Molecular abacus

Figure 7. An example of molecular abacus the ring can be switched between the two stations" of the dumbbellshaped component by base/acid inputs.

It might also be possible to use some of these techniques to prepare rotaxanes [205, 206], in which cyclics are threaded by linear chains, which are then capped with large groups to capture the cyclics. These materials could obviously represent an intriguing type of molecular abacus. 

This approach mimics familiar biological self-assembly phenomena such as protein folding [ 192], protein aggregation [ 192] and nucleotide pairing [ 188]. It incorporates features described in each of the above strategies (i.e., I—III), to give specialized nanoscopic structures, that can be precisely designed, usually with excellent control over CMDPs. Recent examples include so called structure directed synthesis by Stoddart [3a] (see Chapter 1 of this book) to produce toroidal bis-bipyridinium cyclophanes that are reminiscent of a molecular abacus , melamine-cyanuric acid lattices by Whitesides [193] and unique helical structures based on coordination of bipyridyl units to copper (II) ions by Lehn [194],... 

Numerous interlocked assemblies were designed in connection with attempts to gain control of rotational and translational motions at the molecular level, a stepping stone toward possible outstanding development. [ -As-re ards light-operated cases, a representative shuttling scheme for a rotaxane-based molecular abacus is depicted in Fig. As active components. 

Fig. 4 A light-driven "molecular abacus" with movements that are mediated by the covalent bonds and are stationed by the establishment of weak (donor-acceptor) interactions/ ...

Fig. 1.24 Molecular abacus, a cyclodextrin bead (or two) can be manipulated along a polymer chain by means of STM (scanning tunneling micrography).

Figure 35 Structure of the photochemical-driven molecular abacus. (Reproduced from Ref. 68. Wiley-VCH, 2000.)...

A rotaxane is described as an [n]rotaxane when the total number of macrocycles (wheel) and threaded linear subunits (dumbbell) is n. A simple [2]rotaxane is a molecular system in which a macrocycle threads a linear subunit (dumbbell) with two bulky stoppers at the two ends. If there are two or more recognition sites in a rotaxane and the macrocycle can be driven to shuttle between or among these sites by external stimuli, the rotaxane will be a molecular shuttle (Figure 1). Molecular shuttles can be potentially employed to be applied as molecular switches, molecular transporters, logic gates, and molecular abacus, which are able to combine many shuttles together to serve computing. ... 

The pseudopolyrotaxane schematized in Fig. 3 has a supramolecular main-chain bond based on the dimerization of carboxyl groups. Philp and Stoddart had earlier suggested [27] that a molecular chain with appropriately spaced TT-rich rings could thread its way through several macrocycles containing n-acceptors (Fig. 9A) and subsequently be capped with large stoppers to form a permanent rotaxane polymer. The structure may be viewed as a molecular abacus with rotaxane units noncovalently linked to the molecular chain. Newer polyro-taxane polymers are described in this volume in Chapter 8. 

Figure 2.1 Eachofthebluepeaksinthisimageisan individual molecule. The molecules can be moved over a copper surface, making this a molecular abacus or counting device.

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