Recognition Paraquat

The [2]rotaxanes, which contain tetrathiafulvalene (TTF) and 1,5-dioxynaphtha-lene (DNP) as the two recognition stations and cyclobis(paraquat-p-phenylene) (CBPQT4 + ) as the cyclic moiety, have been comprehensively investigated by Stoddart and coworkers.68 We have recently reported two new TTF-DNP-CBPQT4+ [2]rotaxanes 62 and 63. In these two [2]rotaxanes, the TTF moiety is the 4,4 (5 )-dialkylthiotetrathiafulvalene that is rather easily accessible based on the synthetic procedure developed by us previously,69 and two different spacers are used the cyclohexyl and alkyl chains. Two stopper units are the G2-dendritic moieties. 

A template-directed synthesis of [2]-rotaxanes, with a yield in one case of 72%, has been reported. The experiments employed dumb-bell-shaped components incorporating terminal triisopropylsilyl stoppers connected to a central 1,5-dioxynaph-thalene recognition site by [-CH2CH20-] spacers (n = 1-3). - These components were used as templates for the synthesis ( clipping reaction ) of the corresponding rotaxanes incorporating cyclobis(paraquat-p-phenylene) as the ring component. The... 

Other rotaxanes have been prepared using the slippage strategyOne such example consists of a linear component (terminated by carbohydrate stoppers) that contained a hydroquinone recognition site. This was demonstrated to interact with cyclobis(paraquat-/7-phenylene) tetrachloride in D O over one week at room temperature to yield the corresponding water-soluble catenane. ... 

Huang F, Nagvekar DS, ZhouX, Gibson HW. Formation ofa linear supramolecular polymer by self-assembly of two homoditopic monomers based on the bis(m-phenylene)-32-crown-lO/paraquat recognition motif. Aiacromolecules. 2007 40 3561—3567. 

Crown ether-based cryptands are important building blocks for molecular machines. Gibson et al. reported a molecular switch (Figure 6) based on a cryptand/paraquat (A, A -dimethyl-4,4 -bipyridinium) recognition motif. ... 

Figure 6 A molecular switch based on a cryptand/paraquat recognition motif. ...

Stoddart et al. reported a three-component molecular switch (Figure 73) driven by two external inputs. This molecular switch combines the recognitions of DB24C8/ secondary ammonium and DN38C10/paraquat derivative. The former can be switched by pH changes and the latter by electrochemical potentials. They found that the connec-tion/disconnection of the two systems could be controlled independently by an acid/base and redox stimulation. 

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