The electrochemical activity of poly(8-hydroxyquinoline) (PHQ) in acid and alkaline media has been investigated by use of differential pulse polarography (DPP). The reduction peak height (Ip) of PHQ in universal buffer solutions is not useful as an analytical signal, because it is highly affected by hydrogen evolution in acid media and appears as a small peak located at more negative potential values in alkaline media. A new and highly sensitive reduction peak (Ep=–0.45, pH 9.25) appears, however, after addition of trace amounts of PHQ to Cu(II), or vice versa. This reduction peak is a result of the reduction of Cu(II) chelates in the PHQ–Cu(II) complex and is highly promising for the trace determination of PHQ at nanomolar and submicromolar levels. The response current (Ip/μA) for the reduction peak of Cu(II) chelates in a PHQ–Cu(II) matrix results in sensitivity to the concentration of PHQ at least three orders of magnitude higher than that for the reduction peak of PHQ alone under the same conditions. The limit of detection is as low as 5.264 ppsulating poly(vinyl alcohol) (PVA) matrix has been investigated. Electroactive PHQ–Cu(II) at a level of 0.685% could induce a current of approximately 240 nA in an insulating PVA matrix, suggesting possible application for the preparation of a PHQ–Cu(II)– PVA electroactive composite. Keywords Differential pulse polarography · Poly(8-hydroxyquinoline) · Copper(II) determination · Poly(vinyl alcohol)

The electrochemical activity of poly(8-hydroxyquinoline) (PHQ) in acid and alkaline media has been investigated by use of differential pulse polarography (DPP). The reduction peak height (Ip) of PHQ in universal buffer solutions is not useful as an analytical signal, because it is highly affected by hydrogen evolution in acid media and appears as a small peak located at more negative potential values in alkaline media. A new and highly sensitive reduction peak (Ep=–0.45, pH 9.25) appears, however, after addition of trace amounts of PHQ to Cu(II), or vice versa. This reduction peak is a result of the reduction of Cu(II) chelates in the PHQ–Cu(II) complex and is highly promising for the trace determination of PHQ at nanomolar and submicromolar levels. The response current (Ip/μA) for the reduction peak of Cu(II) chelates in a PHQ–Cu(II) matrix results in sensitivity to the concentration of PHQ at least three orders of magnitude higher than that for the reduction peak of PHQ alone under the same conditions. The limit of detection is as low as 5.264 ppsulating poly(vinyl alcohol) (PVA) matrix has been investigated. Electroactive PHQ–Cu(II) at a level of 0.685% could induce a current of approximately 240 nA in an insulating PVA matrix, suggesting possible application for the preparation of a PHQ–Cu(II)– PVA electroactive composite. Keywords Differential pulse polarography · Poly(8-hydroxyquinoline) · Copper(II) determination · Poly(vinyl alcohol)

The electrochemical activity of poly(8-hydroxyquinoline) (PHQ) in acid and alkaline media has been investigated by use of differential pulse polarography (DPP). The reduction peak height (Ip) of PHQ in universal buffer solutions is not useful as an analytical signal, because it is highly affected by hydrogen evolution in acid media and appears as a small peak located at more negative potential values in alkaline media. A new and highly sensitive reduction peak (Ep=–0.45, pH 9.25) appears, however, after addition of trace amounts of PHQ to Cu(II), or vice versa. This reduction peak is a result of the reduction of Cu(II) chelates in the PHQ–Cu(II) complex and is highly promising for the trace determination of PHQ at nanomolar and submicromolar levels. The response current (Ip/μA) for the reduction peak of Cu(II) chelates in a PHQ–Cu(II) matrix results in sensitivity to the concentration of PHQ at least three orders of magnitude higher than that for the reduction peak of PHQ alone under the same conditions. The limit of detection is as low as 5.264 ppsulating poly(vinyl alcohol) (PVA) matrix has been investigated. Electroactive PHQ–Cu(II) at a level of 0.685% could induce a current of approximately 240 nA in an insulating PVA matrix, suggesting possible application for the preparation of a PHQ–Cu(II)– PVA electroactive composite. Keywords Differential pulse polarography · Poly(8-hydroxyquinoline) · Copper(II) determination · Poly(vinyl alcohol)

Preparation and characterization of highly conducting polyaniline (PANI) doped with picric acid (PA) wasproved with the help of various techniques. Elemental analysis, FTIR and XPS spectroscopic measurements confirm that the PA operates as a protonating agent to induce the internal conversion of PANI emeraldine base (PANI-EB) to the PANI emeraldine salt (PANI-ES) with the doping level 50%. Molecular modeling calculations (MMþ) showed that the optimum geometric structure of 2PA:1PANI (energy 38.231388 kcal/mol, and gradient 0.065246). The observed higher conductivity (r 150 S/cm) of PA-doped PANI film prepared at molar ratio 2PA:1PANI (EB) isattributed to the change in the molecular conformation from coil to expanded coil-like. PA-doped PANI isthermally unstable above 135
C and the thermal processing with other insulating matrix is not profitable but the solution casting is highly promising. PA-doped PANI with acrylonitrile-butadiene-styrene copolymer has been fabricated and showed the threshold value 4 wt.% of a conducting material. The reduced PA-doped PANI revealsan ability to store electrical energy of about 110.43 Wh/kg in a condensed lightweight form. The immediate decoloration of the dark green (kmax  815 nm) PANI after addition of 5.5 lg/ml KMnO4 in strong acid medium (pH 1.0, H2SO4, 40% DMF) isdue to the highest oxidized form of PANI. Increasing the absorbance with increases in the KMnO4 concentration (lg/ml) at 385 nm has been successfully applied to the determination of trace amount (0.55 lg/ml) of Mn(VII) in a synthetic solution.  2002 Elsevier Science Ltd. All rights reserved.

Oxidative polymerization reaction of the protonated form of aniline (ANI-HCl) was investigated experimentally in acidic solutions with in situ spectrophotometric technique and computationally using molecular mechanics (MMC) calculations. Welldefined absorbance peaks of an intermediate and of an end product were observed after first scan of the spectrogram, using zeroand first-derivative spectroscopic treatment. Increases in the absorbance at lw420 nm with increasing the oxidant and/or anionic surfactant (sodium dodecyl sulfate, SDS) content in the polymerization medium were observed. This indicates that the presence of nitrenium cations and suggests that the polyaniline evolution goes towards a two-dimensional (D2) polymer with phenazine rings, which can be formed by a cross-linking reaction. It was confirmed by kinetic studies, as well as verified by MMC calculations. Absorbance peak at lw520 nm (dark brown), in the first scan of the spectrogram was observed. This peak increases with increasing the acid surfactant [ poly(acrylic acid)] (PAA) matrix content in the polymerization medium. Kinetic parameters of the oxidative polymerization reaction were deduced employing a computer-aided kinetic analysis of the absorbance (A) at w720 nm against oxidation time (t) data. The results obtained indicate that the rate controlling process are governed by the two-dimensional (D2) diffusion. Good linearity (rw0:985) between DH# and DS# for the series of acids doped PANI matrix was obtained, which suggests the existence of a compensation (or isokinetic) effect. The proposed mechanism for the oxidation of ANI is also supported byMMC calculation. Activation parameters for the rate of oxidation process of ANI have been computed and discussed.

The chromaticity of poly(o-anisidine) (POAN) doped with different acids (HA), HA-doped POAN, has been studied by the spectrophotometric technique and the results were substantiated by molecular mechanics (MM+) calculations. The observed absorbance decrease (λ around 720 nm, dark green coloration) with increasing concentration of the inorganic oxidizing agent (KMnO4) can be attributed to the oxidative hydrolysis mechanism. The oxidative hydrolysis constant (Kh) is highly dependent on the strength of the acid used. The HClO4-doped POAN matrix has the ability to store about 128.878 kJ·g−1 chromogenic energy (CE) at the wavelength 720 nm in a condensed lightweight form. MM+ calculations suggest that the potential energy (PE) in kJ·mol−1 of the optimum molecular geometric (OMG) structure of the HClO4-doped POAN matrix is at least two (2.052) times more stable than the OMG of the base form (POAN-EB) of the POAN matrix. Kinetic parameters of the oxidative hydrolysis reaction of the HA-doped POAN matrix were deduced from absorbance variations with time. The results of computer-oriented kinetic analysis indicate that the rate-controlling step for HA-doped POAN oxidative hydrolysis is governed by the Ginstling-Bronshein equation that represents three-dimensional diffusion (D4). Activation parameters for the oxidative hydrolysis of the HClO4-doped POAN matrix were computed and discussed.

Mechanistic investigation of the oxidative degradation of D-fructose (D-Fruc) has been studied by spectrophotometric technique. Molecular mechanics (MMþ) calculations suggest that the potential energy (PE=kcal mol
1) of the D-fruc (opening structure) is at least three (3.71) times more stable than the PE of the cycling structure of the same matrix. The oxidation constant (Kox) of the anionic form of the D-Fruc (Fruc-NaOH) is about seven times greater than that of the protonated form (Fruc-H2SO4). Therefore, the anionic form is more highly oxidizable than is the cationic form of this matrix. The limit of detection can be as low as 18ppm (mg L
1) of D-Fruc. This is about 60 times lower than the blood sugar level (BSL) or 100 times lower than that reported previously. The proposed procedure was applied successfully for the oxidation of D-Fruc in uni-fructose powder. The anionic form of D-Fruc (Fruc-NaOH) has the ability to store energy about 744.72 kJ g
1 h at 608nm in a condensed lightweight form. Kinetic parameters of the oxidative degradation of the anionic form of DFruc at different concentration were deduced. A number of models were used to evaluate the kinetic parameters. The mechanism of the degradation of D-Fruc is explained on the basis of kinetic parameters.

Aregular two- parameter perturbation analysis based upon the boundary layer approximation is presented here to study the radiative effects of both firs- and second- order resistances due to a solid matrix on the natural convection flows in porous media