Nature Chemistry | The Sceptical Chymist

Element of the month: All about arsenic

The first thing most people think of when they hear ‘arsenic’ is ‘poison’. In fact, it has played such a crucial part in many a high-profile murder throughout history that it used to be called ‘poudre de succession’ in French (inheritance powder) — mostly by women, according to the French Wikipédia page (!)

This month (subscription required), Katherine Haxton from Keele University — who also blogs at Endless Possibilities and can be found on Twitter @kjhaxton — explains why arsenic is a particularly suitable element to illustrate the notion that chemicals might be good or bad depending on their use. And so, as arsenic was inheritance powder for the French, Victorians across the Channel in Britain used it for more entertaining purposes — such as self-medication, for example to improve breathing and stamina, to freshen the skin, as an aphrodisiac, and perhaps even an anti-eczema cream by Charles Darwin.

Although organoarsenic coumpounds were prepared as early as the 1750s, their structures remained elusive until the mid-nineteenth century when Bunsen, with some help from Berzelius, identified tetra-methyl-di-arsane — a “fuming liquid with a strong garlic odour” (maybe this is why it remained elusive for so long!).

Although this sounds surprising arsenic has been used in medicine throughout history. Cyclic compounds with As–As bonds for example went on to become relatively efficient drugs against syphilis, especially after a bit of optimization to reduce some side effects and improve handling procedures (air sensitive compounds weren’t the easiest to administer). But despite medical uses, arsenic — fairly abundant in nature, and present in living systems — can readily make its way into ground water and poison large populations. Yet it seems that in 19th century Austria, people could have consumed about 300 mg of arsenic (more than 4-times the fatal dose) without dropping dead. Could organisms get used to arsenic? Kids, don’t try this at home.

This is a topic that has been thoroughly discussed in light of a recent Science paper describing a bacterium that can supposedly grow by using arsenic instead of phosphorus. Since its publication, it has been widely — and passionately — debated in many venues, including press conferences, magazines, the Internet and as follow-up Technical Comments in Science, and was even mentioned on Nature Chemistry’s very own Blogroll.

Saviour or killer? Check out the article for other anecdotes about arsenic’s ambivalence!

Anne

Anne Pichon (Associate Editor, Nature Chemistry)

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