Cyclophane cyclobis

The versatility and reversibility of exo-active surfaces have been further explored by using pseudo-rotaxane architectures. Pseudo-rotaxanes generated from the electron-deficient cyclophane cyclobi s(paraquat-p-phenylene) (CBPQT4 +) (3) and... 

In [56] we estimate the performance of metad3mamics for a system consisting of a tetracationic cyclophane (Cyclobis(paraquat-p>-phenylene)g ) and a 1,5-dihydroxy-naphthalene solvated in acetonitrile (see Fig. 5). For this system, which is a simple model for a class of nanomachines [58], we compute the free energy as a function of two collective variables, the distance between the centroids of the cyclophane and the naphthalene and the coordination number of the naphthalene with the atoms of the acetonitrile. This is defined as ... 

Some authors based their approach to selective binding of the more lipophilic a-amino acids in water on hydrophobic effects using water-soluble, cavity-containing cyclophanes for the inclusion of only the apolar tail under renouncement of any attractive interaction of the hosts with the zwitterionic head . Kaifer and coworkers made use of the strong affinity of Stoddart s cyclobis(paraquat-p-phenylene) tetracation 33 for electron-rich aromatic substrates to achieve exclusive binding of some aromatic a-amino acids (Trp, Tyr) in acidic aqueous solution [48]. Aoyama et al. reported on selectivities of the calix[4]pyrogallolarene 34 with respect to chain length and t-basicity of aliphatic and aromatic amino acids, respectively [49]. Cyclodextrins are likewise water-soluble and provide a lipophilic interior. Tabushi modified )S-cyclodextrin with a 1-pyrrolidinyl and a carboxyphenyl substituent to counterbalance the... 

Similar results have been reported for the host/guest complex formation between a tetracationic cyclophane host [=cyclobis(paraquat-p-phenylene)j and the planar het-eroarene indole. The binding constants Kg, determined in six solvents of different polarities, increase with increasing solvent polarity, being ca. 100-fold greater in water than in acetone [306]. Further examples of solvent-dependent cyclophane/guest complexation reactions can be found in reference [299],... 

Properties, applications, and syntheses of cyclophane-like tetracation cyclobis(paraquate-/>-phenylene) 04MI26. 

Examples are the 1, l -dibenzyl-4, 4 -bipyridinium electron-acceptor dication threaded into the 1, 5-dinaphtho-38-crown-10 (Fig. 2a) [10], and the acyclic polyether containing a dioxybenzene electron-donor unit threaded into the electron-acceptor cyclobis(paraquat-p-phenylene) tetracationic cyclophane (Fig. 2b) [11]. Although in these cases a large contribution to the association driving force comes from the electron-donor/acceptor (charge-transfer, CT) interactions, hydrogen bonding can also play an important role, as clearly shown in the cases of pseudorotaxanes constituted by 4, 4 -bipyridinium [12a] or l,2-bis(pyridinium)ethane [12b] threads and crown ethers. 

A classic example of the formation of a macrocycle by a neutral template is that of the versatile host compound and component of molecular machines, the so-called blue box, or cyclobis paraquat-para-phenylene. Reaction of the horseshoe precursor with dibromo-para-xylene leads to the formation of a tricationic intermediate that is capable of binding the template molecule (Scheme 3), which closes the macrocycle to form the tetracationic cyclophane. The jT-ir interactions of the charge-transfer variety (the complex of the product and template is colored, whereas the components are not) assisted by the charge on ihe product are a major driving force in the process, as revealed in X-ray structures of complexes. It should be noted that the interaction is of the jr-n type assisted by the complementary positive charge on the bipyridinium residues and r-electron-rich nature of the template. This supramolecu-lar synthon can be used for other cyclophanes, catenanes, and rotaxanes (see Self-Assembly of Macromolecular Threaded Systems, Self-Assembled Links Catenanes, and Rotaxanes—Self-Assembled Links, Self-Processes). 

The controlled movement in this system is controlled by the interaction among redox-active units at the redox-active tetrathiafulvalene (TTF) units. In the neutral, unperturbed state, the tetracationic cyclophane units (cyclobis(paraquat-para-phenylene), CBPQ F ) are most stable coordinated to the TTF moieties, due to electron donation and Jt-stacking interactions. However, upon oxidation of the TTF units, the CBPQT " rings become electrostatically repelled, migrating to the... 

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