Naoki Asao

Atomic origins of the high catalytic activity of nanoporous gold

Distinct from inert bulk gold, nanoparticulate gold has been found to possess remarkable catalytic activity towards oxidation reactions. The catalytic performance of nanoparticulate gold strongly depends on size and support, and catalytic activity usually cannot be observed at characteristic sizes larger than 5 nm. Interestingly, significant catalytic activity can be retained in dealloyed nanoporous gold (NPG) even when its feature lengths are larger than 30 nm. Here we report atomic insights of the NPG catalysis, characterized by spherical-aberration-corrected transmission electron microscopy (TEM) and environmental TEM. A high density of atomic steps and kinks is observed on the curved surfaces of NPG, comparable to 3-5 nm nanoparticles, which are stabilized by hyperboloid-like gold ligaments. In situ TEM observations provide compelling evidence that the surface defects are active sites for the catalytic oxidation of CO and residual Ag stabilizes the atomic steps by suppressing {111} faceting kinetics.

Nanoporous Gold Catalyst for Highly Selective Semihydrogenation of Alkynes: Remarkable Effect of Amine Additives

We report for the first time the highly selective semihydrogenation of alkynes using the unsupported nanoporous gold (AuNPore) as a catalyst and organosilanes with water as a hydrogen source. Under the optimized reaction conditions, the present semihydrogenation of various terminal- and internal-alkynes affords the corresponding alkenes in high chemical yields and excellent Z-selectivity without any over-reduced alkanes. The use of DMF as solvent, which generates amines in situ, or pyridine as an additive is crucial to suppress the association of hydrogen atoms on AuNPore to form H(2) gas, which is unable to reduce alkynes on the unsupported gold catalysts. The AuNPore catalyst can be readily recovered and reused without any loss of catalytic activity. In addition, the SEM and TEM characterization of nanoporosity show that the AuNPore catalyst has a bicontinuous 3D structure and a high density of atomic steps and kinks on ligament surfaces, which should be one of the important origins of catalytic activity.

Stat3 as a Therapeutic Target for the Treatment of Psoriasis: A Clinical Feasibility Study with STA-21, a Stat3 Inhibitor

Epidermal keratinocytes in psoriatic lesions are characterized by activated Stat3, and increased levels of cytokines and growth factors that promote Stat3 activation have been found within psoriatic lesions. K5.Stat3C transgenic mice, in which keratinocytes express a constitutively active Stat3, develop psoriasis-like skin lesions. In this study, we examined whether STA-21, a small Stat3 inhibitor, could be useful in ameliorating the skin lesions not only in the model mouse but also in human psoriasis. Treatment with STA-21 markedly inhibited the cytokine-dependent nuclear translocation of Stat3 in normal human keratinocytes in vitro. Keratinocyte proliferation was inhibited by STA-21 in a dose-dependent manner through downregulation of c-Myc and cyclin D1, whereas involucrin, transglutaminase 1, and keratin 10 levels were upregulated. Topical application of STA-21 abolished the generation of skin lesions in K5.Stat3C mice. Finally, we treated psoriasis patients with STA-21-containing ointment in a nonrandomized study. Psoriatic lesions in six of the eight patients showed improvement after topical STA-21 treatment for 2 weeks. Therefore, we conclude that targeting Stat3 may lead to a therapy for psoriasis.

Bottom-Up Graphene-Nanoribbon Fabrication Reveals Chiral Edges and Enantioselectivity

We produce precise chiral-edge graphene nanoribbons on Cu{111} using self-assembly and surface-directed chemical reactions. We show that, using specific properties of the substrate, we can change the edge conformation of the nanoribbons, segregate their adsorption chiralities, and restrict their growth directions at low surface coverage. By elucidating the molecular-assembly mechanism, we demonstrate that our method constitutes an alternative bottom-up strategy toward synthesizing defect-free zigzag-edge graphene nanoribbons.

Metal‐Catalyzed Annulation Reactions for π‐Conjugated Polycycles

The progress of the metal-catalyzed annulation reactions toward construction of various π-conjugated polycyclic cores with high conjugation extension is described. This article gives a brief overview of various annulation reactions promoted by metal catalysts including C-H bond functionalization, [2+2+2] cycloaddition, cascade processes, ring closing metathesis, electrophilic aromatization, and various cross-coupling reactions. A variety of conjugated polycycles with planar, bowl-shaped, and helical structures have been constructed in high efficiency and selectivity.

Remarkable Catalytic Property of Nanoporous Gold on Activation of Diborons for Direct Diboration of Alkynes

A novel catalytic property of nanoporous gold for activation of bis(pinacolato)diboron has been reported that allows the direct diboration of alkynes to proceed sufficiently in a heterogeneous process. The experimental results revealed that the nanoporous gold catalyst is able to cleave the B-B bond of bis(pinacolato)diboron without using any additives.

Unsupported Nanoporous Gold Catalyst for Highly Selective Hydrogenation of Quinolines

For the first time, the highly efficient and regioselective hydrogenation of quinoline derivatives to 1,2,3,4-tetrahydroquinolines using unsupported nanoporous gold (AuNPore) as a catalyst and organosilane with water as a hydrogen source is reported. The AuNPore catalyst can be readily recovered and reused without any loss of catalytic activity.

A novel metal-free panchromatic TiO2 sensitizer based on a phenylenevinylene-conjugated unit and an indoline derivative for highly efficient dye-sensitized solar cells

A novel donor-π-spacer-acceptor type organic dye (AK01) bearing a phenylenevinylene-conjugated system and a derivative of indoline donor was synthesized for dye-sensitized solar cells. AK01 showed panchromatic TiO(2) sensitization with high overall conversion efficiency of 6.2% under AM 1.5 illumination (100 mW cm(-2)).

Ytterbium triflate catalyzed ring opening of aziridines with amines

Abstract Ring opening of aziridines with amines takes place readily in the presence of catalytic amount of ytterbium triflate, giving the corresponding 1, 2-diamines in good to high yields.

Pd-Catalyzed Cascade Crossover Annulation of o-Alkynylarylhalides and Diarylacetylenes Leading to Dibenzo[a,e]pentalenes

A novel and selective Pd-catalyzed cascade crossover-annulation of o-alkynylarylhalides and diarylacetylenes for the synthesis of dibenzo[a,e]pentalenes has been reported. Various arylacetylenes with a wide range of functional groups were tolerated, producing the corresponding multisubstituted dibenzopentalenes with the different substituents on the aromatic rings in good to high yields under the optimized reaction conditions. The reaction proceeds through a Pd-catalyzed cascade carbopalladation and C-H activation. The use of the combined DBU and CsOPiv bases is crucial for the successful implementation of the present cross-annulation.