Thermodynamic and FTIR studies of the interactions between sodium dodecyl sulphate and strong acids – atypical conductivity pattern

Micellisation of sodium dodecyl sulphate (SDS) was studied in the presence of hydrochloric acid (HCl) and perchloric acid (HClO₄) using conductometry method. The conductivity-[SDS] plots showed abnormal profile pattern at [HCl] > 0.002 mol dm^?3 and [HClO₄] > 0.001 mol dm^?3. Below these acid concentrations, conductivity pattern was normal, and the critical micelle concentration (CMC) values of SDS were lower in both acids than in water. At high acid concentrations, post-micellar slopes were negative. Fourier transform infrared (FTIR) analysis showed significant shifts in the bands suggesting the formation of dodecyl hydrogen sulphate by SDS at high acid concentrations. Thermodynamic parameters for SDS micellisation at low acid concentrations ([HCl] = 0.002 mol dm^?3 and [HClO₄] = 0.001 mol dm^?3) were determined in the temperature range 15–40°C. As temperature increases, the change in enthalpy and entropy of micellisation becomes less positive, and the change in free energy of micellisation becomes increasingly negative.     

Spectral,kinetic, and redox properties of basic fuchsin in homogeneous aqueous and sodium dodecyl sulfate micellar media

Effect of anionic surfactant on the optical absorption spectra and redox reaction of basic fuchsin, a cationic dye, has been studied. Increase in the absorbance of the dye band at 546 nm with sodium dodecyl sulfate (SDS) is assigned to the incorporation of the dye in the surfactant micelles with critical micellar concentration (CMC) of 7.3 × 10^?3 mol dm^?3. At low surfactant concentration (<5 × 10^?3 mol dm^?3) decrease in the absorbance of the dye band at 546 nm is attributed to the formation of a dye–surfactant complex (1:1). The environment, in terms of dielectric constant, experienced by basic fuchsin inside the surfactant micelles has been estimated. The association constant (K_A) for the formation of dye–SDS complex and the binding constant (K_B) for the micellization of dye are determined. Stopped‐flow studies, in the premicellar region, indicated simultaneous depletion of dye absorption and formation of new band at 490 nm with a distinct isosbestic point at 520 nm and the rate constant for this region increased with increasing SDS concentration. The reaction of hydrated electron with the dye and the decay of the semireduced dye are observed to be slowed down in the presence of SDS. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 629–636, 2003     

Reactivities of osmium (VIII) towards some aldoses,amino sugars,and methylated sugars in alkaline medium

The kinetics of oxidation of some aldoses, amino sugars and methylated sugars by osmium (VIII) have been studied spectrophotometrically in alkaline medium. The reactions are first‐order with respect to both [sugar]≤9.0×10⁻³ mol dm⁻³ and [OH⁻]≤10.0×10⁻² mol dm⁻³ but tends toward zero order with respect to each at higher concentration. Activation parameters of the reactions have been calculated and plausible reaction mechanisms have been suggested. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 477–483, 1999     

Kinetics of the diazotization and azo coupling reactions of procaine in the micellar media

The kinetics of the diazotization reaction of procaine in the presence of anionic micelles of sodium dodecyl sulfate (SDS) and cationic micelles of cetyltrimethyl ammonium bromide (CTAB), dodecyltrimethyl ammonium bromide (DDTAB) and tetradecyltrimethyl ammonium bromide (TDTAB) were carried out spectrophotometrically at λ_max = 289 nm. The values of the pseudo first order rate constant were found to be linearly dependent upon the [NaNO₂] in the concentration range of 1.0 × 10⁻³ mol dm⁻³ to 12.0 × 10⁻³ mol dm⁻³ in the presence of 2.0 × 10⁻² mol dm⁻³ acetic acid. The concentration of procaine was kept constant at 6.50 × 10⁻⁵ mol dm⁻³. The addition of the cationic surfactants increased the reaction rate and gave plateau like curve. The addition of SDS micelles to the reactants initially increased the rate of reaction and gave maximum like curve. The maximum value of the rate constant was found to be 9.44 × 10⁻³ s⁻¹ at 2.00 × 10⁻³ mol dm⁻³ SDS concentration. The azo coupling of diazonium ion with β-naphthol (at λ_max = 488) nm was found to linearly dependent upon [ProcN₂⁺] in the presence of both the cationic micelles (CTAB, DDTAB and TDTAB) and anionic micelles (SDS). Both the cationic and anionic micelles inhibited the rate of reactions. The kinetic results in the presence of micelles are explained using the Berezin pseudophase model. This model was also used to determine the kinetic parameters e.g. k_m, K_s from the observed results of the variation of rate constant at different [surfactants].     

Voltammetric Determination of Chlorpheniramine Maleate Based on the Enhancement Effect of Sodium‐dodecyl Sulfate at Carbon Paste Electrode

The voltammetric oxidation and determination of chlorpheniramine maleate (CPM) was studied at a carbon paste electrode (CPE) in the presence of sodium‐dodecyl sulfate (SDS) by cyclic and differential pulse voltammetry. The results indicated that the voltammetric response of chlorpheniramine maleate was markedly increased in the low concentration of SDS, suggesting that SDS exhibits observable enhancement effect to the determination of chlorpheniramine maleate. Under the optimal conditions the peak current was proportional to chlorpheniramine maleate concentration in the range of 8.0×10⁻⁶ to 1.0×10⁻⁴ M with detection limit of 1.7×10⁻⁶ M by differential pulse voltammetry. The proposed method was successfully applied to the determination of chlorpheniramine in pharmaceutical and urine samples.     

Association of sodium dodecyl sulfate in aqueous solutions according to chemical shifts in 1H NMR spectra

Proton chemical shifts of different atomic groups in sodium dodecyl sulfate (SDS) have been studied by ¹H NMR spectroscopy as functions of surfactant concentration in aqueous solutions. Three surfactant concentration ranges of the chemical shifts have been revealed. The first range corresponds to the premicellar solutions, the second one is in the vicinity of critical micelle concentration (CMC₁), and the third range corresponds to high surfactant concentrations, at which intermicellar interactions play a significant role. The parameters of SDS association (CMC₁ and CMC₂) determined based on the concentration dependences of the chemical shifts are in satisfactory agreement with the data available from the literature. The concept of critical dimerization concentration (CDC) has been introduced for the first concentration range. The values of CDC and dimerization constant K ₂ (210 × 60 dm³/mol) have been estimated within the framework of the two-state model.     

Electroactivated Disposable Pencil Graphite Electrode – New,Cost-effective,and Sensitive Electrochemical Detection of Bioflavonoid Hesperidin

In this paper, for the first time, electroactivated disposable pencil graphite electrode (ePGE) was used for the detection of bioflavonoid hesperidin with cyclic and differential pulse voltammetry. The electroactivation efficiency of the pencil graphite electrode (PGE) was examined employing electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) and the enhancement of electron transfer kinetics of the PGE after the electroactivation was found. Hesperidin is irreversibly oxidized on the ePGE and its oxidation was the most pronounced at pH=5.0. Two electrode processes were detected, on one hand, a mixed diffusion and adsorption control was observed for the first electrode process. On the other hand, only diffusion control was observed in the second electrode process. Linear dependence between the peak current and the hesperidin concentration was obtained in the concentration range from 5×10⁻⁷ mol dm⁻³ to 1×10⁻⁵ mol dm⁻³ and the determined lower limit of detection (LOD) was 2×10⁻⁷ mol dm⁻³. Moreover, hesperidin in pharmaceutical formulation (containing active substance, hesperidin, and excipients) was quantified using ePGE. A good correlation was obtained between experimentally obtained hesperidin concentration by voltammetric analysis and concentration determined by standard HPLC technique (R²=0.9462).     

Micelles with highly branched nanoporous interior: Solution properties and binding capabilities of amphiphilic copolymers with linear dendritic architecture

This article describes the solution behavior of model amphiphilic linear‐dendritic ABA block copolymers that self‐assemble in aqueous media and form micelles with highly branched nanoporous cores. The materials investigated are constructed of poly(ethylene glycol), PEG, with molecular weight 5,000 or 11,000 as the water‐soluble B block and poly(benzyl ether) monodendrons [G] of second and third generation as the hydrophobic A fragments. The process of self‐assembly in aqueous media and the character of the micellar core are investigated by fluorescence spectroscopy using pyrene as the molecular probe. The data obtained by different methods indicate that the critical micelle concentrations (cmc) for these systems are between 1.1 × 10⁻⁵ and 2.0 × 10⁻⁵ mol/L for [G‐2]‐PEG5000‐[G‐2] and between 7.08 × 10⁻⁶ and 7.94 × 10⁻⁶ mol/L for [G‐3]‐PEG11000‐[G‐3]. It is found that the ratio of the first and third vibronic bands (I₁/I₃ ) in the fluorescence spectrum of the encapsulated pyrene changes from 1.77 to 1.32 when the concentration of [G‐2]‐PEG5000‐[G‐2] increases from 1.1 × 10⁻⁶ mol/L to 1.1 × 10⁻⁴ mol/L. For [G‐3]‐PEG11000‐[G‐3] these changes are between 1.77 and 1.17 in the same concentration range. The hybrid copolymers form host‐guest complexes with several polyaromatic compounds (phenanthrene, pyrene, perylene and fullerene, C₆₀) that are stable over extended periods of time (more than 12 months). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2711–2727, 2000     

Simultaneous multielement‐specific detection of a novel glutathione–arsenic–selenium ion [(GS)2AsSe]− by ICP AES after micellar size‐ exclusion chromatography

In order to confirm the solution structure of [(GS)₂AsSe]⁻ (GS = glutathione), we have investigated the retention behaviour of a [(GS)₂AsSe]⁻/oxidized glutathione (GSSG) mixture on a Sephadex G‐25 (SF) column with Tris buffers (0.1 mol dm⁻³, pH 8.0) containing ­various surfactants at concentrations above the critical micellar concentration (CMC): hexadecyltrimethlammonium bromide (HDTAB; 30, 40 and 50 mmol dm⁻³); dodecyltrimethylammonium bromide (DDTAB; 50 mmol dm⁻³); and sodium lauryl sulfate (SLS; 50 mmol dm⁻³). ­An inductively coupled plasma atomic emission spectrometer (ICP AES) provided simultaneous on‐line detection of arsenic, selenium and ­sulfur in the column effluent. The chromatographic retention behaviour was used to investigate the association of both compounds with the positively charged micelles (HDTAB and DDTAB mobile phases). The relative strength of association with the micelles provided insight into the effective negative charge on [(GS)₂AsSe]⁻ and GSSG. The chromatograms obtained with 50 mmol dm⁻³ HDTAB indicated that two glutathione molecules are associated with the elution of an arsenic–selenium compound. Combined, these chromatographic data strongly support the spectroscopically derived solution structure of [(GS)₂AsSe]⁻. Copyright ­© 2000 John Wiley & Sons, Ltd.     

Kinetics and mechanism of oxidation of ethylenediamine and related compounds by diperiodatoargentate (III) ion

The oxidation of ethylenediamine by diperiodatoargentate (III) ion has been studied by stopped‐flow spectrophotometry. Kinetics of this reaction involves two steps. The first step is the complexation of silver (III) with the substrate and is over in about 10 ms. This is followed by a redox reaction in the second step that occurs intramolecularly from the substrate to the silver (III) center. The rate of reduction of silver (III) species by ethylenediamine, ethanolamine, and 1,2‐ethanediol were observed to be 1.2 × 10⁴, 1.1 × 10², and 0.14 dm³ mol⁻¹ s⁻¹, respectively, at 20°C. The reaction rate shows an inverse dependence on [IO] and [OH⁻] in the low concentration range (≤1 × 10^‐3 mol dm⁻³). At higher [OH⁻] (>1 × 10⁻³ mol dm⁻³) the rate of reaction starts increasing and attains a limiting value at very high [OH⁻]. The rate of deamination of ethylenediamine is enhanced by its complexation with silver (III). The involvement of [Ag^III(H₂IO₆) (H₂O)₂] and [Ag^III(H₂IO₆) (OH)₂]²⁻ are suggested as the reactive silver (III) species kinetically in mild basic and basic conditions, respectively. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 286–293, 2000     

Metallophthalocyanines Bearing Polymerizable {[5‐({(1E)‐[4‐(Diethylamino)phenyl]methylene}amino)‐ 1‐naphthy1]oxy} Groups as Electrochemical Pesticide Sensor

The synthesis and characterization of novel metallophthalocyanines (MPcs(ea)) carrying {[5‐({(1E)‐[4‐(diethylamino)phenyl]methylene}amino)‐1‐naphthyl]oxy} groups on four peripheral positions have been reported. These complexes have been characterized by a combination of FT‐IR, ¹H and ¹³C NMR, mass and UV‐Vis spectroscopy techniques. Redox active metal centers in the core of the Pc rings (Co (II) [CoPc(ea)], Mn(III) [Cl–MnPc(ea)], and Ti(IV)O [TiOPc(ea)]) and electropolymerizable substituents on the peripheral positions of Pc rings were used to increase redox activity and electrochemically polymerization ability of the complexes. The redox properties of MPcs(ea) were determined with voltammetry and in situ spectroelectrochemistry techniques. Then, GCE/MPc(ea) electrodes were constructed with the electropolymerization of MPcs and these electrodes were tested as the pesticide sensors. Sensing studies indicated that type of the metal center of the complexes effectively influenced the sensing activities. While all complexes showed interaction abilities for the fenitrothion, parathion and eserine, GCE/CoPc(ea) electrode detected the parathion selectively with LOD value of 4.52×10⁻⁷ mol dm⁻³ among studied three pesticides. Moreover, GCE/MnClPc(ea) electrode selectively detected eserine with LOD value of 6.43×10⁻⁷ mol dm⁻³ and GCE/TiOPc(ea) electrode detected parathion with LOD value of 8.64×10⁻⁷ mol dm⁻³. All GCE/MPcs(ea) electrodes showed high sensitivity and wide linear ranges for those pesticides. These sensing data illustrated the usability of these modified electrodes in real samples such as seawater with good selectivity and sensitivity.     

Kinetics and mechanisms of the reactions of aluminium(III) with β-diketones in aqueous solution

The kinetics and mechanisms of the reactions of aluminium(III) with pentane-2,4-dione (Hpd), 1,1,1-trifluoro pentane-2,4-dione (Htfpd) and heptane-3,5-dione (Hhptd) have been investigated in aqueous solution at 25°C and ionic strength 0.5 mol dm⁻³ sodium perchlorate. The kinetic data are consistent with a mechanism in which aluminium(III) reacts with the β-diketones by two pathways, one of which is acid independent while the second exhibits a second-order inverse-acid dependence. The acid-independent pathway is ascribed to a mechanism in which [Al(H₂O)₆]³⁺ reacts with the enol tautomers of Hpd, Htfpd, and Hhptd with rate constants of 1.7(±1.3)×10⁻², 0.79(±0.21), and 7.5(±1.6)×10⁻³ dm³ mol⁻¹ s⁻¹, respectively. The inverse acid pathway is consistent with a mechanism in which [Al(H₂O)₅(OH)]²⁺ reacts with the enolate ions of Hpd, Htfpd, and Hhptd with rate constants of 4.32(±0.18)×10⁶, 5.84(±0.24)×10³, and 1.67(±0.05)×10⁷ dm³ mol⁻¹ s⁻¹, respectively. An alternative formulation involves a pathway in which [Al(H₂O)₄(OH)₂]⁺ reacts with the protonated enol tautomers of the ligands. This gives rate constants of 2.79(±0.12)×10⁴, 3.86(±0.16)×10⁵, and 8.98(±0.25)×10³ dm³ mol⁻¹ s⁻¹ for reaction with Hpd, Htfpd, and Hhptd, respectively. Consideration of the kinetic data reported here together with data from the literature, suggest that [Al(H₂O)₅(OH)]²⁺ reacts by an associative or associative-interchange mechanism. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 257–266, 1998.     

A PVC-based pentathia-15-crown-5 membrane potentiometric sensor for mercury(II)

Poly(vinyl chloride) (PVC)-based membrane of pentathia-15-crown-5 exhibits good potentiometric response for Hg²⁺ over a wide concentration range (2.51 × 10⁻⁵ to 1.00 × 10⁻¹ mol dm⁻³) with a slope of 32.1 mV per decade of Hg²⁺ concentration. The response time of the sensor is as fast as 20 s. The electrode has been used for a period of six weeks and exhibits fairly good discriminating ability towards Hg²⁺ in comparison to alkali, alkaline and some heavy metal ions. The electrode can be used in the pH range from 2.7 to 5.0.     

Detection of Agmatine and Octopamine in Rat Brain and Human Plasma by Microchip Electrophoresis

A microchip electrophoresis method with laser induced fluorescence detection was developed for the detection of agmatine (Agm) and octopamine (Oct). The fluorescent derivatization reagent, fluorescein isothiocyanate was used for precolumn derivatization of Agm and Oct. The sodium dodecyl sulfate (SDS) micelles was employed as pseudostationary phase for the separation of Agm and Oct with other endogenous compounds exist in biological samples. Some parameters including buffer concentration, buffer pH, SDS concentration and separation voltage were investigated in detail. Under the optimum conditions, the separation and determination of Agm and Oct was performed within 40 s. The calibration curves were linear for both Agm and Oct over the concentration range of 1.0 × 10⁻⁷ to 4.0 × 10⁻⁵ M and 1.5 × 10⁻⁷ to 4.5 × 10⁻⁵ M, respectively. The detection limits of Agm and Oct (S/N = 3) are 5.0 × 10⁻⁸ and 8.0 × 10⁻⁸ M, respectively. These values make the method very suitable for the determination of Agm and Oct in rat brain tissue and human plasma as demonstrated in this paper.

     

Two-step one-electron transfer reaction of chromium(III) complex containing levodopa and uridine with N-bromosuccinimide

[Cr^III(LD)(Urd)(H₂O)₄](NO₃)₂?·?3H₂O (LD?=?Levodopa; Urd?=?uridine) was prepared and characterized. The product of the oxidation reaction was examined using HPLC. Kinetics of the oxidation of [Cr^III(LD)(Urd)(H₂O)₄]²⁺ with N-bromosuccinimide (NBS) in an aqueous solution was studied spectrophotometrically, with 1.0–5.0?×?10^?4?mol?dm^?3 complex, 0.5–5.0?×?10^?2?mol?dm^?3 NBS, 0.2–0.3?mol?dm^?3 ionic strength (I), and 30–50°C. The reaction is first order with respect to [Cr^III] and [NBS], decreases as pH increases in the range 5.46–6.54 and increases with the addition of sodium dodecyl sulfate (SDS, 0.0–1.0?×?10^?3?mol?dm^?3). Activation parameters including enthalpy, ΔH*, and entropy, ΔS*, were calculated. The experimental rate law is consistent with a mechanism in which the protonated species is more reactive than its conjugate base. It is assumed that the two-step one-electron transfer takes place via an inner-sphere mechanism. A mechanism for this reaction is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* for some Cr^III complexes. Formation of [Cr^III(LD)(Urd)(H₂O)₄]²⁺ in vivo probably occurs with patients who administer the anti-Parkinson drug (Levodopa), since Cr^III is a natural food element. This work provides an opportunity to identify the nature of such interactions in vivo similar to that in vitro.     

Promotion of the fenton reaction by Cu2+ ions: Evidence for intermediates

The promotion of the Fenton reaction by Cu²⁺ ions has been investigated using a wide range of [Cu²⁺]. Both the disappearance of Fe²⁺ and the evolution of O₂ were followed as a function of time by quenching the reaction mixture with o‐phenanthroline or with excess Fe^{2 +} ions, respectively. Two series of experiments were performed. In one series [H₂O₂] was 5 × 10⁻⁴ mol dm⁻³, and in the other [H₂O₂] was reduced to 5 × 10⁻⁵ mol dm ⁻³. By stopping the reaction with excess Fe²⁺ ions, significant differences in the measured absorbance in the two series were observed. In the higher [H₂O₂] range, the absorbance decreased monotonically in time, due to O₂ formation during the reaction. In the lower range, an initial transient rise of the absorbance was observed, indicating the formation of spectroscopically distinct intermediates in the system. A mechanism involving the intermediates FeOCu⁴⁺ and FeOCu⁵⁺ has been set up. Rate constants of the mechanism have been determined. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 725–736, 2006     

Sol‐Gel Derived Potentiometric Sensor for Determination of Vanadyl Ions

A sol‐gel electrode, based on thiacalix[4]arene as a neutral carrier, was successfully developed for the detection of VO²⁺ in aqueous solutions. The sol‐gel electrode exhibited linear response with Nernstian slope of 29.3±0.3 mV per decade, within the vanadyl ion concentration ranges 1.0×10^?6 – 1.0×10^?1 mol dm^?3. The sol‐gel electrode shows detection limit of 4.9×10^?7 mol dm^?3. The influence of membrane composition, the pH of the test solution, and the interfering ions on the electrode performance were investigated. The electrode exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The effect of temperature on the electrode response showed that the temperature higher than 60 °C deteriorates the electrode performance. Application of the electrode for the determination of vanadyl in spiked samples is reported.     

Application of Non‐Stop‐Flow Differential Pulse Voltammetry at a Tubular Detector of Silver Solid Amalgam for Electrochemical Determination of Lomustine (CCNU)

An application of the flow differential pulse voltammetry with tubular detector based on silver solid amalgam for determination of antineoplastic drug lomustine in pharmaceutical preparations is presented. The highest sensitivity was obtained in [0.10 mol dm^?3 MES; 2.00 mol dm^?3 NaCl; pH 6.0]:EtOH (9 : 1) with flow rate 0.50 mL min^?1, and the magnitude of the modulation amplitude ?0.070 V. The calibration dependence was linear in the range 1×10^?6–1 × 10^?4 mol dm^?3 (R²=0.999). The limit of detection was 1.5×10^?7 mol dm^?3. This method was successfully used for determination of lomustine in real samples of chemotherapy drug CeeNU Lomustine 40 mg.     

Lithium-selective electrodes based on non-cyclic polyether diamide carriers in conjunction with organophosphorus solvent mediators

Series of non-cyclic polyether amides were synthesized as derivatives of pyrocatechol. Poly(vinyl chloride) membrane electrodes based on some of these carriers exhibited lithium selectivities over other alkali or alkaline-earth metal ions when dioctyl phenylphosphonate alone or mixed with o-nitrophenyl octyl ether served as plasticizer. Selectivity coefficients for lithium over sodium were up to 2.1 × 10¹, over potassium up to 1.4 × 10² and over alkaline-earth metals up to 1.5 × 10². The detection limit for lithium was 5.0 × 10⁻⁵ mol dm⁻³.