Mechanochemistry

Mechanochemistry (or mechanical chemistry) is the initiation of chemical reactions by mechanical phenomena. Mechanochemistry thus represents a fourth way to cause chemical reactions, complementing thermal reactions in fluids, photochemistry, and electrochemistry. Conventionally mechanochemistry focuses on the transformations of covalent bonds by mechanical force. Not covered by the topic are many phenomena: phase transitions, dynamics of biomolecules (docking, folding), and sonochemistry. Mechanochemistry also encompasses mechanophores which are molecules that undergo predictable changes in response to applied stress. Two types of mechanophores are mechanochromic ones in which a force causes a change in molecular structure and subsequently color and acid releasing mechanophores that release small amounts of an acid such as HCl in response to an applied force. Mechanochemistry is not the same as mechanosynthesis, which refers specifically to the machine-controlled construction of complex molecular products. In natural environments, mechanochemical reactions are frequently induced by physical processes such as earthquakes, glacier movement or hydraulic action of rivers or waves. In extreme environments such as subglacial lakes, hydrogen generated by mechnochemical reactions involving crushed silicate rocks and water can support methanogenic microbial communities. And mechanochemistry may have generated oxygen in the ancient Earth by water splitting on fractured mineral surfaces at high temperatures, potentially influencing life's origin or early evolution.