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Researchers unmask Janus-faced nature of mechanical forces with supercomputer

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Posted June 18, 2013
The Janus nature of mechanochemistry: Mechanical forces normally accelerate chemical reactions. However, in the case of disulfide bonds, which are present in large numbers in proteins, force-induced structural changes result in a relative deceleration above a certain threshold. The force thus shows its Janus-faced nature. Credit: P. Dopieralski, D. Marx

The Janus nature of mechanochemistry: Mechanical forces normally accelerate chemical reactions. However, in the case of disulfide bonds, which are present in large numbers in proteins, force-induced structural changes result in a relative deceleration above a certain threshold. The force thus shows its Janus-faced nature. Credit: P. Dopieralski, D. Marx

The harder you pull, the quicker it goes. At least, that used to be the rule in mechanochemistry, a method that researchers apply to set chemical reactions in motion by means of mechanical forces. However, as chemists led by Professor Dominik Marx, Chair of Theoretical Chemistry at the Ruhr-Universität Bochum now report in the journal Nature Chemistry, more force cannot in fact be translated one to one into a faster reaction.

 

With complex molecular dynamic simulations on the Jülich supercomputer “JUQUEEN” they unmasked the Janus-faced nature of mechanochemistry. Up to a certain force, the reaction rate increases in proportion to the force. If this threshold is exceeded, greater mechanical forces speed up the reaction to a much lesser extent.

In order to activate chemical reactions, an energy barrier first has to be overcome. This energy can, for example, be supplied in the form of mechanical forces that “distort” the molecules involved. In order to achieve that experimentally, two longpolymer chains are attached to the molecule. These chains serve as ropes to stretch the molecule either using a force microscope or by radiating the solution with ultrasound. Until now it was assumed that the energy barrier decreases steadily, the more mechanical energy is put into the molecule. This hypothesis has now been refuted by the RUB-chemists. The key to success was a particularly complex form of computer simulation, the so-called ab initio molecular dynamics method, which they could only master on Europe’s currently fastest computer at the Jülich Supercomputing Centre within the framework of a “Gauss Large Scale” project.

Read more at: Phys.org

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