Mechanically interlocked molecules rotaxanes

Fig. 2 Graphical representations of the structures of mechanically interlocked molecules (MIMs) a catenane (left) and a rotaxane (right)...

A special issue devoted to molecular machines appeared in Accounts of Chemical Research in 2001. It reflects the current interest for this field in which ruthenium complexes act as important tools. Molecular machines are characterized by a mobile part and a stationary part. Photochemical and electrochemical inputs can make a machine work, offering the advantage of being switched on and off easily and rapidly. Mechanically interlocked molecules, such as rotaxanes and catenanes, are suitable candidates. Crown ethers, cyclophanes, and calixarenes are representative families of the cyclic... 

One of the potential applications of mechanically interlocked molecules is construction of molecular-scale devices such as molecular machines and switches. [2J(Pseudo)rotaxanes containing CB 6] were studied along... 

Fig. 1 Different topologies cf mechanically interlocked molecules (a) catenane, (b) rotaxane. (c) pseudorotaxane,(d) oligocatenane, (e) [3]rotaxane, and (t) pretzelane.

During the past 20 years, mechanically interlocked molecules, known as catenanes and rotaxanes, many of them redox-active, have become readily accessible using template-directed protocols that rely upon the precepts of molecular recognition and self-assembly and the tenets of supramolecular assistance to covalent synthesis. By incorporating different recognition units with dissimilar redox properties into appropriate components, these compounds can often be induced to switch hysteretically between ground and metastable co-con-... 

Rotaxanes are mechanically interlocked molecules constituted of a trapped macrocycle around a suitable sterically hindered molecule at both ends. Thus, the macrocycle 34 can be easily prepared from 33 by RCM, but in the presence of ammonium salt 35, the same RCM reaction affords 73% of the rotaxane 36 in which the ammonium ion with two bulky end groups is trapped into the macrocycle (Scheme 16, left-hand route) [46]. 

Mechanically interlocked molecules (MIMs), such as catenanes and rotaxanes, are molecules with at least two components that are not covalently bound, but interlocked in such a manner that they cannot be separated without the breaking of a covalent bond. Since this physical linkage is known as a mechanical bond [24], we refer to the stereochemistry of MIMs as mechanostereochemistry [25]. MIMs have been appreciated for their synthetic challenge and aesthetic value [26] as well as their potential applications. In particular, MIMs have garnered much interest as artificial molecular switches and machines [27-31] because their internal noncovalent bonding interactions can be modulated by external stimuli to control the relative translational and/or circumrotational motions of their interlocked... 

In contrast, chloride complexation to the macrocycle isophthalamide cleft had no apparent effect on the system s dynamics, presumably due to the absence of any potential axle-anion interactions to lock the rotaxane co-conformation. Overall, the work shows that effective traceless ion pair temptation can prodnce uncharged mechanically interlocked molecules with ion-dependent switchable dynamic properties. 

Like rotaxanes, catenanes are mechanically interlocked molecules. However, instead of interlocking one ring shaped macrocycle and a dumbbell shape, catenanes consist of interlocked macrocycles. The number of macrocycles contained in a catenane is indicated by the numeral that precedes it. Catenanes have bistable and multistable forms and a switchable, bistable [2]catenane is commonly exploited in nanotechnology and molecular electronics because its behavior can be controlled by electrochemical processes [89]. Collier et al. was the first to demonstrate the electroactivity of interlocked catenanes [90]. The authors affixed phospholipid counterions to a monolayer of [2]catenanes and then sandwiched this system between two electrodes. This work resulted in a molecular switching device that opened at a positive potential of 2 V and closed at a negative potential of 2 V. 

ICP-MS = inductively coupled plasma mass spectrometry MIM = mechanically interlocked molecule MOF = metal organic framework MORF = metal-organic rotaxane framework PRF = polyrotaxane framework RCP = rotaxane coordination polymer TCPP = tetra 4-carboxy)-phenyl-porphyrin TGA = thermogravimetric analysis. 

Cucurbit [6] uril and increasingly its higher homologues have been used extensively in a variety of host-guest chemistry and nanostructure assemblies. Of particular appeal are rotaxanes and molecular necklaces, mechanically interlocked assemblies of molecules based on CB [6]. Efficient synthesis of ID, 2D and 3D polyrotaxanes and molecular necklaces (cucurbituril beads linked by a macrocyclic molecule string ) has been achieved by a combination of self-assembly and coordination chemistry. We discuss rotaxanes and molecular necklaces in Section 10.7, and cucurbil-based systems are summarised in a recent review.23... 

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