Chemical oxidative polymerization of dianilinium 5-sulfosalicylate

Dianilinium 5-sulfosalicylate was prepared in situ and then oxidized in aqueous solution with ammonium peroxydisulfate. The precipitated polyaniline 5-sulfosalicylate was soluble in polar aprotic solvents and showed conductivity of ∼0.1 S cm⁻¹. Scanning electron microscopy revealed the coexistence of nanorods and granular morphology of the polyaniline 5-sulfosalicylate. The weight-average molecular weight and poly-dispersity index were determined by gel-permeation chromatography as 53000 and 9.0, respectively. FTIR spectroscopic analysis combined with AM1 and MNDO-PM3 semi-empirical quantum chemical studies of the polymerization mechanism indicate both covalent and ionic bonding of sulfosalicylate to polyaniline chains. Raman spectroscopy proved the presence of substituted phenazine structural units besides ordinary emeraldine segments. The text was submitted by the authors in English.     

Polyaniline-coated cellulose fibers decorated with silver nanoparticles

Cellulose fibers of 20 μm in diameter and aspect ratio of 2 or 10 were coated with protonated polyaniline (PANI) during the oxidation of aniline hydrochloride with ammonium peroxydisulfate in an aqueous medium. The presence of PANI has been proved by FTIR spectroscopy. The conductivity increased from 4.0 × 10⁻¹⁴ S cm⁻¹ to 0.41 S cm⁻¹ after coating the fibers with PANI. The percolation threshold in the mixture of original uncoated and PANI-coated fibers was reduced from 10 mass % PANI to 6 mass % PANI, as the aspect ratio changed from 2 to 10. The subsequent reaction with silver nitrate results in the decoration of PANI-coated cellulose fibers with silver nanoparticles of about 50 nm average size. The content of silver of up to 10.6 mass % was determined as a residue in thermogravimetric analysis. FTIR spectra suggest that the protonated emeraldine coating changed to the pernigraniline form during the latter process and, consequently, the conductivity of the composite was reduced to 4.1 × 10⁻⁴ S cm⁻¹, despite the presence of silver.     

Effect of chain aggregation on the conductivity and ESR spectra of polyaniline

Solutions of polyaniline in m-cresol with and without camphorsulfonic acid (CSA), as well as films cast from these solutions were studied by ESR spectroscopy at 133–423 K and by optical spectroscopy in the range λ = 350–1100 nm. An analysis of the optical and ESR spectra shows that in the solutions and films without CSA polyaniline is fully doped but the conductivity of these films is low (∼10⁻⁸ S cm⁻¹; cf. 100 S cm⁻¹ for the films with CSA). Compared with the CSA-containing samples, the samples without CSA are characterized by broader ESR lines and higher contribution of the Curie spins to the magnetic susceptibility. These facts indicate a weak aggregation of polyaniline chains without CSA, which leads to low conductivity. A formula was proposed, which describes the temperature dependence of the polyaniline ESR linewidth and allows the interchain distance and the mobility of electrons moving along polymer chains to be determined. The conductivity of polyaniline films is affected by moderate heating (363–388 K) of the films and solutions from which the films were cast. It was found that the interchain distances correlate with the conductivity of the films and with the broadening of their ESR lines caused by the effect of O₂. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2701–2711, December, 2005.     

Anilinium 5-sulfosalicylate electropolymerization on mild steel from an aqueous solution of sodium 5-sulfosalicylate/disodium 5-sulfosalicylate

Aniline is electropolymerized on bare and chemically pretreated mild steel from an aqueous solution of 0.10 M anilinium 5-sulfosalicylate in 0.20 M sodium 5-sulfosalicylate/0.20 M disodium 5-sulfosalicylate buffer as the supporting electrolyte, at room temperature. At constant anodic potential black poly(anilinium 5-sulfosalicylate) (PANISSA) films are obtained on bare mild steel and characterized by IR spectroscopy, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). IR spectroscopic analysis confirms typical polyaniline structure with 1,4-disubstituted aromatic nuclei and incorporation of sulfosalicylate anions as dopants. Adhesion of PANISSA films is significantly improved when the mild steel electrode surface is chemically pretreated by 0.10 M ammonium peroxydisulfate aqueous solution. The IR spectra of the films obtained on chemically pretreated mild steel surface indicate an interaction between PANISSA and products of the mild steel oxidation by peroxydisulfate. The SEM images show differences in morphology between PANISSA films synthesized on bare and chemically pretreated mild steel surface. The efficient anticorrosion behavior of adherent PANISSA film on chemically pretreated mild steel is proved by EIS. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 12, pp. 1497–1504. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes.” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Composite films of polyaniline and molybdenum oxide formed by electrocodeposition in aqueous media

Composite films of polyaniline (PANI) and molybdenum oxide (MoO_x) were afforded through a convenient route of electrocodeposition from aniline and (NH₄)₆Mo₇O₂₄. The composite films showed characteristic redox behaviors of PANI and MoO_x, respectively, on the cyclic voltammograms. Chlorate and bromate were catalytically electroreduced with an enlarged current on the composite film at a potential ca. 0.2 V more positive than that on MoO_x. The potential window for the composite film to display pseudocapacitive properties in 1.0 mol·dm⁻³ NaNO₃ was −0.6 ∼ 0.6 V vs SCE. The cathodic potential limit shifted at least 0.4 V negatively from that of polyaniline (PANI)-based materials reported so far. The specific capacitance was 363.6 F·g⁻¹ when the composite film was charged–discharged at 1.5 mA·cm⁻², about two times of that of the similarly prepared PANI. The composite film was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Molybdenum existed in a mixed state of +5 and +6 in the composite film based on XRD and XPS investigations. Figure PANI and (MoO_x) were electrocodeposited in aqueous solutions from aniline and (NH₄)₆Mo₇O₂₄. The composite film obtained displayed catalytic activities toward the electroreduction of oxoanions. The pseudocapacitance of the composite film is nearly two times of that of PANI with the potential window extended negatively up to −0.6 V vs SCE     

Determination of iprodione in agrochemicals by infrared and Raman spectrometry

Two methodologies based on vibrational spectrometry—making use of Fourier transform infrared absorption (FTIR) and Raman spectrometry—were developed for iprodione determination in solid pesticide formulations. The FTIR procedure involved the extraction of iprodione by CHCl₃, and the latter determination involved measuring the peak area between 1450 and 1440 cm⁻¹, corrected using a horizontal baseline defined at 1481 cm⁻¹. FT-Raman determination was performed directly on the powdered solid products, using standard chromatography glass vials as sample cells and measuring the Raman intensity between 1003 and 993 cm⁻¹, with a two-point baseline correction established between 1012 and 981 cm⁻¹. The sensitivities obtained were 0.319 area values g mg⁻¹ for FTIR determination and 5.58 area values g g⁻¹ for FT-Raman. The repeatabilities, taken to be the relative standard deviation of five independent measurements at 1.51 mg g⁻¹ and 10.98% w/w concentration levels, were equal to 0.16% and 0.9% for FTIR and FT-Raman, respectively, and the limits of detection were 0.3 and 0.2% w/w (higher than those obtained for HPLC, 0.016% w/w). FTIR determination provided a sample frequency of 60 h⁻¹, higher than those obtained for the Raman and reference chromatography methods (25 and 8.6 h⁻¹, respectively). On the other hand, the new FT-Raman method eliminates reagent consumption and waste generation, and reduces the need for sample handling and the contact of operator with the pesticide. In spite of their lack of sensitivity, vibrational procedures can therefore provide viable environmentally friendly alternatives to laborious, time- and solvent-consuming reference chromatography methods for quality control in commercially available pesticide formulations.     

Bioelectrochemical response of a choline biosensor fabricated by using polyaniline

On the basis of the isoelectric point of an enzyme and the doping principle of conducting polymers, choline oxidase was doped in a polyaniline film to form a biosensor. The amperometric detection of choline is based on the oxidation of the H₂O₂ enzymatically produced on the choline biosensor. The response current of the biosensor as a function of temperature was determined from 3 to 40°C. An apparent activation energy of 22.8 kJ·mol⁻¹ was obtained. The biosensor had a wide linear response range from 5 × 10⁻⁷ to 1 × 10⁻⁴ M choline with a correlation coefficient of 0.9999 and a detection limit of 0.2 μM, and had a high sensitivity of 61.9 mA·M⁻¹·cm⁻² at 0.50 V and at pH 8.0. The apparent Michaelis constant and the optimum pH for the immobilized enzyme are 1.4 mM choline and 8.4, respectively, which are very close to those of choline oxidase in solution. The effect of selected organic compounds on the response of the choline biosensor was studied.     

Reduction of silver nitrate by polyaniline nanotubes to produce silver-polyaniline composites

Polyaniline (PANI) nanotubes were prepared by oxidation of aniline in 0.4 M acetic acid. They were subsequently used as a reductant of silver nitrate in 1 M nitric acid, water or 1 M ammonium hydroxide at various molar ratios of silver nitrate to PANI. The resulting PANI-silver composites contained silver nanoparticles of 40–60 nm size along with macroscopic silver flakes. Under these experimental conditions, silver was always produced outside the PANI nanotubes. Changes in the molecular structure of PANI were analyzed by FTIR spectroscopy. Silver content in the composites was determined as a residue by thermogravimetric analysis, and confirmed by density measurements. The highest conductivity of a composite, 68.5 S cm⁻¹, was obtained at the nitrate to PANI molar ratio of 0.67 in water. Also, the best reaction yield was obtained in water. Reductions performed in an acidic medium gave products with conductivity of 10⁻⁴–10⁻² S cm⁻¹, whereas the reaction in alkaline solution yielded non-conducting products.     

Synthesis and characterization of inclusion complexes of aliphatic-aromatic poly(Schiff base)s with β-cyclodextrin (highlight)

This paper describes the formation of polymer inclusion complexes(polymer-CD-ICs) between β-cyclodextrin(β-CD) and aliphatic-aromatic poly(Schiff base)s. Fourier transform infrared(FTIR) spectroscopy, ¹H nuclear magnetic resonance spectroscopy(¹H-NMR), thermogravimetric analysis(TGA) and X-ray diffraction(XRD) have been used to observe the formation of polymer-CD-ICs. In FTIR spectra, the characteristic peaks of β-CD at 3391 cm⁻¹ shifted to 3418 cm⁻¹ and the intense peak at 1602 cm⁻¹ due to the –C = N– stretching vibration diminished after formation of inclusion complexes. Compared the ¹H-NMR of polymer-CD-ICs with β-CD, the chemical shift of the protons H-3, H-5 have shifted to higher field after the formation of inclusion complexes, which is perhaps due to the interaction of these protons with polymers. The TGA analysis revealed that the polymer-CD-ICs had better thermal stability than β-CD, suggesting that the polymer increased the stability of β-CD. The X-ray diffraction patterns displayed that the strong peak for both polymer-CD-ICs at approximately 20.0° (2θ) may confirm their IC formation.     

A kinetic analysis of thermal decomposition of polyaniline/ZrO<Subscript>2</Subscript> composite

Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO₂ composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO₂ composite and PANI are all D₃, and the corresponding function is ƒ(α)=1.5(1−α)^2/3[1−(1-α)^1/3]−1. The correlated kinetic parameters are E _a=112.7±9.2 kJ mol⁻¹, lnA=13.9 and E _a=81.8±5.6 kJ mol⁻¹, lnA=8.8 for PANI/ZrO₂ composite and PANI, respectively.     

Potassium ion-selective polyaniline solid-contact electrodes based on 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether ionophore

New ion-selective electrodes for potassium were developed and tested employing 18-crown-6-ether, dibenzo-18-crown-6-ether, and 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether ionophores in PVC membranes with a polyaniline solid contact between the membranes and the Pt substrate. We compared the response characteristics of the solid-contact electrodes (SCEs) based on these ionophores and various plasticizers. Among the three ionophores, 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether-based SCE produced the best results exhibiting a high reproducibility with negligible drifts in the standard potential with a response slope (RS) of 58.2 mV/decade: the detection limit (DL) of the potassium ion was 10^−5.80 M with linearity over five decades. This is a significant improvement for the response slope and detection limit compared to SCEs with valinomycin, 2,3-naphtho-15-crown-ether, and dibenzo-15-crown-5-ether ionophore, which showed 53–56 mV/decade of RS and 10^−5.3 M of DL. The response slope, detection limit, and selectivity were compared with other K⁺ ISEs reported until present. Finally, the new SCE was applied to determine potassium ions in artificial human serum with satisfactory results. However, the detection limit for the artificial serum was slightly diminished yielding a value of 10^−5.19 M (6.5 × 10⁻³ mM) which is still good. Electrodes with polypyrrole in place of polyaniline exhibited comparable results. The text was submitted by the authors in English.     

Spectroscopic Study of SiO2-TiO2 Sols Prepared Using Stabilizing Agents

Two chemical routes were employed to prepare Si−Ti polymers, using acetylacetone (acacH) and acetic acid (HOAc) as modifying agents. The homogeneous and transparent sols were studied at different aging times. The characterization techniques were²⁹Si NMR, FTIR, UV-Vis and TGA. When HOAc was used, the oligomeric species in the first stages of polymerization were assigned by²⁹ Si NMR. The Ti−O−Si bond vibration was detected by FTIR in the 950–960 cm⁻¹ region. UV-Vis spectroscopy showed bands of acac bonded to Ti at 300 nm and 365 nm, and OAc⁻ bonded to Ti was found at 320 nm. The TGA study allowed the establishment of the xerogel formulas.     

Electrochemical and in situ Raman spectroscopic study on the stability of poly(<Emphasis Type="Italic">N</Emphasis>-methylaniline)

The stability of poly(N-methylaniline) (PNMA) as electrode material has been studied in aqueous solutions of sulfuric acid with the use of electrochemical and in situ Raman spectroscopic techniques. It has been shown that the electrochemical decomposition of electrodeposited PNMA films follows a first-order reaction kinetics. The decomposition rate constants vary between 1.2 × 10⁻⁵ and 2.0 × 10⁻³ s⁻¹ for electrode potential varying between 0.2 and 1.0 V vs Ag/AgCl, respectively. In situ Raman spectroscopy has been applied in obtaining kinetic data at selected electrode potentials, and good correlation of these data with the corresponding data obtained by cyclic voltammetry has been found. As compared to polyaniline, the decomposition of PNMA proceeds at nearly the same rate at electrode potentials not exceeding 0.5 V. The decomposition of PNMA proceeds faster within the potential limits of 0.5 to 0.8 V and slower at electrode potentials exceeding 0.8 V as compared to polyaniline. This article is dedicated to Professor Algirdas Vaškelis (Institute of Chemistry, Vilnius, Lithuania) on the occasion of his 70th birthday and in honour of his contributions to electrochemistry and physical chemistry.     

Influence of coagulation temperature on pore size and properties of cellulose membranes prepared from NaOH–urea aqueous solution

The morphology and structure of the regenerated cellulose membranes prepared from its NaOH–urea aqueous solution by coagulating with 5 wt% H₂SO₄–10 wt% Na₂SO₄ aqueous solution with different temperatures and times were investigated. The pore size, water permeability and physical properties of the membranes were measured with scanning electron micrograph (SEM), wide X-ray diffraction (WXRD), Fourier transfer infrared spectroscopy (FTIR), flow rate method, and tensile testing. The SEM observation revealed that the structure and pore size of the membranes changed drastically as a function of the coagulation temperature. The membranes coagulated at lower temperatures tended to form the relatively small pore size than those at higher temperatures. On the contrary, the membranes coagulated at different times exhibited similar pore size. Interestingly, the mean pore size and water permeability of the membranes increased from 110 nm with standard deviation (SD) of 25 nm and 12 ml h⁻¹ m⁻² mmHg⁻¹ respectively to 1,230 nm with SD of 180 nm and 43 ml h⁻¹ m⁻² mmHg⁻¹ with an increase in coagulation temperature from 10 to 60°C. However, the membranes regenerated below 20°C exhibited the dense structure as well as good tensile strength and elongation at break. The result from FTIR and ultraviolet-visible (UV-vis) spectroscopy indicated that the relatively strong intermolecular hydrogen bonds exist in the cellulose membranes prepared at lower coagulation temperatures. This work provided a promising way to prepare cellulose materials with different pore sizes and physical properties by controlling the coagulation temperature.     

Modeling the Kinetics of Hydrosilylation Based Polyaddition

Summary. Platinum(II) chloride was used in the hydrosilylation of 1,1,3,3-tetramethyldisiloxane and divinylbenzene. The reaction was monitored online by FTIR spectroscopy and reaction kinetics were determined by Self Modeling Curve Resolution (SMCR). The hydrosilylation polymerization follows a second order polyaddition kinetics with k = 2.03 × 10⁻⁴ dm³ mol⁻¹ s⁻¹.     

Structure of Iron(III)-containing complexes based on the azomethine — 4,4′-dodecyloxy-benzoyloxybenzoyl-4-salicylidene-<Emphasis Type="Italic">N</Emphasis>′-Ethyl-<Emphasis Type="Italic">N</Emphasis>-ethylenediamine molecule

Iron(III)-containing complexes with an asymmetric tridentate azomethine 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-N′-ethyl-N-ethylenediamine ligand with NO₃⁻, PF₆⁻, Cl⁻, and BF₄⁻ counterions are synthesized. The presence of the complexation ion is confirmed by the far FTIR spectra. The structure of the compounds is determined by the matrix-assisted laser desorption/ionizationtime of flight (MALDI-ToF) method. The results of mass-spectrometric studies are consistent with the elemental analysis data. The complexation of iron salts with the asymmetric tridentate ligand is found to yield compounds of the 1:1 composition with octahedral packing of iron in the complex.     

Simultaneous analysis of three catecholamines by a kinetic procedure: comparison of prediction performance of several different multivariate calibrations

A rapid kinetic method for the simultaneous determination of levodopa, dopamine, and dobutamine was examined and developed. It was based on a consecutive reaction of a reduction of Cu(II) to Cu(I) by catecholamines, followed by the complexation of Cu(I) with neocuproine to form a yellow product in an acetic acid-acetate buffer. Spectrophotometric data were recorded at 453 nm (wavelength at the yellow complex absorption maximum) for 300 s. Linear calibrations were obtained in the concentration ranges of (0.08–1.44) × 10⁻⁵ mol L⁻¹, (0.08–1.44) × 10⁻⁵ mol L⁻¹, and (0.16–1.44) × 10⁻⁵ mol L⁻¹ for levodopa, dopamine, and dobutamine, respectively. A variety of multivariate calibration models was developed for simultaneous analysis of the three analytes; while most models produced satisfactory prediction results for synthetic samples, the hybrid linear analysis method was arguably the best-performing (relative prediction error, RPET = 6.6 %). The proposed method was applied to an analysis of spiked rabbit serum samples and the results showed good agreement with the high performance liquid chromatography measurements.     

Enhanced thermal stability of poly(p-dioxanone) in melt by adding an end-capping reagent

For the enhancement of thermal stability of poly(p-dioxanone) (PPDO), the isocyanate end-capping reagent was prepared by treatment of toluene-2,4-diisocyanate with an equivalent of 1-hexyl alcohol. The end-capping reagent and the end-capping PPDO with an inherent viscosity of 0.26 dL g⁻¹ were characterized by FTIR and ¹H-NMR. Thermal stability of the end-capping PPDO with an inherent viscosity of 0.92 dL g⁻¹ was investigated isothermally and non-isothermally under air atmosphere using thermogravimetry. It has been shown that the addition of the prepared isocyanate can enhance significantly the thermal stability of PPDO. The activation energies for non-isothermal degradation estimated by Kissinger method and Friedman method are 91, 81 kJ mol⁻¹ for as-prepared PPDO, and 160, 149 kJ mol⁻¹ for the end-capping PPDO, respectively. The activation energy increases by about 70 kJ mol⁻¹ through the end-capping.     

A new direct Fourier transform infrared analysis of free fatty acids in edible oils using spectral reconstitution

A new transmission-based Fourier transform infrared (FTIR) spectroscopic method for the direct determination of free fatty acids (FFA) in edible oils has been developed using the developed spectral reconstitution (SR) technique. Conventional neat-oil and SR calibrations were devised by spiking hexanoic acid into FFA-free canola oil and measuring the response to added FFA at 1,712 cm⁻¹ referenced to a baseline at 1,600 cm⁻¹(1,712 cm⁻¹/1,600 cm⁻¹). To compensate for the known oil dependency of such calibration equations resulting from variation of the triacylglycerol ester (C═O) absorption with differences in oil saponification number (SN), a correction equation was devised by recording the spectra of blends of two FFA-free oils (canola and coconut) differing substantially in SN and correlating the intensity of the ester (C═O) absorption at the FFA measurement location with the intensity of the first overtone of this vibration, measured at 3,471 cm⁻¹/3,427 cm⁻¹. Further examination of the spectra of the oil blends by generalized 2D correlation spectroscopy revealed an additional strong correlation with an absorption in the near-infrared (NIR) combination band region, which led to the development of a second correction equation based on the absorbance at 4,258 cm⁻¹/4,235 cm⁻¹. The NIR-based correction equation yielded superior results and was shown to completely eliminate biases due to variations in oil SN, thereby making a single FFA calibration generally applicable to oils, regardless of SN. FTIR methodology incorporating this correction equation and employing the SR technique has been automated.     

Absorption of ammonia on tantalum hydroxide synthesized by a hydrofluoric acid method

Ammonia is strongly absorbed on tantalum hydroxide prepared by ammonia neutralization of TaF₇ ²⁻ or TaF₆ ⁻ complexes. FTIR analysis of tantalum hydroxide shows a characteristic peak around 1,400 cm⁻¹, attributed to NH₄ ⁺. TG and FTIR analyses show that the NH₄ ⁺ decomposes at about 500 °C. The correct chemical formula of tantalum hydroxide prepared by ammonia neutralization of TaF₇ ²⁻ or TaF₆ ⁻ is thus TaO _x (OH)_5-x (NH₄) _x . This conclusion is also confirmed by TG and FTIR analysis of tantalum hydroxide treated with various concentrations of inorganic acid at room temperature. The NH₄ ⁺ in tantalum hydroxide can be exchanged completely in aqueous HNO₃ solution, and the weight loss of the resulting sample is ended at about 415 °C by TG analysis. The NH₄ ⁺ can also be exchanged completely with aqueous H₂SO₄ solution; however, SO₄ ²⁻ is weakly absorbed on the tantalum hydroxide. Finally, the NH₄ ⁺ can be exchanged partially with aqueous H₃PO₄ solution; however, PO₄ ³⁻ is strongly absorbed on the tantalum hydroxide.