Time‐dependent density functional theory study on the hydrogen bonding‐induced twisted intramolecular charge‐transfer excited states of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine

In this work, the time‐dependent density functional theory (TDDFT) method was carried out to investigate the hydrogen‐bonded intramolecular charge‐transfer excited state of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine (DMAPIP) in methanol (MeOH) solvent. All the geometric conformations of the ground state and locally excited (LE) state and the twisted intramolecular charge‐transfer (TICT) state for isolated DMAPIP and its hydrogen‐bonded complexes have been optimized. At the same time, the absorption and fluorescence spectra of DMAPIP and the hydrogen‐bonded complexes in different electronic states are also calculated. We theoretically demonstrated for the first time that the intermolecular hydrogen bond formed between DMAPIP and MeOH can induce the formation of the TICT state for DMAPIP in MeOH solvent. Therefore, the two components at 414 and 506 nm observed in the fluorescence spectra of DMAPIP in MeOH solvent were reassigned in this work. The fluorescence peak at 414 nm is confirmed to be the LE state. Furthermore, the red‐shifted shoulder at 506 nm should be originated from the hydrogen‐bonded TICT excited state. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Spermine-graft-dextran non-covalent copolymer as coating material in separation of basic proteins and neurotransmitters by capillary electrophoresis

Spermine-graft-dextran (Spe-g-Dex) copolymer was synthesized and used as a non-covalent coating for the separation of proteins and neurotransmitters by capillary electrophoresis. The coating was obtained via flushing the capillary with 1.0% Spe-g-Dex copolymer solution for 2 min. Electroosmotic flow (EOF) was strongly suppressed, ranging from −1.60 × 10⁻⁹ to 3.65 × 10⁻⁹ m² V⁻¹ s⁻¹. Effect of experimental conditions, such as the copolymer concentration, the concentration and pH of the background electrolyte (BGE), on the Spe-g-Dex coating was investigated. Separation of lysozyme, cytochrome c, ribonuclease A and α-chymotrypsinogen yielded high separation efficiencies ranging from 141 000 to 303 000 plates/m and recoveries from 85.4% to 98.3% at pH 4.0 (284.0 mM sodium acetate–acetic acid buffer, I = 50 mM). Run-to-run repeatabilities and day-to-day, and capillary-to-capillary reproducibilities were all below 1.7%. In addition, Spe-g-Dex coating allowed the successful separation of five neurotransmitters, 5-hydroxytryptamine, dopamine, epinephrine, isoprenaline, dobuamine at pH 4.0 with high separation efficiencies of 290 000–449 000 plates/m.     

含二苯并-18-冠-6席夫碱型液晶冠醚钾配合物的合成与表征

以顺(反)-4,4＇-双[4-(4＇-正烷氧基联苯基-4-羧基) 苯亚氨基] 二苯并-18-冠-6（I和II）为配体合成了2个系列席夫碱型液晶冠醚钾配合物,产率分别为85.5%~92.1%和88.7%~90.7%。配合物的结构通过元素分析、IR、UV-Vis和AAS等方法确证。液晶行为通过DSC、POM、XRD等方法表征。实验结果表明,所有配合物均具有热致液晶性,且随分子末端烷氧基碳原子数增加,其熔点和清亮点呈规律性变化。近晶相温度范围渐增,向列相温度范围递减。与配体相比,配合物液晶态温度范围变宽     

多重调和Dirichlet问题奇异正解的对称性

我们在穿孔单位球上研究下面多重调和Dirichlet问题{(-Δ)ku=f(u),在B\{0)内,u＞0,在B\{0)内,u=(e)u/(e)v=…=(e)k-1u/(e)vk-1=0,在(e)B上,其中,B是RN中的单位球,v是(e)B的单位外法向量,N＞2k,k≥2.在f满足适当假设条件下,如果0是不可去奇点,我们...     

Silica Microspheres for SPE and Determination of Fungicides in Water by LC

A new method has been developed for the determination of metalaxyl, myclobutanil, and tebuconazole in environmental water samples with preconcentration by cartridges packed with SiO₂ microspheres prior to LC. Several parameters such as the volume and composition of eluent, sample flow rate, sample pH, and sample volume were optimized. Under the optimal conditions, excellent detection limits (S/N = 3) and precision (RSD, n = 6) were 0.02 ng mL^?1, 1.3% for metalaxyl, 0.02 ng mL^?1, and 2.4% for myclobutanil and 0.08 ng mL^?1 and 4.3% for tebuconazole, respectively. The method was applied to the analysis of real-water samples, and satisfactory results were obtained. The average spiked recoveries were in the range of 86.3–97.5%. These results indicate that SiO₂ microspheres have great potential to be used as a novel solid phase extraction adsorbent that could have wide applications in the environmental field.     

Preconcentration sensitive determination of pyrethroid insecticides in environmental water samples with solid phase extraction with SiO2 microspheres cartridge prior to high performance liquid chromatography

Present study developed a new method for the sensitive determination of pyrethroid insecticides with solid phase extraction in combination with high performance liquid chromatography and UV detector. SiO₂ microspheres, a new SiO₂ based material, was investigated for the enrichment ability and applicability as the solid phase extraction sorbent. Four pyrethroid pesticides such as fenpropathrin, cyhalothrin, fenvalevate and biphenthrin were used as the target analytes. Parameters that maybe influence the extraction efficiency such as the eluent type and its volume, sample flow rate, sample pH, and the sample volume were optimized in detail, and the optimal conditions were as followed: sample volume, 100 mL; concentration of methanol, 30%; acetone volume, 5 mL; sample flow rate, 4.2 mL min⁻¹; sample pH, 7. The experimental results indicated that there was good linearity in the concentration range of 0.1–50 μg L⁻¹ except biphenthrin in the range of 0.05–25 μg L⁻¹. The detection limits for fenpropathrin, cyhalothrin, fenvalevate and biphenthrin were in the range of 0.02–0.08 μg L⁻¹. The intra-day and day to day precisions (RSDs, n = 6) were in the ranges of 2.6–4.4% and 5.3–7.2%, respectively. The method was validated with five real environmental water samples, and all these results proved that proposed method could be used as a good alternative for the routine analysis for such pollutants in environmental samples.     

吡喃并[4,3-b]吡喃衍生物与牛血清白蛋白作用的荧光光谱

用荧光光谱法分析了在生理条件下一种吡喃并[4,3-b]吡喃衍生物—2-氨基-7-甲基-4-(4-硝基苯)-5-氧代-4H,5H-吡喃并[4,3-b]吡喃-3-腈与牛血清白蛋白的作用机制。求得不同温度下二者的结合常数和结合位点数,探讨了微量金属离子对实验体系结合常数的影响,并根据热力学参数确定了这种吡喃并[4,3-b]吡喃衍生物与牛血清白蛋白之间的作用力类型。根据Frster非辐射能量转移机理,测定了这种吡喃并[4,3-b]吡喃衍生物与牛血清白蛋白相互结合时,能量给体-受体间的作用距离和能量转移效率,并用同步和三维荧光技术讨论了其衍生物对牛血清白蛋白构象的影响。结果表明,吡喃并[4,3-b]吡喃衍生物主要以静态猝灭方式使牛血清白蛋白荧光强度显著降低,二者主要凭借氢键和范德华力结合。     

荧光法快速检测有机磷农药残留总量

在pH4.60的B-R缓冲溶液中,中性红(NR)与一定浓度的十二烷基苯磺酸钠(SDBS)发生荧光增强反应,在该体系中加入有机磷农药后,在激发波长560 nm,发射波长604 nm处体系的荧光强度明显降低,且降低程度与有机磷农药的加入量呈良好的线性关系,其线性范围和检出限分别为0.024~0.40 mg/L,0.014 mg/L。据此建立了测定有机磷农药残留总量的新方法。方法已用于面粉和土壤中有机磷农药残留总量的检测,回收率在92.0%~100.5%之间,RSD在1.1~1.9%之间。     

液相色谱串联质谱测定液态乳制品中7种光引发剂的迁移量

建立了同时测定液态乳制品中7种光引发剂迁移量的液相色谱质谱法,方法采用混合溶液超声提取样品中光引发剂后,亲水亲脂填料固相萃取柱净化,色谱分离采用MGⅡC18柱,电喷雾正离子多反应监测模式下监测,同位素内标法定量。7种光引发剂的检出限为0.1~5μg/kg;在三个添加浓度水平时回收率为65%~110%,相对标准偏差为5.4%~14%。该方法可确证乳饮料中7种光引发剂的迁移量。     

Codimension-two bifurcation analysis on firing activities in Chay neuron model

Using codimension-two bifurcation analysis in the Chay neuron model, the relationship between the electric activities and the parameters of neurons is revealed. The whole parameter space is divided into two parts, that is, the firing and silence regions of neurons. It is found that the transition sets between firing and silence regions are composed of the Hopf bifurcation curves of equilibrium states and the saddle-node bifurcation curves of limit cycles, with some codimension-two bifurcation points. The transitions from silence to firing in neurons are due to the Hopf bifurcation or the fold limit cycle bifurcation, but the codimension-two singularities lead to complexity in dynamical behaviour of neuronal firing.