离子选择电极测定维生素C生产过程中钠含量

采用钠离子选择电极测定维生素C(VC)生产过程中钠的含量。试验表明:该离子选择性电极对钠具有良好的选择性和电位响应特性。在pH≥10介质中,电极电位呈现能斯特响应,线性范围为1.0～10.0mg.L-1,斜率为55.18mV.pc-1。将该电极用于测定维生素C生产过程中的钠含量,测得方法的回收率在85.4%～99.0%之间,相对标准偏差(n=6)在1.3%～1.4%之间。     

溴酚蓝修饰玻碳电极测维生素C中抗坏血酸含量

使用溴酚蓝修饰的玻碳电极,以快速循环伏安法测定维生素C片剂中抗坏血酸含量并优化实验条件.结果表明,溴酚蓝(BPB)修饰玻碳电极用于抗坏血酸含量的分析,有良好的稳定性和抗干扰能力.在0.0050~0.1500 g.L-1浓度范围内,峰电流与浓度呈良好的线性关系,R=-0.9991,检出限为0.0010 g.L-1,结果令人满意.     

维生素C在多壁碳纳米管/壳聚糖复合膜修饰玻碳电极上的电化学行为及测定

研究了维生素C在多壁碳纳米管/壳聚糖复合膜修饰玻碳电极上的电化学行为及测定。实验结果表明,在0.2 mol/L PBS(pH6.0)缓冲溶液中,修饰电极对抗坏血酸的氧化具有明显的催化和增敏效应,其氧化峰电位由 0.5 V负移至 0.1 V(vs.AgCl/Ag)。对修饰剂碳纳米管的用量、支持电解质、富集电位和富集时间等进行了优化。采用半微分伏安法进行定量测定,其线性范围为4.0×10-6~2.0×10-3mol/L,r=-0.998 3,检出限为1.0μmol/L。对抗坏血酸在修饰电极上的电化学行为进行了探讨,其电极反应为具有吸附特性和不可逆的电极过程,测得参加反应的质子数为2,电极反应的电子转移系数为0.59。测定了维生素C药片中抗坏血酸的含量,回收率在93%~105%。     

维生素C的化学实验

通过实验让学习者了解维生素C的酸性和还原性;了解几种常见蔬菜和水果中维生素C的含量及人体摄入维生素C应注意的事项。     

电导法测定维生素C注射液的含量

建立了电导法测定维生素C含量的方法.实验表明,在温度15～35℃,浓度为1.0～5.0 g·L-1条件下,溶液浓度与电导率呈良好的线性关系(R值在0.9982～0.9999之间),方法平均回收率达99.2%,精密度(RSD)为0.01%.该法简便、快捷、准确、重现性好,可用于维生素C注射液含量的测定.     

复方芦丁片中主要成分的毛细管电泳安培检测

用毛细管电泳安培检测法同时测定了复方芦丁片中芦丁和抗坏血酸的含量 ,研究了各种实验条件对分离效果的影响 ,得到了优化的实验条件。以直径为 5 0 μm的碳纤维微电极为工作电极 ,电极电位为+ 0 .80V(vs.Ag AgCl) ,4 0mmol L的Na2 B4O7 H3 BO3 (pH值为 7 5 0 )为缓冲溶液。在此条件下 ,芦丁和维生素C在 1 0min内得到了良好的分离。芦丁和维生素C分别在 5 .0×1 0 - 8～ 5 .0× 1 0 - 4 g mL、8.0× 1 0 - 8～ 5 .0× 1 0 - 4g mL浓度范围内与电泳峰电流呈现良好的线性关系 ;检测下限分别为 2 .0× 1 0 - 8、5 .0× 1 0 - 8g mL。方法应用于实际样品的测定 ,结果令人满意     

基于细胞色素C双通道比率型过氧化氢生物传感器测定过氧化氢

制备细胞色素C/巯基丙酸修饰电极(Cyt.C/MPA/Au)和六-(二茂铁)-己硫醇修饰电极(FcHT/Au),采用循环伏安法研究了Cyt.C/MPA/Au电极和FcHT/Au电极的电化学行为。结果表明,在pH 7.0的磷酸盐缓冲溶液中,过氧化氢在Cyt.C/MPA/Au电极的还原峰电流随其含量的增加不断增大,而在FcHT/Au电极上的参比峰电流基本不变,构建了一种双通道比率型过氧化氢生物传感器。采用差分脉冲伏安法测定过氧化氢的含量,过氧化氢在Cyt.C/MPA/Au电极上的还原峰电流与FcHT/Au电极上的参比峰电流比值,与其浓度在20.0～100.0μmol·L~(-1)内呈线性关系,检出限(3S/N)为1.19μmol·L~(-1),方法的回收率在71.4%～79.2%之间。     

维生素B_6在纳米Au-N,P/石墨烯修饰电极上的电化学行为

将金纳米粒子(AuNPs)电沉积在N,P/石墨烯(N,P/Graphene)修饰的玻碳电极表面,研究了维生素B_6(VB_6)在该修饰电极上的电化学行为。实验结果表明:VB_6在该修饰电极上出现一个良好的氧化峰,在最佳实验条件下,其氧化峰电流与VB_6的浓度在2.0×10~(-5)~4.0×10~(-4) mol/L范围内呈线性关系,相关系数R=0.998,检出限为9.2×10~(-6) mol/L。一些常见的物质如K~+、Na~+、Zn~(2+)、葡萄糖(Glu)不干扰VB_6的检测。此方法已用于片剂中VB_6含量的检测,获得较好结果。     

中性载体双(N-乙基-N-苯基氨基二硫代甲酸)1,4-丁二醇酯PVC膜银离子选择电极的研制

采用双层膜电位法直接测定了溶剂聚合物膜中载体双(N-乙基-N-苯基氨基二硫代甲酸)1,4-丁二醇酯与金属离子生成的络合物生成常数。制备并考察了以双(N-乙基-N-苯基氨基二硫代甲酸)1,4-丁二醇酯为载体的银离子选择性电极的性能。实验结果表明:该选择电极对银离子有良好的灵敏度和高选择性,在1×10-3~1×10-6mol/L的浓度范围内响应斜率为60.2 mV/paAg+,检出限为2.3×10-7mol/L,碱金属、碱土金属及过渡金属离子不干扰银的测定。该电极可作为Ag+准确滴定卤素阴离子的电位滴定指示电极,用于维生素B1药片中维生素B1含量的测定。     

正交设计法优化PEMFC催化层的最佳配比

利用正交实验设计法优选PEMFC电极催化层制备的最佳条件.实验证实亲水电极(催化层中不含PTFE)性能优于疏水电极.在该工艺条件下,当Nafion的含量为1.4mg·cm-2,Pt含量为0.4mg·cm-2时,以常压的H2和空气分别作为燃料气和氧化剂,电池的最高功率可达到0.37W·cm-2.研究表明,提高Pt/C中的Pt含量将是提高催化剂性能的有效途径.     

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.     

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.     

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.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

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.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

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.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

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.