Kinetic studies and mechanism on the permanganic oxidation of L‐Glutamine in strong acid medium in the presence and absence of Silver (I)

The kinetic study and mechanism of the permanganic oxidation of L‐glutamine in sulfuric acid has been carried out both in the absence and presence of silver (I) using a spectrophotometric technique. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. The overall rate expression for the oxidation may be written as In the presence of silver (I) the rate law is The reaction appears to involve an acid catalyzed and data showed role of water molecules in the rate‐determining step is proton transfer which satisfies Bunnett's theory. A mechanism satisfying the various kinetic parameters has been proposed. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 95–102, 1999     

Solvent extraction studies on cadmium

An extraction study was performed on tracer concentrations of cadmium, zinc and silver halides in absence and presence of phosphoric acid. A long chain amine (Amberlite LA-2) and an organophosphorus solvent (TBP) have been investigated. The presence of phosphoric acid was found to enhance considerably the extraction of most halides. The mechanism of extraction has been discussed in light of the obtained results.     

Linear free‐energy relationships in chromium(VI) oxidation of substituted benzylamines in nonaqueous media

The kinetics of oxidation of 11 para‐ and meta‐substituted benzylamines by imidazolium fluorochromate (IFC) in different organic solvent media has been investigated in the presence of p‐toluenesulfonic acid (TsOH). The reaction was run under pseudo‐first‐order conditions. The rate of the reaction was found to be first order in IFC and found to increase with increase in [TsOH]. Solution IR studies in combination with kinetic measurements were used to get a better insight into the mechanism of the oxidation process. The product analysis was carried out using GC–MS. Various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of the isokinetic relationship. The specific rate of oxidizing species benzylamines reaction (k₂) correlates with Hammett's substituent constants affording positive reaction constants. The rate data failed to correlate with macroscopic solvent parameters, such as ε_r and E^N_T, while showing satisfactory correlation with Kamlet–Taft's solvatochromic parameters (α, β, and π*) which suggests that the specific solute–solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute–solvent complexation. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 362–369, 2007     

Kinetics and mechanism of silver(I) catalyzed oxidation of tris(1,10-phenanthroline)iron(II) with peroxodiphosphate in acetate buffers

A kinetic study of the silver(I)-catalyzed oxidation of tris(1,10-phenanthroline)iron(II) with peroxodiphosphate was carried out by estimating tris-complex at 510 nm. The reaction is found to conform to the rate law (i). with K₂ and K₃ being the acid dissociation constants of H₃P₂O₈^? and H₂P₂O₈^2?, respectively. The silver(I) catalysis in the reaction has been explained on the basis of complex formation between pdp and silver(I).     

Oxidation of Am(III) and stability of Am(IV) and Am(VI) in mineral acid solutions

The oxidation of americium in HNO₃, H₂SO₄ and HClO₄ solutions by a mixture of potassium persulfate with silver salt in the presence of potassium phosphotungstate has been investigated. The influence of acid and its concentration, of (NH₄)₂S₂O₃, K₁₀P₂W₁₇O₆₁ and silver salt on Am(III) oxidation rate, yield and stability of Am(IV) and Am(VI), has been studied. The complexation of Am(III), Am(IV) and Am(VI) with phosphotungstate ions has been investigated. It has been established that Am(III) and Am(IV) form ML₂ complexes and their apparent stability constants have been estimated. The oxidation mechanism is discussed. A method for preparing of Am(IV) in 0.1–6M HNO₃, O.1–3M H₂SO₄, 0.1–1M HClO₄ solutions is proposed. The oxidation of Am(III) to Am(IV) by KBrO₃ and K₂Cr₂O₇ in HNO₃, H₂SO₄, HClO₄ solutions in the presence of K₁₀P₂W₁₇O₆₁ has been investigated.     

Study of interactive free‐energy relationships on ruthenium(III) catalyzed oxidation of phenyl styryl ketone and its substituted analogues by V(V) in acid medium

Kinetics of Ru(III) catalyzed oxidation of phenyl styryl ketone (PSK) and its substituted analogues by V(V) has been investigated in aqueous acetic acid‐sulphuric acid medium in the temperature range 298–313 K. First‐order dependence each on [V(V)], [PSK], [Ru(III)] was observed. Inverse first‐order dependence was observed for [V(IV)]. The rate decreased with the increase in dielectric constant (D) of the medium. The rates were enhanced by electron‐donating substituents in both the phenyl rings and decreased by electron‐withdrawing substituents. Linear Hammett's plots were obtained for various substituents in benzaldehyde moiety of PSK for a given substituent in acetophenone moiety and vice versa. The mechanism proposed envisages formation of Ru(IV) from V(V) + Ru(III) reaction followed by the attack on by Ru(IV). Applicability of interactive free‐energy relationship has been tested. The cross‐interaction constants q_x and q_y have been determined at different temperatures and possible interpretations discussed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 581–588, 2000     

Kinetics and mechanism of silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate in acetate buffers

Summary The kinetics of the silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate (pdp) was studied in acetate buffers. The rate law as represented by-d[pdp]/dt = {(k ₁ K _inf2 ^sup-1 [H⁺]² + k ₂[H⁺] + k ₃ K ₃)/ ([H⁺]²/K ₂ + [H⁺] + K ₃)}[pdp][Ag(I)] conforms to the proposed mechanism. The rate is independent of malonic acid concentrations. Acetate ions do not affect the rate; however, the rate decreases as the ionic strength increases. A probable portrait of reaction events is suggested. A comparative analysis of the reactivity pattern of malonic acid towards peroxodiphosphate and peroxodisulphate in presence of silver(I) has been made.     

Kinetics of Hydrolysis of Diperiodatoargentate(III) Ion and its Reduction by Paracetamol

The kinetics of hydrolysis and reduction of the diperiodatoargentate(III) ion (DPA) has been studied in aqueous acidic medium spectrophotometrically. Upon dilution the silver (III) complex was found to be unstable in the presence of H₂O. Addition of [H⁺], largely increased the hydrolysis rate, whereas [OH⁻] does not have any effect. Under pseudo-first-order conditions ([paracetamol] > [DPA]), the reduction rate was very fast. Second-order conditions were used to determine the reaction rate. The reaction was acid-catalyzed and the rate decreased by the addition of periodate. The Arrhenius equation was valid for the reaction. The changes observed in the direction of the rate constant-[H⁺] profile correspond to aquation of the diperiodatoargentatate(III) complex. The proposed mechanism and the derived rate law are consistent with the observed kinetics.     

Abscisic acid identification in Okra,Abelmoschus esculentus L. (Moench): perspective nutraceutical use for the treatment of diabetes

Abstract

Okra, Abelmoschus esculentus L. (Moench), also known as Lady's Fingers, gombo, or bamje, is an annual plant belonging to the Malvaceae family. Traditional olistic medicine since centuries directly associates this plant and its parts to a beneficial health hypoglycemic effect. Since the abscisic acid (ABA) has been associated to an interesting hypoglycemic effect, this triggered us to verify and quantify the presence of the abscisic acid in the okra phytocomplex. In particular, ABA, a plant derived hormone, has been proven by recent studies to be effective on mammals. To determine and quantify the ABA content, different parts of the Okra plant extracts have been evaluated, and HPLC-DAD analysis has been used allowing us to report for the first time the presence of this isoprenoid compound. Bioaccessibility has been also investigated using a simulated gastro intestinal (GI) digestion protocol with the aim of explore the possibility of okra extract as nutraceutical.     

SWELLING DYNAMICS OF A TERNARY INTERPENETRATING POLYMER NETWORK (IPN) AND CONTROLLED RELEASE OF POTASSIUM NITRATE AS A MODEL AGROCHEMICAL

ABSTRACT

An interpenetrating polymer network (IPN) of carboxymethyl cellulose (CMC), polyethylene glycol (PEG) and crosslinked polyacrylamide (PAM) has been prepared and dynamic water sorption properties have been investigated as a function of chemical architecture of the IPN, pH and temperature of the swelling medium and presence of salt ions in the bathing medium. Based on the Fick's law the swelling exponent (n) and diffusion constant (D) were evaluated suggesting possible modes of water transport through the IPN's. The IPN's synthesized were loaded with KNO₃ as a representative agrochemical and its release dynamics was studied conductometrically. The influences of percent loading and chemical composition of the IPN were also observed on the release rate and released amounts of KNO₃.     

Effects of anionic and cationic micelles on the oxidation of d-dextrose by diperiodatoargentate(III)

The oxidative behavior of d-dextrose toward diperiodatoargentate(III) (DPA) has been studied in the absence and presence of anionic and cationic micelles of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), respectively. The kinetics is based on the reduction of silver(III) to silver(I) by d-dextrose under pseudo-first-order conditions. The monoperiodatoargentate(III) ions act as active oxidants in comparison to that of DPA. The reactions are first- and fractional-order dependence with respect to [DPA] and [d-dextrose], respectively. The reaction rates decrease with [H⁺] and [periodate]. The premicellar environment of SDS and CTAB strongly inhibits the reaction rate. Inhibition is due to favorable thermodynamic/electrostatic binding between the Ag(III) complex and CTAB monomer aggregates. A suitable mechanism involving a one-electron transfer (rate-determining step) from d-dextrose to the silver(III) species has been proposed. Activation parameters have been evaluated and discussed.     

Silver Nanoparticles in Polyacrylamide and Hyperbranched Polyamine Matrix

Silver nanoparticles have been prepared in a polyacrylamide (PA) matrix, as well as in the presence of a hyperbranched polyamine/polyacrylamide combined system (HB‐PA) by using a reductive technique. The stability of colloidal solution of silver nanoparticles is higher (5 months) in combined matrix compared to PA alone (4 months). The prepared silver nanoparticles were characterized by different spectroscopic and analytical techniques such as FTIR, UV‐visible, X‐ray diffraction, TEM etc. TEM and XRD studies confirmed the formation of well‐dispersed nanoparticles with an average size of 9.91 nm and 8.5 nm for PA and HB‐PA matrices, respectively. The antibacterial activity of silver nanoparticles in both the matrices was tested against Bacillus Subtilis bacteria by using the diffusion disc technique. The result shows that the antibacterial activity of the active agent, Ag(0) is a little higher in the case of HB‐PA system. The dielectric constant of the matrices decreases with an increase in frequency, but the values increase with an increase of concentration of silver nanoparticles in PA matrix.     

Differential Pulse Polarographic Investigation of Copper (II) - Cephalexin Complex

Abstract

It has been found by dp polarography that cephalexin forms a complex Cu(CEF)₂, at pH = 8.7, ionic strength μ = 0.2 and room temperature. The stoichiometric ratio and stability constant values have been evaluated by Lingane's and De Ford and Hume's methods. The overall stability constants, logβ₂ = 9.44 and 9.13, have been determined with methods applied.     

Transparent,Electrically Conductive Composites Derived from Polypyrrole and Poly[Vinyl Chloride) by Vapor-Phase Polymerization: Effect of Environment on Polymerization and Reaction Mechanism

Abstract

Transparent, electrically conductive composite films were obtained by vapor-phase polymerization of pyrrole into a poly(vinyl chloride) (PVC) matrix containing FeCl₃. The effects of water and of organic solvents on the polymerization were investigated. It was found that the conductance of the films increases in the presence of both water vapor and of good solvents or swelling agents for PVC. The conductivity of the films rises with reaction time and so does the rate of increase with higher FeCl₃ concentration. The production of HCl was monitored by two methods, the precipitation of AgCl in an aqueous solution of silver nitrate and the increase in conductance of an aliquot of distilled water which had been placed into the reaction chamber. On the basis of our experimental results, we propose a reaction mechanism that explains the observed increase of conductance with time. A universal kinetic formula has been derived which relates the increase of electrical conductance to other parameters characterizing the boundary conditions of the polymerization.     

The Electrochemical Detection of Arsenic(III) at a Silver Electrode

A study of three electrode substrates namely gold, platinum and silver, for arsenic detection via anodic stripping voltammetry is reported. Hitherto it has been accepted that gold is the most suitable metallic surface for use in this context, as suggested by Forsberg and co‐workers (Forsberg, G.; O'Laughlin, J. W.; Megargle, R. G. Anal. Chem. 1975, 47, 1586.). We revisit these experiments and find that by switching from hydrochloric acid to nitric acid the oxidation of silver that had previously masked the arsenic stripping signal at this surface is shifted considerably enough to allow a clear, analytically reliable As(III) stripping signal to be detected. In contrast to silver and gold platinum is found to have poor performance as an electrode substrate for arsenic detection. Using ASV a LOD of 6.3×10^?7 M is found for As(III) detection at a silver electrode, similar to that which we have previously reported at a gold electrode (A. O. Simm, C. E. Banks and R. G. Compton. Electroanalysis, 2005, 17, 335.) The use of ultrasound was then investigated to further reduce the LOD, which was found to be 1.4×10^?8 M. Apart from reduced cost of silver it also has an added advantage over gold in that it has a higher hydrogen reduction overvoltage enabling a 100 mV more negative deposition potential to be used before the onset of hydrogen evolution when compared to a gold electrode.     

Sensitive Spectrophotometric Determination of Copper(II) in the Presence of Manganese

Abstract

This paper recommends a simple and convenient procedure for the determination of copper(II) in the presence of large amounts of manganese. An aqueous solution of hydroxylamine hydrochloride and diluted sulphuric acid was used for dissolution and reduction of MnO₂. The copper(II) was complexed with an ethanolic 0.05% PAN solution in the pH range of 2 - 3 in aqueous medium. The absorbances of copper-PAN complexes are measured at 550 nm where molar absorptivity is 2.10 L.mol^?1.cm^?1.

The complex obeys Beer's Law from 0.1 to 4 ppm. of copper. Manganese(II) up to 1000 ppm. doesn't interfere. The method is sensitive and reproducible.

It has been applied to the analysis of samples containing 0.01 to 5% of copper on manganese dioxide catalysts.     

Kinetics and mechanism of silver(I) catalyzed oxidation of water with bismuth(V) in HClO4?HF mixture

The kinetics of the oxidation of water with bismuth(V) in presence of silver(I) has been investigated in a mixture of HClO₄ (1.0 mol dm^?3) and HF (1.5 mol dm^?3). The reaction is second order, viz., first order with respect to bismuth(V) and silver(I), each, and the second order rate constant is (6.6 ± 0.7) × 10^?3 dm³ mol^?1 s^?1. However, rate is independent of hydrogen ion concentration. A comparative analysis of these results with the results obtained for pdp, pds, and Ce(IV), reactions with silver(I) has also been made to correlate the rate constants and the redox-potentials of the oxidant couples.     

Mechanistic studies of oxidation of maltose and lactose by [H2OBr]+ in presence of chloro-complex of Rh(III) as homogeneous catalyst

Kinetic studies in homogeneously Rh(III)-catalyzed oxidation of reducing sugars, i.e. maltose and lactose, by N-bromoacetamide (NBA) in the presence of perchloric acid have been made at 40 °C using mercuric acetate as Br⁻ ion scavenger. The results obtained for the oxidation of both reducing sugars show first-order dependence of the reactions on NBA at its low concentrations, which shifts towards zero-order at its higher concentrations. First-order kinetics in [Rh(III)] and zero-order kinetics in [reducing sugar] were observed. Positive effect of [Cl⁻] was observed in the oxidation of both maltose and lactose. Order of reaction was found to be one and half (1.5) throughout the variation of [H⁺] in the oxidation of both maltose and lactose. An increase in the rate of reaction with the decrease in [Hg(OAc)₂] and [NHA] was observed for both the redox systems. The rate of oxidation is unaffected by the change in ionic strength (μ) of the medium. The main oxidation products of the reactions were identified as formic acid and arabinonic acid in the case of maltose and formic acid, arabinonic acid and lyxonic acid in the case of lactose. A common mechanism for the oxidation of both maltose and lactose, showing the formation of most reactive activated complex, [RhCl₄(H₃O)H₂OBr]⁺, and an unreactive complex, [RhCl₄(H₂O)(H₂OBrHg)]²⁺, has been proposed. Various activation parameters have also been calculated and on the basis of these parameters, a suitable explanation for the reaction mechanism has been given.     

THE ROLE OF HUMIC SUBSTANCES IN THE PHOTOCATALYTIC DEGRADATION OF WATER CONTAMINANTS

Abstract

Photocatalysis over irradiated Ti0₂ has been proved to efficiently abate more than 80% of the organic carbon pertaining to a commercial humic acid (HA). The presence of HA up to 50 mg L^?1 has been found to decrease the degradation rate of some model pollutants, namely phenol, 2,4-dichlorophenol and tetrachloromethane. However, the total organic carbon measurements and chloride evolution ensure that the disappearance of the initial pollutants is not due to binding to HA structure, but to an efficient mineralization process. HA' s are able to scavenge both the oxidative and the reductive active species as shown by the inhibiting effect on the rate of disappearance of phenol and 2,4-dichlorophenol (essentially oxidative), and of CCI4 (initially reductive).