Mechanosynthesis

Mechanosynthesis is a term for hypothetical chemical syntheses in which reaction outcomes are determined by the use of mechanical constraints to direct reactive molecules to specific molecular sites. There are presently no non-biological chemical syntheses which achieve this aim. Some atomic placement has been achieved with scanning tunnelling microscopes. In conventional chemical synthesis or chemosynthesis, reactive molecules encounter one another through random thermal motion in a liquid or vapor. In a hypothesized process of mechanosynthesis, reactive molecules would be attached to molecular mechanical systems, and their encounters would result from mechanical motions bringing them together in planned sequences, positions, and orientations. It is envisioned that mechanosynthesis would avoid unwanted reactions by keeping potential reactants apart, and would strongly favor desired reactions by holding reactants together in optimal orientations for many molecular vibration cycles. In biology, the ribosome provides an example of a programmable mechanosynthetic device. A non-biological form of mechanochemistry has been performed at cryogenic temperatures using scanning tunneling microscopes. So far, such devices provide the closest approach to fabrication tools for molecular engineering. Broader exploitation of mechanosynthesis awaits more advanced technology for constructing molecular machine systems, with ribosome-like systems as an attractive early objective. Much of the excitement regarding advanced mechanosynthesis regards its potential use in assembly of molecular-scale devices. Such techniques appear to have many applications in medicine, aviation, resource extraction, manufacturing and warfare. Most theoretical explorations of advanced machines of this kind have focused on using carbon, because of the many strong bonds it can form, the many types of chemistry these bonds permit, and utility of these bonds in medical and mechanical applications. Carbon forms diamond, for example, which if cheaply available, would be an excellent material for many machines.