Cross patterning on MgO based on dislocations using femtosecond laser irradiation

We show a unique technique to form dense dislocations locally inside a MgO single crystal with a rock-salt type structure using femtosecond (fs) laser irradiation. Cross-shaped patterns of micrometer size, originating from densely introduced dislocations, are formed spontaneously around the focal point. We controlled the three-dimensional propagation of the dislocations by adjusting the pulse energy of the fs laser and NA of objective lens. The technique may open up a new field of dislocation technology for optical applications.     

Kinetic resolution of racemic tertiary allylic alcohols through SN2′ reaction using a chiral bisphosphoric acid/silver(i) salt co-catalyst system

A highly efficient kinetic resolution (KR) of racemic tertiary allylic alcohols was achieved through an intramolecular allylic substitution reaction using a co-catalyst system composed of chiral bisphosphoric acid and silver carbonate. This reaction afforded enantioenriched diene monoepoxides along with the recovery of tertiary allylic alcohols in a highly enantioselective manner, realizing an extremely high s-factor in most cases. The present method provides a new access to enantioenriched tertiary allylic alcohols, multifunctional compounds that are applicable for further synthetic manipulations.

A highly efficient KR of racemic tertiary allylic alcohols was developed through the intramolecular S_N2′ reaction using the chiral bisphosphoric acid/silver carbonate co-catalyst system, affording cis-epoxides and recovered alcohols in a high s-factor.     

A metallocene catalyst system for olefin polymerization using a heteropolyacid as the counter-anion

Polymerization of ethylene and propene were conducted with bis(cyclopentadienylzirconium dichloride) (Cp₂ZrCl₂) and ethylenebis(1-indenyl)zirconium dichloride (Et(Ind)₂ZrCl₂) combined with trialkylaluminium compounds using heteropolyacids as the counter-anions, giving linear polyethylene and isotactic polypropene, respectively. No polymer was obtained when using Cp₂Zr(CH₃)₂ instead of Cp₂ZrCl₂. The mechanism of the formation of active species is briefly discussed on the basis of these results.     

An Optochemical Oxygen Scavenger Enabling Spatiotemporal Control of Hypoxia

We present an optochemical O₂ scavenging system that enables precise spatiotemporal control of the level of hypoxia in living cells simply by adjusting the light intensity in the illuminated region. The system employs rhodamine containing a selenium or tellurium atom as an optochemical oxygen scavenger that rapidly consumes O₂ by photochemical reaction with glutathione as a coreductant upon visible light irradiation (560–590 nm) and has a rapid response time, within a few minutes. The glutathione-consuming quantum yields of the system were calculated as about 5 %. The spatiotemporal O₂ consuming in cultured cells was visualized with a hypoxia-responsive fluorescence probe, MAR. Phosphorescence lifetime imaging was applied to confirmed that different light intensities could generate different levels of hypoxia. To illustrate the potential utility of this system for hypoxia research, we show that it can spatiotemporally control calcium ion (Ca²⁺) influx into HEK293T cells expressing the hypoxia-responsive Ca²⁺ channel TRPA1.     

Supramolecular membranes for optical resolutions and molecular recognitions

Poly(L-glutamate) having amphiphilic side chains was designed as membrane materials for optical resolution of α -amino acids. Solvent- cast films of the poly(L-glutamate) had a self-ordered structure containing α-helix of the poly(L-glutamate). Optical resolutions of various amino acids were carried out through the thin membranes of the amphiphilic poly(L-glutamate). Racemic mixtures of Tryptophan were completely separated through the membrane. Mechanism of the optical resolutions was investigated in terms of molecular recognitions of racemic Tryptophan by the ordered structure of the mambrane.     

Flux-Assisted Synthesis of Y2Ti2O5S2 for Photocatalytic Hydrogen and Oxygen Evolution Reactions

Photocatalytic water splitting is an ideal means of producing hydrogen in a sustainable manner, and developing highly efficient photocatalysts is a vital aspect of realizing this process. The photocatalyst Y₂Ti₂O₅S₂ (YTOS) is capable of absorbing at wavelengths up to 650 nm and exhibits outstanding thermal and chemical durability compared with other oxysulfides. However, the photocatalytic performance of YTOS synthesized using the conventional solid-state reaction (SSR) process is limited owing to the large particle sizes and structural defects associated with this synthetic method. Herein, we report the synthesis of YTOS particles by a flux-assisted technique. The enhanced mass transfer efficiency in the flux significantly reduced the preparation time compared with the SSR method. In addition, the resulting YTOS showed improved photocatalytic H₂ and O₂ evolution activity when loaded with Rh and Co₃O₄ co-catalysts, respectively. These improvements are attributed to the reduced particle size and enhanced crystallinity of the material as well as the slower decay of photogenerated carriers on a nanosecond to sub-microsecond time range. Further optimization of this flux-assisted method together with suitable surface modification is expected to produce high-quality YTOS crystals with superior photocatalytic activity.