Contributions of restructuring and oxidation to the aging of the surface of plasma polymers containing heteroatoms

The properties and composition of plasma polymer surfaces stored in air can change considerably over time, especially as a result of oxidative reactions. When plasma polymers contain an element other than O, it is possible to probe for mechanisms in addition to oxidation that contribute to the aging of the surface. Plasma polymers containing N were fabricated from either 1,3-diaminopropane (DAP),n-heptylamine (nHA), or allylamine (AA), and studied by X-ray photo-electron spectroscopy (XPS) and air/water contact angles (CA). For each of the plasma polymers, a multiexponential increase in the O/C ratio was observed over time using XPS. The N/C ratios remained constant (AA) or decreased somewhat (nHA and DAP). In contrast, the trends in CA values differed, declining for the nHA surfaces, rising for the AA, and changing little for the DAP. Surface roughness, assessed by scanning tunnelling or atomic force microscopy, did not change over time. The diverse adjustments in the polarity of each surface and the similar compositional changes between them are reconcilable if the aging of the plasma polymer surface is a manifestation of the superposition of concurrent oxidative reactions and partial surface reorientation; the former introduce polar groups and the latter transports then from the surface to deeper regions beyond the CA probe depth but within the XPS analysis depth. These processes vary between different plasma polymers. Data for the alkylamine plasma polymers is also compared with that for two plasma polymers fabricated from methanol. The change in composition, but not polarity, of the DAP surface after 4 days of storage demonstrates the importance of using multiple techniques to characterize the aging of plasma polymer surfaces.     

聚硅氧烷涂敷的反相高效液相色谱固定相

用甲基乙烯基聚硅氧烷涂敷于硅烷化的微粒硅胶上，制备出一种新型的涂敷型反相高效液相色谱固定相。该固定相对极性、非极性和碱性化合物均有良好的分离能力，峰对称性好。对其恶性循环 了考察，连续使用三个月后，固定相的碳量和色谱性能仍保持不变。     

负载稀土型酸活化膨润土的酯化催化活性

负载稀土型酸活化膨润土的酯化催化活性李永绣，冯天泽，胡平贵，何小彬，辜子英，廖荣辉（南昌大学化学系南昌３３００４７）关键词稀土，膨润土，催化酯化可用稀土、膨润土单独作酯化催化剂，但活性不高［１～３］。本文将稀土用离子交换的方法负载到酸活化膨润土中，寻...     

Elution of organic solutes from different polarity sorbents using subcritical water

The intermolecular interactions between organic solutes and sorbent matrices under subcritical water conditions have been investigated at a pressure of 50 bar and temperatures ranging from 50 to 250°C. Both polar and nonpolar organics (chlorophenols, amines, n-alkanes, and polycyclic aromatic hydrocarbons) and five different sorbent matrices (glass beads, alumina, Florisil, silica-bonded C₁₈, and polymeric XAD-4 resins) were used. From the same matrix, the polar solutes always eluted at lower temperatures, while the moderately polar and nonpolar solutes only eluted at higher temperatures. Similar to matrix effects previously observed using supercritical carbon dioxide, the sorbent type greatly influenced the elution efficiency under subcritical water conditions. Lower temperatures are sufficient to elute a particular solute from glass beads, alumina, and Florisil, but higher temperatures (less polar water) are needed to elute the same solute from silica-bonded C₁₈. The highest temperatures were required to elute aromatic organics from XAD-4. These matrix effects demonstrate that, while low temperature water can break inert or dipole interactions between solutes and glass beads, alumina, and Florisil, higher temperature water is required to interrupt the van der Waals attractions between solutes and silica-bonded C₁₈, and even higher temperatures needed to overcome the π-electron interactions between aromatic solutes and XAD-4.     

Mechanism and Kinetics of Thermal Dissociation of Inclusion Complex of Benzaldehyde with β-Cyclodextrin

The inclusion complex of benzaldehyde (BA) with β-cyclodextrin (β-CD) was prepared and was studied by thermal analysis and X-ray diffractometry. The composition of the complex was identified by TG and elemental analysis as β-CD·BA·9H₂O. TG and DSC studies showed that the thermal dissociation of β-CD·BA·9H₂O took place in three stages: dehydration in the range 70-120°C; dissociation of β-CD·BA in the range 235-270°C; and decomposition of β-CD above 280°C. The kinetics of dissociation of β-CD·BA in flowing dry nitrogen was studied by means of TG both at constant temperature and at linearly increasing temperature. The results showed that the dissociation of β-CD·BA was dominated by a one-dimensional random nucleation and subsequent growth process (A₂). The activation energy E was 124. 8 kJ mol^-1, and the pre-exponential factor A 5.04·10¹¹ min^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heterocycles. XXVI. A total synthesis of optically pure (+)-catechin pentaacetate

A total synthesis of optically pure (+)-catechin pentaacetate has been established using the (-)-chalcon epoxide (100% ee) derived from 3,4,2′,4′,6′-pentakis(methoxymethoxy)chalcon as the starting material. The optical purity of the product is confirmed by ¹H nmr analysis in the presence of a shift reagent.     

一种利用质谱信息进行结构特征鉴定的模式识别方法

本文提出了分段式离子系列谱编码方法,实验证明具有很好的结构表征能力。本程序主要是以模式识别技术为基础,实现了对未知物谱图的KNN分类,进而得到未知物的主要结构特征。这个程序应用于有机化合物的分类,取得了满意的结果。     

Determination of medecamycin by adsorptive stripping voltammetry with an activated electrode

The adsorptive and electrochemical behaviors of medecamycin were investigated on a glassy carbon electrode (GCE) pretreated by anodic oxidation at +1.8 V for 5 min in 0.025 mol l^–1 NH₃-NH₄Cl (pH 8.6) solution. An adsorptive stripping voltammetric method for the determination of medecamycin at the pretreated glassy carbon electrode has been developed. Medecamycin was accumulated in NH₃-NH₄Cl buffer (pH 9.0) at a potential of –0.7 V (vs. saturated calomel electrode (SCE)) for a certain time, and then determined by second-order differential anodic stripping voltammetry. The second-order differential anodic stripping peak current at +0.72 V was proportional to the concentration of medecamycin in the range 2.0 g ml^–1 to 50.0 g ml^–1. The detection limit (three times the signal-to-noise) was 1.0 g ml^–1 and the relative standard deviation of the results was 3.28% for eight successive determinations of 10.0 g ml^–1 medecamycin. This method has been applied to the direct determination of medecamycin in commercial tablets and spiked urine samples with satisfactory results.     

利用选择性激发核磁共振对混合物中的两种化合物进行结构解析

利用现代NMR的1D、2D技术对一个混合物进行了分析。结果表明：混合物由两种化合物组成。为了同时准确确定两种化合物的结构，本工作应用了1D-TOCSY技术，利用该技术选择性强的特点来补充常规的1D、2DHMR实验所提供的分子结构的信息。在没有进行预分离的条件下，顺利地完成了样品中两种化合物的核磁信号归属，并最终确定了它们的结构。     

Dendritic nanowire ultraviolet laser array

Self-organized dendritic crystal growth is explored to assemble uniform semiconductor nanowires into highly ordered one-dimensional microscale arrays that resemble comb structures. The individual ZnO nanowires have uniform diameters ranging from 10 to 300 nm. They are evenly spaced on a stem with a regular periodicity of 0.1-2 micrometer. Under optical excitation, each individual ZnO nanowire serves as a Fabry-Perot optical cavity, and together they form a highly ordered nanowire ultraviolet laser array.