Self-assembly of metallo-supramolecular block copolymers in thin films

The self-assembly of a metallo-supramolecular PS-[Ru]-PEO block copolymer, where -[Ru]- is a bis-2,2':6',2 ''-terpyridine-ruthenium(II) complex, in thin films was investigated. Metallo-supramolecular copolymers exhibit a different behavior as compared to their covalent counterparts. The presence of the charged complex at the junction of the two blocks has a strong impact on the self-assembly, effecting the orientation of the cylinders and ordering process. Poly(ethylene oxide) cylinders oriented normal to the film surface are obtained directly regardless of the experimental conditions over a wide range of thicknesses. Exposure to polar solvent vapors can be used to improve the lateral ordering of the cylindrical microdomains. (C) 2008 Wiley Periodicals, Inc

Mechanically linked polycarbonate

The synthesis, by solid-state copolymerization, and characterization of the first polycatenanes based on a commercial polymer are reported. Various amounts of a benzylic amide [2]catenane, the corresponding macrocycle, and a rigid bisphenol fluorene derivative have been quantitatively and homogeneously incorporated into bisphenol A polycarbonate. The resulting copolymers were characterized by size exclusion chromatography coupled with viscosimetry, H-1 NMR, differential scanning calorimetry, and dynamic mechanical analysis. The unexpectedly small influence of [2]catenane incorporation on the glass transition temperature of the copolymers points to remarkable internal mobility of the catenane comonomer rings. A new relaxation linked to the flexible catenane units is also observed. The studies represent a detailed structural characterization of a polymer containing small amounts of mechanical linkages in its backbone and demonstrate that significant effects can be induced by doping conventional polymers with small percentages (2-6% of repeat units) of flexible catenanes.</p

Supramolecular self-assembled Ni(II), Fe(II) and Co(II) ABA triblock copolymers

The self-assembly of amphiphilic metallo-supramolecular A-b-B-b-A triblock copolymers containing a B block formed from a bisfunctional terpyridine monomer and an A block based on a monofunctional terpyridine polymer is described. These polymers have been prepared by a polycondensation approach, based on metal–ligand complexation, in which the molecular weight of the central B block has been controlled by the addition of a monofunctional chain-stopper A. Details for the preparation of the A-b-B-b-A triblock copolymers based on the tpy2Ni(II), tpy2Fe(II), and tpy2Co(II) connectivity are given. The influence of the different binding strength of Ni(II), Fe(II), and Co(II) metal ions with terpyridine ligands on the metallo-polycondensation reaction and on the micellization behavior of those materials was studied. Micelles of the obtained block copolymers were prepared and studied by DLS and cryo-TEM

Mechanically linked polycarbonate

The synthesis, by solid-state copolymerization, and characterization of the first polycatenanes based on a commercial polymer are reported. Various amounts of a benzylic amide [2]catenane, the corresponding macrocycle, and a rigid bisphenol fluorene derivative have been quantitatively and homogeneously incorporated into bisphenol A polycarbonate. The resulting copolymers were characterized by size exclusion chromatography coupled with viscosimetry, H-1 NMR, differential scanning calorimetry, and dynamic mechanical analysis. The unexpectedly small influence of [2]catenane incorporation on the glass transition temperature of the copolymers points to remarkable internal mobility of the catenane comonomer rings. A new relaxation linked to the flexible catenane units is also observed. The studies represent a detailed structural characterization of a polymer containing small amounts of mechanical linkages in its backbone and demonstrate that significant effects can be induced by doping conventional polymers with small percentages (2-6% of repeat units) of flexible catenanes.</p

A single synthetic small molecule that generates force against a load

Some biomolecules are able to generate directional forces by rectifying random thermal motions. This allows these molecular machines to perform mechanical tasks such as intracellular cargo transport or muscle contraction in plants and animals. Although some artificial molecular machines have been synthesized and used collectively to perform mechanical tasks, so far there have been no direct measurements of mechanical processes at the single-molecule level. Here we report measurements of the mechanical work performed by a synthetic molecule less than 5 nm long. We show that biased Brownian motion of the sub-molecular components in a hydro- gen-bonded [2]rotaxane—a molecular ring threaded onto a molecular axle—can be harnessed to generate significant directional forces. We used the cantilever of an atomic force microscope to apply a mechanical load to the ring during single-molecule pulling–relaxing cycles. The ring was pulled along the axle, away from the thermodynamically favoured binding site, and was then found to travel back to this site against an external load of 30 pN. Using fluctuation theorems, we were able to relate measurements of the work done at the level of individual rotaxane molecules to the free-energy change as previously determined from ensemble measurements. The results show that individual rotaxanes can generate directional forces of similar magnitude to those generated by natural molecular machines