Exercising Demons: A Molecular Information Ratchet

Nature uses molecular-sized motors and machines in virtually every important biological process and their extraordinary success is inspiring scientists to try to create synthetic devices that mimic the function of these amazing natural systems. However, it is far from obvious to see how to design such machines because mechanical behaviour at the molecular level, where everything is constantly moving (under kinetic energy supplied by the heat of the surroundings) and being buffeted by other atoms and molecules (Brownian motion), is very different to that which we observe in our everyday world. One cannot just scale down the design of a motor car to the nanoscale, for example, it simply could not operate because friction, heat dissipation and many other factors are so different. The problem of controlling motion on the molecular level is not a recent one, however, it has occupied the minds of scientists for as far back as the middle of the 19 th Century.