Structure and hydrodynamics of polyamic acid chains in solutions. Effect of “pin-joint” oxygen atom

The hydrodynamic characteristics and weight-average molecular weights of some samples of poly-(4,4′-oxydiphenylene) pyromellitamic acid (I) and poly (4,4′-phenylene) pyromellitamic acid (II) in DMF have been obtained by sedimentation, viscometry and light scattering. For (I) the dependence of S₀ on M was obtained and it was found that the hydrodynamic parameters $\text{F}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{P}{}^{\mathrm{?1}}$ depend on M up to M = 10⁵. The experimental results were treated by using two models, viz. a Yamakawa-Fujii persistent chain and a rotational isomeric chain with free rotation about valence bonds. It was shown that the hydrodynamic behaviour of macromolecules of (I) with a pin-joint oxygen atom in the main chain is satisfactorily described by the rotational isomeric chain model with free rotation about valence bonds. The dependence of [η] on M was obtained and the constants K and a in an equation of the Mark-Kuhn-Houwink type were determined for (II). The flexibility of the chain was estimated and the Kuhn segment was found to be 200 Å using the Yamakawa-Fujii theory. The flexibilities of the chains of (I) and (II) are compared; it is shown that the rigidity of the chain of (II) without a pin-joint oxygen atom in the monomer unit is much higher than that of the chain of (I). The dependence of S₀ on M obtained for (II) suggests that its macromolecules show a more pronounced tendency for formation of aggregates than those of (I).     

激光光散射研究丙烯酰胺-二甲基二烯丙基氯化铵共聚物的溶液行为

用激光光散射技术表征了阳离子含量受控的丙烯酰胺 二甲基二烯丙基氯化铵共聚物 (简称P(AM DMDAAC) )在 0 1mol LNaCl溶液中的基本参数和溶液行为 .表观基本参数 : Mw ,app =5 0 4× 10 5g·mol- 1 、app =39 9nm和A2 ,APP =1 5× 10 - 4cm3·mol·g- 2 .动态光散射研究结果表明 ,扩散系数Dt 与角度、浓度皆呈非线性依赖关系 ,当C >C 或在较大的散射角域 ,Dt 偏离线性关系所预示的理论值而向减小的方向发展 ,表明存在缔合物 ;流体力学半径Rh 分布有大、小两个范围 ,并随温度升高向小尺寸方向发展 ,证明了体系中存在缔合行为以及升温的解缔合作用 .在一定条件下 ,“亚稳定性”的存在有力地旁证了体系的缔合行为     

Regioselective synthesis of pentasubstituted benzene derivatives: TBAF as an effective catalyst for the sequential Michael addition-intramolecular aldolization

Polysubstituted benzene derivatives were synthesized starting from the Baylis-Hillman adducts via the sequential introduction of primary nitroalkane at the primary position, Michael addition to β-branched Michael acceptor, aldol condensation, elimination of nitrous acid, and the final aromatization process.     

Stereo- and regioselective synthesis of 1,3-diaryl-3-chloro-1-propanols via the reaction of aryl aldehydes with styrene and (E)-β-methylstyrene

Reactions of aryl aldehydes with styrene and (E)-β-methylstyrene in the presence of phenylboron dichloride regioselectively generate 1,3-diaryl-3-chloro-1-propanols and 1,3-diaryl-3-chloro-2-methyl-1-propanols in good to excellent yields with high stereoselectivity.     

Gas chromatographic study of the urinary codeine-to-morphine ratios in controlled codeine consumption and in mass screening for opiate drugs

The urinary codeine-to-morphine ratios in fifteen volunteers administered codeine tablets at intervals were studied by gas chromatography (GC) and compared with one month's GC results for enzyme multiplied immunoassay technique (EMIT)-screened urine specimens in a mass-screening programme for abuse of opiate drugs, particularly heroin. It appears that when M less than 2 and C/M greater than 0 or when M greater than 2 and C/M greater than 0.5, where C and M are codeine and morphine concentrations in micrograms per 10 ml of urine, codeine consumption has to be presumed.     

二氧化硫的电化学氧化过程：Ⅲ.SO2在聚钴卟啉电极上的氧化机理

采用循环伏安法，稳态法，计时电位法等研究了ＳＯ２在聚钴卟啉膜电极上的电化学氧化过程，并和ＳＯ２在贵金属电极上的行为进行了比较。     

Calix[4]crown in dual sensing functions with FRET

A new calix[4]crown chemosensor based on dual sensing probes reveals Pb²⁺ ion selectivity over other metal ions, which arises from a hypsochromic shift of azo units in UV spectrum as well as a fluorescence enhancement of pyrenyl parts in fluorescence spectrum via a suppressed FRET.     

Study of hydantoin. III . Mass spectrometric behaviour in the electron impact of 2-imino-4-thiazolidinone derivatives

The mass spectral decomposition modes of a series of 2-imino-4-thiazolidinone derivatives are reported and discussed. The fragmentation patterns and mechanisms postulated have been confirmed by the analysis of the MIKE spectra and using DADI technique and the effects of heteroatoms and substituents on the MIKE spectrum of these compounds are compared with that of 3-substituted hydantoins.     

π-Allyl palladium approach toward the diazabicyclo[3.2.1]octane core of the naphthyridinomycin alkaloids

A novel and efficient protocol for the synthesis of the 3,8-diazabicyclo[3.2.1]octane system found in the naphthyridinomycin, dnacin, and tetrazomine families of alkaloids is described. The key transformation involves an intramolecular palladium-catalyzed allylic alkylation. The cyclization proceeds smoothly under mild conditions (20 mol % Pd₂dba₃, 1.5 equiv DBU, 65 °C, THF, 20 min) to afford 3,8-diazabicyclo[3.2.1]octanes in excellent yields (94-98%).     

κ-卡拉胶热可逆凝胶化行为研究

用固体小角激光散射方法研究κ 卡拉胶 (KC)的热可逆凝胶化行为 .以散色斑点的突停点温度为体系的凝胶化点Tgel,考察了溶液中加入Na+ ,K+ ,NH+4,Ca2 + ,Cu2 + ,Zn2 + 等抗衡离子对Tgel的影响 .结果是随抗衡离子浓度增大Tgel上升 ;Tgel与Na+ 的浓度呈线性关系 ,与K+ ,NH+4,Ca2 + ,Cu2 + ,Zn2 + 等离子浓度的平方根成线性关系 ;另外 ,还得到 30℃时KC在KCl盐溶液中的溶胶 凝胶相图 ,并对比了KC在NaCl溶液中透析前后Tgel的变化 .