The biosynthesis of vitamin B12 has fascinated generations of scientists, but part of the pathway was unknown. The missing enzymatic link has now been found, only to raise more mechanistic questions.

The stability of the chemical bonds in saturated hydrocarbons makes them generally unreactive. But the invention of processes in which carbon–hydrogen (C–H) bonds in hydrocarbons can be activated is allowing chemists to exploit organic compounds in previously unimaginable ways.