Molecular devices: Caroviologens as an approach to molecular wires—synthesis and incorporation into vesicle membranes

Abstract

Molecular wires, which would allow electron flow to take place between different components, are important elements in the design of molecular devices. An approach to such species would be molecules possessing an electron-conducting conjugated chain, terminal electroactive polar groups, and a length sufficient to span a lipid membrane. To this end, bispyridinium polyenes of different lengths have been synthesized and their incorporation into the bilayer membrane of sodium dihexadecyl phosphate vesicles has been studied. Since they combine the features of carotenoids and of viologens, they may be termed caroviologens. Vesicles containing the caroviologen whose length approximately corresponds to the thickness of the sodium dihexadecyl phosphate bilayer display temperature-dependent changes of its absorption spectrum reflecting the gel --liquidcrystal phase transition of the membrane. The data agree with a structural model in which the caroviologens of sufficient length span the bilayer membrane, the pyridinium sites being close to the negatively charged outer and inner surfaces of the sodium dihexadecyl phosphate vesicles and the polyene chain crossing the lipidic interior of the membrane. These membranes may now be tested in processes in which the caroviologen would function as a continuous, transmembrane electron channel-i.e., as a molecular wire. Various further developments may be envisaged along these lines.Molecular devices may be defined as structurally organized and functionally integrated chemical systems built into supramolecular architectures. The development of such devices requires the design of molecular components performing a given function (e.g., photoactive, electroactive, ionoactive, thermoactive, or chemoactive) and suitable for assembly into an organized array. A major requirement is that these components and the devices that they build up should perform their function(s) at the molecular and supramolecular (1) levels, as distinct from the level of the bulk material.

Spontaneous assembly of double-stranded helicates from oligobipyridine ligands and copper(I) cations: structure of an inorganic double helix.

“…From Finally, the structural and physical features of the present and related species may be of use in the design of molecular devices (30), taking advantage of cooperativity and selfassembly processes.…”

Temperature-Dependent In-Plane Structure Formation of an X-Shaped Bolapolyphile within Lipid Bilayers

“…charge carrier conducting rods, into lipid membranes is possible due to the fact that  interactions can stabilize the trans-membrane orientation of the bolapolyphiles in the bilayer. This is of wider interest for molecular electronics in well-organized hybrid-and superstructures [43][44][45][46][47] , especially for the addressing of cells by external electrical signals as required in devices coupling sensors, stimulators or chips with living cells or protocells. [48][49] …”

Conducting Polyaniline Filaments in a Mesoporous Channel Host

“…Previous studies have shown that conjugated systems with appropriate end groups (3)(4)(5) and confined aromatic systems (6) can transfer excitations upon photon absorption or after reduction or oxidation. A major challenge is to achieve charge transfer with low fields as in metallic wires and to establish communication with individual, electrically separated nanometer structures or molecules.…”