Molecular level machines

In this chapter we will illustrate examples of three families of molecular-level devices (i) devices for the transfer of electrons or electronic energy, (ii) devices capable of performing extensive nuclear motions, often called molecular-level machines, and (Hi) devices whose function implies the occurrence of both electronic and nuclear rearrangements. Most of the examples that will be illustrated refer to devices studied in our laboratories. 

Devices Based on Nuclear Motions (Molecular-Level Machines)... 

A molecular-level machine is a particular type of molecular-level device in which the component parts can display changes in their relative positions as a result of some external stimulus.13,9 131 Although there are many chemical compounds whose structure and/or shape can be modified by an external stimulus (see, e.g., the photoinduced cis-trans isomerization processes), the term molecular-level machines is only used for systems showing large amplitude movements of molecular components. 

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... 

The first attempt at designing1221 a photochemically driven molecular-level machine of a pseudorotaxane type was based (Figure 6a) on the use of an... 

P. R. Ashton, V. Balzani, O. Kocian, L. Prodi, N. Spencer, J. F. Stoddart, A Light-Fueled Piston-Cylinder Molecular-Level Machine , J. Am. Chem. Soc. 1998,120,11190-11191. 

Molecular hydrogen, 23 759 Molecular imprinting, 6 397 Molecular interactions, 25 103 Molecular interaction theories, 24 38 Molecular Laser Isotope Separation (MLIS) process, 25 416 417 Molecular level machine, 2 7 58 Molecularly imprinted plastics (MIPs) smart, 22 717)... 

A Credi. Molecular-Level-Machines and Logic Gates. PhD thesis, Universita di Bologna, Italy, 1998. 

In the last few years, several examples of molecular machines and motors have been designed and constructed. It should be noted, however, that the molecular-level machines described in this chapter operate almost in solution. Although the solution studies of chemical systems as complex as molecular machines are of fundamental importance, it seems reasonable that, before functional supramolec-ular assemblies can find applications as machines at the molecular level, they have to be interfaced with the macroscopic world by ordering them in some way. 

Abstract To appreciate the technological potential of controlled molecular-level motion one only has to consider that it lies at the heart of virtually every biological process. When we learn how to build synthetic molecular motors and machines that can interface their effects directly with other molecular-level sub-structures and the outside world it will add a new dimension to functional molecule and materials design. In this review we discuss both the influence of chirality on the design of molecular level machines and, in turn, how molecular level machines can control the expression of chirality of a physical response to an inherently achiral stimulus. 

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... 

Much better than physicists, chemists are in an ideal position to develop bottom-up strategies towards the design of molecular-level machines, since they are able to manipulate molecules, i.e., the smallest entities of matter that have distinct shapes and properties. Forty years ago, however, the chemical community was not ready to receive Feynman s stimulation. Only recently, after the development of supra-molecular chemistry [1], has the study of artiflcial molecular-level machines become an important research topic in chemistry [15, 26-28, 33]. 

A. Credi, Molecular-level machines and logic gates , Ph. D. Dissertation, University of Bologna, 1998. 

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 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). 

Molecular-level machines operate via nuclear rearrangements and, like macroscopic machines, are characterized by... 

Finally, as far as point (v) is concerned, molecular-level machines performing various kinds of functions can be imagined, as described here and in other chapters of this volume. 

For space reasons, in this chapter we will only review recent advances in the field of molecular-level machines operating by means of photoinduced electron-transfer processes. Since such machines are based on pseudorotax-anes, rotaxanes, and catenanes, we will first recall some important features of these kinds of supramolecular systems. 

It can be noted that in all cases (Fig. 7) the machine-like behavior consists in the reversible change of the state of the system (from state 1 to state O , and then back to state O ). This shows that such molecular-level machines behave according to binary logic. Therefore, they could be used, in principle, for information processing at the molecular level [22]. 

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