左旋多巴在单层碳纳米管修饰电极上的电化学行为

单层碳纳米管修饰电极对左旋多巴的电化学氧化还原具有很高的催化活性.在pH 4.6的0.1 mol/L HAc-NaAc缓冲溶液中,可得到一对峰形很好的氧化还原峰.电极反应受扩散控制,反应过程中电子的得失伴随着等量的质子参与.氧化峰电流与左旋多巴浓度在2.1×10-4～5.0×10-6 mol/L范围内成线性关系,检测限为2.0×10-6 mol/L.     

碳纳米管修饰电极对多巴胺和肾上腺素的电分离及同时测定

研究了多巴胺 (DA)和肾上腺素 (EP)在多壁碳纳米管 (MWNT)修饰电极上的电化学性质 ,发现该修饰电极对神经递质DA和EP有显著的增敏和电分离作用。还原峰电位差达ΔEp=390mV ,可同时测定DA和EP。DA和EP的还原峰电流与其浓度分别在 2 .0× 10 -6～ 1.0× 10 -3 mol/L和 1.0× 10 -6～ 1.0× 10 -3 mol/L浓度范围内呈良好的线性关系 ;方法的检出限分别为 1× 10 -6mol/L和 5× 10 -7mol/L。由于抗坏血酸 (AA)在MWNT修饰电极上的氧化是不可逆的 ,因此利用还原峰进行测定 ,消除了AA对DA和EP的干扰     

L-半胱氨酸自组装膜电极对米吐尔的电催化及其分析应用

研究了米吐尔在L 半胱氨酸自组装膜修饰金电极上的电化学行为。米吐尔在该修饰电极上的CV曲线仅出现一对峰 ,其峰形对称 ,ΔEp =42mV ,氧化还原峰电流之比约等于 1,为可逆反应 ;扩散系数D =2 .2 4× 10 - 6 cm2 ·s- 1 。初步探讨了电催化机理。差分脉冲伏安法测定其氧化峰电流与米吐尔浓度在 5 .0× 10 - 7～ 2 .0× 10 - 5mol/L和 5 .0× 10 - 5～ 1.0× 10 - 3 mol/L范围内分段呈线性关系 ;相关系数分别为 0 .9987和 0 .9972 ;检测限 1.0× 10 - 8mol/L     

核黄素的微分脉冲溶出伏安分析

采用循环伏安法和微分脉冲溶出伏安法,对核黄素在裸金电极和巯基化合物分子自组装膜修饰金电极上的电化学行为进行了研究,发现在pH4.8的B-R缓冲溶液中,核黄素在裸金电极和分子自组装膜修饰金电极上均于-0.35V左右产生一对可逆的氧化还原峰。核黄素在裸金电极和谷胱甘肽、三巯基丙酸、二巯基苯丙咪唑分子自组装膜修饰金电极上,其浓度分别在3.0×10-7～2.3×10-4mol/L、1.05×10-6～2.0×10-4mol/L、2.1×10-6～2.08×10-4mol/L、1.05×10-6～2.0×10-4mol/L范围内与微分脉冲伏安峰峰电流之间有良好的线性关系,其相关系数分别为0.9932、0.9909、0.9857、0.9832,核黄素的检出限为2.1×10-7mol/L、5.2×10-7mol/L、8.6×10-7mol/L、5.2×10-7mol/L。对浓度为1.0×10-5mol/L的核黄素进行10次平行测定,所得峰电流的相对标准偏差为2.0%。将该方法用于核黄素片剂和复合维生素B片剂的测定,结果令人满意。     

聚L-谷氨酸/石墨充蜡修饰电极测定多巴胺

用充蜡石墨电极 (WGE)在L 谷氨酸 (GA)无水乙醇溶液中恒电位于 1.6V(vs.SCE)氧化制备了一种聚GA修饰电极 (GA/WGE) ,该电极可用于肾上腺素 (EP)和抗坏血酸 (AA)共存下对多巴胺 (DA)的测定。该电极的灵敏度和选择性主要取决于阳极极化电位与极化时间、富集电位和溶液的pH。DA在该电极上呈现一对循环伏安峰 ,Em=0 .14 5V ,为 1电子 / 1质子的准可逆氧化还原过程。AA和EP也能够在电极上富集和催化氧化 ,伏安峰分别在 0 .30V和 0 .17V。当AA浓度小于 0 .1mmol/L时 ,电极对AA基本不响应 ,可以用DA的氧化峰电流做定量分析。线性范围为 2 .0× 10 -4～ 5 .0× 10 -7mol/L ;检出限为 2 .5× 10 -7mol/L。当AA的浓度较大或在AA、EP共存下 ,可利用DA氧化的再还原峰电流做定量分析。线性范围为 1.0× 10 -4～ 2 .5× 10 -6mol/L ;检出限为 7.5× 10 -7mol/L。该电极制作简便 ,重现性良好 ,定量结果也令人满意     

嵌入式超薄碳膜电极的伏安行为及其应用

以镍铬合金为基体,在其表面嵌入碳膜或碳纳米管,制备了超薄碳膜电极,并用于酚磺乙胺(ETA)的测定。超薄碳膜电极对ETA有良好的电催化作用和增敏作用,与玻碳电极相比,氧化峰电位负移120mV,还原峰电位正移160mV,电流响应明显增大。在最优条件下,ETA浓度在5×10-7 ~9×10-6 mol/L和9×10-6~6×10-5 mol/L之间与其氧化峰电流呈良好的线性关系,相关系数分别为0. 9967和0. 9979。该电极制备简便,价格低廉,用于酚磺乙胺的测定结果令人满意。     

肾上腺素在咖啡酸修饰电极上的电化学研究

研究了咖啡酸(CFA)修饰电极的性质,测定了电极反应的动力学常数.结果表明在pH 7.0的的磷酸盐缓冲溶液中,肾上腺素(Ep)在该修饰电极上产生一灵敏的氧化峰,峰电流与Ep浓度在5.0×10-6～1.0×10-4 mol/L范围内线性关系良好,检出限为7.0×10-7 mol/L.修饰电极制备简单,稳定性好.     

5-羟色胺在碳纤维微电极上的电化学测定及伏安行为研究

本文研究了5 羟色胺在Na2HPO4 KH2PO4(pH6.0)缓冲溶液中,于自制的碳纤维微电极上的伏安行为。在此缓冲溶液中5 羟色胺有一对氧化还原峰,峰电位分别为0.2V和0.4V。峰电流与5 羟色胺的浓度分别在4.0×10-6～4.0×10-5mol/L和5.0×10-6～5.0×10-5mol/L范围内呈良好的线性关系,检出限分别为4.70×10-6mol/L和1.76×10-6mol/L。同时利用多种电化学方法求出了动力学参数。     

多巴胺在DTNB自组装膜上的电催化研究

在金电极表面制备了DTNB(5,5′ Di thiobis(2 nitrobenzoicacid))自组装单分子层膜(DTNB/AuSAM)。多巴胺在DTNB自组装膜上有一对可逆性良好的氧化还原峰,其氧化峰电流与多巴胺的浓度在5.0×10-6mol/L～1.0×10-4mol/L的范围内呈线性关系,检出限为1.0×10-6mol/L。在pH3.5的缓冲溶液中,在DTNB自组装膜上多巴胺和抗坏血酸的电化学响应可以明显区分,氧化峰电位分离达276mV。可用于抗坏血酸存在下多巴胺的检测。测定了盐酸多巴胺注射液中多巴胺的含量,其平均回收率为104%。     

微渗析-液相色谱电化学检测法测定全血中的半胱氨酸和谷胱甘肽

采用微渗析取样作为样品预处理技术,与高效液相色谱电化学检测联用,建立了一种测定血中半胱氨酸(Cys)和谷胱甘肽(GSH)的新方法。电化学检测以玻碳电极为工作电极,结果表明在3.5×10-6～1.0×10-3mol/L浓度范围内,Cys和GSH的浓度分别与氧化峰的峰电流呈良好的线性关系,线性相关系数分别为0.9971和0.9982,检测限分别为1.2×10-6mol/L和3.2×10-6mol/L。     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

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.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

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%).     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

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.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.     

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.