Fabrication of optically transparent chitin nanocomposites

This paper demonstrates the preparation of chitin nanofibers from crab shells using a simple mechanical treatment. The nanofibers are small enough to retain the transparency of neat acrylic resin. Possessing hydroxyl and amine/N-acetyl functionalities, water suspension of chitin nanofibers was vacuum-filtered 9 times faster than cellulose nanofibers to prepare a nanofiber sheet of 90 mm in diameter. This is a prominent advantage of chitin nanofibers over cellulose nanofibers in terms of commercial application. Interestingly, chitin acrylic resin films exhibited much higher transparency than cellulose acrylic resin films owing to the close affinity between less hydrophilic chitin and hydrophobic resin. Furthermore, the incorporation of chitin nanofibers contributes to the significant improvement of the thermal expansion and mechanical properties of the neat acrylic resin. The properties of high light transmittance and low thermal expansion make chitin nanocomposites promising candidates for the substrate in a continuous roll-to-roll process in the manufacturing of various optoelectronic devices such as flat panel displays, bendable displays, and solar cells.     

Synthesis and Spectroscopic Studies of Arylethynylsilanes

A variety of arylethynylsilanes (Ar‐C?C? C₆H₄? C?C)_nSiMe_4?n were prepared successfully by reaction of the corresponding chlorosilanes Me_4?nSiCl_n with Ar? C?C? C₆H₄? C?CM (M=Li, MgBr), which was prepared by treatment of ethynyl(diarylethyne)s Ar? C?C? C₆H₄? C?CH with BuLi or MeMgBr. The ethynyl(diarylethyne)s were readily prepared in good yields by the double‐elimination method: addition of lithium hexamethyldisilazide to a mixture of ArCH₂SO₂Ph, TMS? C?C? C₆H₄? CHO, and ClP(O)(OEt)₂, followed by desilylation. In the tetrakis(arylethynyl)silanes (Ar? C?C? C₆H₄? C?C)₄Si thus prepared, through‐space conjugation of four triple bonds on the silicon atom emerges as a result of participation of the silicon orbitals in the acetylenic π orbitals. This participation enhances the emissive quantum yields of arylethynylsilanes with an increase in the number of arylethynyl moieties on silicon: quantum yields of emission (Φ_F) of 0.72 for (MeOC₆H₄? C?C? C₆H₄? C?C)₄Si, 0.53 for (MeOC₆H₄? C?C? C₆H₄? C?C)₂SiMe₂, and 0.47 for MeO‐C₆H₄? C?C? C₆H₄? C?CSiMe₃ were obtained. Although this enhancement effect was also observed in the phenylethynylarylsilane (MeOC₆H₄? C?C? C₆H₄)₂SiMe₂, the bis(arylethynyl)disilane (MeOC₆H₄? C?C? C₆H₄? C?C‐SiMe₂)₂ exhibited non‐enhanced emission.     

Facile Preparation of Organometallic Nanorods from Various Ethynyl-Substituted Molecules

A facile method to prepare one-dimensional (1D) organometallic nanomaterials from various ethynyl-substituted molecules is reported. The reactions of 3-chloro-1-ethynylbenzene, p-tBu-phenylacetylene and 4-ethynylbiphenyl with Cu⁺ ions in acetonitrile yield nanorod-shaped copper acetylides (Cu−C≡C−R) crystals. In the case of linear alkynes, namely, propyne, 1-pentyne and 1-hexyne, it was found that using an aqueous ammonia/ethanol mixed solvent instead of acetonitrile is a better approach to obtain 1D nanostructures. This procedure also enables us to prepare functional 1D nanomaterials. We demonstrate the preparation of a paramagnetic nanorod from the organic radical p-ethynylphenyl nitronyl nitroxide, and fluorescent nanorods from 9-ethynylphenanthrene and 2-ethynyl-9,9′-spirobifluorene.     

Design of Mononuclear Ruthenium Catalysts for Low‐Overpotential Water Oxidation

Water oxidation is a key reaction in natural photosynthesis and in many schemes for artificial photosynthesis. Inspired by energy challenges and the emerging understanding of photosystem II, the development of artificial molecular catalysts for water oxidation has become a highly active area of research in recent years. In this Focus Review, we describe recent achievements in the development of single‐site ruthenium catalysts for water oxidation with a particular focus on the overpotential of water oxidation. First, we introduce the general scheme to access the high‐valent ruthenium–oxo species, the key species of the water‐oxidation reaction. Next, the mechanisms of the O? O bond formation from the active ruthenium–oxo species are described. We then discuss strategies to decrease the onset potentials of the water‐oxidation reaction. We hope this Focus Review will contribute to the further development of efficient catalysts toward sustainable energy‐conversion systems.     

Silver technology for stabilization of simple (Z)-enethiols: stereoselective synthesis and reaction of silver (Z)-enethiolates

Reported here for the first time are the stereoselective synthesis and reaction of simple silver (Z)-enethiolates, which serve as stabilized (Z)-enethiol storage. In contrast to labile enethiols, silver (Z)-enethiolates are stable even in solutions, and their isolation and purification are very simple. The method for synthesis of silver (Z)-enethiolates involves an unusual vinylic SN2 reaction of (E)-vinyl-lambda3-iodanes with thiobenzamides yielding the inverted (Z)-S-vinylthioimidonium salts, followed by their regioselective C-S bond cleavage with silver acetate. Alkylation, arylation, and Michael addition of silver (Z)-enethiolates yielding (Z)-vinyl sulfides were dramatically accelerated by the addition of Bu4NI (LiI), which probably generates reactive ammonium (Z)-enethiolates with an increased nucleophilicity.