As it turns out, sulfur is a little difficult to describe in a concise manner: although in its elemental form it mostly adopts a crown-shaped 8-membered ring structure, it also exists in 7-membered rings (those are the bright yellow ones) and even traces of smaller rings; and it happily converts to a one-dimensional elastomer when heated. Its anions also like to form chains, which can be extended or reduced, and easily catenated, through redox chemistry.
Similarly, its reactivity can be puzzling, and in particular its catalytic activity. Even though sulfur is well-known to poison industrial catalysts, it actually acts as a catalyst in biological systems — among many other roles. Metal sulfide clusters can quickly transfer electrons, a very desirable property for catalytic functions, and are widespread in biology. Take methanogens, for example, those microbes that produce methane under anaerobic conditions, thus contributing to global warming. Although the precise mechanism continues to intrigue chemists, at least one step involves breaking a methyl–sulfur bond. A reverse reaction, catalyzed by nickel, is now also attracting attention. Another example is the microorganisms that also use metalloenzymes with iron–sulfide sites to convert CO2 to CO or N2 to NH3. Check out the article to find out other sulfur roles.
Even its spelling is a little controversial, with both ‘sulfur’ and ‘sulphur’ widespread in the literature — have a look at our editorial (free but you have to be (freely) registered on nature.com) to find out why we’ve adopted ‘sulfur’ (and nope, this time it’s not simply the Oxford English vs American English spelling, the arguments are more etymologic).
Anne Pichon (Associate Editor, Nature Chemistry)