The Electrochemical Oxidation of N,N‐Diethyl‐p‐Phenylenediamine in DMF and Analytical Applications. Part I: Mechanistic Study

The electrochemical oxidation of N,N‐diethyl‐p‐phenylenediamine in dimethylformamide has been studied at platinum and gold microdisk electrodes of various radii between 6.7 and 66 μm. The voltammetric responses revealed two electrochemically reversible waves the second of which becomes larger at higher concentrations and bigger electrode radii. The voltammetric signals have been modelled and the electrochemical oxidation reaction is not inconsistent with an EC_revECE reaction. Kinetic parameters are reported.     

四种α,α'-二氧代烯酮环二硫代缩酮类化合物的电化学性质及光谱研究

本文应用循环伏安法(CV)、UV-Vis、交流阻抗(EIS)和X射线光电子能谱(XPS)等技术研究了4种α-羰基二硫缩烯酮化合物在有机溶剂中的电化学和光谱性质及其在金电极上的自组装膜行为, 根据循环伏安数据计算了此类化合物在DMSO溶液中的扩散系数和电极反应速率常数.     

Selective Detection of p‐Phenylenediamine in Hair Dyes Based on a Special CE Mechanism Using MnO2 Nanowires

We report a novel approach for selective determination of p‐phenylenediamine in hair dyes using β‐MnO₂ nanowires modified glassy carbon (GC) electrodes through an electrochemical co‐deposition process with chitosan hydrogel. A special CE (chemical reaction and electron transfer) process on the surface of β‐MnO₂ nanowires modified GC electrode is proposed and proved by cyclic voltammetry and UV‐Vis spectroscopy in the presence of p‐phenylenediamine. p‐Phenylenediamine can react with MnO₂ nanowires to produce diimine and the equilibrium of the two‐electron and two‐proton redox process of p‐phenylenediamine on the electrode is changed, and consequently the reductive current is enhanced significantly. At a constant potential of 0 V vs. SCE, other main components of hair dyes including o‐, m‐phenylenediamine, catechol, resorcinol, and p‐dihydroxybenzene do not interfere in the determination of p‐phenylenediamine in the amperometric measurement because of their much lower chemical reaction activities with MnO₂ nanowires. It shows a determination range of 0.2–150 μM and a low detection limit of 50 nM to response p‐phenylenediamine. This modified electrode is successfully used to analyze the amount of p‐phenylenediamine in hair dyes without preseparation procedures.     

Basicity of Phenyl‐ and Methyl‐Substituted 1,2,4‐Oxadiazoles

The basicity of a series of 3,5‐disubstituted 1,2,4‐oxadiazoles in aqueous H₂SO₄ was examined by means of UV and ¹H‐NMR spectroscopy. The experimental data were analyzed by the modified Yates–McClelland method to yield the following pK values: 3,5‐dimethyl‐1,2,4‐oxadiazole, −1.66±0.06; 3‐methyl‐5‐phenyl‐1,2,4‐oxadiazole, −2.61±0.02; 3‐phenyl‐5‐methyl‐1,2,4‐oxadiazole, −2.95±0.01; 3,5‐diphenyl‐1,2,4‐oxadiazole, −3.55±0.06. A pK value of ca. −3.7 was estimated for the parent unsubstituted 1,2,4‐oxadiazole based on substituents' additivity increments. Possible protonation sites of the compounds were discussed in terms of both experimental data and theoretical calculations (HF/6‐31G**). Generally, protonation is most likely to occur at N(4) of the 1,2,4‐oxadiazole ring. However, concurrent formation of both N(4)‐ and N(2)‐protonated species in comparable amounts is possible in the case of 3‐phenyl‐1,2,4‐oxadiazoles.     

取代基对腺嘌呤与胸腺嘧啶氢键复合物体系结合能的影响

优化得到了17个取代胸腺嘧啶与腺嘌呤形成的氢键复合物的结构, 并计算了这些复合物的结合能, 探讨了胸腺嘧啶上不同取代基对结合能的影响. 结果表明, CF₃取代的胸腺嘧啶与腺嘌呤间的结合能大于胸腺嘧啶与腺嘌呤间的结合能, 这可能是屈氟尿苷具有阻止病毒及肿瘤扩散功能的原因所在. SO₃H, CN和NO₂取代的胸腺嘧啶与腺嘌呤间具有更大的结合能, 表明这3个基团取代的胸腺嘧啶也可能具有潜在的抗肿瘤作用. 分子中原子理论与自然键轨道分析表明, 在所有体系中, 氢键N—H…N最强, N—H…O=C次之, C—H…O=C最弱, 轨道作用在氢键作用中占有重要地位.     

取代基对腺嘌呤与胸腺嘧啶氢键复合物体系结合能的影响简

优化得到了17个取代胸腺嘧啶与腺嘌呤形成的氢键复合物的结构,并计算了这些复合物的结合能,探讨了胸腺嘧啶上不同取代基对结合能的影响. 结果表明,CF3取代的胸腺嘧啶与腺嘌呤间的结合能大于胸腺嘧啶与腺嘌呤间的结合能,这可能是屈氟尿苷具有阻止病毒及肿瘤扩散功能的原因所在. SO3H,CN和NO2取代的胸腺嘧啶与腺嘌呤间具有更大的结合能,表明这3个基团取代的胸腺嘧啶也可能具有潜在的抗肿瘤作用. 分子中原子理论与自然键轨道分析表明,在所有体系中,氢键N—H…N最强,N—H…O=C次之,C—H…O=C最弱,轨道作用在氢键作用中占有重要地位.     

Perylene‐based Solution‐processable Conjugated Molecules for Optoelectronic Applications: Synthesis and Comparison of Different Substituents on the Optical,Thermal, and Electrochemical Properties

A series of small organic molecules were synthesized by exploiting the bay and imide positions of the perylene nucleus. The synthesized compounds 1 – 11 were characterized by spectroscopic and elemental analyses. These molecules show yellowish color in solution and are highly soluble in dichloromethane. Compound 7 shows a bandgap of 1.7 eV and a Stokes shift of 27. From these results, we infer that this compound can serve as structural template in the design of organic electronics. Moreover, compound 7 shows higher T_d (370°C) and T_g (132°C) values, which reflect its high thermal stability.     

溶剂效应和取代基效应对2-(2-氨基苯基)苯并噻唑光谱性质及激发态分子内质子转移的影响

合成了多种2-(2-氨基苯基)苯并噻唑(APBT)氨基氢原子被供电子及吸电子基团取代的衍生物, 并用紫外光谱﹑荧光光谱等方法和密度泛函理论(DFT)计算研究了溶剂效应和取代基效应对衍生物的光谱性质及激发态分子内质子转移(ESIPT)的影响规律. 结果表明, 相比于非极性溶剂环己烷, 随溶剂极性的增加及APBT-溶剂分子间氢键的形成, APBT的紫外-可见最大吸收峰和荧光最大发射峰均发生了一定程度的红移, 并对APBT的ESIPT产生了影响. 在APBT分子的氨基氮原子上引入不同的吸电子或斥电子取代基, 对氮原子的电荷性质有较大的影响. 在环己烷溶剂中, 甲基取代后的APBT仅有单重荧光发射峰, 体系未发生ESIPT过程; 而COCH₂Cl等吸电子基团能促进APBT的ESIPT, 其荧光发射光谱出现了明显的双重峰, 表明体系发生了激发态分子内质子转移反应. 量子化学的理论计算较好地验证了光谱实验结果.     

The Electrochemical Behavior of p‐Sulfonated Sodium Salt of Calix[6]arene

The water‐soluble p‐sulfonated sodium salt of calix[6]arene (p‐SC6) is synthesized and characterized by FT‐IR and UV‐vis spectra. The purity of the product is checked as 97.6% by HPLC. The electrochemical behavior of p‐SC6 in NaAc+HAc (pH 3.9) buffer solution is studied. The results showed that p‐SC6 can be oxidized irreversibly when the potential scanned from 0 to 1.0 V (vs. SCE). The peak potential locates at about 0.83 V (vs. SCE) which depends on the scan rate and acidity. The number of electrons, n, transferred in the electrochemical reaction is 1. The diffusion coefficient of p‐SC6 is 1.4×10^?6 cm² s^?1 at 25 °C. The electrochemical oxidation of p‐SC6 is strongly affected by acidity. For example, when pH is 10.6, n becomes 3. But the diffusion coefficient of p‐SC6 is 1.1×10^?6 cm² s^?1 which is close to that measured at pH 3.9.     

Parametrization of Substituents: Effects of Fluorine and Other Heteroatoms on OH,NH, and CH Acidities

Fluorine, the heterosubstituent par excellence , which can have a stronger impact on the reactivity in its vicinity than any other element, may serve as a crucial test of any model of the origin and transmission of electronic effects. To what extent fluoro substituents in organic compounds (A−H) increase their kinetic proton mobility (H/D and H/metal (M) exchange) and thermodynamic acidity in aqueous media and in the gas phase (see below) depends on many factors such as induction, resonance, polarization, hyperconjugation, and dipolar interactions.     

Electrochemical and Spectroelectrochemical Analysis of 4‐(4‐(5‐Phenyl‐1,3,4‐oxadiazole‐2‐yl)phenoxy)‐Substituted Cobalt(II), Lead(II) and Metal‐Free Phthalocyanines

Electrochemical and spectroelectrochemical analyses of 4‐(4‐(5‐phenyl‐1,3,4‐oxadiazole‐2‐yl)phenoxy)‐substituted metal‐free phthalocyanine ( H₂Pc ( 1 )) and metallated phthalocyanines ( PbPc ( 2 ) and CoPc ( 3 )) were performed in solution. Voltammetric characterizations of the phthalocyanine complexes were investigated by using cyclic voltammetry and square wave voltammetry techniques. CoPc ( 3 ) gave common metal and ring based electron transfer reactions; however they split due to the aggregation. Although PbPc ( 2 ) illustrated reversible reduction processes during the voltammetric measurements, it was de‐metallized and thus turned to the metal free phthalocyanine during repetitive voltammetric cycles and in situ spectroelectrochemical measurements.     

Electropolymerized o‐Phenylenediamine on Graphite Promoting the Electrochemical Detection of Nafcillin

By combining molecular modelling and electrochemistry we envision the creation of modified electrodes tailored for a more sensitive and selective detection of a single analyte. In this study we report on a graphite screen printed electrode modified with electropolymerized o‐phenylenediamine, selected by rational design, which promotes the detection of nafcillin (NAF), an antibiotic. Parameters such as monomer concentration, pH and number of electropolymerization cycles were optimized to obtain the highest current signal for the target upon amperometric detection. NAF identification was based on the redox process at +1.1 V (vs pseudo Ag), ascribed to the oxidation of the C‐7 side chain. With the optimized modification protocol, a two‐fold increase in nafcillin signal could be obtained: the calibration plot in 0.1 M Britton‐Robinson buffer pH 4 showed a limit of detection of 80 nM with improved sensitivity and reproducibility (RSD<5 %) compared to the detection at non‐modified electrodes.     

Electrospun Mesoporous Poly(Styrene‐Block‐Methyl‐ Methacrylate) Nanofibers as Biosensing Platform: Effect of Fibers Porosity on Sensitivity

The present work demonstrates the use of mesoporous nanofibers for the enhanced analytical performance of electrochemical biosensor. By exploiting the phase separation property of the block copolymers, a simple three‐step process was used to generate the porosity in the nanofibers. Here we present the effect of the porosity on the sensing ability of the electrospun PS‐b‐PMMA nanofibers. The functional groups present on the nanofiber surface were characterized using DPV. The nanofibers modified electrode showed a large decrease in the oxidation current with the increase in the pH from 4.2 to 6.8 for the anionic redox couple whereas the change in the current is negligible for a neutral redox couple, this suggested the presence of ‐COOH groups. A one‐step process was used for the immobilization of biotin. There were about 35.5 % and 66.6 % decrease in the redox current for the as‐spun and porous nanofibers after functionalization respectively which indicate the presence of a high amount of active sites in the porous nanofibers. Finally, the sensor response was studied using streptavidin (1μg/ml–1fg/ml) as a model analyte. CV studies showed a 2.7‐fold increase whereas DPV showed a 6‐fold increase in the sensitivity for the porous nanofibers as compared to the as‐spun nanofibers.     

Synthesis,Characterization and Electrochemistry of New Soluble Porphyrazine Complexes Bearing Octakis 3‐Methylbutylthio Substituents

Porphyrazines, MPz (M = Mg, H, Ni, Zn and Co) with octakis 3‐methylbutylthio substituents have been synthesized starting with the corresponding unsaturated dicarbonitrile derivative. These new compounds have been characterized by UV‐Vis, FT‐IR, ¹H NMR, MS and elemental analysis methods. Voltammetric properties of the complexes were also investigated by CV, DPV and CPC techniques. Electrochemical studies show that three reversible one electron reductions and one reversible one electron oxidation processes (two for Co^IIPz) are observed for all of the complexes. The E_1/2 values are similar for the H₂Pz, Ni^IIPz and Zn^IIPz derivatives with negative shift due to the different effective nuclear charges of the central metal ion. Peak to peak separations and separation between the first reduction and first oxidation couples related with the HOMO‐LUMO gap of the complexes are in harmony with the common porphyrazine complexes.     

The Use of Light in the Study of Interfacial Electrochemical Reactions

Spectroscopic analysis techniques have become particularly important in the study of interfacial electrochemical processes since it has become possible to increase their sensitivity to the extent where changes occurring in the absorption of light by fractions of monolayers can be detected. At the same time the development of new techniques in surface physics, though most of these can only be used in ultra-high vacuum, has also had a considerable influence on electrochemistry since it has enabled studies to be carried out on electrodes after transfer to UHV. The availability of well-defined semiconductors in which photocurrents can be generated by the absorption of light has led to the development of photoelectrochemical methods that can be used for the study of electrode reactions at semiconductors or at metal surfaces which are covered with a semiconducting film. Finally, it has been observed during the study of semiconductor electrodes that redox reactions at an electrode can result in the generation of luminescence. This, in turn, can lead to important information on the mechanism of the charge transfer process. These recent developments are reviewed in the present article.     

取代基效应对N-4-取代苯亚甲基苯胺与N-4-取代苯亚甲基环己胺NMR和UV光谱影响的差异性

合成了N-4-取代苯亚甲基苯胺(1)与N-4-取代苯亚甲基环己胺(2)两个系列化合物, 测定其¹³C和¹H 核磁共振(NMR)化学位移以及紫外(UV)吸收光谱. 定量对比了取代基效应对两个系列化合物CH=N键的¹³CNMR化学位移δ_C(C=N)和¹H NMR化学位移δ_H以及UV吸收光谱最大波长能量(v_max)的影响差异. 研究结果表明,对于分子骨架相似的化合物(1)和(2), 取代基效应的作用方式存在多样性: (i)化合物(1)的δ_C(C=N)、δ_H以及v_max受到基团的特殊交叉相互作用(Δσ²)的影响显著, 而Δσ²对化合物(2)相应性能的影响很小; (ii)无论化合物(1)还是化合物(2), 取代基场/诱导效应σ_F和共轭效应σ_R对δ_C(C=N)的影响为负相关, 而对δ_H的影响为正相关, 它们对δ_C(C=N)和δ_H的影响正好相反. 另一方面, 场/诱导效应σ_F对(1)和(2)的δ_C(C=N)影响重要, 而对它们的δ_H影响很小; (iii)化合物(1)和(2)的δ_C(C=N)、δ_H以及v_max的变化规律, 可分别建立通用方程表达, 其中与CH=N的N原子键连苯基的影响可由指示变量(I)表示, 该苯基对三种性能分别有固定的贡献.     

新型氯代苯基咔咯的合成及电化学和光谱性质

通过吡咯和具有相应取代基的苯甲醛在甲醇和水的混合溶剂中生成胆色烷, 然后用四氯苯醌氧化胆色烷, 合成了2种新型的咔咯化合物: 三(4-氯苯基)咔咯[(ClPh)₃CorH₃]和三(2,4-二氯苯基)咔咯[(Cl₂Ph)₃CorH₃]. 采用紫外-可见、荧光、¹H NMR、MS和IR等光谱技术对化合物进行了表征. 研究了化合物在二氯甲烷和二甲基甲酰胺中的电化学及光谱电化学性质. 讨论了溶剂和取代基对紫外-可见光谱以及氧化还原电位和电子转移过程的影响. 提出了化合物在2种不同溶剂中的氧化还原反应机理.     

Electrochemical Study of Tryptophan‐containing Peptides‐Cu(II) Complexes

This article presents rotating ring‐disc electrode investigations of (A = alanine, F = phenylalanine, G = glycine, L = leucine, W = tryptophan) W, GW, WGG, GWG, GGW, GWGG, and GGWA. In addition, the analyses of the copper complexes of the same peptides plus GF, FGG, GFG, FGG, GGFL, GGGG, AAAA, and GGGGGG have been carried out. The results suggest that an influential step in the reaction mechanism of the copper complexes of the tryptophan‐containing peptides (W‐peptides) is the alteration of the peptide structure after the one‐electron oxidation of tryptophan. This change in structure leads to a positive shift in redox potential for the Cu(III)/Cu(II) couple. The analytical implications for the electrochemical detection of W‐peptides as their copper complexes are applied for detection of W‐containing bioactive peptides. Application of the optimized detection conditions of peptides as their Cu(II) complexes are as follows: (1) If sensitivity is paramount, detect the copper complexes at a relatively high potential, around 0.7 V vs. Ag/AgCl. (2) If selectivity is paramount, use a dual electrode detector, oxidize at an upstream anode at 0.4 V, and detect at the downstream cathode at 0–0.1 V.