Chemistry Splitting sulphur bridges in water is more complicated than one thinks
They are indispensable in proteins and rubber: bonds between two sulphur atoms that link the long molecules together. If one pulls on the sulphur bridges from outside, unexpectedly complicated processes occur.
From a chemical viewpoint, splitting bonds between two sulphur atoms is a much more complicated process than one has thought so far – at least if one places the bond under tensile stress. Depending on how hard one pulls, the sulphur bridge splits with different reaction mechanisms.
“We did not know that until now, and it makes the correct interpretation of experimental data, in particular, much more complicated than we had thought,” says Prof Dr Dominik Marx, who describes the results of extensive computer simulations on the Jülich-based supercomputer “Juqueen” with his RUB colleagues in the journal “Nature Chemistry”.
Virtually pulling on the bond
Sulphur bridges occur, for instance, in proteins. They keep these in certain structural arrangements, but also act as switches for biological processes. If these are in an alkali aqueous solution and this is heated, it brings about a certain chemical reaction. The chemists from Bochum investigated what happens when you also place the bond under tensile stress.
They replicated a molecule with sulphur bridges in an aqueous solution on the computer and pulled virtually on both ends of the bond. With elaborate simulations, they calculated which reactions occur with different tensile forces.
Immense computing effort
Correctly incorporating the role of the surrounding water – being the usual solvent for chemical processes in alkaline solution – was crucial for the success of the simulation. Theorists usually use methods that drastically simplify the effects of the surrounding solvent in order to reduce the processing power required. Not the case in the current work.
“Our ab initio simulations require an immense computing effort,” explains Marx. This was made possible through a special “Large Scale Project” granted by the Gauss Centre for Supercomputing in Jülich. The research underlying this publication has been supported by the German Research Foundation over many years in the framework of the Reinhart Koselleck Project “Understanding Mechanochemistry”. It is also part of the cluster of excellence Resolv, in which the role of the solvent is a key area of research.