Since their discovery [1] in 1993, single-walled carbon nanotubes (SWNTs) have found numerous applications [2] in chemistry and physics on account of their anisotropic shapes (diameters of around 1 nm and lengths of micrometers), remarkable strengths and elasticities, and unique physical properties, for example, high thermal and electrical conductivities. By contrast, and despite their clear potential, SWNTs have not yet been fully integrated into biological systems, [3] mainly because of the considerable difficulty in rendering them soluble in aqueous solutions.Initially, the challenge of achieving soluble SWNTs in organic solvents was addressed by their covalent modification-examples include both end-group [4] and side-wall [5] functionalization. Covalent modification, however, has the disadvantage that it impairs their physical properties. For these, and other reasons, we have been attracted by a supramolecular approach [6] to the solubilization problemnamely, the noncovalent functionalization of SWNTs by wrapping polymers around them in the knowledge that desired features can be grafted onto the polymers, prior to their being self-assembled around the SWNTs. Considerable progress [6, 7] has been made in the use of synthetic polymers to render SWNTs soluble in organic solvents. However, while some water-soluble polymers [8] and surfactants [9] can bring aqueous solubilities to SWNTs, they may not be as biocompatible as would be desirable.It was for this reason, amongst others, that we decided to explore the possibility of solubilizing SWNTs in aqueous solutions of starch. [10] We knew from our knowledge of the supramolecular chemistry of fullerenes [11] that cyclodextrins (CDs) of the appropriate dimensions (g-CD commonly and d-CD occasionally), and in the correct stoichiometries, will dissolve fullerenes (C 60 and C 70 , for example) in water. [12] CDs are the macrocyclic analogues [13] of starch. The connection is clear. Here, we report 1) that common starch, provided it is activated toward complexation by wrapping itself helically around small molecules, will transport SWNTs competitively into aqueous solutions, 2) that the process is sufficiently reversible at high temperatures to permit the separation of SWNTs in their supramolecular starch-wrapped form by a series of physical manipulations from amorphous carbon, and 3) that the addition of glucosidases to these starched carbon nanotubes results in the precipitation of the SWNTs from aqueous solution.

Intimate electrical contact occurs between a substituted poly(metaphenylenevinylene) (PmPV) and bundles of single‐walled nanotubes (SWNT) as evidenced by atomic force microscopy, optical, and electronic measurements carried out on single, isolated SWNT/PmPV structures (see picture). PmPV may provide a useful route toward “functionalizing” the SWNT without destroying their electrical character.

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We report on the kinetics and ground-state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular-switch tunnel junctions (MSTJs). For all rotaxanes a pi-electron-deficient cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT4+ ring encircles predominantly (>90 %) the TTF unit at equilibrium, and this equilibrium is relatively temperature independent. In the third rotaxane (RBPTTF4+), the TTF unit is replaced by a pi-extended analogue (a bispyrrolotetrathiafulvalene (BPTTF) unit), and the CBPQT4+ ring encircles almost equally both recognition sites at equilibrium. This equilibrium exhibits strong temperature dependence. These thermodynamic differences were rationalized by reference to binding constants obtained by isothermal titration calorimetry for the complexation of model guests by the CBPQT4+ host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT4+ ring to the DNP site. Reduction back to TTF0 (BPTTF0) is followed by relaxation to the equilibrium distribution of translational isomers. The relaxation kinetics are strongly environmentally dependent, yet consistent with a single electromechanical-switching mechanism in acetonitrile, polymer electrolyte gels, and MSTJs. The ground-state equilibrium properties of all three bistable [2]rotaxanes were reflective of molecular structure in all environments. These results provide direct evidence for the control by molecular structure of the electronic properties exhibited by the MSTJs.