Anionic Sodium Dodecyl Sulfate Micelles Research Articles

Kinetics and Mechanism of Paracetamol Oxidation by Chromium(VI) in Absence and Presence of Manganese(II) and Sodiumdodecyl Sulphate

The kinetics of paracetamol oxidation are first order each in [paracetamol] and [HClO4]. The kinetic study shows that the oxidation proceeds in two steps. The effects of anionic micelles of sodiumdodecyl sulphate (SDS) and complexing agents (ethylenediammine tetraacetic acid (EDTA) and 2,2′-bipyridyl (bpy)) were also studied. Fast kinetic spectrophotometric method has been described for the determination of paracetamol. The method is based on the catalytic effect of manganese(II) on the oxidation of paracetamol by chromium(VI) in the presence of HClO4 (= 0.23 mol dm−3). Optimum reaction time is 4 to 6 minutes at a temperature of 30∘C. The addition of manganese(II) ions largely decreased the absorbance of chromium(VI) at 350 nm. This reaction can be utilized for the determination of paracetamol in drugs.

Selective Entrapment of the Cationic Form of Norfloxacin within Anionic Sodium Dodecyl Sulfate Micelles at Physiological pH and its Effect on the Drug Photodecomposition†

The binding of the photosensitizing fluoroquinolone (FQ) antibiotic norfloxacin (NX) to sodium dodecyl sulfate (SDS) micelles and the photoreactivity of the NX/SDS complex under physiological pH conditions are investigated by means of absorption and emission spectroscopy, steady-state and laser flash photolysis. It is shown that the photolabile zwitterionic form of NX, which is dominant at physiological pH, is not the most abundant species in the presence of SDS micelles. This medium exhibits a high preference for the cationic form of the drug, which is selectively and successfully entrapped within the micellar cage (K(ass) = 6 x 10(4) M(-1) +/- 3000), becoming the largely dominant species at neutral pH. The effect of this trapping is drastically reflected on both efficiency and nature of the drug photodecomposition. It is observed that the photostability of NX incorporated in the micellar pseudophase increases of more than one order of magnitude if compared to that of the "free" drug. Furthermore, the radical photodecomposition mechanism occurring in phosphate buffered solution is suppressed by the micellar medium and the low photodegradation observed seems to take place preferentially through an ionic pathway. Hopefully, the results presented herein may contribute to a better understanding of the bio-distribution of NX in biological systems and provide helpful and stimulating information in order to get the control of FQ photoreactivity under physiological pH conditions.

Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions

Photoinduced electron transfer (ET) between coumarin dyes and aromatic amine has been investigated in two cationic micelles, namely, cetyltrimethyl ammonium bromide (CTAB) and dodecyltrimethyl ammonium bromide (DTAB), and the results have been compared with those observed earlier in sodium dodecyl sulphate (SDS) and triton-X-100 (TX-100) micelles for similar donor-acceptor pairs. Due to a reasonably high effective concentration of the amines in the micellar Stern layer, the steady-state fluorescence results show significant static quenching. In the time-resolved (TR) measurements with subnanosecond time resolution, contribution from static quenching is avoided. Correlations of the dynamic quenching constants (k(q) (TR)), as estimated from the TR measurements, show the typical bell-shaped curves with the free-energy changes (DeltaG(0)) of the ET reactions, as predicted by the Marcus outersphere ET theory. Comparing present results with those obtained earlier for similar coumarin-amine systems in SDS and TX-100 micelles, it is seen that the inversion in the present micelles occurs at an exergonicity (-DeltaG(0)> approximately 1.2-1.3 eV) much higher than that observed in SDS and TX-100 micelles (-DeltaG(0)> approximately 0.7 eV), which has been rationalized based on the relative propensities of the ET and solvation rates in different micelles. In CTAB and DTAB micelles, the k(q) (TR) values are lower than the solvation rates, which result in the full contribution of the solvent reorganization energy (lambda(s)) towards the activation barrier for the ET reaction. Contrary to this, in SDS and TX-100 micelles, k(q) (TR) values are either higher or comparable with the solvation rates, causing only a partial contribution of lambda(s) in these cases. Thus, Marcus inversion in present cationic micelles is inferred to be the true inversion, whereas that in the anionic SDS and neutral TX-100 micelles are understood to be the apparent inversion, as envisaged from two-dimensional ET theory.

Micelle-Sensitized Constant-Energy Synchronous Fluorescence Spectrometry for the Simultaneous Determination of Pyrene, Benzo[a]pyrene and Perylene

The use of micellar media in constant-energy synchronous fluorescence spectrometry has been proposed. The influence of some aqueous micellar systems on the determination of pyrene, perylene and benzo[a]pyrene has been investigated. The presence of these micellar systems allows their determination in aqueous media, thus avoiding the use of an organic solvent, and greatly enhances the fluorescence signals. The combination of a constant-energy synchronous scanning technique and a micellar system provided a single spectrum for the simultaneous identification and quantitative determination of the three polycyclic aromatic hydrocarbons (PAHs). Further there was no energy transfer among them, making the measurement simple and fast. A constant-energy difference of 2800 cm(-1) was selected. The analytical characteristics of the proposed method in the presence of anionic micelles of sodium dodecylsulfate (SDS) were studied. The detection limits were at a level of ng ml(-1). Analysis of water samples from two different origins spiked with known amount of pyrene, perylene and benzo[a]pyrene also gave satisfactory results, and total average recoveries were greater than 97.1%.

Protolytic Photodissociation and Proton-Induced Quenching of 1-Naphthol and 2-Octadecyl-1-Naphthol in Micelles

Kinetics of excited-state proton-transfer reactions and proton-induced fluorescence quenching of 1-naphthol (1N) and 2-octadecyl-1-naphthol (2O1N) in micellar solutions of cetyltrimethylammonium bromide (CTAB), polyoxyethylene(23) lauryl ether (Brij 35), and sodium dodecyl sulfate (SDS) was studied by using stationary and time-resolved fluorescence techniques. The ground-state acidity constant of 2O1N in cationic micelles of CTAB was found to be significantly smaller than that of the parent compound (ΔpK = 0.5). However, similar rate and equilibrium constants of the protolytic dissociation were obtained for 1N and 2O1N in the singlet excited state. Effects of nonionic micelles of Brij 35 closely resemble those of CTAB. In anionic micelles of SDS, the protolytic photodissociation was much slower for 2O1N than for 1N. The protonation rate for the excited anions in micellar solutions increases by approximately 2 orders of magnitude in the series CTAB, Brij 35, SDS. Excited-state kinetics was rationalized wit...

Effect of surfactants on the oxidation of oxalic acid by soluble colloidal MnO 2

Kinetics of the oxidation of oxalic acid by water-soluble colloidal MnO 2 has been studied spectrophotometrically in the absence and presence of non-ionic octylphenoxypolyethoxyethanol (Triton X-100, TX-100) and anionic sodium dodecyl sulfate (SDS) surfactant micelles. Anionic SDS micelles were found ineffective whereas those of TX-100 increased the rate that reached a plateau at higher [TX-100]. The reaction followed first- and fractional-order kinetics with respect to [MnO 2] and [H +], respectively, both in the absence and presence of TX-100. The activation parameters ( E a, Δ H #, and Δ S #) were evaluated and the effect of added manganese(II) sulphate is also reported in both aqueous and aqueous–micellar media. On the basis of experimental findings, a probable mechanism is proposed. The reaction proceeds through the adsorption of oxalic acid and hydrogen ions on the surface of the colloidal MnO 2. Freundlich isotherm is used to explain the adsorption of oxalic acid on colloidal MnO 2.

PFG-NMR Investigations of the Binding of Cationic Neuropeptides to Anionic and Zwitterionic Micelles

The mechanism by which peptides bind to micelles is believed to be a two-phase process, involving (i) initial electrostatic interactions between the peptide and micelle surface, followed by (ii) hydrophobic interactions between peptide side chains and the micelle core. To better characterize the electrostatic portion of this process, a series of pulse field gradient nuclear magnetic resonance (PFG-NMR) spectroscopic experiments were conducted on a group of neuropeptides with varying net cationic charges (+1 to +3) and charge location to determine both their diffusion coefficients and partition coefficients when in the presence of detergent micelles. Two types of micelles were chosen for the study, namely anionic sodium dodecylsulfate (SDS) and zwitterionic dodecylphosphocholine (DPC) micelles. Results obtained from this investigation indicate that in the case of the anionic SDS micelles, peptides with a larger net positive charge bind to a greater extent than those with a lesser net positive charge (bradykinin > substance P > neurokinin A > Met-enkephalin). In contrast, when in the presence of zwitterionic DPC micelles, the degree of mixed-charge nature of the peptide affects binding (neurokinin A > substance P > Met-enkephalin > bradykinin). Partition coefficients between the peptides and the micelles follow similar trends for both micelle types. Diffusion coefficients for the peptides in SDS micelles, when ranked from largest to smallest, follow a trend where increasing net positive charge results in the smallest diffusion coefficient: Met-enkephalin > neurokinin A > bradykinin > substance P. Diffusion coefficients when in the presence of DPC micelles, when ranked from largest to smallest, follow a trend where the presence of negatively-charged side chains results in the smallest diffusion coefficient: bradykinin > Met-enkephalin > substance P > neurokinin A.

Compositional heterogeneity effects in multisticker associative polyelectrolytes prepared by micellar polymerization

AbstractAn aqueous micellar radical polymerization technique has been used to prepare water‐soluble polyelectrolytes of acrylamide (AM) and sodium 2‐acrylamido‐2‐methylpropanesulfonate (NaAMPS) hydrophobically modified with low amounts (2–4 mol %) of N,N‐dihexylacrylamide (DiHexAM). This synthesis method leads to multisticker polymers, in which the number and length of the hydrophobic blocks vary with the degree of conversion. Kinetic studies show an appreciable compositional heterogeneity for these polymers, in contrast to their neutral analogues (i.e., AM/DiHexAM copolymers). The drift in composition observed for the AM/NaAMPS/DiHexAM terpolymers is attributed to the electrostatic repulsion between the negatively charged growing polymeric chains, located in the aqueous continuous medium, and the anionic sodium dodecyl sulfate micelles, inside of which the hydrophobic monomer is entrapped. It is shown that an optimization of the polymerization process can be achieved, which gives terpolymers of homogeneous and well‐defined compositions. The thickening ability of the hydrophobically modified polyelectrolytes is directly affected by the extent of their compositional heterogeneity: an increase in the sample homogeneity leads to a significant viscosity enhancement and marked elastic properties of the polymer solutions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3261–3274, 2003

Electron-Transfer Reactions in Micelles: Dynamics of Psoralen and Coumarin Radical Cations

Radical cations of several psoralens and coumarins have been generated by photoionization in aqueous micellar solution for a comparison of their dynamic behavior with results observed previously in aqueous solution. The photoionization efficiencies are significantly higher in anionic sodium dodecyl sulfate (SDS) micelles than in aqueous solution as a result of favorable electrostatic effects that lead to rapid ejection of the electron into the aqueous phase. By contrast, much lower quantum yields are measured in neutral and cationic micelles. Experiments with anionic quenchers that are soluble only in the aqueous phase demonstrate that exit of the radical cations from anionic SDS micelles is too slow to measure (<105 s-1) under our conditions. Exit rate constants from neutral Triton X-100 micelles are approximately an order of magnitude faster. Comparison of equilibrium constants for both triplet and radical cations of 4,5‘,8-trimethylpsoralen demonstrates that electrostatic effects lead to an order of ma...

Occurrence of Cloud Points in Sodium Dodecyl Sulfate−Tetra-n-butylammonium Bromide System

Here we report the clouding phenomenon with sodium dodecyl sulfate (SDS) in combination with tetra-n-butylammonium bromide (Bu4NBr). Cloud point (CP) vs [Bu4NBr] curves are constructed for various fixed [SDS], and the minimum Bu4NBr concentrations required to produce CP are determined. A relationship between [SDS] and [Bu4NBr] is established that exists down to fairly low [SDS]. The presence of aromatic hydrocarbons (added up to their solubility limits) decreases the CP of a fixed SDS−Bu4NBr system. Furthermore, an increase in hydrophobicity of the aromatic hydrocarbon decreases the CP. An unusual CP-decreasing effect of thio compounds is observed, which is discussed in terms of direct interaction of these compounds with anionic SDS micelles.

Synthesis and characterization of polyaniline nanoparticles in SDS micellar solutions

Polyaniline (PANI) dispersions consisting of 10–20 nm sized nanoparticles were prepared by oxidation with ammonium peroxydisulfate (APS) in sodium dodecylsulfate (SDS) micellar solutions. Coalescence and coagulation were prevented by electrostatic repulsive interaction between anionic SDS micelles. Particle morphology was dependent on the initial shape of surfactant aggregates (micelles) and the molar ratio of SDS to aniline monomer. Spherical particles were obtained at very low monomer concentration and the shape of particles began to be distorted from the spherical shape as monomer concentration increased at constant 0.2 M SDS concentration. The size of spherical particles was the same order of the micellar size or slightly larger. UV–VIS spectroscopy, compositions of PANI powder, morphology, crystalline structure, thermal stability, molecular weight and conductivity of PANI particles synthesized at various monomer and surfactant concentrations were investigated.

Determination of five polycyclic aromatic hydrocarbons in aqueous micellar media by fluorescence at room temperature

The influence of some aqueous micellar systems in the determination of pyrene, phenanthrene, benzo(a)pyrene, acenaphthene and fluorene by fluorescence at room temperature has been investigated. The presence of these micellar systems allows its determination in an aqueous media eliminating the use of an organic solvent. The analytical characteristics of the proposed method (linear range, sensitivity and detection limits) in presence of anionic micelles of sodium dodecylsulfate (SDS) have been studied. The detection limits found, for the five polycyclic aromatic hydrocarbons (PAHs) are at the level of ng ml −1. The method has been applied to the determination of these PAHs in water samples spiked with three concentration levels and in all cases average recoveries greater than 93% was obtained.

Room temperature phosphorescence characteristics of platinum(II) chelates with 8-quinolinol derivatives in aqueous micellar solutions

Phosphorescence from platinum(II) chelates of 8-quinolinol (8-Q), 5-sulfo-8-quinolinol (SQ), and 5-sulfo-7-iodo-8-quinolinol (SIQ) at ca. 630 nm is strongly enhanced in certain kinds of surfactant micellar solutions in the presence of sulfite ion as a chemical de-oxygenator. Among these ligand systems the [Pt(II)(SIQ) 2] 2− chelate is most highly phosphorescent with a quantum yield of 0.028 in n-dodecyl-β- d-maltoside (DOM) micelles at 298 K because of the heavy-atom effect of iodine. The emission due to the dianionic 1 : 2 chelates of SQ and SIQ are strongly facilitated either in cationic and non-ionic surfactant micelles such as hexadecyltrimethylammonium chloride (CTAC) or bromide (CTAB), Brij-35, Triton X-100, and DOM in sharp contrast to the slight sensitization by sodium dodecylsulfate (SDS) micelles of similar charge. Anionic SDS micelles do not work well even for the uncharged [Pt(II)(8-Q) 2] chelate. The emission decay lifetimes of the chelates in de-oxygenated micellar solutions are in a similar range of 28 μs with CTAB to 37 μs with DOM, at 298 K. In a pre-micellar region of CTAC, below the critical micelle concentration, the chelate is also luminescent as the ion-pair of (CTA) 2[Pt(II)(SIQ) 2]. The highly sensitive phosphorescence detection of Pt(II) ion is achievable using the SIQ–DOM–sulfite system, giving a 3 σ detection limit of 30 nM or 6 ng Pt ml −1

Interactions of Water-Insoluble Tetraphenylporphyrins with Micelles Probed by UV−Visible and NMR Spectroscopy,

For developing clinically useful porphyrin drugs, it is essential to characterize porphyrin−membrane interactions and to determine the factors that modulate such interactions. To this end, four uniquely p-phenyl-substituted tetraphenylporphyrins were synthesized. These water-insoluble, unsymmetrically substituted porphyrins were allowed to diffuse into aqueous micellar solutions formed by the surfactants tetradecyltrimethylammonium bromide (TTAB), sodium dodecyl sulfate (SDS), and poly(ethylene glycol)-p-t-octylphenol (TX-100). The abilities of the porphyrins to localize in these micelles were determined by UV−vis and NMR spectroscopy. The data show that the NO2−phenyl-substituted porphyrin did not diffuse into any of the micellar solutions. The COO--substituted porphyrin was solubilized in cationic TTAB and in nonionic TX-100 micellar solutions under neutral and basic conditions. The NH3+-substituted porphyrin incorporated in anionic SDS micelles at pH = 2 and in TX-100 micelles at pH 2 and 7. These resu...

Preconcentration of cadmium by MEUF in sodium dodecylsulphate solutions

The ultrafiltration preconcentration of Cd2+ using micellar extraction with 8-hydroxyquinoline (8-HQ), solubilized in anionic micelles of sodium dodecylsulphate (SDS)) were studied. The n-butanol was used as a co-surfactant. Ultrafiltration yields (R, %) on cellulose acetate membranes (wet, 20000 MW-CO) under 400 kPa pressure were determined. Distribution ratios (D) of cadmium between bulk liquid phase and micellar pseudophase were estimated. The constants (app.) for the cadmium-sodium exchange on SDS micelles surface at pH values of 4.8 and 5.3 (3.36 and 3.86, respectively) were determined. It was found, that the values of ultrafiltration yields of the cadmium (at constant concentration of 8-HQ) are influenced not only by the pH and by the concentration values, but also by the ratio of the concentrations of the metal and the anionic surfactant.

Regulatory role of surfactants in the kinetics of glucose oxidase-catalyzed oxidation ofd-glucose by ferrocenium andn-butylferrocenium ions

The effect of micelles of different surfactants (cationic, anionic, and neutral) on the kinetics of the glucose oxidase-catalyzed reduction of ferrocenium cations RFc+ (R=H, Bun) byd-glucose was studied by spectrophotometry. In micellar media of Triton X-100 and sodium dodecyl sulfate (SDS), the Michaelis dependence of the reaction rate on the HFc+ concentration is observed, while this dependence has an extreme character in cationic micelles of cetyltrimethylammonium bromide (CTAB). The nature and concentration of surfactants of all types have a slight effect on the rate of reduction of HFc+. The level of enzymatic activity is approximately equal in the case of Triton X-100 and CTAB and is considerably lower in the SDS micelles. On going from HFc+ to BunFc+, the reaction rate is maximum in the cationic CTAB micelles, the anionic SDS micelles exhibit almost no activity, and the activity has an intermediate value in neutral micelles of Triton X-100. The conditions are presented under which the micellar medium controls the catalytic activity of glucose oxidase with respect to ferrocenium cations.

Study of the Reactions I- + IrCl62- and Fe(CN)64- + S2O82- in Micellar Solutions

The kinetics of the reactions I- + IrCl62- and Fe(CN)64- + S2O82- have been studied in anionic micelles of sodium dodecylsulfate (SDS) at 298.2 K. The results obtained in this work, as well as those obtained in sodium bis-2-ethylhexyl sulfosuccinate (AOT)/decane/water microemulsions and aqueous sodium nitrate solutions, can be explained by using as a starting point the Bronsted equation.

Spectroscopic and photophysical properties of some new rhodamine derivatives in cationic, anionic and neutral micelles

The spectroscopic and photophysical characterization of rhodamine 123 (dye 1), 4,5-dibromorhodamine methyl ester (dye 2) and 4,5-dibromorhodamine n-butyl ester (dye 3) are reported in homogeneous media like water and some alcohols and also in microheterogeneous media; anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral triton X-100 (TX) micelles. The selective biodistribution of these ionic drugs in tissues and membranes strongly influence their photosentisizing properties which have been part of our earlier studies. Results suggest that the hydrogen bonding capability of the amino end group lone pair of these dyes dominates in water. All these dyes interact with anionic SDS micelles. The interaction is mainly electrostatic in nature. At low SDs concentrations (below c.m.c.), dye-SDS aggregate formation takes place. But above c.m.c. only the monomeric dye form is observed. The penetration of dye 3 in SDS is a little less compared to dyes 1 and 2. Dyes 2 and 3 show a finite interaction with CTAB micelle unlike dye 1. With neutral TX micelles all the dyes form strong complexes. The fluorescence quantum yield ( Φ F) of these three dyes in TX is lower. In time-resolved fluorescence experiments, two lifetimes are observed. The effects of the TX concentration on the fluorescence decay are measured. The decay associated spectra of dye 2 in TX are obtained by global compartmental analysis. The dye-surfactant interaction mechanisms are also discussed.

Determining Counterion Exchange Selectivities at Micelle Surfaces from Fluorescence Decay Measurements*

ABSTRACTA method for determining counterion exchange selectivities at the surface of ionic micelles from time‐resolved fluorescence quenching measurements is developed. This method is employed to determine selectivity coefficients for thiosulfate/chloride exchange at the surface of cati‐onic hexadecyltrimethylammonium chloride micelles (KTS/CI, = 1.1 ± 0.4) and for copper (II)/sodium exchange at the surface of anionic sodium dodecyl sulfate micelles (KCu/Na= 1.3 ± 0.3). In both cases, the selectivity coefficients are found to be independent of detergent and added salt concentration.

Porphyrin Synthesis in Surfactant Solution: Multicomponent Assembly in Micelles.

A synthesis of meso-substituted porphyrins in anionic sodium dodecyl sulfate micelles has been developed. Polar, functionalized aromatic aldehydes condense reversibly with pyrrole in the micellar phase. Oxidation of the porphyrinogen then provides functionalized porphyrins in yields of 10-48%. Hydrophobic aldehydes condense irreversibly to give low yields at practical substrate concentrations. Synthesis in D(2)O solution results in per-beta-deuterated porphyrins. A two-phase model is used to rationalize the dependence of porphyrin yield on reactant and surfactant concentration. Micelles are viewed as potential wells which promote porphyrinogen assembly by binding products more tightly than reactants.