Nafion修饰碳纤维微电极在抗坏血酸共存下选择性测定去甲肾上腺素

制备了碳纤维微电极,将洁净的碳纤维微电极浸入Nafion溶液中,采用电沉积的方法制得Nafion修饰碳纤维微电极。采用循环伏安法(CV)、差分脉冲伏安法(DPV)研究了去甲肾上腺素(NE)和抗坏血酸(AA)在电极上的电化学行为。结果表明:在最优条件下制备的Nafion修饰电极能完全屏蔽AA的电化学响应,而对NE仍表现出良好的电化学响应。修饰电极能在1.0 mmol/L AA的共存下选择性地测定NE,采用DPV进行检测,NE的氧化峰电流与其浓度在1.0×10~(-6)~1.0×10~(-4)mol/L范围内呈良好的线性关系,相关系数(r~2)为0.991 2,检出限(S/N=3)为8.6×10~(-7)mol/L。利用该方法测定了模拟样品中NE的含量,平均加标回收率为101.6%。该电极的重现性和稳定性良好,且具有良好的灵敏度和选择性,有望用于复杂生物环境中NE浓度的检测。     

2010 Pittcon会议(Ⅲ)

电分析化学学会组织的特邀报告(电化学与材料)组有:(1)A Bralter-Toth等,微电极的傅里叶转换伏安法——原理与应用;(2)N Kim,单壁碳纳米管的扫描电化学显微术;(3)P J Kalesza等,高效率生物电催化集成系统的研发与特性鉴定;(4)B J Marguis等,暴露在可变物理性能的贵金属纳米材料下,进行塔电池的改变的衰减功函数的电化学分析;(5)A Karomerich等,可能应用于神经刺激与传感的、导电聚合物改性的电极;(6)Y SSingh等,活体伏安法的长期稳定性与准确性的因素——碳纤维微电极涂层;(7)J G Roberts等,碳纤维微电极电化学预处理引起的表面改变的研究;(8)A Polpke等,碳纳米管阵列的提高功能化的处理。     

多壁碳纳米管修饰电极分子印迹传感器测定咖啡因

以咖啡因为模板分子,通过电聚合邻苯二胺,在羧基化多壁碳纳米管修饰的玻碳电极表面制备了对咖啡因有特异响应的分子印迹聚合物膜。通过循环伏安法和线性扫描伏安法对传感器的性能进行表征,并优化了检测条件,研究了印迹传感器对模板分子咖啡因及其结构类似物的选择性响应。在最优实验条件下,电化学探针K3[Fe(CN)6]的峰电流与咖啡因浓度在2.0×10-7~2.0×10-5mol·L-1范围内呈良好的线性关系,检出限为4.0×10-8mol·L-1。该传感器应用于铁观音茶叶中咖啡因含量的测定,其回收率为94%~106%。     

一种新型低噪音碳纤维纳米电极

近年来,碳纤维超微电极在生命科学领域中已取得了广泛应用,电极的超微尺寸使之能对生物微环境进行实时监测^[1],还可作为微柱分离的检测 ^[2],自Adams研究组1976年开展微电极伏安法对细胞外液中生物胺以及有关代谢物的检测研究以来,碳纤维超微电极已成为探测脑内甚至单个细胞内神经递质的一种有力的工具,人们已对单个细胞内神经递质^[3]及激素^[4]的释放进行了探索性研究。     

分子烙印聚合物固定相分离咖啡因和茶碱的研究

分子烙印是一种新兴的分子识别技术,利用该技术可制备对烙印分子具有“预定”识别能力的高分子聚合物,即分子烙印聚合物（MIP）,从而可以对性质和组成相近的组如对映体等进行分离^[1,2],咖啡因与茶碱的分子烙印聚合物的制备以及二者分析已有报道^[3-9],但存在两种完全相反的结论。一种观点认为,即使以咖啡因为烙印分子,所制备的聚合物对咖啡因分子的选择性吸附能力也小于茶碱^[3-6]。而另一种观点则认为,在一定条件下,如以咖啡因分子为烙印分子的烙印聚合物对咖啡因分子具有更强的吸附能力^[7-9]。本文分别采用茶碱和咖啡因作为烙印分子,以甲基丙烯酸等为功能单体,在不同条件下制备了多种非共价型分子烙印聚合物,并系统地考察了其作 为HPLC固定相对咖啡因和茶碱的分离能力,同时也对烙印分子应具备的条件加以探讨。     

聚乙烯/碳纤维复合材料的PTC效应

近几年 ,由导电粒子 (如碳黑、碳纤维、金属和金属氧化物等 ) [1～ 3] 填充结晶或半结晶型聚合物的导电复合材料备受人们关注 ,并逐渐得到了开发与利用 .其中有一类功能材料 ,随温度的升高 ,相继呈现正温度系数 (PTC)和负温度系数 (NTC)效应[4～ 8] .这类材料广泛应用于发热体制造、抗静电、过电流保护和电磁屏蔽等领域 .长期以来 ,以碳黑填充聚合物的 PTC效应报道得较多 .近年来 ,以碳纤维为填料或部分填料的高聚物复合材料的 PTC效应 [9～ 11]开始引起了人们的兴趣和关注 .本文着重讨论了碳纤维的加入对聚合物结晶形态的影响以及γ射…     

VB_6在微电极上的电化学行为及测定

VB_6又称吡哆素,是一种含吡哆醇、吡哆醛或吡哆胺的B族维生素.目前测定的方法主要有:微生物法、高效液相色谱法、光谱法、电位法、修饰电极伏安法~([1,2])等.本实验采用碳纤维微电极,利用多种电化学方法循环伏安法(CV)、示差脉冲伏安法(DPV)、线性扫描伏安法(LSV)等研究了VB_6的电化学行为,并对药物中的VB6进行了检测.该方法灵敏度高、操作简便、快捷,具有一定的应用价值,并为今后研究纳米电极测定VB_6奠定基础.     

Nafion基氧化还原聚合物在空气中的电荷传输性能

利用三明治电池和伏安法测试了不同制备条件的Nafion基氧化还原聚合物膜在空气中的电荷传输性能. 研究结果表明, 混合适量聚乙二醇(PEG)的Nafion基金属联吡啶配合物{Nafion[M(bpy)2+3, PEG](M=Ru, Fe)}膜的表观电荷传递扩散系数(Dct)达到10-6-10-7 cm2·s-1 , 电子或空穴迁移率(μ)达到10-4-10-5 cm2·V-1·s-1. 在导电玻璃(ITO)电极与Nafion基氧化还原聚合物膜界面引入一层导电聚苯胺(PANI)后, 降低了其接触电阻, 使氧化还原聚合物膜的Dct提高至10-5-10-6 cm2·s-1, μ提高至10-3-10-4 cm2·V-1·s-1, 且工作电流提高了近两个数量级. 该固态氧化还原聚合物膜的性能比较稳定, 在空气中放置30天后其Dct和μ降低得很少.     

基于碳纳米管/钯纳米粒子复合材料的电化学传感平台

在碳纳米管存在下合成了直径2~10nm的钯纳米粒子,利用全氟磺酸盐聚合物Nafion溶解碳纳米管/钯纳米粒子复合物,构建了检测H2O2的电化学传感平台.循环伏安法证实所合成的钯纳米粒子在复合材料中保持了其电化学活性,该纳米复合物对H2O2具有催化能力.将葡萄糖氧化酶固定在碳纳米管/钯纳米粒子复合物修饰的玻碳电极上,制备...     

碳纤维微电极研究(Ⅺ)——利用温度效应测定电极反应的热力学和动力学参数

研究了温度对碳纤维微电极上伏安曲线的影响及温度与电极电位的关系,测定了电极反应的热力学参数.由电流与温度的关系测定了去极剂的扩散活化能E_(al)和D_o,利用微电极具有高速传质的特性,测定了常规电极上为可逆反应的电极反应标准速率常数(?),并通过(?)与温度的关系测定了电极反应的活化能.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.