胆绿素在甲醇—水混合溶液中的电化学行为研究

在甲醇-水混和溶液中。胆绿素可在-0.90 V(vs.SCE)左右产生一灵敏的极谱波,该波波高与胆绿素在8×10~(-8)～1×10~(-6)mol/L范围内呈线性关系,其检出限为4×10~(-8)mol/L。因此,该波可用于胆绿素的测定。本文采用多种电化学方法对胆绿素的极谱波性质进行了研究,发现此波为一与氧有关的吸附催化波。     

泼尼松的示波极谱测定及其电化学行为

基于泼尼松产生的极谱还原波 ,提出了测定泼尼松的单扫描示波极谱法。在0 .1 2 mol/ L HAc-0 .0 8mol/ L Na Ac ( p H 4.6)的缓冲溶液中 ,泼尼松于 -1 .1 3 V处产生一极谱还原波。二阶导数峰电流与其浓度在 2 .4× 1 0 - 6～ 1 .6× 1 0 - 5mol/ L范围内有良好的线性关系 ( r=0 .9991 ,n=8) ,检出限为 8.0× 1 0 - 7mol/ L。测定了片剂中泼尼松的含量。讨论了泼尼松的电化学行为     

盐酸羟胺存在下极谱动力波法测定阿托品

研究了NH2 OH·HCl存在下测定阿托品的极谱动力波法。在 0 .1mol/LLiCl 4.4× 1 0 - 3 mol/LNH2 OH·HCl支持电解质溶液中 ,阿托品于 - 1 .90V(vs.SCE)处产生一个极谱动力波 ,其二阶导数峰电流与阿托品在 6.0× 1 0 - 5～ 4.0×1 0 - 4 mol/L浓度范围内呈线性关系 (r=0 .9992 ,n =5 )。与无NH2 OH·HCl存在时相应还原波相比 ,该动力波电流可提高分析灵敏度一个数量级。讨论了该动力波的产生机理     

黄芩甙的极谱催化波研究及应用

在 0 .2 4mol/L混合酸 NaOH(Britton Robinson) (pH 2 .0 ) -8× 1 0 -3 mol/LKIO3 支持电解质中 ,黄芩甙产生一极谱催化波 ,峰电位为 -1 .2 0V(vs.SCE)。该波的一阶导数峰峰电流与黄芩甙浓度在 1×1 0 -7～ 3× 1 0 -6mol/L范围内呈线性关系 (r=0 .9988)。用该法测定了三黄片中黄芩甙的含量。该催化波是有机化合物极谱催化波的一种新类型—缔合 /平行催化波。IO-3 有双重作用 :( 1 )IO-3 作为配位体与吸附在电极表面的质子化黄芩甙形成离子对缔合物 ,引起峰电位的负移 ;( 2 )IO-3 及其还原中间体作为氧化剂氧化黄芩甙羰基经单电子单质子还原产生的自由基 ,产生了极谱催化波     

单扫描示波极谱法测定药物中的卡托普利

报道了卡托普利 Cu+络合物的极谱吸附波。在 0 .0 2mol LH3 PO4溶液中 ,卡托普利与Cu2 +发生氧化还原反应 ,生成卡托普利 Cu+络合物 ,在单扫描示波极谱仪上于 - 0 .44V(vs.SCE)处产生一灵敏的吸附还原波。该吸附还原波二阶导数峰电流与卡托普利浓度在 1.8× 10 - 7～ 1.8× 10 - 5mol L范围内呈线性关系 ;方法的检出限为 8.0× 10 - 8mol L ;回收率在 98.0 %～ 10 3%。     

血红蛋白模拟过氧化物酶催化反应体系的极谱分析

用极谱分析法研究了血红蛋白催化H2O2氧化邻苯二胺(OPD)的反应体系.血红蛋白具有类似过氧化物酶的功能,它能够催化OPD-H2O2的反应生成一种具有电化学活性的产物,该产物在滴汞电极上-0.64V(vs.SCE)产生一个峰形良好的极谱还原峰.优化了血红蛋白的催化反应条件和催化反应产物的极谱测定条件 在最佳条件下,该体系可用于血红蛋白含量的测定,线性范围为2.0×10-9～2.0×10-7mol/L,检测限为1.0×10-9mol/L;也可用于痕量H2O2的测定,线性范围为1.0×10-6～2.0×10-4mol/L,检测限为1.0×10-6mol/L.     

极谱催化波法测定地塞米松

基于地塞米松在过硫酸钾存在下产生的极谱催化波 ,拟定了测定地塞米松的新方法。与基于还原波的差分脉冲极谱法相比 ,本方法用线性变位极谱法获得的分析灵敏度提高了两个数量级。在 2 .0× 10 - 3mol LH2 SO4 ～ 2 .0× 10 - 2 mol LK2 S2 O8底液中 ,地塞米松于 - 1 0 8V (vs .SCE)处产生一极谱催化波 ,其二阶导数峰电流与地塞米松浓度在 3.2× 10 - 8～ 3.2× 10 - 7mol L范围内呈线性关系 (r =0 .9994 ,n =6 ) ,检出限为 1.0×10 - 8mol L。讨论了极谱催化波产生的机理。     

单扫描示波极谱法测定磷酸氯喹

建立了极谱测定磷酸氯喹的方法。在4.0×10-2mol LNH3·H2O NH4Cl(pH9.5)支持电解质中,磷酸氯喹极谱还原波的峰电位Ep为-1.61V(vs.SCE),其二阶导数峰峰电流ip″与磷酸氯喹浓度在1.0×10-8mol L～1.0×10-6mol L和1.0×10-6mol L～1.0×10-4mol L范围内呈线性关系。10次测量1.0×10-6mol L磷酸氯喹还原波二阶导数峰峰电流,相对标准偏差RSD为0.92%。该方法用于片剂中磷酸氯喹的测定。     

极谱催化波法测定马蔺子素

报道了在Na2 B4 O7 KH2 PO4 K2 S2 O8体系中马蔺子素的极谱催化波。拟定了测定马蔺子素的新方法。在 8.0× 10 - 3mol/LNa2 B4 O7 1.6× 10 - 2 mol/LKH2 PO4 (pH =7.7) 5 .0× 10 - 3mol/LK2 S2 O8底液中 ,极谱催化波峰电位Ep=-1.2 3V(vs .SCE) ;二阶导数峰峰电流i″p 与马蔺子素浓度在 2 .0× 10 - 9～ 2 .0× 10 - 6 mol/L范围内呈良好线性关系 ,检出限为 1.0× 10 - 9mol/L。催化波灵敏度比相应马蔺子素还原波高 75倍。采用该法测定了胶囊中马蔺子素的含量     

苯噻草胺的极谱特性研究

在 p H3.4 H3PO4-Na H2 PO4缓冲溶液中 ,苯噻草胺在 -1 .1 0 V左右产生一灵敏示波极谱波 ,利用此波可测定微量苯噻草胺 ,线性范围为 3.0× 1 0 - 8～ 2 .0× 1 0 - 5 mol/L,检出限为 1 .8× 1 0 - 8mol/L。     

Catalytic reaction of methanol with alkanethiols

Methanol reacts with primary alkanethiols (R=C₁–C₃) over alumina catalysts to yield dialkyl sulfides. Methanethiol is completely converted to dimethyl sulfide. Ethane-and 2-propanethiols give methyl alkyl sulfides. However, the process is complicated by side reactions producing olefins and dimethyl sulfide. If mixed thiols are used, their transformations hinder each other.     

Influence of methanol addition during selective hydrogenation of benzene to cyclohexene

The addition of a certain methanol concentration during benzene hydrogenation on Ru/Al₂O₃ improves the selectivity to cyclohexene because of a preferential adsorption of methanol on the most active Ru sites.This revised version was published online in December 2005 with corrections to the Cover Date.     

Electron solvation in methanol revisited

Suggestions for the mechanism of electron solvation in methanol during the last three decades were mostly based on limited time resolution measurements, or indirect observations. The two-channel solvation scheme proposed by Lewis and Jonah (1986) based on indirect observations in electron scavenging experiments is checked here to see if it is in accordance with recent sub-picosecond pump-and-probe laser experimental results. We confirm the applicability of this solvation mechanism and calculate quantitative kinetic and spectral parameters involved.     

The torsion-vibration spectrum of methanol trapped in neon matrix

The spectra of six isotopic species of methanol trapped in neon matrix have been recorded between 30 and 11,000 cm⁻¹. Noticeable temperature effects are observed for the OH species. They allow two kinds of absorptions to be identified for most of the vibrational transitions: those low temperature (LT) predominating at 2.7 K and those high temperature (HT) significantly increasing in intensity when varying temperature from 2.7 to 7 K. The conversion is perfectly reversible and has been examined from two points of view: the kinetics of interconversion and the activation energy associated to the process. The kinetic study shows that the limiting factor of the measurements is the time required for spectral acquisition (about 5 s). The activation energy deduced from Arrhenius plots is found equal to 6.7 ± 0.5 cm⁻¹. From the comparison with gas phase data one concludes that the internal rotation about the C–O bond is not strongly altered by the matrix surrounding, the activation energy corresponding to the E–A tunneling splitting of the ground state (9.12 cm⁻¹ for CH₃OH in the gas phase). The pure torsion and the torsion-vibration spectra are generally consistent with those in the gas phase. In particular the complex structure of the COH bending mode is well reproduced, with a clear identification of the transitions issuing from the A and E sublevels of the ground state.     

Microfluidic distillation chip for methanol concentration detection

An integrated microfluidic distillation system is proposed for separating a mixed ethanol-methanol-water solution into its constituent components. The microfluidic chip is fabricated using a CO₂ laser system and comprises a serpentine channel, a boiling zone, a heating zone, and a cooled collection chamber filled with de-ionized (DI) water. In the proposed device, the ethanol-methanol-water solution is injected into the microfluidic chip and driven through the serpentine channel and into the collection chamber by means of a nitrogen carrier gas. Following the distillation process, the ethanol-methanol vapor flows into the collection chamber and condenses into the DI water. The resulting solution is removed from the collection tank and reacted with a mixed indicator. Finally, the methanol concentration is inversely derived from the absorbance measurements obtained using a spectrophotometer. The experimental results show the proposed microfluidic system achieves an average methanol distillation efficiency of 97%. The practicality of the proposed device is demonstrated by detecting the methanol concentrations of two commercial fruit wines. It is shown that the measured concentration values deviate by no more than 3% from those obtained using a conventional bench top system.     

Phytochemical investigation and antioxidant activities of methanol extract,methanol fractions and essential oil of Dillenia suffruticosa leaves

Oxidative stress has been known as a key factor of many disorders affecting human beings. Reactive oxygen species (ROS) attack vital biomolecules, weakening their functioning, thus exacerbating diseases. To attenuate oxidative stress-associated diseases a novel approaches of antioxidant therapies have been anticipated. Antioxidants have the potential to inhibit the propagation and formation of ROS. Dillenia suffruticosa is a medicinal plant, used by the local people for the treatment of various ailments. The study aimed to evaluate the phytochemical screening, antioxidative activity, total phenolic and flavonoid contents of methanol extract, fractions and essential oil of D. suffruticosa. Furthermore, the analysis of phytochemicals was done using gas chromatography and mass spectrometry (GCMS). The result showed the existence of alkaloids, anthraquinones, flavonoids, phytosterol, saponins, tannins, triterpenoids and steroids in the methanol extract and fractions of D. suffruticosa. The butanol fraction and methanol extract showed high phenolic (379.00 ± 9.25 and 277.00 ± 3.50 mg/g) and flavonoid values (74.44 ± 2.18 and 34.83 ± 0.71 mg/g) as compared to ethyl acetate, n-hexane and chloroform fractions. The scavenging capacity of butanol fraction and methanol extract was also higher than other fractions. GCMS analysis indicated the presences of various compounds in methanol extract, fractions and essential oil including methyl glycolate, lauryl acetate, phenol, 2,4-bis (1,1-dimethylethyl), 9,12-octadecadienoic acid, hexadecanoic acid, methyl ester, methyl stearate, phenol, benzyl alcohol, 3-hexen-1-ol, acetate and phytol. Thus, methanol extract, fractions and essential oil of D. suffruticosa leaves mainly contain vital phytochemical and shows good antioxidant activity.     

Structural characterization of methanol substituted lanthanum halides

The first study into the alcohol solvation of lanthanum halide [LaX₃] derivatives as a means to lower the processing temperature for the production of the LaBr₃ scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(μ-Br)(H₂O)₇](Br)₂}₂ (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H₂O)₇(MeOH)₂](Br)₃ (2) compound was isolated where the La metal center retains its original 9-coordination through the binding of two additional MeOH solvents but necessitates the transfer of the innersphere Br to the outersphere. In an attempt to in situ dry the reaction mixture of 1 in MeOH over CaH₂, crystals of [Ca(MeOH)₆](Br)₂ (3) were isolated. Compound 1 dissolved in MeOH at reflux temperatures led to the isolation of an unusual arrangement identified as the salt derivative {[LaBr_2.75·5.25(MeOH)]^+0.25 [LaBr_3.25·4.75(MeOH)]^−0.25} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr₃ in MeOH forming the 8-coordinated [LaBr₃(MeOH)₅] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX₃ derivatives were isolated as [(MeOH)₄(Cl)₂La(μ-Cl)]₂ (6) and [La(MeOH)₉](I)₃·MeOH (7). Beryllium Dome XRD analysis indicated that the bulk material for 5 appear to have multiple solvated species, 6 is consistent with the single crystal, and 7 was too broad to elucidate structural aspects. Multinuclear NMR (¹³⁹La) indicated that these compounds do not retain their structure in MeOD. TGA/DTA data revealed that the de-solvation temperatures of the MeOH derivatives 4–6 were slightly higher in comparison to their hydrated counterparts.     

Electrochemical behaviour of p-Si in methanol solutions of chlorides

The mechanism of anodic dissolutions of p-Si single crystals in CH₃OH–LiCl and CH₃OH–LiCl–HCl solutions was investigated by means of the following electrochemical methods: linear sweep voltammetry, the potentiostatic transient technique and XPS surface analysis. The dissolution of p-Si proceeds by a two-step mechanism with the creation of a Si(II) surface intermediate. At low anodic overvoltage the dissolution proceeds with the formation of porous silicon, probably through the reaction: 2Si(II)Si+Si(IV). Structural etching of the single crystals surface was observed at high anodic overvoltage (E>2 V). At this potential range, silicon dissolves with the formation of a Si(IV) soluble product. Electrolysis of the methanol solvent containing Si(IV) in the cell p-Si|CH₃OH–LiCl–Si(IV)|M, where M=Pt, Cu or 18/8 stainless steel, leads to the deposition of an amorphous organosilicon layer on the cathode. The analysis of the deposit performed by means of XPS, FTIR and SEM allows determination of the morphology and composition of the film. The layer consists of Si–OCH₃ compounds and can be created only in methanol solvent. The film is unstable in a humid atmosphere and undergoes transformation into a Si–OH layer.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

Decatungstate photocatalyzed oxygenation of methanol in acetonitrile under photostationary state conditions

Complementary techniques including laser flash photolysis have been used to investigate the mechanism of decatungstate photocatalyzed oxygenation of methanol in acetonitrile. A particular attention has been directed to determine the most important chemical and photophysical kinetic parameters of this peculiar reaction. Under continuous photolysis, kinetics of both oxygen consumption and hydrogen peroxide formation has been followed in a closed system. The reaction was stopped when a conversion of less than 10% in oxygen-saturated solutions was reached. Our work enlightens the following findings: (i) as expected on the basis of a hydrogen-atom-abstraction mechanism and relative CH bond dissociation energy, the reaction constant rate of reactive species wO with methanol is the weakest of all alcohols already studied, (ii) the methanol decatungstate photocatalyzed oxygenation in acetonitrile satisfies the photostationary state conditions only up to [CH₃OH] ∼ 2.5 M, (iii) the role of peroxyl radical is crucial since it not only leads to the resulting products, but it also oxidizes the reduced form of decatungstate H⁺W₁₀O₃₂⁵⁻ to regenerate the catalyst, thus closing the catalytic cycle, and (iv) progressive establishment of anaerobic conditions results in both ending of the substrate conversion and the decay of hydrogen peroxide. Hence, these findings offer new insights into the nature of the rate-determining step in the photocatalytic cycle.     

Comparative study of CO2 hydrogenation to methanol on cubic bixbyite-type and rhombohedral corundum-type indium oxide

Hydrogenation of CO₂ to value-added chemicals has attracted much attention all through the world. In₂O₃ with cubic bixbyite-type (denoted as c-In₂O₃) is well known for its high CO₂ hydrogenation activity and CH₃OH selectivity at high temperature. However, the other structure of In₂O₃ with rhombohedral corundum-type (denoted as rh-In₂O₃) rarely been investigated as catalyst. Herein, c-In₂O₃ and rh-In₂O₃ were prepared and comparatively studied for CO₂ hydrogenation. The results indicated that c-In₂O₃ showed higher CO₂ conversion activity than rh-In₂O₃ due to the impressive reducibility and reactivity. Whereas rh-In₂O₃ had higher CH₃OH selectivity due to weaker CH₃OH and stronger CO adsorption on rh-In₂O₃. Although c-In₂O₃ and rh-In₂O₃ catalysts showed different CO₂ hydrogenation performance, in-situ diffuse reflectance infrared Fourier transform spectroscopy showed CO₂ can be reduced to CO through redox cycling and hydrogenation to CH₃OH through formate path.