Synthesis characterizations and properties of a new fluoro-maleimide polymer

Novel 4-(4-trifluoromethyl)phenoxy N-phenyl-maleimide (FPMI) was synthesized. The free radical-initiated polymerization of FPMI was carried out in 1,4-dioxane solution using azobisisobutyronitrile as initiator. The monomer was investigated by FTIR, ¹H NMR, ¹³C NMR and elemental analysis, while the polymer was investigated by FTIR, ¹H NMR and ¹³C NMR. The effect of the monomer concentration, initiator concentration and temperature on the rate of polymerization (R_p) was studied. The activation energy of the polymerization was calculated (ΔE = 48.94 kJ/mol). The molecular weight of PFPMI and polydispersity index of the polymer were determined by gel permeation chromatography and were equal to 73,500, 16,700 and 2.27, respectively. The properties of PFPMI, including thermal behavior, thermal stability, the glass transition temperature (T_g = 236 °C), photo-stability, solubility and solution viscosity were studied.     

An environmentally friendly flow system for high-sensitivity spectrophotometric determination of free chlorine in natural waters

A green and highly sensitive analytical procedure was developed for the determination of free chlorine in natural waters, based on the reaction with N,N-diethyl-p-phenylenediamine (DPD). The flow system was designed with solenoid micro-pumps in order to improve mixing conditions by pulsed flows and to minimize reagent consumption as well as waste generation. A 100-cm optical path flow cell based on a liquid core waveguide was employed to increase sensitivity. A linear response was observed within the range 10.0 to 100.0 µg L^− 1, with the detection limit, coefficient of variation and sampling rate estimated as 6.8 µg L^− 1 (99.7% confidence level), 0.9% (n = 20) and 60 determinations per hour, respectively. The consumption of the most toxic reagent (DPD) was reduced 20,000-fold and 30-fold in comparison to the batch method and flow injection with continuous reagent addition, respectively. The results for natural and tap water samples agreed with those obtained by the reference batch spectrophotometric procedure at the 95% confidence level.     

Conformation dependence of DNA electrophoretic mobility in a converging channel

The electrophoresis of λ‐DNA is observed in a microscale converging channel where the center‐of‐masses trajectories of DNA molecules are tracked to measure instantaneous electrophoretic (EP) mobilities of DNA molecules of various stretch lengths and conformations. Contrary to the usual assumption that DNA mobility is a constant, independent of field and DNA length in free solution, we find DNA EP mobility varies along the axis in the contracting geometry. We correlate this mobility variation with the local stretch and conformational changes of the DNA, which are induced by the electric field gradient produced by the contraction. A “shish‐kebab” model of a rigid polymer segment is developed, which consists of aligned spheres acting as charge and drag centers. The EP mobility of the shish‐kebab is obtained by determining the electrohydrodynamic interactions of aligned spheres driven by the electric field. Multiple shish‐kebabs are then connected end‐to‐end to form a freely jointed chain model for a flexible DNA chain. DNA EP mobility is finally obtained as an ensemble average over the shish‐kebab orientations that are biased to match the overall stretch of the DNA chain. Using physically reasonable parameters, the model agrees well with experimental results for the dependence of EP mobility on stretch and conformation. We find that the magnitude of the EP mobility increases with DNA stretch, and that this increase is more pronounced for folded conformations.     

聚丙烯酸锂与1-丁基-3-甲基咪唑溴离子液体的阳离子交换反应

通过聚丙烯酸锂(PAALi)与1-丁基-3-甲基咪唑溴(BmimBr)离子液体进行阳离子交换, 将1-丁基-3-甲基咪唑阳离子引入到聚丙烯酸锂结构中, 形成了丙烯酸锂(AALi)与1-丁基-3-甲基咪唑丙烯酸盐(BmimAA)离子液体的无规共聚物[P(AALi-BmimAA)]. 研究了反应时间、温度、投料比、反应物浓度及聚丙烯酸锂分子量等对离子交换程度的影响. 对不同离子交换程度时聚合物电导率的研究结果表明, 所有共聚物的电导率均比聚丙烯酸锂的有明显提高, 并且随着阳离子交换程度的增加, 电导率出现极值. 在聚丙烯酸锂的15%水溶液中, 当Bmim+与Li+的投料摩尔比为1∶1时, 在80 ℃下交换反应24 h, 得到的共聚物的Bmim+与Li+摩尔比为0.0387, 其电导率最高, 为1.44×10-8 S/cm, 比聚丙烯酸锂的电导率(1.06×10-11 S/cm)提高了3个数量级. 向此共聚物中掺杂LiTFSI, 电导率再次提高2个数量级, 最高可达2.90×10-6 S/cm.     

Evaluation of lipid peroxidation inhibition and free radical scavenging abilities of 5,6,7-trimethoxy dihydroflavonols

Four naturally rare 5,6,7-trimethoxy-2,3-cis-dihydroflavonols(3-6) and two 5,6,7-trimethoxy-2,3-trans-dihydroflavonols(7-8) were designed and synthesized.Their antioxidative properties were evaluated by way of examining their scavenging capacities towards DPPH and O_2~(·-) free radicals,as well as by measuring their inhibitory ability against LPO.Both the 2,3-trans and the 2,3- cis conformers exhibited certain quenching abilities to DPPH and O_2~(·-) radicals,while most of the synthetic dihydroflavonols ...     

多壁碳纳米管/溴/聚苯乙炔三元复合材料导电性能的研究

通过机械共混和溶液共混制备了多壁碳纳米管(MWNTs)/溴/聚苯乙炔(PPA)三元复合材料, 复合材料表现出良好的导电性能, 电导率为10 S/m, 达到掺溴MWNTs的导电水平. 通过固体紫外光谱、XPS和SEM分析了复合材料中MWNTs、溴与PPA三者之间的相互作用, 研究了独立导电单元的形成, 以及导电单元对电导率提高所起的作用. 结果表明, 当MWNTs含量较低时, MWNTs和PPA之间的溴转移导致复合材料电导率降低; MWNTs含量较高时, 独立导电单元的数目增多, 复合材料的电导率随之大幅提高.     

The first asymmetric esterification of free carboxylic acids with racemic alcohols using benzoic anhydrides and tetramisole derivatives: an application to the kinetic resolution of secondary benzylic alcohols

A variety of optically active carboxylic esters are produced by the kinetic resolution of racemic secondary benzylic alcohols using free carboxylic acids with benzoic anhydride and tetramisole derivatives. 4-Methoxybenzoic anhydride (PMBA) is the best reagent to use in producing the corresponding esters in high ee when the reaction is catalyzed by (+)-benzotetramisole (BTM); by contrast, when non-substituted benzoic anhydride is used as a coupling reagent, the resulting optically active alcohols are obtained with high selectivities. This protocol directly produces chiral carboxylic esters from free carboxylic acids and racemic secondary alcohols by utilizing the trans-acylation process to generate mixed anhydrides from acid components and benzoic anhydride derivatives under the influence of chiral catalysts.     

Separation and evaluation of free radical-scavenging activity of phenol components of Emblica officinalis extract by using an HPTLC-DPPH* method

A new procedure has been developed to separate and quantify the free radical-scavenging activity of individual compounds from an Emblica officinalis extract based on the combination of HPTLC with a diode array detector (DAD) and postchromatographic DPPH* radical derivatization. Free gallic and ellagic acids and emblicanins A and B in the E. officinalis extract were separated by TLC and identified. All the compounds of the extract were capable of scavenging of DPPH* radicals. It was established that the DPPH* scavenging activity of emblicanins A and B was 7.86 and 11.20 times more than that of ascorbic acid and 1.25 and 1.78 times more than gallic acid, respectively. From the estimated ID50 values, it can be seen that the increasing order of activity was emblicanin B > emblicanin A > gallic acid > ellagic acid > ascorbic acid. Probably, the antioxidant activity of E. officinalis extract is associated with the presence of hydrolyzable tannins having ascorbic acid-like action.     

Effects of oxygen in gamma irradiated aromatic polyesters in film

The effect of gamma irradiation in air is investigated on four thermoplastic polyesters (PET, PBT, PEN, PCT-co-ET) in films containing aromatic rings, in order to evaluate the influence of aromatic density and the role of oxygen on radiation resistance. Physical-chemical-nuclear analyses were used to this purpose. EPR measurements were carried out to detect radical stability against oxygen permeation. Viscometric investigations reported a very similar trend for all the investigated polyesters: a chain break effect that decreases at the highest doses. FT-IR analyses focused on the formation of oxidized species. Positron annihilation spectra pointed out a decrease of the intensity of ortho-positronium formation, while its lifetime remains unchanged with radiation dose.     

Synthesis and Biological Evaluation of Bromo‐ and Fluorodanicalipin A

We disclose the syntheses of (+)‐bromodanicalipin A as well as (±)‐fluorodanicalipin A. The relative configuration and ground‐state conformation in solution of both molecules was secured by J‐based configuration analysis which revealed that these are identical to natural danicalipin A. Furthermore, preliminary toxicological investigations suggest that the adverse effect of danicalipin A may be due to the lipophilicity of the halogens.