which is essential for binding cells together. Chemically, ascorbic acid has two ionisable hydroxyl groups and at physiological pH it exists as the ascorbate mono-anion. This ion can undergo two one electron oxidations making it a very good reducing agent and also an effective antioxidant.

Over a hundred thousand tons of L-ascorbic acid are produced annually worldwide, and the market price is less than a penny a gram. Vitamin C was first isolated in 1928 and by 1936 a process devised by the chemist Tadeus Reichstein, using D-glucose as a starting material, resulted in industrial production. The recommended dose for vitamin C is approximately 50mg a day, and you can reach that target by a healthy diet or supplement it with tablets. If you eat a camu camu or kakadu plum you will hit your target no problem, with more common fruits such as oranges and lemons having on average about 50mg per 100g (red peppers and blackcurrants are your best bet if you are looking for your vitamin C hit in the fruit and veg isle in Tesco’s!). Vitamin C can’t be stored in the body so daily ingestion is required and don’t worry about an overdose because vitamin C is water soluble. Interestingly it’s not just humans who don’t produce vitamin C, looks like we have more in common with guinea pigs than you would think! We both don’t have L-gulonolactone oxidase (GLO), the enzyme required for the last step in ascorbate synthesis, making our dietary intake vital (and therefore a vitamin).

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