Masayoshi Higuchi

Stepwise radial complexation of imine groups in phenylazomethine dendrimers

Dendrimers are highly branched organic macromolecules with successive layers or ‘generations’ of branch units surrounding a central core. Organic–inorganic hybrid versions have also been produced, by trapping metal ions or metal clusters within the voids of the dendrimers. The unusual, tree-like topology endows these nanometre-sized macromolecules with a gradient in branch density from the interior to the exterior, which can give rise to an energy gradient that directs the transfer of charge and energy from the dendrimer periphery to its core. Here we show that tin ions, Sn2+, complex to the imine groups of a spherical polyphenylazomethine dendrimer in a stepwise fashion. This behaviour reflects a gradient in the electron density associated with the imine groups, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. By attaching an electron-withdrawing group to the dendrimer core, we are able to change the complexation pattern, so that the core imines are complexed last. By further extending this strategy, it should be possible to control the number and location of metal ions incorporated into dendrimer structures, which might find uses as tailored catalysts or building blocks for advanced materials.

Excellent Redox Properties of Poly(thienylphenylamine)s

Triphenylamines with thienyl groups are electro-oxidatively polymerized to yield the corre sponding branched polymers on an electrode. The resulting polymers show significantly better redox properties, such as radox activity, catalytic analytic and conductivity when compared with for example the linear polymeric analog. The good properties of the branched polymers are based on the higher electronic conductivity (2-6 S/cm), since the branching provides multiple routes for charge carriers. The redox-active polymers show high capacity (ca. 40 mC/cm 2 ) and catalytic activity for the electron transfer of ferrocene on the electrode.

Synthesis of DPA dendron encapsulated gold clusters with metal-assembling function

Abstract Gold clusters modified with first, second and third generation dendritic polyphenylazomethines (DPA) were synthesized by an exchanged reaction of corresponding DPA dendron thiols. Measurements by high performance perfect sizer (HPPS) and TEM reveal that their diameters increase with a change in the chain length of the modifying molecules from the first to third generation. These gold clusters with DPA dendrons exhibit coordination quantitatively to metal ions such as Fe3+,Sn2+, etc., because of their imine groups; this then resulted in self-aggregation to form a large sphere.

Electron transfer rate on mixed valence states of Class II/III transition for N, N'-diphenyl-1,4-phenylenediamine structures as a polyaniline unit

Abstract The first example of the determination of the electron transfer rate ( λ , V , Δ G * , k th ) for N , N ′ -diphenyl-1,4-phenylenediamine derivatives using the Marcus–Hush theory is described. These results were in good agreement with the ones obtained using variable-temperature IR spectra measurements.

Dendritic polyphenylazomethines: Synthesis, structure, and metal-assembling function

Dendritic polyphenylazomethines (DPAs) were synthesized as novel topological polymer ligands with pi-conjugated structures by the convergent method via dehydration of aromatic ketones with aromatic amines in the presence of TiCl4. DPA G4 molecules are revealed to have a sphere-like structure with a 2.3-nm diameter and are regularly assembled without deformation of the molecule on a plate as observed by means of gel permeation chromatography (GPC), molecular modeling, transmission electron microscopy (TEM), atomic force microscopy (AFM), and pi-A measurements. The stepwise radial complexation in DPAs with SnCl2 was observed as a stepwise shift in the isosbestic point in the UV-vis spectra. The number of added equivalents of SnCl2 required to induce a shift was in agreement with the number of imine groups present in the different shells of the DPAs. These spectral changes suggest that the complexation is proceeding in a stepwise fashion from the core imines to the terminal imines of the DPAs, which was further supported by shell-selective reduction (SSR) of the imines.

Formation of (FeCl 3 )@phenylazomethine dendrimer (DPA): Fine control of the release and encapsulation of Fe ions in dendrimers*

Phenylazomethine dendrimers (DPAs) act as a strong coordination site for metal ion assembly. DPA G4 is regarded as a molecular capsule having 30 metal-assembling sites with a 2.7 nm diameter. We have reported the radial stepwise complexation with Sn2+ ions in the dendrimers, which means the location and number of metal ions can be controlled. Therefore, DPA G4 should realize a ferritin-like redox nanocapsule with precise control of the number of Fe ions. On the other hand, the Fe ion is a typical paramagnetic molecule. For creating an advanced memory with a high density, ferritin is one of the candidates for use as a magnetic quantum dot. Many attempts to use biomaterials, for example, ferritins and chapero-nins, as metal storage capsules have been demonstrated. Some research groups fabricate a device by assembling ferritins on a plate using their rigid and uniform structure. The attempts to use dendrimers have also been demonstrated. We now describe the successful attempt to control the encapsulation and release of iron ions in a dendrimer in order to mimic a ferritin through the redox reaction. Furthermore, the assembling structures of (FeCl3)n@DPA on a plate were first observed by scanning tunneling microscopy (STM) as a dendrimer complex, which shows that a highly oriented film is formed on a plate only by solvent casting.