Artificial molecular-level machines

R. Ballardini, V. Balzani, A. Credi, M.T. Gandolfi, M. Venturi, Artificial Molecular-Level Machines Which Energy to Make Them Work , Acc. Chem. Res., 34,445 (2001)... 

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... 

Ballardini, R., Balzani, V., Credi, A., Gandolfi, M. T., Venturi, M., Artificial Molecular level Machines Which Energy to Make them Work Acc. Chem. Res. 2001, 34, 445 455. 

Balzani V, Credi A, Marchioni F, Stoddart JF. 2001. Artificial molecular level machines. Dethreading rethreading of a pseudorotaxane powered exclusively by light energy. Chem Commun 18 1860 1861. 

The idea of constructing artificial molecular-level machines is recent. This topic was first discussed by R. P. Feynman, Nobel Laureate in Physics, in his famous address. "There is plenty of room at the bottom." to the American Physical Society in 1959. His idea was that of constructing nanoscale machines "atom by atom." a concept later expanded with fascinating perspectives but almost no practical progress, by K. E. Drexler. " With the advent of supramolecular chemistry."" it became... 

If an artificial molecular-level machine has to work by inputs of chemical energy, it will need the addition of fresh reactants ("fuel") at any step of its working cycle. 

The problem of the construction of artificial molecular-level machines was posed for the first time by Richard P. Feynman, Nobel Laureate in Physics, in his famous address There Is Plenty of Room at the Bottom to the American Physical Society in 1959 [12] "... What are the possibilities of small but movable machines . ..An internal combustion engine of molecular size is impossible. Other chemical reactions, liberating energy when cold, can be used instead.. ..Lubrication might not be necessary bearings could run dry they would not run hot because heat escapes from such a small device very rapidly... 

The unique architecture of rotaxanes and catenanes (as well as pseudorotaxanes see Volume III, Part 2, Chapter 6) lend themselves to the occurrence of large-amplitude motions by their component parts—a property reminiscent of the movements displayed by the working parts of machines in the macroscopic world. The concept of machine at the molecular level is not a new one. Our body can be looked upon as an extremely complex ensemble of molecular-level machines that power our movements, repair damage, and orchestrate our inner worlds of thought, sense, and emotion [69]. The challenge of constructing artificial molecular machines was posed for the first time by Feynman [70] in his famous address, There is Plenty of Room at the Bottom, to the American Physical Society in 1959. In his address, he raised a number of interesting issues, such as ... 

The concept of machine at the molecular level is not new. Our body can be viewed as a very complex ensemble of molecular-level machines that power our motions, repair damage, and orchestrate our inner world of sense, emotion, and thought [5]. The problem of the construction of artificial molecular-level... 

For the sake of space, in this chapter we will only discuss examples of molecular-level machines based on photoinduced electron transfer processes. An extensive review on artificial molecular machines [3c] and more detailed discussions on electron-transfer processes involving pseudorotaxanes [23a], and rotaxanes and catenanes [23b] are reported elsewhere. 

Balzani V, Credi A, Venturi M (2002) Controlled disassembling of self-assembling systems toward artificial molecular-level devices and machines. Proc Natl Acad Sci USA 99 4814 817... 

Two kinds of macroscopic devices play a very important role in our civilization machines and electronic computers. One can wonder whether it is possible to construct devices of these kinds at the molecular level. In the last few years prototypes of very simple molecular-level machines [7] and molecular-level components related to the construction of molecular-based (chemical) computers [8] have been developed by several research groups. For space reasons, we will only illustrate a few of the systems investigated in our laboratory. We would like to recall, however, that an outstanding result has recently been obtained with molecular-level devices, namely the light-driven production of ATP in an artificial photosynthetic membrane [9]. 

In the following years supramolecular chemistry grew very rapidly [1-3] and it became clear that the supramolecular bottom-up approach opens virtually unlimited possibilities concerning design and construetion of artificial molecular-level devices and machines. It also became increasingly evident that such an approach can make an invaluable contribution to a better understanding of molecular-level aspects of the extremely complicated devices and machines that are responsible for biological processes [18]. 

In general terms, these results indicate that, as the structural complexity increases, the overall properties of the system cannot be easily rationalized solely on the basis of the type and sequence of the functional units incorporated in the molecular framework—that is, its primary structure. Higher level conformational effects, which are reminiscent of those related to the secondary and tertiary structures of biomolecules,4d have to be taken into consideration. The comprehension of these effects constitutes a stimulating scientific problem and a necessary step for the design of novel artificial molecular devices and machines. 

Molecular-Level Artificial Machines Based on Photoinduced Electron-Transfer Processes... 

---