Spectrophotometric, potentiometric and chromatographic pKa values of polyphenolic acids in water and acetonitrile-water media

The pK_a values of nine polyphenolic acid substances in water and acetonitrile-water mixtures using potentiometric, spectrophotometric, and liquid chromatographic (LC) measurements, have been determined. Also, a new method based on the absorbance spectra at the maximum of chromatographic peaks previously obtained has been applied. This method can be applied to data obtained from LC-UV (diode array detection (DAD)) instruments and retains all the advantages of LC and spectrophotometric methods, such as the possibility of working with impure samples. Finally, the advantages of the different methods to the determination of pK_a values of nine polyphenolic acids have been described in order to verify the applicability of the proposed methods in aqueous and acetonitrile-water media.     

Studies of thermooxidative degradation process of chlorinated natural rubber from latex

The thermooxidative degradation of chlorinated natural rubber (CNR) from latex were studied by thermogravimetry (TG) coupled with Fourier Transform Infrared Spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy and difference FTIR. The CNR degraded in air atmosphere with two distinct steps of weight loss. The first step ranging from 160 to 390 °C, mainly is a dehydrochlorination reaction with a little oxidative scission of molecular backbones to release carbon dioxide and the conjugated polyene sequences (---[C=C]---)_n=3,4 are formed on the molecules of CNR. The second step ranging from 390 to 585 °C, is an oxidative degradation reaction of the molecular backbones of CNR and the evolved gas is only carbon dioxide.     

Optical absorption and fluorescence studies on imidazolium ionic liquids comprising the bis (trifluoromethanesulphonyl)imide anion

Optical absorption and fluorescence behaviour of two rigorously purified imidazolium ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide are studied in the neat condition and in solution. Non-negligible absorption in the UV region with a long tail extending into the visible region is the main feature of the absorption. Excitation wavelength-dependent two-component fluorescence characterizes the emission behaviour of these liquids. That ion association gives rise to the long absorption tail and shifting fluorescence maximum, which appears to be common to most of the imidazolium ionic liquids, is evident from the effect of the conventional solvents     

Solid state spectroelectrochemistry of microparticles of ruthenium diimine complexes immobilised on optically transparent electrodes

The solid state electrochemistry and solid state spectroelectrochemistry of two ruthenium complexes, ruthenium tris-(4,7-diphenyl-1,10-phenanthroline) bis-hexafluorophosphate, [Ru(dpp)₃](PF₆)₂, and ruthenium bis-(2,2′-bipyridine)(4,6-diphenyl-2,2′-bipyridine)bis-hexafluorophosphate, [Ru(bpy)₂(dpb)](PF₆)₂, is described. Microparticles of the material are immobilised on ITO electrodes, and stable voltammetric signals are obtained in contact with aqueous electrolyte solution. Spectral changes monitored during a slow cyclic voltammetric scan confirm the exhaustive oxidation of the Ru²⁺ species to the Ru³⁺ form. The derivative of the absorbance signal monitored at a single wavelength during potential cycling is morphologically identical to a cyclic voltammogram with no background current. This technique is shown to be useful when peaks of small magnitude are obscured by capacitive background or when peaks close to the solvent limit are obscured by solvent electrolysis current. The technique effectively widens the electrochemical window available for voltammetric measurements. After suitable correction of the signal, the value of the voltammetric peak height (I _p) as well as peak potential (E _p) may be obtained from the derivative absorbance signal. Chronospectrometry is demonstrated to provide the equivalent to a chronocoulometric response, but is closer to the ideal simulated response. A facile method for simulating time or potential-dependant spectroelectrochemical responses using commercial electrochemical simulation software is described. Absorbance transients monitored during the electrolysis of solid particles of [Ru(dpp)₃](PF₆)₂ show best agreement with simulated data at very short and very long timescales. This observation, in conjunction with the observations from the potential scan experiments, suggests that the absorbance, charge, or current vs. time behaviour of the system can be adequately described by a semi-infinite diffusional model at short experimental timescales and by a finite diffusional model at sufficiently long timescales. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Dedicated to the 80th birthday of Keith B. Oldham.     

四苯骈卟啉与铜（Ⅱ）、锌（Ⅱ）配位反应及其波谱学研究

用光度法测定了四苯骈卟啉（Ｈ２ＴＢＰ）与ＣＵ２＋、Ｚｎ２＋配位反应速率常数、活化能及热力学参数．结果表明：Ｈ２ＴＢＰ与Ｃｕ２＋配位反应速率较快，△Ｈ＜０，而与Ｚｎ２＋配位速率较慢，且△Ｈ＞０．报导了ＺｎＴＢＰ的荧光光谱，ＣｕＴＢＰ的ＥＳＲ谱．     

新型多氮杂环金属配合物的合成及其光谱研究

采用溶液析出法,合成了以2-(2′-羟基-5′-甲基苯基)苯并三唑(HMPB)为配体的多氮杂环金属配合物M(HMPB)₂(M=Co, Ni),利用元素分析、激光解析飞行时间质谱等进行了表征,并研究了新配合物的红外特征光谱和紫外-可见电子吸收光谱。结果表明：HMPB配体通过N和O原子与中心金属以二齿形式配位,中心金属的配位数为4;配合物红外特征吸收谱带位于400～2 500 cm-1,形成金属配合物后,2-(2′-羟基-5′-甲基苯基)苯并三唑的羟基的伸缩振动吸收、CN振动峰和C─O特征吸收有明显改变,同时确定了配位键M─N和M─O的特征峰位置;配合物在紫外区有强吸收,其最大吸收峰位于335～345 nm。     

N-芳基-N′-(4-乙氧基苯甲酰基)硫脲衍生物阴离子识别性能的光谱研究

利用紫外-可见吸收光谱及1H NMR考察了两种N-芳基-N′-(4-乙氧基苯甲酰基)硫脲作为受体分子与F-,Cl-,Br-,I-,CH₃COO-,H₂PO-₄,HSO-₄,NO-₃等阴离子的作用。结果表明,客体阴离子F-,CH₃COO-,H₂PO-₄可以与该类受体分子形成氢键配合物,溶液颜色由无色转变为黄色,而加入其他阴离子则无变化。测定了主客体配合物的稳定常数和化学配位比,对苯环上不同取代基的受体分子与不同阴离子客体的识别作用以及同一受体对不同阴离子的识别作用进行了比较,其识别性能呈现规律性变化, 提出了可能的配合物的结合模式。     

纳米银导电膜的制备及其光谱学分析

为了以温和的化学反应制备纳米银导电膜,在PET薄膜上涂布柠檬酸银乳液,并用抗坏血酸(Vc)还原,用红外光谱仪、紫外-可见光分光光度计、X射线衍射仪(XRD)、扫描电子显微镜、原子力显微镜等,研究柠檬酸银乳液及其还原涂层的微观形貌、晶体结构和导电性能。发现PVP保护的柠檬酸银乳液粒径分布在60～150 nm。银膜的UV-Vis吸收峰位于430 nm,表明其具有纳米结构。XRD分析表明,还原后的涂层形成了不完整的银晶体,水洗比乙醇处理更能促进柠檬酸银的彻底还原和银膜的晶型完善,降低银膜表面电阻。     

光谱法研究盐酸非那吡啶与牛血清白蛋白的结合作用

运用光谱学方法研究了在生理pH值条件下盐酸非那吡啶(PHE)与牛血清白蛋白之间的结合作用。通过荧光光谱和紫外吸收光谱确定了盐酸非那吡啶对牛血清白蛋白的荧光猝灭机理。依据Scatchard方程测定了不同温度下该结合反应的结合常数和结合位点数。根据热力学方程讨论了两者间的主要作用力类型。结合同步荧光光谱分析了盐酸非那吡啶对牛血清白蛋白构象的影响。盐酸非那吡啶对牛血清白蛋白的荧光猝灭机制主要为静态猝灭和非辐射能量转移。在15, 25, 37℃时盐酸非那吡啶与牛血清白蛋白的结合常数K_b分别为2.47×107, 9.15×106, 4.36×106 L·mol-1,它们之间平均结合位点数n为1。结合反应的热力学参数为ΔH=-71.2 kJ·mol-1,ΔS=124.8 J·mol-1·K-1。热力学函数计算结果表明,该作用过程是一个熵增加,Gibbs自由能降低的自发分子间作用过程。依据Frster能量转移理论确定PHE与BSA间的结合距离为1.61 nm。两者结合的主要作用力类型是静电作用力。盐酸非那吡啶在体内能够被血清蛋白存储和转运,但结合时对蛋白构象有一定影响。     

小牛胸腺DNA与细胞色素C相互作用的电化学和光谱研究

利用电化学和紫外-可见(UV-Vis)反射吸收光谱技术研究了固定到带正电的尼龙膜上的小牛胸腺DNA(CT-DNA)与马心细胞色素C之间的相互作用,发现马心细胞色素C能以其带正电的活性区域一端吸附到带负电的CT-DNA表面,因此CT-DNA能促进马心细胞色素C的直接电化学反应。