钠型蒙脱石修饰碳糊电极测定微量的铜离子

报道了一种高灵敏度 ,快速测定水体中铜离子的化学修饰碳糊电极。详细研究了测定铜离子的条件。该修饰电极测定铜离子的线性范围为 1× 1 0 - 9～ 1 .5× 1 0 - 7mol/L ,富集 6min后的检出限为 3× 1 0 - 10 mol/L。该方法简便、快速、灵敏。用该修饰电极测定了实际水样中的铜离子 ,平均回收率为 1 0 0 .8%。     

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     

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     

基于十六烷基三甲基溴化铵存在下铅、银离子的高灵敏度电化学测定

报道了在适量十六烷基三甲基溴化铵 (CTMAB)存在下 ,高灵敏度测定水体中铅、银离子的化学修饰碳糊电极。在pH 2 .5 0 .1mol LKNO3溶液中 ,铅、银离子在钠型蒙脱石修饰碳糊电极上通过离子交换而富集 ,同时被还原。在阳极扫描过程中 ,分别在 - 0 .5 2V和 0 .2 3V(vs.SCE)处出现灵敏的溶出峰。详细研究了测定水样中铅、银离子的条件 ,如介质的pH、CTMAB用量、修饰剂用量、富集电位和时间等。该修饰电极连续测定铅、银离子的线性范围为 5 .0× 10 - 9mol L～ 1.0× 10 - 7mol L(Pb2 + )和 8.0× 10 - 9mol L～ 1.0× 10 - 7mol L(Ag+ ) ,富集 4min后检出限分别为 1.0× 10 - 1 0 mol L(Pb2 + )和 3.0× 10 - 1 0 (Ag+ )。     

乳酸氧化酶共价交联于蛋膜上制备乳酸传感器

以牛血清白蛋白 戊二醛为交联剂 ,将乳酸氧化酶固定于鸡蛋膜上 ,氧电极作电化学敏感元件 ,制成乳酸氧化酶电极。传感器的线性响应范围为 5 .0×1 0 - 5～ 2 .5× 1 0 - 2 mol/L ,检测限为 2 .0× 1 0 - 5mol/L ,RSD为 1 .4% (n =1 1 ) ,回收率为 97.5 %～ 1 0 4 .0 %。该传感器可用于临床乳酸的测定。     

槲皮素修饰碳糊电极吸附溶出伏安法测定人血清中铜

制作了用槲皮素作修饰剂的修饰碳糊电极 ,利用此电极为工作电极 ,建立了测定痕量铜的新方法。在甲酸钠 -盐酸缓冲溶液 ( p H4.7)中 ,于 0 .2 0 V( vs.SCE下同 )处搅拌富集 ,铜 ( )与碳糊修饰电极表面的槲皮素形成电活性络合物而吸附富集于电极表面 ,于 - 0 .40 V静止还原后 ,阳极化线性扫描 ,在 - 0 .0 3V左右获得一灵敏的二次导数溶出峰。在不同富集时间下 ,其二次导数峰电流与铜 ( )浓度分别在1 .5× 1 0 - 9～ 8.0× 1 0 - 8mol/ L和 1 .5× 1 0 - 8～ 9.0× 1 0 - 7mol/ L两个范围内成良好的线性关系 ,检出限可达 8.0× 1 0 - 10 mol/ L。同时探讨了电极反应机理。方法应用于人血清中痕量铜的测定 ,获得了令人满意的结果     

双硫腙修饰玻碳电极阳极溶出伏安法测定痕量镉和铅

报道了双硫腙修饰玻碳电极同时测定痕量镉和铅的电分析方法。镉和铅离子通过与电极表面的双硫腙发生螯合作用而富集在电极表面 ,同时在 -1 .2 0V(vs.SCE)还原成零价镉和铅 ,当电极电势从 -1 .2 0V向 -0 .3 0V扫描时 ,被还原的镉和铅从电极表面溶出 ,分别于 -0 .78V和 -0 .4 8V左右形成灵敏的阳极溶出峰。优化了支持电解质及pH值、双硫腙用量、富集电位及时间等实验参数。利用该修饰电极测定镉、铅的线性范围分别为 1 .0×1 0 - 8～ 2 .5× 1 0 - 6 mol L和 5 .0× 1 0 - 9～ 2 .5× 1 0 - 6 mol L。检测限分别为 5 .0× 1 0 - 9mol L和7.0× 1 0 - 1 0 mol L。该法用于实际水样中镉和铅的测定 ,平均回收率分别为 99.3 0 %和 99.5 4 %。     

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     

壳聚糖修饰电极上的铁氰根离子对抗坏血酸的电催化氧化作用

在玻碳电极表面滴涂一层壳聚糖膜 ,壳聚糖分子中 -NH2 在酸性溶液中发生质子化 ,靠静电引力作用吸附富集荷负电的电子介体Fe(CN) 63 -,使其固定在电极表面 ,研究了此Fe(CN) 63 - 壳聚糖 GC修饰电极对抗坏血酸的催化氧化作用。抗坏血酸的浓度在 3.0× 1 0 -6～ 5 .0× 1 0 -3 mol L范围内呈很好的线性关系 ,相关系数为 0 .998,检测限达 1 .0× 1 0 -6mol L。该法已用于测定蔬菜中抗坏血酸的含量。     

聚吖啶橙修饰电极伏安法测定黄嘌呤

报道了聚吖啶橙 (POAO)修饰电极多阶半微分伏安法测定黄嘌呤 (Xa)。在pH 5 .3的磷酸盐缓冲溶液中 ,Xa在POAO电极上于 0 .8V处产生一灵敏的氧化峰 ,峰电流与其浓度在 7.8× 1 0 - 8～ 1 .1× 1 0 - 6mol/L和 1 .1× 1 0 - 6～ 1 .0×1 0 - 5mol/L范围内呈良好的线性关系 ,检出限为 7.8× 1 0 - 9mol/L。方法可用于人尿中Xa的测定     

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.     

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.     

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.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Microwave-assisted copper-catalyzed stereoselective ring expansion of three-membered heterocycles with α-diazo-β-dicarbonyl compounds

Microwave-assisted copper-catalyzed ring expansions of three-membered heterocycles with α-diazo-β-dicarbonyl compounds were investigated. Thiiranes generated 3-acyl-5,6-dihydro-1,4-oxathiines in the presence of copper sulfate and trans-3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis-thiiranes through an intramolecular S_N2 process. Oxiranes gave rise to 2-acyl-5,6-dihydro-1,4-dioxines under the catalysis of copper hexafluoroacetylacetonate and cis-3-acyl-5,6-dihydro-1,4-dioxines as stereospecific products for 1,2-disubstituted cis-oxiranes via an intimate ion-pair mechanism. The current method provides a direct and simple strategy in efficient preparation of 3-acyl-5,6-dihydro-1,4-oxathiines and 2-acyl-5,6-dihydro-1,4-dioxines, important agents in medicinal and agricultural chemistry, from readily available thiiranes and oxiranes, respectively.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.