1,4-Dehydrogenation with a Two-Coordinate Cyclic (Alkyl)(amino)silylene

Cyclic (alkyl)(amino)silylene (CAASi) 1 has been found to successfully dehydrogenate 1,4-dihydroaromatic compounds containing various substituents to afford the corresponding aromatic compounds. The observed high substrate generality proves 1 to be a potential 1,4-dehydrogenation reagent for organic compounds. For the reaction with 9,10-dimethyl-9,10-dihydroanthracene, silylene 1 activated not only benzylic C−H bonds but also aromatic C−H bonds to yield a silaacenaphthene derivative, which is an unprecedented reaction of silylenes. The results of the experimental and computational study of the reaction of CAASi 1 with 9,10-dihydroanthracene and 1,4-cyclohexadiene are consistent with the notion that 1,4-dehydrogenation with CAASi 1 proceeds mainly through a stepwise hydrogen-abstraction mechanism.     

Thermal and optical properties of highly fluorinated copolymers of methacrylates

Copolymers of pentafluorophenylhexafluoroisopropyl methacrylate (FPPMA) with trifluoroethyl methacrylate (TFEMA) were prepared in THF solution and in bulk using azobisisobutyronitrile as a free radical initiator. The monomer reactivity ratios of TFEMA (M₁) and FPPMA (M₂) were calculated as r₁ = 0.55 and r₂ = 0.07. The refractive indices of poly(TFEMA) and poly(FPPMA) are very similar as 1.435 and 1.430, respectively, at 532 nm, and the copolymer films were transparent. The glass transition temperatures (T_g) of the copolymers were in the range of 80–90°C and showed a negative deviation from the Gordon–Taylor equation. The thermal decomposition temperature (T_d) was increased with the content of FPPMA in copolymers. Low water absorption for 1:1 FPPMA/TFEMA copolymer was detected. Copolymers of FPPMA with hexafluoroisopropyl methacrylate (HFPMA) were also prepared. The monomer reactivity ratios of HFPMA (M₁) and FPPMA (M₂) were calculated as r₁ = 0.43 and r₂ = 0.10. The T_gs of the copolymers were in the range of 88–95°C and showed also a negative deviation from the Gordon–Taylor equation. T_g and T_d of the copolymers were increased with the content of FPPMA. The refractive index of poly(HFPMA) (1.384 at 532 nm) is much lower than that of FPPMA homopolymer, but copolymer films obtained were clear and transparent. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of Bis(aromatic) Pendants on Recognition of Nucleobase Thymine by Zn2+ -1,4,7,10-tetraazacyclododecane (Zn2+ -cyclen)

We have previously shown that the nucleobase thymine binding to Zn²⁺ -cyclen (cyclen=1,4,7,10-tetraazacyclododecane) complex became stronger by appending acridine, naphthalene, or quinoline rings to the cyclen. Amongst these, the pendant bis((1-naphthyl)methyl) or bis((4-quinolyl)methyl) groups yielded the most effective thymine-recognizing Zn²⁺ -cyclen complexes [J. Am. Chem. Soc., 121 (1999) 5426]. The present study was undertaken to find causes of the bis(aromatic) ring effect by X-ray crystal structure analysis and NMR studies. The crystal structure of the Zn²⁺ -bis((1-naphthyl)methyl)-cyclen complex with a deprotonated 1-methylthymine (1-MeT) failed to show the anticipated evidence for the double ~ - ~ stacking interactions between the two naphthalenes and the Zn 2+ -bound 1-MeT m (1-MeT m =N(3')-deprotonated 1-MeT). Crystal data: formula C₃₆ H₄₇ N₇ O₇ Zn, M r =755.19, monoclinic, space group P2₁/ c (No. 14), a =15.438(2) Å, b =14.093(3) Å, c =16.726(2) Å, g =90.53(1) V =3638.7(8) Å 3 Z =4, R =0.035, R _w =0.049. However, the ¹H NMR studies of Zn²⁼ -bis((4-quinolyl)methyl)-cyclen with 1-MeT in varying H₂O/CH₃ CN solution showed increasing upfield shifts of Me(5') and H(6') of the Zn²⁺ -bound 1-MeT in more aqueous media, indicating that the double intercalation with the two quinolines became more significant in more protic environments. We conclude that the double ~ - ~ stacking effect accounts for the enhanced recognition of thymine base by the appended bis((1-naphthyl)methyl) or bis((4-quinolinyl)methyl) groups.     

Effect of dopant structure on refractive index and glass transition temperature of polymeric fiber‐optic materials

Graded‐index plastic optical fibers, composed of doped polymers, have advantages over conventional glass optical fibers, but need to be developed further for practical application. Here, a variety of aromatic sulfide dopants were synthesized, and their effects on the refractive indexes and glass transition temperatures (T_g) of poly(methyl methacrylate) and methyl 2‐chloroacrylate/2,2,2‐trichloroethyl methacrylate copolymers were studied. While polymers containing large dopants exhibited relatively high refractive indices, their T_g values were low, making these materials unsuitable for graded‐index plastic optical fiber applications. Six dopants yielded polymers that exhibited higher T_g values than the conventionally used (diphenyl sulfide)‐doped polymer. The dopant dibenzothiophene, in particular, yielded polymers with the highest refractive indexes and T_g values, and polymers containing (phenylthio)benzene dopants also performed well. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of a biodegradable polymeric supramolecular assembly for drug delivery

A novel design of a biodegradable carrier for drug delivery was established by constructing a supramolecular assembly of drugs and polymer backbones without any covalent bonds. A biodegradable polyrotaxane was synthesized in which α-cyclodextrins (α-CDs) as drug carriers were threaded onto poly(ethylene glycol) chains which then were capped at each chain end by L -phenylalanine via peptide linkages. The release of α-CDs was observed only when the terminal peptide linkages were degraded.     

Preparation and dehydration behaviour of thomsonite with ideal chemical composition

Thomsonite with ideal chemical composition and with an ordered framework structure was synthesised hydrothermally from zeolite Na?A, which was ground to X-ray amorphous, with 0.05 mol dm^?3 CaCl₂ solution at 200°C. The dehydration behaviour of the prepared thomsonite was examined by TG-DTA. It was revealed that thomsonite lost most of zeolitic water below 450°C in three steps at about 180°, 340° and 390°C. The peak profiles of, the two higher-temperature endotherms were sharp and similar, and the weight loss at each step was approximately equal.     

常温下从离子液体电解液中电沉积金属钴

研究了离子液体镀液中Co、Zn的共沉积行为。ZnCl2-EMIC -CoCl2电解液的循环伏安曲线上出现了三个电流峰,对应的电极电位分别为250mV、50mV、-200mV（vs. Zn2+/Zn）。结合EDS成分分析,可断定这三个电流峰分别对应着Co的电沉积、Co电极上Zn的欠电位沉积和Co-Zn合金的电沉积。恒电位沉积表明,当控制阴极电位在100 mV（vs. Zn2+/Zn）左右时,可得到高纯度的钴镀层;若进行恒电流沉积,则当电流密度为85mA/cm2左右时能够得到高纯度的钴镀层。对Co、Zn的共沉积机理研究表明,Co的电沉积过程和Zn 在Co上的欠电位沉积过程均受扩散过程控制。     

One‐Pot Synthetic Procedure for2,2′‐Disubstituted Biaryls via the Suzuki Coupling Reaction of Aryl Triflates in a Biphasic Solvent System

A one‐pot synthetic procedure for 2,2′‐disubstituted biaryls was developed via a Suzuki cross‐coupling reaction of aryl triflates in a biphasic solvent system. The effects of various bases and solvents were investigated. Results showed that the Na₂CO₃–toluene/H₂O combination gave the highest yields.