Dynamic crossover in hydration water of curing cement paste: the effect of superplasticizer

The influence of a new comb-shaped polycarboxylate-based superplasticizer (CSSP) on the hydration kinetics and transport properties of aged cement pastes has been investigated by high-resolution quasi-elastic neutron scattering (QENS) and low temperature differential scanning calorimetry (LT-DSC). A new method of analysis of QENS spectra is proposed. By applying the refined method we were able to access to four independent physical parameters including the self-diffusion coefficient of the hydration water confined in the cement paste. Mean squared displacement (MSD) of the hydrogen atom for mobile water molecules displays a dynamic crossover temperature in agreement with DSC data. The experimental results indicate that CSSP polymer added into cement paste moderates the hydration process and decreases the dynamic crossover temperature of the hydration water.     

Study on asymmetric syntheses of steroids: XIII. Synthesis of two new (±)-3-oxa-A-nor steroids 1a and 1b

This paper deals with the synthesis of two new (±)-3-oxa-A-nor steroids 1a and 1 b. The conjugated addition of 5′-methylfurandithane anion 8b to the CD-ring synthon 9 in HMPA-THF afforded 9, 10-seco-3-oxa-A-nor steroid 22. The intramolecular cyclization of 22 in acidic medium gave 23, which underwent hydrolytic desulfurization at elevated temperature in acidic medium to give 1b. The desulfurization of 23 over Raney nickel gave 1a.     

丁磺酸内酯对锂离子电池性能及负极界面的影响

用循环伏安(CV)、电化学阻抗谱(EIS)、扫描电镜(SEM)、能谱分析(EDS)及理论计算等方法研究了添加剂丁磺酸内酯(BS)对锂离子电池负极界面性质的影响. 研究表明, 在初次循环过程中, BS具有较低的最低空轨道能量, 优先于溶剂在石墨电极上还原分解, 并形成固体电解质相界面膜(SEI膜). 在含BS的电解液中形成的SEI膜的热稳定性高, 在70 ℃下储存24 h后, 膜电阻和电荷迁移电阻大小基本保持不变, 而在不含BS的电解液中形成的SEI膜的热稳定性较差, 在70 ℃下储存24 h后, 膜电阻和电荷迁移电阻大小有明显的增加. 从BS对锂离子电池电化学性能影响的研究表明, 加入少量的BS能够显著提高锂离子电池的室温放电容量、低温及高温储存放电性能.     

H2S-induced reorganization of mixed monolayer of carboxylic derivatives on silver surface

The structure of self-assembled monolayers ofp-terphenyl-4-carboxylic acid and the mixed monolayers of this acid with n-hexadecanoic acid on silver surface were studied by reflection-IR spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) measurement, X-ray photoemission electron microscopy (X-PEEM), and atomic force microscopy. Exposure of the p-terphenyl-4-carboxylate monolayer to H2S vapor resulted in reorganization of the film structure into clusters of the corresponding free acids, in tens of nanometer dimension. Exposure of the mixed monolayer to H2S resulted in reorganization of the mixed monolayer film into phase-separated clusters of respective component molecules. The saturated aliphatic acid formed clusters of submicrometer size, whereas the p-terphenyl-4-carboxylic acid formed clusters of tens of nanometer size, presumably due to different surface mobility and/or intermolecular interaction of the two types of molecule. Restoration of the monolayer film from the clusters, driven by the reaction between the free acid molecules and the basic surface sites, proceeded at different speeds for the two types of molecules. The saturated acid monolayer was restored much faster than the p-terphenyl-4-carboxylic acid monolayer. A domain-separated monolayer in several micrometers scale was obtained. The process was imaged by tapping mode atomic force microscopy.     

锂离子电池PMMA-VAc聚合物电解质的制备与性质研究

以甲基丙烯酸甲酯(MMA)和醋酸乙烯酯(VAc)为单体, 用乳液聚合法合成聚甲基丙烯酸甲酯-醋酸乙烯酯聚合物(PMMA-VAc), 并以此聚合物制备了新型聚烯烃膜支撑的聚合物膜及聚合物电解质. 用红外光谱(FTIR)、凝胶色谱(GPC)、差热和热重分析(DSC/TG)、扫描电镜(SEM)及电池充放电实验等方法研究了聚合物、聚合物膜和聚合物电解质的性质. 红外光谱结果表明, MMA与VAc通过各自的C＝C双键打开聚合成PMMA-VAc. PMMA-VAc易于分散在混合碳酸酯溶剂中并形成凝胶, 凝胶粘度随PMMA-VAc浓度的增加而增加, 当浓度为4%时成膜效果最佳. PMMA-VAc膜具有大量的微孔结构, 具有极强的吸液性能. PMMA-VAc膜具有良好的热稳定性: 在380 ℃范围内保持稳定. 聚烯烃膜支撑的PMMA-VAc膜室温下的离子电导率为1.85×10^－3 S•cm^－1, 用作为锂离子电池的聚合物电解质时, 电池具有良好的循环稳定性和倍率性能.     

Studies on the identification and synthesis of insect pheromone: XXIV. Synthesis of (7R, 8S)-(+)- and (7S, 8R)-(−)-sex pheromone of gypsy moth and stereochemistry of β-hydroxysilane

Condensation of the epoxy aldehyde 2 or 2 prepared by Sharpless asymmetric epoxydation in 96—97% yield, with trimethylsilane lithiated 3 gave 7 or 7 ′, which after transformation to the corresponding acetoxyl compound 8 or 8 ′ afforded the title compound 1a or 1b via β-acetoxysilane elimination and catalytic homogeneous hydrogenation. The configurations of the stereoisomers 7 and 7 ′ were determined.     

Studies on steroidal plant-growth regulator: VII. Synthesis of 2α, 3α-dihydroxy-7-oxa-6-oxo-23, 24-dinor-B-homo-5α-cholanic acid and 2α, 3α-dihydroxy-7-oxa-6-oxo-24-nor-B-homo-5α-cholanic acid

Two brassinolide analogues, (2) and (3), have been synthesized from hyodeoxycholic acid (4) through a sequence of reactions as shown in Scheme 1 and 2 of the text.     

Studies on the structures and syntheses of arteannuin and related compounds: XV. Determination of A/B ring configuration of arteannuic acid

5-Oxo-compound 7 and its epimer 8 prepared from epoxidation of methyl arteannuinate followed by rearrangement with BF₃ · Et₂O exhibited a negative and a positive Cotton effect near 294 nm in CD, respectively, a cis A/B ring fusion for 7 and a trans A/B ring fusion for 8 were assigned. It is consistent with the prediction from the octant rule. Therefore the cis A/B ring fusion for arteannuic acid is established. In a similar way, compounds 13a, b and 14 were obtained from the dihydroarteannuinate. Compounds 13a, b showed the same signs as that of 7 and compound 14 as that of 8. Thus the cis A/B ring configuration of arteannuic acid is further proved.     

A concise and stereoselective synthesis of squalamine

[reaction: see text] A short and highly stereoselective synthesis of the novel steroid squalamine (1) was accomplished in nine steps from easily available methyl chenodeoxylcholanate 2. Our synthesis featured improved dehydrogenation of 4 followed by conjugate reduction to construct the trans AB-ring system and efficient asymmetric isopropylation of aldehyde 6 to introduce the C-24R-hydroxyl group.     

A stereoselective synthesis of squalamine

Squalamine (1) was synthesized stereoselectively in 14 steps and 19% overall yield from 3-keto-5-chenodeoxycholanate (2) by using a modified Sharpless asymmetric dihydroxylation as the key step.