Pseudorotaxane self-assembly

The pseudorotaxane self-assembles through hydrogen bonding, and the binding constant, calculated using steady-state fluorescence, is 1.4 x 10. The zinc phthalocyanine derivative exhibited an excited-state lifetime of approximately 3.1 ns. The fast decay of the excited state of 1 ZnPc upon complexation with the fullerene... 

Scheme 3 daisy chain pseudorotaxanes self-assembling in dichloromethane through hydrogen BONDS BETWEEN AMMONIUM IONS AND CROWN ETHERS. THE STRUCTURES OF THE MONOMERS 7 AND 8 ARE SHOWN ABOVE A CARTOON ILLUSTRATING THE DIMERIZATION OF TWO MONOMERS. 

Self-assembly of secondary dialkylammonium ions with macrocyclic polyethers and formation of pseudorotaxanes 96CC1483. 

Self-assembly in construction of pseudorotaxanes, rotaxanes, and catenanes with crown ether fragments 98PAC419. 

Pseudorotaxanes are precursors of both rotaxanes and catenanes they consist of a guest molecule threaded through a macrocyclic host. Stoppering both ends of the threaded molecule gives a rotaxane, cycliza-tion of the thread gives a catenane. Pseudorotaxane formation may occur by spontaneous self-assembly, or may be template-controlled. Anion size can be of paramount importance for such templates - Cl- is effective, Br, I- less good, and PFe ineffective when the recognition motif demands a small template (454). 

Further studies by the same authors have demonstrated that PFj acts a hydrogen bond-acceptor template in the assembly of several other interwoven structures. In an extensive study aimed at using a combination of hydrogenbonding motifs to self-assemble pseudorotaxanes into more complex structures it was discovered that PFj assists on the organization of the components that yield the final superstructure [74]. Particularly, it was found that this anion dictates the orientation of the two carboxylic acid groups of the [3]pseudorotaxanes 58 and 59 (see Schemes 27 and 28) when these groups are co-directional with respect to each other the formation of discrete hydrogen-bonded dimers is observed. 

An admixture of 16b and 17b self-assembles quantitatively at millimolar concentration in chloroform solution to produce an inclusion complex whose absorption and emission maxima are red-shifted by 40 nm [56]. Clicking both ends of this pseudorotaxane with two molar equivalents of stopper S2 produces the squaraine rotaxane 16b D 19b in near-quantitative yield [58]. Pseudorotaxane 16b D 17b partially dissociates at micromolar concentrations in chloroform and produces two emission peaks, one at 638 nm which corresponds to free squaraine 17b and one at 694 nm, corresponding to the pseudorotaxane. In contrast, the squaraine rotaxane 16b D 19b does not dissociate under these conditions or in more polar solvents such as pure methanol. 

Sainsbury, T. and D. Fitzmaurice, Carbon-nanotube-templated and pseudorotaxane-formation-driven gold nanowire self-assembly. Chemistry of Materials, 2004.16(11) p. 2174-2179. 

A pseudorotaxane is the supramolecular product of the self-assembly of two components (i.e., a [2]pseudorotaxane), a molecular ring (macrocycle) and a molecular wire (thread) threaded into it. The occurrence of specific interactions between the two components lowers the free energy of the assembled system with respect to the separate components and drives the self-assembly of the pseudorotaxane (threading process). Threading occurs generally in solution and, upon changes of solvent... 

Figure 13. The self-assembly of [2]pseudorotaxanes incorporating the tetracationic cyclophane 15-4PF6 and the acyclic dioxyarene-based polyethers 16-22.

The ability of cyclodextrins to bind acyclic guests with pseudorotaxane geometries has been employed (Figure 30) by Harada et al. [46, 47] to self-assemble [2]rotaxanes after the threading procedure depicted schematically in Figure la. The diamine 92 is bound by the methylated a-cyclodextrins 93 and 94 with 1 1 stoichiometries in H20. Reaction of the terminal amine groups of the guest with... 

A similar template-directed approach was employed (Figure 31) by Anderson et al. [48] to self-assemble azo-dye [2]rotaxanes. The azobenzene diazonium salt 98 is bound by a-cyclodextrin 99 and also by / -cyclodextrin 100 in H20 with pseudorotaxane geometries. Reaction of the terminal diazonium functions with / -naphthol 101 affords the purple [2]rotaxanes 102 and 103 in yields of 12 and 15%, respectively. These two [2]rotaxanes were characterized by electrospray mass spectrometry which revealed peaks corresponding to the loss of all four sodium cations in both cases. By irradiating some of the protons of the dumbbellshaped components of these [2]rotaxanes, enhancement of the resonances of some of the cyclodextrin protons could be observed as a result of an intercomponent... 

Nakashima et al. [49] have self-assembled (Figure 32) a Tight-driven molecular shuttle by relying upon the threading of one a-cyclodextrin (99) on to an acyclic guest, followed by the covalent attachment of two stoppers at both its ends. The azobenzene-based guest 104 is bound by a-cyclodextrin 99 with a pseudorotaxane... 

Sleiman, H., Baxter, P. N. W., Lehn, J. M., Airola, K., Rissanen, K., Multicomponent self-assembly Generation of rigid-rack multimetallic pseudorotaxanes. Inorg. Chem. 1997, 36, 4734-4742. 

For a number of years the research interests of the Beer group have covered many areas of macrocychc coordination and supramolecular chemistry. This article reviews our latest results of current research by focusing on three major sections sensing of cations and anions anion templated assembly of pseudorotaxanes and rotaxanes, and metal-directed self-assembly using the dithiocaibamate ligand. 

Ionically self-assembled monolayers possessing exceptional temporal and thermal stability of % relative to poled polymers were prepared [45], Molecules of non-polymeric azo dyes (Mordant Orange 10) form pseudorotaxanes with /i-cyclodcxtrin in... 

The self-assembly of threaded supramolecular complexes on solid surfaces can be obtained in systems in which either the acyclic or the macrocyclic component of a pseudorotaxane is immobilized on an appropriate surface.86... 

Noncovalent self-assembly of complementary pairs of homoditopic building blocks (AA/BB-type), such as bis(crown ether) 125 and diammonium salt 126, has afforded well-defined supramolecular oligomeric/polymeric assemblies <2003JA3522>. In dilute solutions, entropy favored the formation of the cyclic dimer, whereas high equimolar concentration (>0.5 M) of the two components led almost exclusively to linear species aggregation, as revealed by H NMR analysis and viscosity measurements. Closely related linear poly[3]pseudorotaxane supramolecular arrays have also been prepared from cylindrical bis(crown ether) 127 and bisparaquat derivative 128 <2005CC1696>. 

The generality of this ordering process was established by the further syntheses of the [2]-pseudorotaxane shown in Figure 4.5 and the (then) novel [3]-pseudoro-taxane shown in Figure 4.62 The first of these species involves the 1 1 self-assembly of 14 with one molecule of the bis(paraquat- -phenylene) tetracationic macrocycle, while in the second species the polyether component is 15 and the corresponding ratio is 1 2. The successful construction of the latter species represented somewhat of a landmark in the use of self-assembly processes of the present type since it demonstrated the feasibility of extending the work to large synthetic... 

While the above studies are representative of the area, it should be noted that a considerable number of other [2]-pseudorotaxanes have been investigated. These include a system exhibiting enantioselective self-assembly during its formation as well as systems incorporating a new structural motif involving a l,2-bis(pyridini-um)ethane axle and a 24-crown-8 ether wheel .A number of poly-pseudoro-taxanes (and related poly-rotaxanes) as well as constitutionally asymmetric and chiral [2]-pseudorotaxanes have been reported. New, multiply-stranded and multiply-encircled systems have also been prepared. The solid state structure of... 

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