纳米金修饰玻碳电极在抗坏血酸共存下选择性测定去甲肾上腺素

利用电沉积的方法制得纳米金修饰玻碳电极 ,该修饰电极对去甲肾上腺素 (NE)氧化反应有催化作用。去甲肾上腺素在纳米金修饰玻碳电极上有很强的吸附作用。研究了磷酸缓冲溶液的pH值和浓度对NE的电化学行为的影响。从去甲肾上腺素和抗坏血酸在纳米金修饰电极的循环伏安图上可观察到两个明显分开的氧化峰 ,峰电位差达到 1 3 1mV ,因此 ,可利用该修饰电极在抗坏血酸存在下选择性测定去甲肾上腺素 ,线性范围为 1× 1 0 - 4 ～5× 1 0 - 6 mol L。     

纳米金/三聚氰胺修饰电极检测亚硝酸盐

采用电聚合方法制备三聚氰胺(MA)膜修饰玻碳电极(GCE),然后采用原位恒电位沉积法制备金纳米颗粒(Au),并将其修饰于膜电极表面,制得纳米金/三聚氰胺修饰玻碳电极(Au/MA/GCE)。用扫描电子显微镜(SEM)对修饰电极进行表面形貌和元素成分分析。用循环伏安法研究亚硝酸根(NO2-)在该修饰电极上的电化学行为发现,NO2-在0.85 V出现一灵敏的氧化峰。在优化的实验条件下,NO2-在1.0×10-5～1.0×10-3mol/L浓度范围内与其氧化峰电流成线性关系,检测下限为8.9×10-7mol/L。将修饰电极用于实际样品中NO2-的检测,效果良好。     

纳米金修饰玻碳电极在抗坏血酸共存下选择性测定多巴胺

利用电沉积的方式制备了纳米金 ( Nano- gold,NG)修饰玻碳电极 ( GCE)。该电极对多巴胺 ( DA)和抗坏血酸 ( AA)均有催化作用 ,且多巴胺在纳米金修饰玻碳电极上有较强的吸附作用。同时研究了磷酸缓冲溶液的 p H值和离子强度对 DA的电化学行为的影响。纳米金修饰玻碳电极在 DA和 AA的混合溶液中的循环伏安图上可观察到两个明显分开的氧化峰 ,峰电位差达到 1 5 0 m V。据此 ,提出了两种利用该电极在抗坏血酸共存下选择性测定多巴胺的方法 ,线性范围分别为 3.0× 1 0 - 6 ～1 .0× 1 0 - 4mol/ L和 1 .2 5× 1 0 - 6 ～ 1 .0× 1 0 - 4mol/ L。     

聚L-白氨酸修饰电极伏安法测定痕量多巴胺的研究

用循环伏安法制备了聚L-白氨酸修饰玻碳电极,研究了多巴胺在聚L-白氨酸修饰玻碳电极上的电化学行为,建立了循环伏安法测定痕量多巴胺的新方法。实验结果表明,在pH 6.0的磷酸盐缓冲溶液中,多巴胺在聚L-白氨酸修饰玻碳电极上产生一对灵敏的氧化还原峰,峰电位分别为Epa=0.281V,Epc=0.170 V(相对Ag/AgCl电极)。峰电流与多巴胺的浓度在5.0×10-8~5.0×10-4mol/L的范围内有线性关系,检出限为5.0×10-9mol/L。对1.0×10-5mol/L多巴胺溶液平行测定9次,其相对标准偏差为4.0%。已用于针剂中多巴胺的测定。     

介孔炭/纳米金修饰玻碳电极的制备及其应用研究

制备了介孔炭/纳米金修饰玻碳电极,并对对苯二酚(HQ)在该修饰电极上的电化学行为进行了研究。与HQ在纯介孔炭材料修饰玻碳电极上的电化学响应相比,HQ在该修饰电极上的氧化峰和还原峰电流均大大增加,表明纳米金与介孔炭复合后对HQ具有良好的催化作用。HQ在该修饰电极上经过富集后,峰电流明显增大。采用循环伏安法对HQ电化学行为进行研究,结果表明,HQ在3.0×10-8~1.0×10-6mol/L和1.0×10-6~1.0×10-4mol/L浓度范围内与峰电流呈良好的线性关系,据此建立了检测HQ的电化学分析方法。该方法的相对标准偏差为0.69%,检出限(S/N=3)为1.0×10-8mol/L,具有较高的稳定性和灵敏度。     

新型纳米金直接修饰玻碳电极的制备及其电催化活性

在不使用交联剂的情况下,借助种子媒介纳米金属生长法将纳米金直接修饰到玻碳电极表面.试验发现纳米金粒子在电极表面覆盖率为5.4×10-10 mol·cm-2,[Fe(CN)6]3-/[Fe(CN)6]4-氧化还原电子探针的试验证明,纳米金修饰玻碳电极表面的电子传递速率是使用交联剂制备电极的四倍.与裸玻碳电极相比,抗坏血酸在该电极表面的氧化峰电位负移150 mV,峰电流提高2.2μA,同时与尿酸的氧化峰电位差达到186 mV,可用于抗坏血酸和尿酸的同时检测.     

吡啶 -Dawson型磷钼杂多酸超分子薄膜修饰电极

采用电化学方法在玻碳电极上制备了吡啶 -Dawson型磷钼杂多酸超分子配合物薄膜修饰电极。研究了它在 0.3 mol/L H2SO4溶液中的电化学行为及其对酸性水溶液中抗坏血酸的电催化氧化作用。发现膜电极对抗坏血酸的催化峰电流与其浓度在 3.5× 10-5～ 5.0× 10-3 mol/L范围内呈良好的线性关系,线性相关系数 r=0.999 1,检出限 8.0× 10-6 mol/L,用于维生素 C片剂的测定,结果令人满意。初步探讨了电催化氧化机理。     

纳米铂直接修饰玻碳电极的制备及在半胱氨酸中的电化学行为

采用一步化学原位还原法将球形纳米铂颗粒直接修饰在玻碳电极上,用SEM、EDS和电化学方法对该电极进行表征并与铂片电极、裸玻碳电极进行了对比。结果表明,纳米铂修饰电极的峰电流与扫描速度呈线性关系,纳米铂在电极表面覆盖率为1.28×10-7mol/cm2。循环伏安法研究结果表明纳米铂修饰电极对半胱氨酸的催化氧化作用和铂片电极相比提高了数倍,且峰电位负移了0.3V。在纳米铂修饰的玻碳电极上,半胱氨酸的浓度在1.0×10-7mol/L到1.0×10-5mol/L范围内和催化电流呈线性关系。     

多巴胺在聚茶碱/Nafion双层修饰玻碳电极上的电化学行为

研究聚茶碱／Nafion双层修饰玻碳电极的制备和其电化学性质,并用于测定多巴胺（DA）。在pH7．4的PBS缓冲溶液中,DA在聚茶碱／Nafion双层修饰玻碳电极上产生一灵敏的氧化峰。峰电流与DA浓度在1×10－7～4×10-4mol/L范围内呈良好线性关系,检出限为5×10－8mol/L。该双层膜对DA有增敏作用,对抗坏血酸（AA）有排斥作用,重现性良好,可用于DA的测定。     

芦丁在铂纳米/碳纳米管修饰电极上电化学行为研究

通过电沉积的方式在多壁碳纳米管(MWCNTs)修饰玻碳电极表面上沉积铂(pt)纳米粒子,并运用循环伏安法(CV)、示差脉冲伏安法(DPV)探讨了芦丁在铂纳米/碳纳米管/玻碳电极上的电化学行为.实验结果表明,芦丁在该修饰电极上呈现一对良好氧化还原峰,其氧化峰电流与浓度在3.2×10(-8)～1.2×10(-5)mol/L...     

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.     

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.     

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.     

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.