On generalized null polarities

Assuming that a linear complex of planes without singular lines exists, the properties of the related generalized polarity are investigated.     

具有温度敏感和荧光特性的侧链查尔酮共聚物的研究

采用2,2′-偶氮二异丁腈作为引发剂,将N-异丙基丙烯酰胺和4-甲基丙烯酰氧基-4′-二甲氨基查尔酮单体,在四氢呋喃溶剂中通过自由基共聚制备了一系列具有溶剂和温度双重敏感荧光特性的侧链查尔酮共聚物,并通过红外光谱、核磁共振氢谱和紫外-可见光谱对其结构进行表征,通过吸光度法测定了共聚物中查尔酮单元的含量.研究了侧链查尔酮共聚物的温敏性以及溶剂极性和温度双重敏感的荧光特性.结果表明,侧链查尔酮共聚物是一类具有最低临界溶解温度(LCST)的温敏性聚合物,其LCST温度随着共聚物中查尔酮含量的增加而降低;随着溶剂极性的增加,侧链查尔酮共聚物的紫外-可见最大吸收波长红移,其荧光发光波长红移并且发光强度先增强后降低,具有溶剂极性敏感的荧光特性;同时对比侧链查尔酮共聚物水溶液低温和高温下的荧光,发现低温下几乎无荧光,高温下其荧光得到明显增强,其荧光具有可逆的温度"开/关"特性。     

Polyurethane anionomers synthesised with aromatic, aliphatic or cycloaliphatic diisocyanates, polyoxyethylene glycol and 2,2-bis-(hydroxymethyl)propionic acid. Part 3. Electrical properties of polyurethane coatings

The following electrical properties were found for polymer coatings obtained from polyurethane anionomers synthesised with the use of various diisocyanates: volume resistivity, permittivity and dielectric dissipation factor. The effects were discussed from the molecular structures and phase structures of those anionomers on the value of their ionic conductivity and polarizability. The anionomer prepared from the aliphatic diisocyanate was found to offer ionic conductivity; hence, that material can be considered to be a solid electrolyte, which exhibits a considerable susceptibility to structural modifications in the alternating electric field.     

Synthesis and fluorescence properties of 2-aryl-3-hydroxyquinolones, a new class of dyes displaying dual fluorescence

A series of 2-aryl-3-hydroxyquinolones (3HQs) with different electron donating aryl substituents at the position 2 were synthesized. Their absorption and fluorescence properties were studied in solvents of medium and high polarity. Almost all the synthesized 3HQs display dual fluorescence in the tested solvents, in line with an excited state intramolecular proton transfer reaction. For N-methyl substituted compounds, the intensity ratio of the two emission bands was found to be exquisitely sensitive to solvent polarity, with a two orders of magnitude change from toluene to dimethylsulfoxide. Consequently, these compounds appear as prospective polarity fluorescent labels for proteins and nucleic acids.     

On the polarity of stationary phases in straight-phase LC

Summary The LC retention strength of non-bonded silica gel is compared with that of seventeen derivatized silica gels and polystyrenes in straight-phase conditions with hexane-dioxan and hexane-tetrahydrofuran mobile phases. For this purpose a polarity mixture containing UV-active polar compounds is used. Larger retention with dioxan containing eluents is observed. This is an indication that non-displacement H-bond and dipole interactions with adsorbed dioxan contribute to the retention of polar solutes. The linear correlation between log k′ and lox Xs was verified for all phases.     

Relation between interdiffusion and polarity for MBE growth of GaN epilayers on ZnO substrates

We report on GaN growth on Zn-polar ZnO substrates using plasma-assisted molecular-beam epitaxy (P-MBE). Before GaN growth, ZnO substrate annealing conditions were optimized. Reflection high-energy electron diffraction (RHEED) patterns after low-temperature GaN buffer layer annealing changed from streaky to spotty, suggesting that zinc and oxygen atoms interdiffuse from the ZnO substrate into the GaN epilayer. This interdiffusion results in a mix-polar GaN epilayer.     

Application of a flow-tunable, serially coupled gas chromatographic capillary column system for the analysis of complex mixtures

Summary A capillary column gas chromatographic system employing two serially coupled fused-silica columns and a simple coupling element is described. The system is operated in flow-tunable mode (flow-tunable tandem system). The very fact of continuous tuning over a large polarity (selectivity) range, ultimately determined by the two constituent columns, offers several possibilities in the analysis of complex mixtures. In this paper two applications are discussed in detail: optimization of peak separation and peak identification. For these applications it is feasible to use, retention data collected from experiments on the tandem system, and empirical formulas. A relatively simple theoretical mathematical model valid for the flow-tunable tandem system, however, furnishes an easy way of calculating retention data on the system from data collected from the individual single columns, thus, creating a new possibility for optimization and peak identification. Optimization and peak identification processes using the empirical and theoretical models are both demonstrated by analysis of solvent mixtures. Dedicated to the memory of Dr. Tibor Tóth Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Partial Protection of Carbohydrate Derivatives. Part 21. Lead(II) Nitrate Mediated Triisopropylsilyl Ether Formation; Preparation of 2′-Deoxy-3′-O-triisopropylsilylribonucleosides

Introduction of the triisopropylsilyl protecting group to the 3′-position of 5′-O-aroyl-2′-deoxyribonucleosides wa effectively performed by the use of triisopropylsilyl chlor ide in DMF in the presence of pyridine and lead(II) nitrate the latter was substituted in this reaction for silver nitr ate. Simple treatment of the resulting triisopropylsilyl ethers with sodium methoxide in THF gave 2′-deoxy-3′-O-tri-isopropylsilylribonucleosides in excellent yields.