Sodium Dodecyl Sulfate Micellar Solutions Research Articles

Photoinduced intermolecular electron transfer from aromatic amines to coumarin dyes in sodium dodecyl sulphate micellar solutions

Photoinduced intermolecular electron transfer interaction between coumarin dyes and aromatic amines has been investigated in sodium dodecyl sulphate micellar solutions using steady-state and time-resolved fluorescence quenching measurements. Steady-state fluorescence quenching of the coumarin dyes by the amine quenchers always shows a positive deviation from linear Stern–Volmer relationship, which arises due to the localized high quencher concentrations at the micellar Stern layer. In time-resolved fluorescence measurements, the analysis of the fluorescence decays following a micellar quenching kinetics model assuming a unified quenching constant (kq′) per quencher occupancy does not give satisfactory results, especially for the higher quencher concentrations used. The observed fluorescence decays are, however, seen to fit reasonably well following a bi-exponential analysis for all the quencher concentrations used. The average fluorescence lifetimes of the coumarin dyes in the micellar solution as estimated from the bi-exponential decay analysis are seen to undergo a systematic reduction with the effective mean quencher concentrations. The bimolecular quenching constants (kq) thus estimated are seen to be much smaller than those reported in the homogeneous solutions (e.g., in acetonitrile), indicating that the electron transfer in the micellar media is inherently inefficient. Correlation of the observed kq values in the micellar solutions with the free-energy changes (ΔG0) for electron transfer reactions show an inversion in the observed rates as predicted by Marcus’ outer sphere electron transfer theory at exergonicities more that ∼0.65 eV. To the best of our knowledge this is the first report on the Marcus inverted region observed for the electron transfer reactions in micellar solution.

Optimised procedures for the reversed-phase liquid chromatographic analysis of formulations containing tricyclic antidepressants

The chromatographic behaviour (retention, selectivity, peak shape and resolution) of seven tricyclic antidepressants (TCAs), amitryptiline, clomipramine, doxepin, imipramine, maprotiline, nortryptiline and trimipramine, was examined. Conventional unendcapped C 8 and C 18 columns and an endcapped XTerra MS C 18 column recommended for the analysis of basic compounds were used together with acetonitrile–water and micellar sodium dodecylsulfate (SDS)–pentanol mobile phases. The two best combinations were XTerra C 18/acetonitrile, which yielded the largest efficiencies and resolution, and C 8/SDS–pentanol, which eliminated the peak tails that were still observed with the XTerra C 18 column. Both the systems were used to develop simple chromatographic procedures for the control of TCAs in pharmaceutical formulations using UV detection. The selected mobile phase compositions were 35% (v/v) acetonitrile (XTerra C 18 column) and 0.075 M SDS–6% (v/v) pentanol (C 8 column), both at pH 3. Satisfactory recoveries were achieved in both cases, with intra- and inter-day relative standard deviations (RSDs) always below 0.6 and 2.0%, respectively. The preparation of the samples was simple in both modes, since a previous extraction of the drugs was not needed. The micellar mode has, however, the advantage of using a smaller amount of organic solvent, which is retained in the micellar SDS solution. The C 8 column is also less expensive.

Characterization of Solvation Environment Provided by Dilute Poly(sulfonyl maleic anhydride‐co‐dodecyl vinyl ether) Solutions at Various pH Using Pyrene and 1,3‐Bis(1‐pyrenyl)propane as Fluorescence Probes

AbstractSolubilization environments afforded by dilute aqueous solutions of poly(sulfonyl maleic anhydride‐co‐dodecyl vinyl ether) [PSMADVE, 1 wt.‐%] at pH 4, 7, and 10 are investigated using pyrene and 1,3‐bis(1‐pyrenyl)propane as fluorescence probes. While pyrene is a common polarity probe, intramolecular excimer formation in 1,3‐bis(1‐pyrenyl)propane makes it an interesting cybotactic region microviscosity probe. Results for pyrene II/IIII indicate that the most hydrophobic solubilization site is afforded at pH 4 followed by pH 10 and pH 7. The dipolarity indicated by pyrene is similar to that observed in m‐ and o‐xylene, toluene, and butyl benzoate. The solvation microenvironment afforded by the PSMADVE solutions is more hydrophobic than that observed within sodium dodecyl sulfate micellar solution. Additionally, further investigation of the relative size of the solubilization site revealed that the polymer solutions promoted intermolecular pyrene excimer formation at relatively low pyrene concentrations, indicating the possibility of localized concentration enhancement within the solvation pockets and/or compartmentalization of the solute molecules. This observation was most prominent at pH 10 and least at pH 7. 1,3‐Bis(1‐pyrenyl)propane intramolecular excimer formation efficiency at pH 4 is slightly higher than that for neat ethylene glycol, while at pH 10 is similar to that observed in 1‐octanol or dimethyl sulfoxide. Anomalously high excimer‐to‐monomer intensity ratio at pH 7 could be due to probe ground state heterogeneity, i.e., the existence of probe moieties in the ground state where the two pyrenyl groups are already aggregated. This is demonstrated by the fluorescence excitation data. Presence of the ground state aggregated form may give rise to anomalously high excimer formation efficiency. Structures of fluorescence probes pyrene and 1,3‐bis(1‐pyrenyl)propane.imageStructures of fluorescence probes pyrene and 1,3‐bis(1‐pyrenyl)propane.

Analysis of polycyclic aromatic hydrocarbons by sensitized room temperature phosphorescence

Direct and selective simultaneous determination of several polycyclic aromatic hydrocarbons by sensitized room temperature phosphorescence in sodium dodecylsulphate micellar solutions was studied. This approach improved, for example, the selectivity factor in determining pyrene in the presence of fluoranthene by a factor of 350, and determined benz[a]anthracene and anthracene in the presence of pyrene with the selectivity factors as high as 200–220. Triphaflavine and acridine orange as triplet energy donors, thallium (I) nitrate as a heavy atom, and sodium sulphite were used as scavengers of oxygen. A comparative study of linear concentration ranges, detection limits and selectivity factors is presented here for pyrene, benz[a]anthracene and anthracene determination by fluorescence, phosphorescence and sensitized phosphorescence.

The Dynamics of Ultrafast Excited State Proton Transfer in Anionic Micelles

Fast excited state proton transfer reactions at the surface of anionic sodium dodecyl sulfate (SDS) micelles have been investigated using the photoacid 4-methyl-7-hydroxyflavylium (HMF) chloride as probe. The acid−base kinetics of excited HMF are straightforward in water, with biexponential fluorescence decays reflecting ultrafast deprotonation of the excited acid (AH+)* (kd = 1.5 × 1011 s-1 or ca. 6 ps) and diffusion-controlled protonation of the excited base A* (kp = 2.3 × 1010 L mol-1 s-1 at 20 °C). In aqueous micellar SDS solutions, the kinetics are much more complex; triple exponential fluorescence decays are observed at all pH values and temperatures examined. The longest decay time (τ1 = 760 ps at 22 °C), observed only for (AH+)* and uncoupled from the acid−base equilibrium, is assigned to excitation of HMF in orientations incapable of prompt transfer of the proton to water, i.e., that must rotate to expose the acidic OH group to water (krot = 1.2 × 109 s-1 or ca. 800 ps at 22 °C). The other two decay times, τ3 and τ2, are due to emission from the species involved in the acid−base reaction at the micelle surface. Deprotonation of (AH+)* is slightly slower in SDS micelles (kd = 3.4 × 1010 s-1 or ca. 20 ps) than in water. Two processes are operative in the back protonation of A*: (i) pH-independent unimolecular reprotonation in the initially formed geminate compartmentalized pair (A*···H3O+) (kr = 8.8 × 109 s-1) and (ii) pH-dependent bimolecular protonation of A* via entry of an aqueous phase proton into the micelle (kp = 1.6 × 1011 M-1 s-1). Dissociation of the geminate pair (kdiss = 1.6 × 109 s-1) forms A* at the micellar surface. The present study thus provides a rather detailed kinetic picture of the initial steps involved in an ultrafast excited state proton transfer process at the surface of a typical anionic micelle.

Study by Small-Angle Neutron Scattering of Sodium Dodecyl Sulfate Micelles with the Macrocyclic Ligand [2.2.2]Cryptand

The addition of [2.2.2]cryptand (C222) to sodium dodecyl sulfate (SDS) micelles in aqueous solution is studied by small-angle neutron scattering (SANS). Hydrogenated and perdeuterated SDS micelles with 8% (wt/wt) concentration have been studied in the presence of 0.5, 1.0, and 1.5 mole ratio C222/surfactant, SANS analysis was performed using a two-shell model for the micelle form factor (core plus interfacial layer) and a screened Coulomb interactive potential for the interparticles potential. For both deuterated and hydrogenated surfactant, C222 ligand complexes the sodium micellar counterion and is mainly located at the interface partially screening the micelle surface charge. Counterion complexation produces, as compared to pure SDS micellar solutions, an increase of the interfacial layer thickness and a decrease of the micellar surface charge, of the contact potential, and of the average aggregation number. We report a detailed analysis of the micelle structure and intermicellar interaction potential.

Laser flash photolysis study of the photochemical formation of colloidal Ag nanoparticles in the presence of benzophenone

Sensitized photoreduction of Ag+ ions and subsequent formation of colloidal Ag nanoparticles take place when an aqueous solution of a mixture of AgClO4, sodium dodecylsulfate (SDS) and benzophenone (BP) is irradiated with near-UV light. In this study, the mechanism and kinetics of the reaction have been studied by means of nanosecond laser flash photolysis, time-resolved emission spectroscopy and also steady-state photolysis. Benzophenone ketyl radial (BPK) is formed by the hydrogen abstraction reaction of the benzophenone triplet (BPT) from SDS, which reduces Ag+ ions. It is found that the yield of colloidal Ag nanoparticle formation decreases remarkably with increasing concentration of Ag+ ions, indicating the efficient quenching process of BPT by Ag+ ions. Rate constants for the oxidation of BPK as well as the quenching of BPT by Ag+ ions in SDS micellar solution are considerably larger than those expected in the bulk solution, reflecting that Ag+ ions and BP molecules are concentrated in the SDS micelles. The rate of colloidal Ag nanoparticle formation, VAg, and BP photobleach, VBP, under steady-state irradiation with near-UV light (λ = 365 nm) were evaluated and the dependence of VAg and VBP on the concentration of Ag+ ions is interpreted quantitatively in terms of rate constants estimated by laser flash photolysis.

The kinetics of solvolysis of phosphorus acid esters in the ternary sodium dodecyl sulfate-ethylene glycol -La 3+ micellar system

By methods of conductivity measurements, micellization of sodium dodecyl sulfate in ethylene glycol at the concentration above 0.18 M is shown. The La 3+ ion catalysis of solvolysis of phosphorus acid ester both in the absence of surfactant and in the micellar sodium dodecyl sulfate solution in ethylene glycol is found. The influence of the other lanthanide ions on the kinetics is also studied. The La 3+ and Pr 3+ are found to exert an identical effect while Sm 3+ is less effective. By methods of polarizing microscopy, the formation of liquid crystalline mesophase at high lanthanum (tris(dodecyl)sulfate concentrations in ethylene glycol is revealed. The investigation of the catalytic effect of the sodium dodecyl sulfate -La 3+ (3 : 1 molar) composition has shown a sharp acceleration of the reaction at high surfactant concentration.

Determination of the kinetic parameters of radical pairs with heavy atom substitutions in micellar solution by optical detected × and Ku band ESR

A study is reported of the dynamics of radical pairs formed by the photochemical reaction of benzophenone and its heavy atom substitutions, dichlorobenzophenone and bromobenzophe-none, in a sodium dodecylsulphate micellar solution. Changes were observed in the time profiles of the transient absorptions and in the yields of the escaping radicals induced by the irradiation of an × (9.15 GHz) or Ku band (17.44 GHz) microwave short pulse. From these experiments, the hydrogen abstraction reaction rates, the recombination rates of the singlet radical pairs, the relaxation rates, the escape rates, the decay rates of the radical pairs without the external magnetic field, and the intersystem recombination rates due to the spin-orbit coupling were determined.

Magnetic field dependence of spin dynamics of radical pairs studied by time-resolved RYDMR

The photochemical reaction of 2-methyl-1,4-naphthoquinone in sodium dodecyl-sulphate micellar solution was investigated with an optical detection ESR apparatus working at 17.44 GHz (Ku-band). The Ku-band RYDMR spectra are obtained from the transient optical absorption and the stationary absorption of the reaction product, and the shift of the spectral peak compared with the spectra at 331 mT is reproduced well by the difference in g of the component radicals. The microwave pulse length dependence shows the quantum beat originated from the conversion between triplet ±1 states and the mixed state of singlet and triplet 0 states by the microwave field. The decay rate of the radical pair in triplet ±1 at 622 mT was determined to be 7.1 ± 1.1 × 105 s−1 by changing the irradiation time of a short (20 ns) microwave pulse with reference to the laser excitation. This value is smaller than that at 331 mT, as expected by the relaxation mechanism.

Critical micelle concentration and phase behavior of aqueous mixtures of dodecylsulfates and sodium ethoxydodecylsulfate

Mixed aqueous micellar solutions of sodium dodecylsulfate+potassium dodecylsulfate and sodium dodecylsulfate+sodium ethoxydodecylsulfate have been studied. Experimental data on the critical micelle concentration (CMC) versus the relative concentration of two surfactants, results of the micellar solution/liquid crystal and liquid solution/solid phase equilibrium measurements are presented. The data obtained are interpreted in the framework of the pseudo-phase model of micellar solutions. The effect of salts added to solutions of dodecylsulfates is discussed.

Synthesis and NMR studies of (13)C-labeled vitamin D metabolites.

Isotope-labeled drug molecules may be useful for probing by NMR spectroscopy the conformation of ligand associated with biological hosts such as membranes and proteins. Triple-labeled [7,9,19-(13)C(3)]-vitamin D(3) (56), its 25-hydroxylated and 1 alpha,25-dihydroxylated metabolites (58 and 68, respectively), and other labeled materials have been synthesized via coupling of [9-(13)C]-Grundmann's ketone 39 or its protected 25-hydroxy derivative 43 with labeled A ring enyne fragments 25 or 26. The labeled CD-ring fragment 39 was prepared by a sequence involving Grignard addition of [(13)C]-methylmagnesium iodide to Grundmann's enone 28, oxidative cleavage, functional group modifications leading to seco-iodide 38, and finally a kinetic enolate S(N)2 cycloalkylation. The C-7,19 double labeling of the A-ring enyne was achieved by the Corey-Fuchs/Wittig processes on keto aldehyde 11. By employing these labeled fragments in the Wilson-Mazur route, the C-7,9,19 triple-(13)C-labeled metabolites 56, 58, and 68 as well as other (13)C-labeled metabolites have been prepared. In an initial NMR investigation of one of the labeled metabolites prepared in this study, namely [7,9,19-(13)C(3)]-25-hydroxyvitamin D(3) (58), the three (13)C-labeled carbons of the otherwise water insoluble steroid could be clearly detected by (13)C NMR analysis at 0.1 mM in a mixture of CD(3)OD/D(2)O (60/40) or in aqueous dimethylcyclodextrin solution and at 2 mM in 20 mM sodium dodecyl sulfate (SDS) aqueous micellar solution. In the SDS micellar solution, a double half-filter NOESY experiment revealed that the distance between the H(19Z) and H(7) protons is significantly shorter than that of the corresponding distance calculated from the solid state (X-ray) structure of the free ligand. The NMR data in micelles reveals that 58 exists essentially completely in the alpha-conformer with the 3 beta-hydroxyl equatorially oriented, just as in the solid state. The shortened distance (H(19Z))-H(7)) in micellar solutions as compared to that in the solid state is most easily rationalized on the basis that the 5(10)-torsion angle in 58 is decreased in micellar solutions as compared to that in the solid state.

Effect of hydroxypropyl-β-cyclodextrin on the electrochemical oxidation and polymerization of 3,4-ethylenedioxythiophene

The electrochemical oxidation of 3,4-ethylenedioxythiophene (EDOT) on platinum is studied in electrolyte solutions containing hydroxypropyl-β-cyclodextrin (HP-β-CD). HP-β-CD is found to increase the solubility of EDOT up to a concentration of 0.026 M in aqueous solutions. Addition of HP-β-CD (0.1 M) produces a slight red shift of the EDOT main absorption band from 254.9 to 257.7 nm and an increase of the HP-β-CD concentration decreases the absorption coefficient, ε max to 6150 l mol −1 cm −1 in the UV–vis region, indicating complex formation. The cyclic voltammetric response of EDOT in 0.1 M aqueous LiClO 4 solutions consists of an ill-defined wave (P 1) and an adsorption peak (P 2). Contrary to the case of oxidation in acetonitrile medium, a post-peak is observed in the voltammograms of EDOT electro-oxidation in aqueous LiClO 4 solutions due to the adsorption of the oxidized EDOT species. A gradual reduction of the peak current of P 2 with increasing [HP-β-CD] and its total disappearance at high [HP-β-CD] suggest complex formation between HP-β-CD and EDOT + and also the peak P 2 to be due to adsorption of EDOT + species. The experiments intended to show the effect of ‘pre-adsorbed’ HP-β-CD on EDOT oxidation led to the conclusion that adsorbed HP-β-CD also solubilizes EDOT at the electrode surface. The CV behaviour of EDOT in HP-β-CD is discussed in comparison with that in sodium dodecylsulfate micellar solutions. Addition of increasing amounts of HP-β-CD shifts P 1 positively and P 2 negatively while also suppressing P 2 totally and reducing the peak current of P 1 to a significant extent. At a higher concentration of HP-β-CD, viz. 0.05 M, a peak appears at 1.29 V as a result of the above two opposing effects of CD on the peak potentials of P 1 and P 2. This resultant peak (P composite) is more positive relative to the position of P 1 observed in the absence of HP-β-CD. The positive shift of the peak and peak current reduction indicate that EDOT (or an oxidized EDOT species) possibly interacts with the outer nucleophilic part of HP-β-CD. The electro-oxidation processes occurring at P 1 and P 2 are explained using an oligomeric approach, in which the electrochemical reactions are coupled to chemical reactions or adsorption of the oxidized species. Potential cycling of the platinum electrode in solutions containing 0.026 M EDOT+0.05 M HP-β-CD+0.1 M LiClO 4 between −0.5 and 1.2 V yields an adherent and smooth polymer film of poly(ethylenedioxythiophene), as shown in the SEM examination. In situ resistance measurements carried out with the polymer films in the electroactive region show a minimum resistance in the potential range of 0.3–0.4 V. Even the electrochemically-reduced films are found to possess some residual electrical conductivity.

Solubilization of some Hydrophobic Food Flavouring Agents in Single and Mixed Micellar Systems.

Water insoluble food flavouring agents, viz, benzyl acetate, 2-phenyl ethanol and geraniol were solubilized in SDS (sodium dodecyl sulphate) and Triton X-100 surfactant solutions respectively and also in the mixture of these two surfactants. 2-phenyl ethanol was found to be more solube in SDS (anionic) micellar solution as compared to that in TX-100 (non-ionic) micellar solution. Solubilization of Geraniol was found to be more in TX-100 than SDS solution. The solubilization of benzyl acetate remained almost the same in both types of micellar solutions, but its solubilization was almost twice in the mixed micellar solution. Interestingly, there was no change in the solubilization of 2-phenyl ethanol and geraniol in the mixed micellar solution.

Quenching of Pyrene Derivatives' Fluorescence by Nitroxide Radicals in Sodium Dodecyl Sulfate Micellar Solutions

Dynamic fluorescence quenching measurements have been performed on pyrene derivatives (pyrene (Py), 1-pyrenebutanoic acid (PBA), and 1-pyrenedodecanoic acid (PDA)), using as quenchers nitroxide free radicals (2,2,6,6-tetramethyl-1,1-piperidinyloxyl, 4-hydroxy-2,2,6,6-tetramethyl-1,1-piperidinyloxyl, and 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (TEMN)) in aqueous solutions of sodium dodecyl sulfate. The mean aggregation number values are comparable with the literature data only when the partition coefficient of the quencher is higher than 1100 M−1. It is shown that the dynamic fluorescence quenching for the PBA/TEMN pair cannot be described by the Infelta—Tachiya model owing to the fact that the intramicellar quenching rate constant is lower than the exit rate constant of the quencher from the micelle. The average location of the fluorescent probes is also discussed, Py and PDA having the pyrenyl moieties located at approximately the same depth in the micellar core, while in the case of PBA the pyrenyl moiety is buried deeper.

Microwave-Induced Quantum Beats in Micellized Radical Pairs under Spin-Locking Conditions

The effect of short microwave pulse irradiation on the spin correlated radical pairs generated by the hydrogen abstraction reaction of triplet excited xanthone with tert-butyl-substituted phenols in a micellar sodium dodecyl sulfate solution is investigated by a time-resolved transient optical absorption technique. An increase in the microwave pulse duration under the electron spin resonant conditions leads to the alternation of the radical pair concentration. It is explained by the periodical change of the radical pair spin state population with an angular frequency of ω1 = γeB1 due to the pumping with resonant microwave field B1. The double frequency (2ω1) quantum beats are observed under spin-locking conditions. The behavior of quantum beats in this case is rationalized by the effect of microwave pulse on the electron spins of both radicals in the radical pair and reflects the spin dynamics in the triplet manifold of radical pairs that is isolated from that of the singlet during the microwave pulse by ...

Excimer Formation in a Naphthalene-Labeled Dendrimer

Steady-state and time-resolved fluorescence measurements were conducted on newly synthesized Frechet-type dendrimers with naphthalene peripheral groups in homogeneous and sodium dodecyl sulfate (SDS) micellar solutions. Intense excimer emission was observed for the third-generation dendrimer 3 but not for the first-generation dendrimer 1a. This different spectroscopic behavior was attributed to the geometry of dendrimer 3, where excimeric interactions between adjacent π-stacked naphthyl groups are present.

Solubilization-Site-Dependent Micellar Morphology: Effect of Organic Additives and Quaternary Ammonium Bromides

Here we report systematic viscosity measurements under Newtonian flow conditions for sodium dodecyl sulfate (SDS) micellar solutions in the presence of aliphatic hydrocarbons (n-hexane, n-heptane, n-octane), toluene, and 1-alkanols (1-heptanol, 1-octanol) at 30 °C. The influence of 0.1 M quaternary ammonium bromides (R4NBr; R = H, CH3, C2H5, n-C3H7, n-C4H9, n-C5H11) was seen on relative viscosity (ηr) vs additive concentration profiles. Lower members of R4NBr (R = H, CH3, C2H5) have marginal influence on viscosity profiles and hence on micellar morphology. This may be due to the less pronounced effect on association structures as well as on solubilization sites (and on solubilizate content at a particular site) of added organics. As the alkyl part of R4NBr was increased (R ≥ n-C3H7), the effect, which depended upon the nature of the additive (i.e., its hydrophobic/polarity character), was significant. This is possibly due to salts affecting the partitioning content of organic additives at different micell...

Sensitized room temperature phosphorescence of pyrene in sodium dodecylsulfate micelles with triphaflavine as energy donor

The sensitized room temperature phosphorescence (SRTP) of pyrene in micellar solutions of sodium dodecylsulfate (SDS) based on triplet–triplet (T–T) energy transfer has been investigated. Triphaflavine as a triplet energy donor, thallium(I) nitrate as a heavy atom, and sodium sulfite as a scavenger of oxygen were used. The effects of triphaflavine, SDS, and thallium nitrate concentrations on pyrene-SRTP intensity, lifetime, and decay rate constants were studied. A comparative study of selectivity factors for pyrene determination by room temperature phosphorescence (RTP) and SRTP has also been made. The analytical figures of merit for SRTP determination of pyrene are given.

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.