Defining Molecular-Level Machines

The concept of machine can be extended to the molecular level [2], A molecular-level machine can be defined as an assembly of a discrete number of molecular components (that is, a supramolecular structure) designed to perform mechanical-like movements (output) as a consequence of appropriate external stimuli (input). 

Easton et al. have discussed the applications, potential, and limitations of molecular machines and reactors [15]. They define molecular reactors as miniature vessels for the assembly of reactants at the molecular level, in order to change the nature of chemical transformations. Molecular machines consist of interrelated parts with separate functions, and perform some kind of work, at the molecular level. However, practical examples are not based on individual functions of singlemolecule devices. 

Charcoal is a special form of graphite. To be useful it must be reactive. This reactivity comes mainly from the structure of the graphite at the molecular level. Reactive charcoals have such poorly defined structure that special computer enhancement techniques are necessary to find a structure by X-ray diffraction techniques. Only in the last ten years has the solid state autogoinometerimetric digitalized diffraction machine become a commonly available tool. Digital computers can solve in a few hours the crystal structures of very complex materials. Charcoal is essentially a poorly formed graphite in more or less the physical form that the original plant material had formed. 

A molecular machine, a machine at the molecular level, is defined as a discrete number of molecular components that perform mechanical-like movements (output) in response to specific stimuli (input). Molecular machines include both naturally occurring devices found in biological systems and artificial molecular machines. There are many molecular machines in biological systems. Among the most prominent examples of molecular machines in living organisms are the muscle linear and ATPase rotary motors. In order to develop artificial machinery, scientists have constructed a variety of molecular and supramolecular systems with differences in shape, switching processes, or movements... 

In this context, performing useful work by the molecular machines of living cells implies that the conversion of one form of stored energy into another does not occur via thermal exchange, as takes place in all conventional macroscopic chemical machines. This statement not only defines useful work at the level of individual molecules, but also points out that the difference between work and heat disappears at the molecular level [3-5]. 

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