In 1929, Dirac stated that relativistic effects in general would not affect chemistry and chemical reactivity. However, we now know that in heavy elements such as mercury or gold, some of the electrons travel at near-light speeds and relativistic corrections have to be taken into account. The color of gold, the liquid nature of mercury, and the voltage of the lead battery used to start our cars are all examples of relativistic effects in chemistry.

Pawel M. Kozlowski, University of Louisville, KY, USA, and Medical University of Gdansk, Poland, and colleagues have used density functional theory (DFT) calculations to demonstrate that relativistic effects can also influence enzymatic reactions, e.g., those of corrinoid-dependent methyltransferases.

Ignoring relativistic effects, mercury methylation by cobalt corrinoids was found to proceed in a stepwise manner via a methyl carbanion. This is a very unusual mechanism for such methylation reactions. When properly accounting for relativistic effects, the reaction was instead found to proceed in a single step involving a methyl radical.

With this result, the researchers have shown for the first time that relativistic effects are essential for describing an enzymatic reaction involving heavy metals.

• Mercury Methylation by Cobalt Corrinoids: Relativistic Effects Dictate the Reaction Mechanism,
  Taye B. Demissie, Brady D. Garabato, Kenneth Ruud, Pawel M. Kozlowski,
  Angew. Chem. Int. Ed. 2016.
  DOI: 10.1002/anie.201606001