Studies on monitoring the composition of the copolymer by cyclic voltammetry and in situ spectroelectrochemical analysis

Electrochemical copolymerization of diphenylamine (DPA) with ortho-toluidine (OT) was carried out in 4 M sulphuric acid medium by cyclic voltammetry. Cyclic voltammograms (CVs) of the copolymer films were recorded to deduce the electrochemical characteristics. In situ UV-visible spectroelectrochemical studies on copolymerization were carried out using indium tin oxide (ITO) coated glass plate as working electrode for different feed ratios of DPA and OT. UV-visible spectral characteristics show clear dependencies on the molar feed composition of DPA or OT used in electropolymerization. Derivative cyclic voltabsorptogram (DCVA) was deduced at the wavelength corresponding to the absorption by the intermediate species and used to identify the intermediates generated during the electropolymerization. The molar composition of DPA and OT units in the copolymer for the copolymers synthesized with different molar feed ratios of DPA and OT was determined by UV-visible spectroscopy. Reactivity ratios of DPA and OT were deduced by using Fineman-Ross and Kelen-Tudos methods and the observed differences in the composition of DPA/OT in the copolymers were correlated with CV characteristics and results obtained from in situ spectroelectrochemical studies.     

The role of intrachain and interchain interactions of regioregular poly(3-octylthiophene) chains on the optical properties of a new amphiphilic conjugated random copolymer in solution

The synthesis of a random copolymer through free radical copolymerization of a properly vinyl monofunctionalized regioregular poly(3-octylthiophene) (rrP3OT) macromonomer and N,N'-dimethylacrylamide (DMAM) is presented. The optical properties of the copolymer in water and in several organic solvents of varying polarity, as well as in THF/water and THF/methanol mixtures, were explored using UV-vis and photoluminescence spectroscopy. It is demonstrated that the rrP3OT chains adopt a coil conformation in solvents such as tetrahydrofuran (THF) and chloroform with the appearance of the absorption and emission maxima at 439 and 565 nm, respectively. On the contrary, the rrP3OT chains are organized on a single chain packing form (intrachain interactions) in polar solvents such as ethanol and methanol, as it is verified with the observation of the characteristic three vibronic features of the absorption spectra of the copolymer with maxima at 513, 550, and 603 nm and emission maxima at 560 nm. However, when water is used as solvent, the rrP3OT chains self-assemble into a stacklike structure due to the increased interchain interactions, as confirmed by the different aggregation process of the rrP3OT chains in the THF/water mixture, the broader absorption spectrum in water compared to those recorded in ethanol and methanol, and the 80 nm red-shifted emission maximum, centered at 640 nm.     

In situ UV-visible spectroelectrochemical evidences for conducting copolymer formation between diphenylamine and m-methoxyaniline

Electrochemical copolymerization of diphenylamine (DPA) with m-methoxy aniline (MA) was carried out in 4 M H(2)SO(4) by cyclic voltammetry (CV). Cyclic voltammograms (CVs) of the copolymer films were recorded in monomer-free background electrolyte. In situ sepectroelectrochemical studies were carried out on an optically transparent electrode (Indium tin oxide (ITO) coated glass) in 4 M H(2)SO(4) for different feed ratios of the comonomers. Constant potential and potential sweep methods were employed for performing polymerization. UV-visible absorption spectra were collected continuously and concurrently during the copolymerization in both the cases. The results from constant potential electropolymerisation indicated the formation of an intermediate with an absorption peak at 576 nm. Derivative cyclic voltabsorptogram (DCVA) was deduced from the results of cyclic spectrovoltammetry. The DCVA derived at 576 nm confirms the intermediates formed during the electrochemical copolymerization. The compositional changes of the two monomers in the copolymers with changes in feed composition of two monomers as predicted from in situ spectro electrochemical studies are evident from elemental analysis. A plausible copolymerization mechanism is suggested.     

In situ UV-visible spectroelectrochemical studies on the copolymerization of diphenylamine with ortho-methoxy aniline

UV-visible spectroelectrochemical studies on copolymerization of diphenylamine (DPA) with ortho-methoxy aniline (OMA) were carried out for different feed ratios of DPA and OMA using indium tin oxide (ITO)-coated glass as working electrode. The UV-visible spectra show clear dependencies on the molar feed composition of DPA or OMA used in electropolymerization. Derivative cyclic voltabsorptogram (DCVA) was deduced at the wavelengths corresponding to the absorption by the intermediate species and used to confirm the intermediates generated during the electropolymerization. The composition of DPA and OMA in the copolymer for the copolymers synthesized with different molar feed ratios of DPA and OMA was determined by UV-visible spectroscopy. Reactivity ratios of DPA and OMA were deduced by using Fineman-Ross and Kelen-Tudos methods and correlated with spectroelectrochemical results.     

苯胺与邻甲氧基苯胺共聚的原位紫外-可见光谱电化学研究

运用循环伏安法(CV)和原位紫外-可见光谱电化学法研究了苯胺(AN)和邻甲氧基苯胺(OMA)单独聚合及二者共聚的电化学过程。在1.0 mol/L HCl溶液中,AN和OMA单独聚合及二者共聚时不同的电化学行为表明AN和OMA之间产生了共聚作用。原位紫外-可见光谱的研究表明,在AN与OMA的共聚过程中,AN和OMA首先分别被氧化生成其阳离子自由基,然后,AN和OMA的阳离子自由基与溶液中的AN和OMA单体发生交互反应产生混合二聚物中间体,在紫外-可见吸收光谱中对应于440 nm处的吸收峰。进一步研究发现,AN和OMA的共聚过程与溶液中各单体的浓度比有关,当混合溶液中OMA的浓度较大时,会对共聚产生抑制作用。采用红外光谱技术对共聚物进行了表征并初步探讨了共聚机制。结果表明,在AN和OMA共聚过程中,OMA分子掺杂进入AN聚合物骨架。     

Poly(diphenylamine-4-sulfonic acid) modified glassy carbon electrode for voltammetric determination of gallic acid in honey and peanut samples

In this study, a sensitive and selective voltammetric method based on poly(diphenylamine-4-sulfonic acid) modified glassy carbon electrode (poly(DPASA)/GCE) was developed for determination of gallic acid. Appearance of an irreversible oxidative peak at both bare GCE and poly(DPASA)/GCE for gallic acid with about three folds current enhancement and much reduced potential at poly(DPASA)/GCE showed catalytic property of the modifier towards oxidation of gallic acid. Under optimized conditions, Adsorptive stripping square wave voltammetric peak current response of the poly(DPASA)/GCE showed linear dependence with gallic acid concentration in the range 5.00 × 10^?7–3.00 × 10^?4 mol L^?1 with limit of detection of 4.35 × 10^?9. Spike recovery results between 94.62 and 99.63, 95.00–99.80 and 97.25–103.20% of gallic acid in honey, raw peanut, and commercial peanut butter samples respectively, interference recovery results with less than 4.11% error in the presence of uric acid and ascorbic acid, lower LOD and relatively wider dynamic range than most of the previously reported methods validated the potential applicability of the method based on poly(DPASA)/GCE for determination of gallic acid real samples including in honey and peanut samples.     

氯金酸-罗丹明S缔合纳米微粒体系的共振散射增强与荧光猝灭研究

在0．2mol/L HCl介质中，罗丹明S(RDS)分别在520nm和550nm处有一个吸收峰和荧光峰。当有Au(Ⅲ）存在时，Au（Ⅲ）与Cl^-形成AuCl4^-，AuCl^-与RDS^ 借助于静电引力形成疏水性的AuCl4-RDS缔合物分子。AuCl4-RDS分子间存在较强的分子间作用力和疏水作用力而生成(AuCl4-RDS)。缔合纳米微粒，粒径为45nm。在360nm产生瑞利散射峰，在600nm产生共振散射峰。由于纳米微粒形成后，只有裹露在(AuCl4-RDS)n纳米微粒界面的RDS荧光分子才能吸收激发光子跃迁到激发态，进而返回基态产生荧光。而体相的RDS荧光分子无法与激发光作用产生荧光，即受激RDS分子数大为降低，故550nm荧光峰和520nm吸收峰的降低。当缔合纳米微粒体系加入乙醇后，体系的红紫色和共振散射峰消失，吸收峰和荧光峰恢复，由于乙醇致使(AuCl4-RDS)。纳米微粒分解为AuCl4-RDS分子。结果表明：红紫色(AuCl4-RDS)n纳米粒子的形成是其共振散射增强、荧光猝灭和产生共振散射峰的根本原因。     

Electrochemistry of microparticles of tris (2,2′-bipyridine) ruthenium(II) hexafluorophosphate

The electrochemical behaviour of tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate (Ru(II)) microparticles, immobilised on a graphite electrode and adjacent to an aqueous electrolyte solution, has been studied by cyclic voltammetry and an in situ spectroelectrochemical technique. The solid Ru(II) complex exhibits one reversible redox couple with a formal potential (E_f) of 1.1 V versus Ag¦AgCl. The continuous cyclic voltammetric experiments showed that the Ru(II) microparticles are stable during the electrochemical conversions. The in situ spectroelectrochemical study showed that the absorbance at 463 nm decreased due to the oxidation of Ru(II) to Ru(III). Upon reduction, the growth of absorbance at 463 nm was observed due to the formation of Ru(II) complex and this process was reversible.     

NANOSECOND LASER PHOTOLYSIS OF RHODOPSIN AND ISORHODOPSIN

Kinetic and spectral measurements have been carried out on the primary intermediate in the photolysis of rhodopsin and isorhodopsin, initiated by a 457 nm, 6 ns (FWHM) laser pulse. In rhodopsin the kinetic decay of bathorhodopsin was found to be 140 ± 15 ns at 20°C. The decay of bathorhodopsin to lumirhodopsin has an activation energy of 51 ± 4 kJ/mol (12.2 ± 1 kcal/mol). The decay kinetics of bathorhodopsin were found to be the same for rhodopsin in membrane and detergent solubilized suspensions. The kinetic decay of the batho product in the photolysis of isorhodopsin was found to be the same as rhodopsin.
The corrected transient spectrum 50 ns following excitation in rhodopsin has two peaks near 560 and 440 nm. A peak was also observed in isorhodopsin near 550 nm at 50 ns following excitation but no transient was observed in the blue. The 550 nm peak in isorhodopsin has an intensity similar to that in rhodopsin indicating that the quantum yields for the formation of batho products of rhodopsin and isorhodopsin are similar under the irradiation conditions used here. Transient spectra for rhodopsin and isorhodopsin 1 μs following excitation are also different. In isorhodopsin the corrected transient spectrum has a peak at 500 nm, similar to low temperature steady state irradiation spectra. The 1 μs transient spectrum in rhodopsin is more intense than in isorhodopsin and shows a peak at 475 nm.     

Room temperature synthesis of hollow CdMoO(4) microspheres by a surfactant-free aqueous solution route

Hollow cadmium molybdate microspheres have been successfully prepared via a template-free aqueous solution method with the assistance of NaCl at room temperature. The structure and morphology of the CdMoO(4) hollow microspheres were characterized by X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The microspheres have diameters of 3-6 microm and hollow interiors of 2-3 microm. The shell is composed of numerous single-crystalline nanorods with diameters of 30-120 nm and lengths of 1-2 microm which are radially oriented to the center. A certain concentration of NaCl plays a key important role in the formation process of hollow microspheres, which might provide a suitable chemical environment to favor the formation of hollow CdMoO(4) microspheres. A possible NaCl-induced Ostwald ripening process is proposed for the formation of hollow CdMoO(4) microspheres on the basis of scanning electron microscopy observation of intermediate products at different precipitation stages.     

Spectroelectrochemical responsiveness of a freestanding, boron-doped diamond, optically transparent electrode toward ferrocene

The spectroelectrochemical responsiveness of an optically transparent diamond electrode (OTE) toward ferrocene was investigated. A freestanding, mechanically polished, boron-doped diamond disk (0.38 mm thick and 8 mm in diameter) served as the OTE for UV-Vis transmission spectroelectrochemical measurements. A specially designed, thin-layer spectroelectrochemical cell was constructed for the measurements in which ferrocene was electrooxidized to ferricinium ion via a one-electron redox reaction. The oxidation reaction product was spectroscopically monitored in the ultraviolet (λ=252, 285 nm) region of the electromagnetic spectrum. Well-defined and highly stable spectroelectrochemical responses were observed for this type of diamond OTE. The results indicate that diamond is a useful OTE material for spectroelectrochemically studying nonaqueous redox reactions.     

Kinetic model for supercritical water gasification of algae

The article reports the first quantitative kinetics model for supercritical water gasification (SCWG) of real biomass (algae) that describes the formation of the individual gaseous products. The phenomenological model is based on a set of reaction pathways that includes two types of compounds being intermediate between the algal biomass and the final gaseous products. To best correlate the experimental gas yields obtained at 450, 500 and 550 °C, the model allowed one type of intermediate to react to gases more quickly than the other type of intermediate. The model parameters indicate that gas yields increase with temperature because higher temperatures favor production of the more easily gasified intermediate and the production of gas at the expense of char. The model can accurately predict the qualitative influence of the biomass loading and water density on the gas yields. Sensitivity analysis and reaction rate analysis indicate that steam reforming of intermediates is an important source of H(2), whereas direct decomposition of the intermediate species is the main source of CO, CO(2) and CH(4).     

聚次甲基蓝膜的生长及性质

在铂电极和金电极上,次甲基蓝在低电位 0～－ 0.5 V范围内的氧化还原已有报导,它在 － 0.2 V处有可逆的氧化还原峰 [1,2].近来,已将次甲基蓝的氧化升高至 1.2 V（ vs Ag/AgCl参比电极）, 在玻炭电极上形成一层聚合物膜 [3],这种聚合物可被用来固定葡萄糖氧化酶制成葡萄糖生物传感器 [3].在扫描电位为－ 0.6～ 1.0 V（ vs SCE）范围内, 聚次甲基蓝膜的生长已通过电化学石英晶体微天平技术得到了证实,同时证实了,在氧化还原过程中阴离子能够在聚次甲基蓝膜中掺杂和去掺杂 [4].聚次甲基蓝在 pH为 2.0至 8.0范围内具有很好的电化学…     

Mechanisms of silk fibroin sol-gel transitions

Silk fibroin sol-gel transitions were studied by monitoring the process under various physicochemical conditions with optical spectroscopy at 550 nm. The secondary structural change of the fibroin from a disordered state in solution to a beta-sheet-rich conformation in the gel state was assessed by FTIR and CD over a range of fibroin concentrations, temperatures, and pH values. The structural changes were correlated to the degree of gelation based on changes in optical density at 550 nm. No detectable changes in the protein secondary structure (FTIR, CD) were found up to about 15% gelation (at 550 nm), indicating that these early stages of gelation are not accompanied by the formation of beta-sheets. Above 15%, the fraction of beta-sheet linearly increased with the degree of gelation. A pH dependency of gelation time was found with correlation to the predominant acidic side chains in the silk. Electrostatic interactions were related to the rate of gelation above neutral pH. The overall independencies of processing parameters including concentration, temperature, and pH on gel formation and protein structure can be related to primary sequence-specific features in the molecular organization of the fibroin protein. These findings clarify aspects of the self-assembly of this unique family of proteins as a route to gain control of material properties, as well as for new insight into the design of synthetic silk-biomimetic polymers with predictable solution and assembly properties.     

Photoreactions of aromatic compounds—XXIX : Pathway and intermediates of the photoreactions of 3,5-dinitroanisole with nucleophiles

The photoreactions of 3,5-dinitroanisole with nucleophiles (mostly hydroxide ion) have been studied by sensitization and quenching as well as by flash photolysis experiments. The photosubstitution starts mainly from the π-π* triplet excited state (λ_max ～ 475 nm; τ 5·10^?8s or shorter depending on the concentration of nucleophile). The formation of substitution product is completed within ～ 10^?6s. The occurrence of the radical anion (λ_max ～ 550 nm; τ ～ 10^?2-10^?4s depending on the nature of the nucleophile) could be established. This cannot be intermediate in the photosubstitution reaction but is so in the formation of reduction products. The radical anion and, probably also, the substitution product seem to originate from a complex (λ_max ～ 410 nm; τ ～ 5·10^?7s) between the triplet excited aromatic compound and its nucleophilic reaction partner. The formation of this complex is a very fast process.     

Copolymer Formation Between Two N‐Substituted Anilines—Electrochemical and Spectroelectrochemical Studies

Abstract

Electrochemical polymerization of diphenylamine, DPA with N‐methyl aniline, NMA was performed using cyclic voltammetry in a 4?M sulfuric acid medium. The electrochemical parameters representing the polymer deposition showed a strong dependence on the molar concentration ratios of DPA or NMA in the feed. In situ spectroelectrochemical studies were performed during the electropolymerization with different molar concentration feed ratios of DPA. The results reveal the formation of intermediates together with DPA and NMA units. Derivative cyclic voltabsorptograms (DCVAs) were deduced at the wavelength of absorbance corresponding to the intermediates and explained with redox characteristics in cyclic voltammogram. Results from cyclic voltammetry and spectroelectrochemical studies favor copolymer formation between DPA and NMA. Copolymers were prepared for different molar concentrations feed ratios of DPA and the composition of the monomer units in the copolymers were determined. Reactivity ratios of DPA and NMA were deduced using Fineman–Ross and Kelen–Tudos methods and correlated with the results from cyclic voltammetry and spectroelectrochemical studies.     

An in‐situ Mössbauer Study of the Formation of Cementite,Fe3C

The formation of cementite, Fe₃C, from thin iron foils has been studied at 550 and 650 °C by means of in‐situ Mössbauer spectroscopy. At 550 °C, the kinetics of the reaction have been determined from time‐resolved experiments performed at different carbon activities. The product formation follows a two‐step process exhibiting two different kinetic regimes. The slow initial stages of the reaction as well as its rapid final part can be described by an Avrami‐type kinetics with a characteristic parameter of n = 3/2.     

Ratiometric Fluorescent Nanosensors for Copper(II) Based on Bis(rhodamine)‐Derived PMOs with J‐Type Aggregates

By using pentyl‐linked bis(rhodamine)‐derived tetra‐siloxane (PRh‐Si₄) as the organosilica precursor, highly ordered PRh‐bridged periodic mesoporous organosilicas (PRhPMOs) were prepared. When excited at λ=500 nm, the PRhPMO suspension that contained metal ions showed two separate emission peaks at λ=550 and 623 nm. The first peak, located at λ=550 nm, was due to ring‐opening of the spiro structure in the rhodamine moiety and the second, located at λ=623 nm, originated from fluorescent aggregates of the PRh units embedded in the silica framework of the PRhPMO. By using the different intensity ratios of the two fluorescence signals (FI_550/623), PRhPMOs could be used as turn‐ON type fluorescent ratiometric chemosensors for Cu²⁺. Furthermore, based on the single‐exciton theory, it was deduced that the fluorescent aggregates formed were of the J‐type and had a coplanar configuration. Consequently, PRhPMOs display a longer fluorescence lifetime and greater fluorescent quantum yield than the respective monomers dissolved in solution, which is consistent with the experimental results.     

Mechanisms of pH-dependent activity for water oxidation to molecular oxygen by MnO2 electrocatalysts

Manganese oxides function as efficient electrocatalysts for water oxidation to molecular oxygen in strongly alkaline conditions, but are inefficient at neutral pH. To provide new insight into the mechanism underlying the pH-dependent activity of the electrooxidation reaction, we performed UV-vis spectroelectrochemical detection of the intermediate species for water oxidation by a manganese oxide electrode. Layered manganese oxide nanoparticles, δ-MnO(2) (K(0.17)[Mn(4+)(0.90)Mn(3+)(0.07)□(0.03)]O(2)·0.53H(2)O) deposited on fluorine-doped tin oxide electrodes were shown to catalyze water oxidation at pH from 4 to 13. At this pH range, a sharp rise in absorption at 510 nm was observed with a concomitant increase of anodic current for O(2) evolution. Using pyrophosphate as a probe molecule, the 510 nm absorption was attributable to Mn(3+) on the surface of δ-MnO(2). The onset potential of the water oxidation current was constant at approximately 1.5 V vs SHE from pH 4 to pH 8, but sharply shifted to negative at pH > 8. Strikingly, this behavior was well reproduced by the pH dependence of the onset of 510 nm absorption, indicating that Mn(3+) acts as the precursor of water oxidation. Mn(3+) is unstable at pH < 9 due to the disproportionation reaction resulting in the formation of Mn(2+) and Mn(4+), whereas it is effectively stabilized by the comproportionation of Mn(2+) and Mn(4+) in alkaline conditions. Thus, the low activity of manganese oxides for water oxidation under neutral conditions is most likely due to the inherent instability of Mn(3+), whose accumulation at the surface of catalysts requires the electrochemical oxidation of Mn(2+) at a potential of approximately 1.4 V. This new model suggests that the control of the disproportionation and comproportionation efficiencies of Mn(3+) is essential for the development of Mn catalysts that afford water oxidation with a small overpotential at neutral pH.     

Probing the reaction mechanism of the D-ala-D-ala dipeptidase, VanX, by using stopped-flow kinetic and rapid-freeze quench EPR studies on the Co(II)-substituted enzyme

In an effort to probe the reaction mechanism of VanX, the d-ala-d-ala dipeptidase required for high-level vancomycin resistance in bacteria, stopped-flow kinetic and rapid-freeze quench EPR studies were conducted on the Co(II)-substituted enzyme when reacted with d-ala-d-ala. The intensity of the Co(II) ligand field band at 550 nm decreased (epsilon550 = 140 to 18 M-1 cm-1) when VanX was reacted with substrate, suggesting that the coordination number of the metal increases from 5 to 6 upon substrate binding. The stopped-flow trace was fitted to a kinetic mechanism that suggests the presence of an intermediate whose breakdown is rate-limiting. Rapid-freeze quench EPR studies verified the presence of a reaction intermediate that exhibits an unusually low hyperfine constant (33 G), which suggests a bidentate coordination of the intermediate to the metal center. The EPR studies also identified a distinct enzyme product complex. The results were used to offer a detailed reaction mechanism for VanX that can be used to guide future inhibitor design efforts.