Natural molecular-level machines

Dethreading/rethreading of the wire and ring components of a pseudorotaxane is reminiscent of the movement of a piston in a cylinder (see Figure 1), and therefore such a system may be considered as a very simple molecular-level machine. While natural molecular-level machines have long been known (our own body can be viewed as a complex ensemble of molecular-level machines) [31], the problem of the construction of artificial molecular-level machines was posed for the first time by... 

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. 

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... 

While the methods discussed represent appHed modalities that promise to be implemented within years, the scope of nanobiotechnology encompasses research which, though currently on the very frontiers of modern science, present innumerable possibihties for the future of nanomedicine. The prophesied abihty of nanoscale machines, or nanobots, to provide molecular level construction and repair to exterminate disease and erase genetic defects represents the pinnacle of nanomedicine aspirations. Although the inherent difficulties in the design and manufacture of such devices raise questions as to their feasibihty [153], research continues to explore nature s nanomachines and issues crucial to the development of nanobots. In cells, proteins are nanomachines that act as transporters, actuators, and motors, and are responsible for meticulous monitoring and repair processes [154,155],... 

Interestingly, this mechanical performance is accompanied by an extraordinary biocompatibiUty, although, however, the most striking properties are perhaps their acute smart and self-assembhng nature. These properties are based on a molecular transition of the polymer chain in the presence of water when their temperature is increased above a certain level. This transition, called the inverse temperature transition (ITT), has become the key issue in the development of new peptide-based polymers as molecular machines and materials. The understanding of the macroscopic properties of these materials in terms of the molecular processes taking place around the ITT has established a basis for their functional and rational design [102]. 

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