日経産業新聞 「原子の数自在に」

Fine Control of the Release and Encapsulation of Fe Ions in Dendrimers through Ferritin-like Redox Switching

R. Nakajima, M. Tsuruta, M. Higuchi, K. Yamamoto
J. Am. Chem. Soc. 2004, 126, 1630-1631.

Fine Control of the Release and Encapsulation of Fe Ions in Dendrimers through Ferritin-like Redox Switching

Numerous dendrimers incorporating metal ions or clusters have received much attention as catalytic and drug delivery materials. We expanded the variety of metal ions that complex with DPA through a radial stepwise complexation to create novel organic−inorganic hybrid materials. As one of the most common and significant iron ions, Fe3+ was used. It was confirmed that iron ions, FeCl3, are coordinated to the imine groups of a spherical phenylazomethine dendrimer (DPA) in a stepwise radial fashion, which should make it possible to control the number and location of the Fe3+ ions incorporated into the dendrimers. Iron possesses very interesting properties such as magnetism, redox chemistry, and catalysis and is also one of the essential elements of our body. Here, we show the first successful attempt to control the biomimetic switching of iron ions' release/encapsulation in the dendrimer driven by their redox response of the Fe2+/Fe3+ couple, which might find uses as a drug delivery system.

日経産業新聞 「大画面化容易な有機EL素子」

化学日報 「新規デンドリマー合成」

Control of Stepwise Radial Complexation in Dendritic Polyphenylazomethines

M. Higuchi, M. Tsuruta, H. Chiba, S. Shiki, K. Yamamoto
J. Am. Chem. Soc. 2003, 125, 9988-9997.

Control of Stepwise Radial Complexation in Dendritic Polyphenylazomethines

The fourth generation of a dendritic polyphenylazomethine (DPA G4) has 2, 4, 8, and 16 imine groups in the first, second, third, and fourth shells, respectively (total, 30 imine groups). DPA G4 can trap 30 equiv of SnCl2 molecules, because the imine group is complexed with SnCl2 at a ratio of 1:1. During addition of 30 equiv of SnCl2 to DPA G4, four shifts in the isosbestic point were observed in the UV−vis spectra, and the amount of SnCl2 added in each step is in agreement with the number of imine groups in each shell of DPA G4. This result shows that the complexation of the imine groups in DPA G4 with SnCl2 occurs stepwise in the order of the first, second, third, and fourth shells. The unique stepwise complexation was also observed in DPA G2 and G3 as two and three shifts of the isosbestic point, respectively. The stepwise complexation was supported by TEM, NMR, and a novel shell-selective reduction (SSR) method for imines. An expansion in the molecular size of DPA G4 by the complexation was revealed by molecular modeling and TEM measurements. The stepwise complexation is caused by the different basicity of the imine groups between the shells, which was supported by the chemical shifts of the peaks attributed to the imine carbons in the 13C NMR spectra. The gradients in the basicity were controlled by the introduction of electron-withdrawing or -releasing groups to the core of the dendrimers; the core imines were complexed last in DPAs having a 2,3,5,6-tetrafluoro or 2,5-dichlorophenyl core due to the low basicity of the core imines. The different complexation pattern was also clearly confirmed by the SSR method.

Novel Triarylamine Dendrimers as a Hole-Transport Material with a Controlled Metal-Assembling Function

N. Satoh, J. Cho, M. Higuchi, K. Yamamoto
J. Am. Chem. Soc. 2003, 125, 8104-8105.

Novel Triarylamine Dendrimers as a Hole-Transport Material with a Controlled Metal-Assembling Function

A series of phenylazomethine dendrimers with a triarylamine core (TPA−DPA) were synthesized by dehydration using TiCl4. The complexation of the fourth genereration (G4) TPA−DPA with SnCl2 proceeds in not a random but a stepwise fashion from the core to the terminal imines of the G4 dendrimer. The molecular size of TPA−DPA G4 is larger than that of DPA G4 in THF solution and has a rigid sphere structure like a globular protein. Organic light-emitting diodes (OLEDs) were fabricated, and the EL performances of the devices using the TPA−DPA−metal complexes as the hole-transport materials are drastically increased (ca. 20 times) by metal complexation.

Metal Assembly in Novel Dendrimers with Porphyrin Cores

T. Imaoka, H. Horiguchi, K. Yamamoto
J. Am. Chem. Soc. 2003, 125, 340-341.

Metal Assembly in Novel Dendrimers with Porphyrin Cores

A series of phenylazozmethine (DPA) dendrimers with a porphyrin core (PnH2) were synthesized by dehydration using TiCl4 from meso-tetrakis(4-aminophenyl)porphyrin and the DPA dendrons. The addition of SnCl2 to a dichloromethane/acetonitrile solution of dendritic cobalt porphyrin resulted in a stepwise spectral change. By using UV−vis spectroscopy to monitor the complexation of the P4CoIIICl until an equimolar amount of SnCl2 has been added, four changes in the position of the isosbestic point were observed during the addition of SnCl2. Titration results suggest that four different complexes are successively formed upon the SnCl2 addition and that the complexation proceeds in, not a random, but a stepwise fashion from the core imines to the terminal imines of P4CoIIICl. The electrochemical study reveals that their dendrimers with Tb ion act as a multielectron mediator in CO2 reduction at high applied potential on the electrode.