DETERMINATION OF DEGREE OF CRYSTALLINITY OF NYLON 1212 BY WIDE-ANGLE X-RAY DIFFRACTION

Based on the X-ray scattering intensity theory and using the approximate expression for the atomic scattering factor, the correction factors for three crystalline peaks and an amorphous peak of Nylon 1212 were calculated and the formula of degree of crystallinity of Nylon 1212 was derived by a graphic multipeak resolution method. The degree of crystallinity calculated from the WAXD method is compatible with those obtained by density and calorimetry methods.     

A ‘one pot’ microwave-mediated synthesis of the basic canthine skeleton: expedient access to unnatural β-carboline alkaloids

In a ‘one pot’ microwave reaction, an acyl hydrazide-tethered indole underwent a 3-component condensation to form a triazine, followed by an inverse-electron demand Diels-Alder reaction and subsequent chelotropic expulsion of N₂ to deliver novel, unnatural β-carboline alkaloids in good isolated yields.     

A facile synthesis of bifunctional phospholipids for biomimetic membrane engineering

We report a facile synthesis of bifunctional phospholipid conjugates by acylation of N-protected lyso-phosphatidylethanolamine with 12-acryloxy-1-dodecanoic acid and followed with deprotection and conjugation with biotin, FITC, Texas Red, or EMC groups. The lipid conjugates can be used to generate a multifunctional substrate-supported phospholipid membrane via bioconjugation reaction to biotin or covalent attachment to EMC at their hydrophilic terminus. In addition, conjugation to fluorophores, FITC or Texas Red, provides a convenient mechanism to monitor lipid membrane formation and stability. Significantly, in situ photopolymerization of the acrylate group at the end of one of two hydrophobic alkyl chains stabilizes the phospholipid membrane.     

Determination of trace amounts of silver with a chemically modified carbon paste electrode

A method for the determination of trace amounts of silver with a chemically modified carbon paste electrode is described. The modified electrode is prepared by simply mixing a chelating resin (a polythioether backbone and dioxymonosulphur polyethylene polyimines in the side-chain polymer) with graphite powder and Nujol oil. By immersing the electrode in a silver sample solution (pH = 6.5–7.5), silver can be adsorbed on the electrode surface and then determined by voltammetry in a separate blank solution. The response depends on the concentration of silver and the preconcentration time. For a preconcentration time of 5 min, the detection limit is about 3 × 10^?10 M and the linear range is from 5 × 10^?10 to 1 × 10^?7 M with a relative standard deviation of 4%. Many common metal ions have no or little effect on the determination of silver. The recommended procedure was applied to the determination of trace amounts of silver in waste water.     

Hydrogenation of benzaldehyde and cinnamaldehyde in compressed CO2 medium with a Pt/C catalyst: a study on molecular interactions and pressure effects

The hydrogenation of benzaldehyde and cinnamaldehyde has been studied with a 5% Pt/C catalyst in compressed CO(2). The effect of CO(2) pressure on the total conversion was found to be different between the two aldehydes. The total conversion of benzaldehyde merely decreases with increasing CO(2) pressure, while that of cinnamaldehyde shows a maximum at a certain pressure. High-pressure FTIR measurements indicate the existence of interactions of CO(2) with the aldehydes. The absorption of nu(C=O) red-shifts at increasing CO(2) pressure, and this red-shift is more significant for cinnamaldehyde than for benzaldehyde, indicating that the C=O bond of the former becomes more reactive than the latter. The difference in the mode of interactions of CO(2) with these aldehydes has also been indicated by changes of nu(C=O) of CO(2). Thus, the conversion of benzaldehyde will decrease with increasing CO(2) pressure because of a simple dilution by introducing a larger quantity of CO(2). For cinnamaldehyde, the conversion will increase at low pressures because of increasing interactions with CO(2) molecules (increasing the reactivity of the C=O bond) but decrease at high pressures because of the simple dilution effect, similar to the case of benzaldehyde. The dense CO(2) molecules are not likely to change the catalytic activity of supported Pt particles, which was previously suggested from optical absorption of supported fine metal (Au) particles in a compressed CO(2) medium.     

大孔交联甲基丙烯酸缩水甘油酯共聚物的合成及其结构性能研究(Ⅰ)

甲基丙烯酸缩水甘油酯（GMA）为单体，三烯丙基氰尿酸酯（TAC）为交联剂，在致孔剂甲苯、正庚烷存在下，用悬浮聚合法制得一系列大孔共聚物（GT）。测定了共聚物的孔结构性能，讨论了不同交联剂及致孔剂用量和配比对共聚物结构的影响，并初步讨论了特大孔共聚物的形成机理。     

尼龙—6／丙烯酸接枝膜的结构与性能

应用ＩＲ确定了尼龙－６与丙烯酸接枝反应的接枝点位于尼龙大分子酰胺键的Ｎ原子上，用Ｘ射线衍射研究了接枝膜的结晶状况，探讨了接枝率对接枝膜的电阻、离子交换容量、强度等性能的影响．     

Electronic effects steer the mechanism of asymmetric hydrogenations of unfunctionalized aryl-substituted alkenes

Density functional theory (PBE and B3LYP) was used to study asymmetric hydrogenations of alkenes catalyzed by an iridium imidazolylidine oxazoline complex. The calculation predicts that the alkene preferentially coordinates to the site trans to the carbene. The coordinated alkene then reacts first with the H2 ligand, then with the hydride to form alkane. Finally, the alkane is released by equilibrating with extrinsic H2 and alkene. Enantioface selectivities for hydrogenations of trisubstituted alkenes seem to be driven primarily by steric interactions with the adamantyl part of the ligand; only the smallest substituents can adopt a site close to it. Application of this theoretical model leads to correct predictions regarding the experimentally observed sense and magnitude of the enantioselectivities.     

丙烯腈水相沉淀聚合研究进展

结合近几年的研究成果,笔者对丙烯腈水相沉淀聚合机理、聚合动力学、动力学数学模型诸方面问题进行了系统的综述,反映了该领域的研究概况和最新研究成果.     

Mechanistic evaluation of the halocyclization of 4-penten-1-ol by some Bis(2-substituted pyridine) and Bis(2,6-disubstituted pyridine)bromonium triflates

The halocyclization reaction of 4-penten-1-ol mediated by various bis(2-substituted pyridine) and (2,6- disubstituted pyridine)bromonium triflates (P(2)Br(+)OTf(-)) was investigated to determine the influence of the substituents on the mechanism of reaction. In all cases, the reaction proceeds via a two-step process where the starting P(2)Br(+) reversibly dissociates to a reactive monosubstituted PBr(+), which then is captured by 4-penten-1-ol to form halocyclized product (2-bromomethyltetrahydrofuran). The dissociation rate constant of P(2)Br(+) (k(d)) is sensitive to the steric bulk at the 2- and 6-positions, and in the case of the 2, 6-dicyclohexylpyridine or 2,6-dicyclopentylpyridine, the P(2)Br(+) species are too unstable to isolate. The partitioning ratio of the reactive intermediate (PBr(+)) between reversal and product formation (k(-)(d)/k(2)) is not particularly sensitive to the nature of the pyridine, the limiting values being 3-7 except in the case of bis(2(-)-menthylpyridine)bromonium triflate where the k(-)(d)/k(2) ratio is approximately 80. The reaction of 4-penten-1-ol and its OD isotopomer with bis(lutidine)bromonium triflate was investigated to determine the deuterium kinetic isotope effect (dkie) on the bromocyclization reaction. The (k(-)(d)/k(2))(H/D) ratio is 1.0, indicating that the rate-limiting step for the bromocyclization is probably formation of a PBr(+)-4-penten-1-ol complex which does not involve substantial changes in the bonding of the OH. The cyclization of 4-penten-1-ol and 4-pentenoic acid mediated by bis(2(-)-menthylpyridine)bromonium triflate produces an enantiomeric excess in the cyclized products of only 2.4% and 4.8% respectively.