Bulletin of the Chemical Society of Japan

Hara, Mitsuo; Oguri, Ryota; Sarkar, Shingo; Nagano, Shusaku; Seki, Takahiro

doi: 10.1246/bcsj.20210391pmid: N/A

We propose a simple technique to fabricate a uniform nanodot array of titanium dioxide via two-dimensional shrinkage in the amorphous-to-crystalline (anatase) transformation during calcination of a precursor film. Increasing the calcination temperature from 400 °C to 600 °C enhances the crystal size diameter from ca. 10 to 20 nm, while mixing the precursor film with a thermotropic liquid crystalline amphiphilic block copolymer results in dot arrays with more uniform particle size.

Yamamoto, Yoshihiko

doi: 10.1246/bcsj.20210402pmid: N/A

The mechanism of the Rh/phanephos-catalyzed enantioselective [2+2+2] cyclization of an ester-tethered enediyne, which produces a lactone-fused cyclohexadiene bearing an all-carbon quaternary bridgehead carbon, was computationally analyzed using density functional theory (DFT) calculations. This study suggests that the initial oxidative coupling occurs with the 1,6-diyne moiety rather than the 1,6-enyne moiety of the enediyne substrate, and the subsequent insertion of the pendant alkene into the resultant rhodacyclopentadiene intermediate is the enantioselectivity determining step. Further, it is suggested that the experimentally favored enantiomer should be produced through endo-mode alkene insertion followed by two-step reductive elimination. Moreover, DFT calculations show that the Rh/2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) catalyst enables the [2+2+2] cyclization of an enediyne bearing a methyl substituent at the propiolate terminus, which is not feasible using the Rh/phanephos catalyst.

Nakao, Toshiki; Goto, Masaki; Kurashina, Masashi; Tamai, Nobutake; Yasuzawa, Mikito; Matsuki, Hitoshi

doi: 10.1246/bcsj.20210395pmid: N/A

An unnatural phospholipid with two amide linkages, dipalmitoylamidodeoxyphosphatidylcholine (DPADPC), was synthesized and its bilayer phase transitions were observed by differential scanning calorimetry under atmospheric pressure and light-transmittance measurements under high pressure. The DPADPC bilayer membrane showed different phase transitions depending on the thermal history of the lipid sample under atmospheric pressure. The thermal-history dependent transitions were also observed under high pressure. The temperature–pressure phase diagram and thermodynamic quantities of the phase transitions of the DPADPC bilayer membrane were compared with those of bilayer membranes of hydrophobic chain-linkage isomers, ester-linked dipalmitoylphosphatidylcholine (DPPC) and ether-linked dihexadecylphosphatidylcholine (DHPC). The thermodynamic quantities of the main transition for these PC bilayer membranes were similar to one another, whereas the suppression of the interdigitation and great stabilization of the hydrated crystal phase were observed for the DPADPC bilayer membrane. Furthermore, the results of nuclear magnetic resonance measurements indicated that the motility of PC molecules in both gel and liquid crystal phases of the DPADPC bilayer membranes were much lower than those of the DPPC and DHPC bilayer membranes. From the above results, we concluded that the molecular interaction in the PC bilayer membranes increases in the order of ether-, ester- and amide-linkage isomers.

Mukai, Masakiyo; Nagao, Kazunori; Yamaguchi, Shigeru; Ohmiya, Hirohisa

doi: 10.1246/bcsj.20210349pmid: N/A

A molecular-field-based regression analysis using computational screening data for N-heterocyclic carbene (NHC)-Cu-catalyzed asymmetric carbonyl additions of a silylboronate to aldehydes is reported. A computational screening was performed to collect enantioselectivity data (ΔΔG‡: energy differences between the transition states leading to each enantiomer) via transition-state (TS) calculations using density functional theory (DFT) methods. A molecular field analysis (MFA) was carried out using the obtained calculated ΔΔG‡ values and TS structures (30 samples in total). Important structural information for enantioselectivity extracted by the MFA was visualized on the TS structures, which provided insight into an asymmetric induction mechanism. Based on the obtained information, chiral NHC ligands were designed, which showed improved enantioselectivity in these carbonyl additions (designed ligands: up to 96% ee, initial training samples: up to 73% ee).

Sugiyama, Yasukazu; Soda, Yasuki; Yoritate, Makoto; Tajima, Hayato; Takahashi, Yoshito; Shibuya, Kana; Ogihara, Chisato; Yokoyama, Takashi; Oishi, Takeshi; Sato, Takaaki; Chida, Noritaka

doi: 10.1246/bcsj.20210372

Matsuhisa, Masayuki; Kishimoto, Fuminao; Furusawa, Kosuke; Tsubaki, Shuntaro; Wada, Yuji

doi: 10.1246/bcsj.20210401pmid: N/A

Microwaves (MWs) with a frequency of sub–gigahertz or multi–gigahertz can promote a rotation of polar molecules and a vibration of electric charges through an interaction with the alternating electric fields which comprise the MWs. The MWs can also promote the rotation of dipoles formed at the interface of Schottky junctions and semiconductor heterojunctions (e.g. p–n junction), leading us to expect that photoinduced electron transfer reaction at the interface can be perturbed by the dipole rotation induced by MWs. In this paper, we successfully demonstrated that 2.45 GHz MWs can boost the photocurrents of FTO/TiO2 and FTO/TiO2/CdS electrodes, which are typically used electrode structures in quantum dot- or dye-sensitized solar cells. From photoelectrochemical analysis using precisely controlled MW power and illuminant wavelength, a model is proposed in which the tunneling electron transfer reactions occurring in photoelectrodes are accelerated by MW-induced perturbations of the interfacial dipoles at the tunneling interfaces. The model proposed here would open the way for novel applications of MWs in the fields of photo-, electro-, and photoelectrocatalysis with the aim of solar energy conversion.

Mori, Keiji

doi: 10.1246/bcsj.20210420pmid: N/A

An efficient catalytic internal redox reaction (hydride shift mediated C(sp3)–H bond functionalization) has been developed, which has the following salient features: (1) C(sp3)–H bond functionalization, (2) Lewis and/or Brønsted acid catalyzed reaction (transition metals employed in conventional C–H bond functionalization are not required), and (3) construction of complex polycycles that are otherwise difficult to synthesize by conventional methods. Our recent efforts on the development of novel types of C(sp3)–H bond functionalization mediated by the hydride shift/cyclization system are described.

Kusamoto, Tetsuro; Ohde, Chie; Sugiura, Shiori; Yamashita, Satoshi; Matsuoka, Ryota; Terashima, Taichi; Nakazawa, Yasuhiro; Nishihara, Hiroshi; Uji, Shinya

doi: 10.1246/bcsj.20210411pmid: N/A

Quantum spin liquid (QSL) is a novel quantum state of matter, where spins are strongly entangled and highly fluctuating even at very low temperature. In this study, an organic QSL was newly synthesized, and the structure and physical properties were investigated. The antiferromagnetic interaction (J ≈ 24 K) detected between the spins was much smaller than that in the other organic QSLs, while the χ0 and γ values were larger. The results enable significant scalings, γ, χ0 ∝ 1/J for all the organic QSLs, which show the formation of the spinon energy band with the width of J. These findings provide good evidence of the spinon Fermi surface in the QSLs, where the spinon excitation follows the Fermi liquid behavior.

Aoyama, Yurina; Sato, Naoko; Toyotama, Akiko; Okuzono, Tohru; Yamanaka, Junpei

doi: 10.1246/bcsj.20210356pmid: N/A

Adsorption of particles on soft hydrogels, which plays an important role in various scientific and industrial fields, has often been studied using interactions such as hydrogen bonding. Here, we demonstrate that submicron-sized colloidal particles can be adsorbed onto gels, solely by van der Waals (vdW) attraction, without any special interaction. We investigated the adsorption of silica, polystyrene, and titania particles on polyacrylamide (PAAm) and polydimethylacrylamide (PDMA) hydrogels. The vdW force was tuned by the refractive index of media. Previously, we studied the particle adsorption on gels (N. Sato et al., Sci. Rep. 7(1), 2017) and concluded that the vdW force is a strong driving force. However, the influence of the medium viscosity on the adsorption rate and the contribution of interactions other than the vdW force needed to be clarified. The PDMA linear polymer adsorbed strongly on the silica particles, but the PAAm polymer did not. On the other hand, both PDMA and PAAm hydrogels strongly adsorbed silica and all other particles in water. The amount of adsorption varied with the magnitude of Hamaker constant. These results indicate that the vdW force is a sufficiently strong driving force for the particle adsorption to polymer hydrogel surfaces in water.

Umeno, Keitaro; Onoue, Hisaaki; Konoki, Keiichi; Torikai, Kohei; Yasuno, Yoko; Satake, Masayuki; Oishi, Tohru

doi: 10.1246/bcsj.20210397pmid: N/A

Synthesis of the WXYZA′B′C′D′E′F′ ring segment of maitotoxin, a ladder-shaped polyether produced by the dinoflagellate Gambierdiscus toxicus, was achieved based on a convergent strategy via α-cyano ethers developed in our laboratory. The WXYZ ring aldehyde and the C′D′E′F′ diol were combined through the construction of the B′ ring via ring-closing metathesis and the A′ ring via O,S-acetal formation followed by radical reduction. Introduction of a terminal olefin in the side chain culminated in the convergent synthesis of the WXYZA′B′C′D′E′F′ ring segment in 16 steps.