Supramolecular machine

Finally, to produce the structural and functional devices of the cell, polypeptides are synthesized by ribosomal translation of the mRNA. The supramolecular complex of the E. coli ribosome consists of 52 protein and three RNA molecules. The power of programmed molecular recognition is impressively demonstrated by the fact that aU of the individual 55 ribosomal building blocks spontaneously assemble to form the functional supramolecular complex by means of noncovalent interactions. The ribosome contains two subunits, the 308 subunit, with a molecular weight of about 930 kDa, and the 1590-kDa 50S subunit, forming particles of about 25-nm diameter. The resolution of the well-defined three-dimensional structure of the ribosome and the exact topographical constitution of its components are still under active investigation. Nevertheless, the localization of the multiple enzymatic domains, e.g., the peptidyl transferase, are well known, and thus the fundamental functions of the entire supramolecular machine is understood [24]. 

Rotaxanes and catenanes are two of such interlocked systems which can be described simply as a rod threaded in a macrocycle and captured by two stoppers at each end (rotaxane), and two or more rings which can not be separated unless one or more covalent bonds are broken (catenane). Specific non-covalent interactions are not required to make these systems stable. They do not break apart because of the presence of mechanical bonds [4] in these structures. The fact that they are interlocked does not mean that they are frozen . Conversely, the motions within the final supramolecule can be tailored and controlled by external stimuli making them supramolecular machines... 

Kuhn, H. and Forsterling, H.-D. (2000). Principles of Physical Chemistry Understanding Molecules, Molecular Assemblies and Supramolecular Machines, Wiley, Chichester, UK. 

We have developed a number of these supramolecular machine-like systems in collaboration with the Balzani group, and have used them to perform logic functions. An example is presented in the next section. Figure 28 illustrates the chemical switching [20a] of the [2]pseudorotaxane [8=>39]2+, which incorporates a re-electron-deficient unit (dia-zapyrenium dication) in its thread-like component 392+ and two re-electron-rich units (DNP) in the crown ether 1/5-DN38C10 (8). Since the thread-like component 392+ forms adducts... 

Wilber, I., Eichen, Y, Doron, A., and Marx, S. Effects of electrostatic and 7t-jt-intcractions on the stabilities of xantene dye-4,4 -bipyridinium complexes - Structural design of a geared supramolecular machine. Isr. J. Chem. 1992, 32, 53-59. 

Processive catalysis of this kind involves extremely sophisticated molecular machinery including both RNA and protein components suggesting that it emerged relatively late in evolutionary terms. Processive catalysis is now a target for the design of artificial supramolecular machines and an interesting recent example is discussed in Section 10.7.3. 

H. Kuhn and H.-D. Forsterling, Principles of physical chemistry Understanding molecules, molecular assemblies, supramolecular machines, Wiley, New York, 1999. 

Functional electrochemically controlled supramolecular machines based on CyD units now being actively studied and already presenting motor-like behavior on the molecular level, following new routes in the bottom-up approach, should soon enter the world of useful micro- and mesoscale electromechanical devices. This subject is discussed in Chapter 16. 

Chia S, Cao J, Stoddart JF, Zink JE 2001. Working supramolecular machines trapped in glass and mounted on a film surface Angew Chem Int Ed 40 2447 2451. 

Fig. 6 A photochemically driven translation isomerism in a [2]rotaxane supramolecular machine according to Ashton et al. The flash photolysis data, together with electrochemistry observations, allowed the authors to obtain a complete electronic picture of the processes governing the switching mechanism in this [2Irotaxane, from both energy and kinetic perspectives.

Lin, K.J., S.J. Fu, C.Y. Cheng, W.H. Chen, and H.M. Kao. 2004. Towards electrochemical artificial muscles A supramolecular machine based on a one-dimensional copper-containing organopho-sphonate system. Angew Chem Int Edit 43 4186. 

Supramolecular machines contain a discrete number of molecular components capable of converting energy into mechanical work [74]. Like macroscopic machines, users of molecular machines are concerned with energy input, processing... 

Bunker, B.C. et al. (2007) Switching surface chemistry with supramolecular machines. Langmuir, 23, 31-34. 

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