Readers of this blog will be familiar with last year’s essay competition — as Stuart mentioned here a few days ago, the winning essay on copper, written by Tiberiu Moga, appears in this month’s ‘in your element’ feature.
Copper has been part of our lives pretty much for ever — the Copper Age started around 5,000 BC (give or take a couple of thousand years depending on whether you count the Copper–Stone Age or not), made its way into epic poetry (read the article to find out how it features in the Kalevala) and copper-based materials are still virtually everywhere, from the humble penny to electrical wiring. So what exactly does copper do, apart from giving her copper(II) carbonate-green colour to the Statue of Liberty? Scientifically speaking, lots of things.
Moga is a Medical Doctor student at the University of Toronto, and previously studied both chemistry and biology at Dartmouth College — he is thus particularly interested in copper’s biological functions and catalytic role in the synthesis of new medicines. He identifies three processes that cover most of its abilities: Lewis-acid catalysis, single-electron-transfer processes, and two-electron-transfer reactions.
One of the best-known reactions involving copper as a Lewis acid is the popular ‘click’ azide–alkyne cycloaddition that connects the two groups to form an azole ring. This fast, reliable reaction is generally easy to carry out and makes for a highly efficient step in a wide variety of processes including, for example, natural product total syntheses.
Single-electron-transfer processes where copper adopts either a Cu+ or Cu2+ form are widespread in biosystems. Cellular respiration in organisms, for example, relies on a succession of these steps carried out by copper-containing enzymes to oxidize glucose, and extract its energy. Two-electron transfer reactions are also common — they go through a slightly more complex mechanism involving a halide ion.
Of course, this is by no means an exhaustive list. Copper is looking increasingly like a good alternative to palladium catalysts, and it’s also a useful building block — remember the copper nanotubes?
As it turns out, we’re still very much in a copper age, and it looks all set for the duration.
Anne Pichon (Associate Editor, Nature Chemistry)