Total Synthesis of d,l-Isospongiadiol: An Intramolecular Radical Cascade Approach to Furanoditerpenes

A stereoselective oxidative free-radical cyclization of beta-keto ester polyenes 7 and 19 has been accomplished as a one-step entry to the tricarbocyclic synthons 8and 21 which contain five and six stereogenic centers, respectively. These key synthons possessing an axial carboethoxy group at C-4 were ultimately converted to the spongian skeleton (8--> 14 and 21 --> 25 -->14). The synthesis of d,l-isospongiadiol (3) from the common intermediate 14 was realized after introduction of the 2alpha-hydroxy group in the spongian A-ring via epoxidation of silyl enol ether 28 and subsequent desilylation.     

n-GaAs为基的光电化学电池输出特性

GaAs 的禁带宽度为1.428eV,而且是直接跃迁,是光电化学电池中很好的电极材料.一些作者研究了 n-GaAs 为基的光电化学电池^[1,2].本文讨论了光强,化学刻蚀、氧化还原对浓度及离子修饰对 n-GaAs 光电化学电池输出特性的影响.所用的电极为低阻 n-GaAs[(100)面],N_D=5.1×10¹⁷cm^-3,试验前通高纯氮20分钟.测光强用的辐照计经上海计量局校正,其它测试方法同前文^[3].     

End-functionalized polyethylene oxide coated silica particles for packed capillary column supercritical fluid chromatography

Summary Polyethylene oxide (PEO)-based polymers with hydroxy, methoxy, and aminopropoxy terminal groups were coated on diol functionalized and hexamethyldisilazane end-capped silica particles. Proton-donor and proton-acceptor test solutes, including carboxylic acids, hydroxy-containing compounds, arylamines, and alkylamines were used to evaluate the chromatographic performances of these polymer coated particles under SFC conditions with neat CO₂ as mobile phase. It was found that the particles coated with hydroxy-terminated PEO were suitable for the separation of proton-donor compounds such as hydroxy-containing compounds and carboxylic acids, and the particles coated with aminopropoxy-terminated PEO could be used for the separation of amines. That is, the proton-accepting stationary phase is suitable for the separation of proton accepting solutes, including strong basic alkylamines (pK_b4), using neat CO₂ as mobile phase, while the protondonating stationary phase is suitable for the separation of proton-donating compounds such as carboxylic acids (pK_a4). Hydrogen bond basicity was found to be a critical factor for the chromatography of basic amines. Low volatility acidic and basic drugs were chromatographed using the new stationary phases. The stability of the PEO coated particles was determined by measuring the loss of organic carbon under SFC conditions. It was found that approximately 18 % of the coating (average molecular weight of 15,000) was washed out of the particles by supercritical CO₂ after 7 h at 350 atm and 50°C     

A new cyclic peptide from the marine fungal strain <Emphasis Type=Italic>Aspergillus</Emphasis> sp<Emphasis Type=Italic>.</Emphasis> AF119

A new cyclic heptapeptide containing γ-aminobutyric acid in the ring, namely unguisin E (1), was isolated from the fermentation culture of Aspergillus sp. AF119. The structure was elucidated by spectroscopic analyses, including 1D and 2D NMR experiments, and HR ESI-Q-TOF mass spectrometry, and by comparison with those reported. Compound 1 was evaluated for its antimicrobial activities by the paper diffusion method.     

Proton-coupled electron-transfer processes in photosystem II probed by highly resolved g-anisotropy of redox-active tyrosine YZ

The oxidation of a redox-active tyrosine residue Y(Z) in photosystem II (PSII) is coupled with proton transfer to a hydrogen-bonded D1-His190 residue. Because of the apparent proximity of Y(Z) to the water-oxidizing complex and its redox activity, it is believed that Y(Z) plays a significant role in water oxidation in PSII. We investigated the g-anisotropy of the tyrosine radical Y(Z)(?) to provide insight into the mechanism of Y(Z)(?) proton-coupled electron transfer in Mn-depleted PSII. The anisotropy was highly resolved by electron paramagnetic resonance spectroscopy at the W-band (94.9 GHz) using PSII single crystals. The g(X)-component along the phenolic C-O bond of Y(Z)(?) was calculated by density functional theory (DFT). It was concluded from the highly resolved g-anisotropy that Y(Z) loses a phenol proton to D1-His190 upon tyrosine oxidation, and D1-His190 redonates the same proton back to Y(Z)(?) upon reduction.     

Glucokinase-activating sesquinlignans from the rhizomes of Acorus tatarinowii Schott

Three novel sesquinlignans, tatanans A (1), B (2), and C (3), have been isolated from the rhizomes of Acorus tatarinowii Schott. Their structures were established by spectroscopic techniques and single-crystal X-ray analysis. Tatanans A-C potently increase GK enzymatic activity with EC(1.5) values in the range of 0.16-1.85 μM. The potent GK activity and unique structural features of tatanans make them promising leads for therapeutic development of antihyperglycemic drugs.     

Low band gap copolymers consisting of porphyrins,thiophenes, and 2,1,3‐benzothiadiazole moieties for bulk heterojunction solar cells

Two novel low band gap conjugated copolymers containing porphyrins, thiophenes, and 2,1,3‐benzothiadiazole ( BTZ ) moieties were synthesized and applied in bulk heterojunction solar cells. The thermal, optical, electrochemical, and photovoltaic properties of the two copolymers were examined to investigate the effect of the introduction of BTZ moiety in the backbone of the porphyrin polymers. The copolymers exhibited good thermal stability and film‐forming ability. The absorption spectra indicated that the BTZ moiety has significant influence on the UV–visible region spectra of the copolymers: with increasing the molar amount of BTZ moieties in conjugated main chain, the absorption in the range of 450–700 nm is largely broadened and red‐shifted compared to the similar polymers without BTZ moiety, and the optical band gaps of copolymers were narrowed to ～1.50 eV. The photoluminescence spectra showed that there is effective charge transfer in the whole conjugated main chain. Cyclic voltammetry displayed that the band gaps were reduced effectively by the introduction of the BTZ moieties. The bulk heterojunction solar cells were fabricated based on the blend of the copolymers and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) in a 1:2 weight ratio. The maximum power conversion efficiency of 0.91% was obtained by using P2 as the electron donor under the illumination of AM 1.5, 100 mW/cm². © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Etherification of Ferrocenyl Alcohol by Highly‐efficient Ytterbium Triflate

Nucleophilic substitution of ferrocenyl alcohols with various aliphatic alcohols in the presence of a catalytic amount of ytterbium triflate [Yb(OTf)₃] was studied. It was found the unsymmetrical ferrocenyl ethers could be easily obtained in excellent yields when the reactions were performed in primary and secondary alcohols. However, in other organic non‐alcoholic solvents such as acetonitrile, the formation of symmetrical ferrocenyl ethers rather than unsymmetrical ones was observed.