席夫碱壳聚糖修饰电极的制作及其在对苯二酚测定中的应用

通过共价键合的方法将所制备的席夫碱壳聚糖修饰在玻碳电极表面 ,制成席夫碱壳聚糖修饰电极(SBCME) ,并对其电化学特性进行了研究。利用微分脉冲伏安法测定了对苯二酚 (HQ) ,结果表明 :在 0 .5mol L三羟甲基氨基甲烷 (tris)底液 (pH 3 .0 )中 ,电极对HQ具有良好的吸附性与选择性 ,HQ浓度在 1 .0× 1 0 - 6～ 2 .0×1 0 - 3mol L范围内与其氧化峰电流呈线性关系 ,检出限可达 1 .0× 1 0 - 7mol L。利用此电极测定样品 ,结果满意     

流动注射化学发光抑制法测定痕量抗坏血酸

研究发现在碱性介质下，抗坏血酸对 Luminol-K3Fe（CN）6体系发光反应具有强烈的抑制作用，建立了化学发光抑制快速测定痕量抗坏血酸的新方法。本法测定抗坏血酸的线性范围为4．0×10－8～1．0×10-6mol／L，D．L＝40×10－8mol／L，对1．0×10－7mol／L抗坏血酸连续11次测定的相对标准偏差为0．5％，应用于医用维生素C片剂、维生素针剂以及血样中抗坏血酸的测定，结果满意。     

壳聚糖修饰玻碳电极卷积伏安法测定环境水中的EDTA

制备了壳聚糖修饰玻碳电极 ,研究了Fe(EDTA) -在修饰电极上的吸附还原行为 ,用卷积伏安法通过Fe(EDTA) -的检测测定了环境水中的EDTA。在优化的实验条件下 ,峰电流值与 8.0× 1 0 -7～ 5 .0× 1 0 -6mol L的EDTA呈线性关系 ,回归方程为epp′ =0 .75 2 5c - 0 .661 3,r =0 .991 ,最低检出限为 5 .0× 1 0 -7mol L ,5次测定的相对标准偏差小于 5 .8%。对实际样品测定的回收率为98 1 %～ 1 0 5 % ,对比HPLC的结果 ,相对偏差小于 5 %。     

碳纳米管修饰电极对多巴胺和抗坏血酸的电催化氧化

研究了碳纳米管修饰玻碳电极 (NTCME)的制备方法及对多巴胺 (DA)和抗坏血酸 (AA)的电催化氧化作用。在磷酸盐缓冲溶液 (PBSpH 7.4)中 ,以NTCME为工作电极时 ,DA与AA的氧化电位分别为 0 .2 6和 0 .0 1V(vs.SCE) ,比在裸玻碳电极 (GC)上分别降低了 0 .0 7和 0 .6 2V。NTCME能消除DA与AA共存时测定的相互干扰。利用二阶导数卷积伏安法测定 ,DA与AA分别在 2 .0 0× 10 - 6～ 3.84× 10 - 4 和 7.99× 10 - 5～ 3.6 6× 10 - 3 mol L浓度范围内 ,峰高与浓度呈线性关系 ;检出限分别为 1.90× 10 - 7和 5 .96× 10 - 5mol L。     

毛细管电泳-电化学检测测定茶叶中咖啡因、表儿茶素和抗坏血酸

高效毛细管电泳电化学检测同时测定了6种茶叶中的咖啡因、表儿茶素和抗坏血酸的含量,考察了实验参数对分离、检测的影响。在最佳实验条件下,以300 靘直径的碳圆盘电极为检测电极,检测电极为1.20 V(vs.SCE),在25 mmol/L硼酸盐25 mmol/L磷酸盐(pH 7.6)的混合运行缓冲液中,上述各组分在16 min内能完全分离。咖啡因、表儿茶素和抗坏血酸在2×10-3mol/L～１×10-5 mol/L、5×10-5mol/L～5×10-7mol/L、2×10-4 mol/L～1×10-5mol/L范围内呈线性关系,检测下限分别为6×10-6mol/L、4×10-7mol/L和1×10-6mol/L。该法直接用于茶叶中咖啡因、表儿茶素和抗坏血酸的测定,结果令人满意。     

基于尼古丁对胆碱氧化酶的抑制作用测定尼古丁的研究

基于尼古丁对胆碱氧化酶(CHOD)的抑制作用,将胆碱氧化酶电极用于微量尼古丁的测定。酶电极制作中,先在铂电极表面修饰一层壳聚糖膜,再用戊二醛交联CHOD。采用这种酶固定化方法,电极在4. 0×10-6 ~ 3×10-3 mol/L胆碱的浓度范围呈线性关系。探讨了工作电位、pH、底物浓度等实验条件对酶电极性能及抑制过程中响应电流的影响,测定了电极的重现性、干扰及使用寿命。电极检测尼古丁的线性范围为1. 5×10-5 ~3×10-3 mol/L;检出限为1. 25×10-5 mol/L。将电极用于实际样品烟草中尼古丁回收率的测定,结果良好。     

流动注射化学发光增强法测定健民咽喉片中的没食子酸

在pH 9.4的Na2 CO3 NaHCO3介质中 ,没食子酸对鲁米诺 K3Fe(CN) 6 发光体系有很强的增敏作用。据此建立了流动注射化学发光增强法测定没食子酸的方法。发光信号的增强值 (ΔI)与没食子酸的浓度在1 0× 1 0 - 6 ～ 8.0× 1 0 - 9mol L的范围内呈良好的线性关系 ,检出限为 5 .6× 1 0 - 9mol L。对于 1 .0× 1 0 - 7mol L的没食子酸测定 ,相对标准偏差为 2 .2 % (n =1 1 )。该法可用于健民咽喉片中没食子酸含量的测定     

L-半胱氨酸自组装膜修饰金电极对抗坏血酸的电催化作用及其测定

金电极表面对L 半胱氨酸 (L Cys)有特性吸附 ,而L Cys分子在等电点pH附近因静电引力和氢键作用形成分子对 ,从而在电极表面自组装形成L Cys双层膜。L Cys修饰金电极对抗坏血酸 (AA)具有良好的电催化作用。用示差脉冲伏安法对AA进行了测定 ,氧化电流与AA的浓度在 1.0× 10 -3 ～ 4× 10 -6mol/L范围内呈良好的线性关系 ,线性相关系数为 0 .9981;检出限为 4× 10 -7mol/L。用于药片中AA含量的测定 ,结果令人满意。     

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。     

壳聚糖共价键合化学修饰电极测定亚硝酸根

用共价键合法把壳聚糖修饰在玻碳电极表面,研究了NO-2在修饰电极上的阳极溶出伏安特性.实验结果表明:修饰电极在0.1 mol/L NaNO3(pH 2.60)底液中对NO-2有良好的吸附性和选择性,其峰电流与NO-2的浓度在1.5×10-6～1.0×10-3 mol/L范围内呈较好的线性关系;检测限可达2.0×10-7 mol/L.将壳聚糖修饰电极应用于雨水、湖水中NO-2的测定,结果满意.     

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.