A laser photolysis study of the effect of a magnetic field on the kinetics of the recombination of radical and radicalion pairs in micelles

Conclusions The recombination of the radical pairs formed upon the transfer of a hydrogen atom from phenols and amines to triplet quinones in micelles is hindered upon the application of an external magnetic field and accelerated in the presence of atmospheric oxygen. The magnetic field effect is explained within the framework of a relaxation mechanism. The magnetic field has no effect on the kinetics of the deactivation of triplet exciplexes in micelles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 464–467, February, 1986.     

Effect of a magnetic field on the kinetics of the geminal recombination of triplet radical pairs adsorbed on glass with small pores

Conclusions A kinetic study was carried out for the geminal recombination of triplet radical pairs adsorbed in glass with small pores. The application of an external magnetic field is accompanied by a significant decrease in the fraction of radicals, which recombine in the cage. The magnetic effects in microporous glass are comparable in magnitude with the analogous phenomena in micelles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1202–1205, May, 1989.     

Diffusion of sodium dodecyl sulfate micelles in agarose gels

The gradient diffusion of ionic sodium dodecyl sulfate micelles in agarose gel was investigated at moderate concentrations above the CMC. Of particular interest were the effects of micelle, gel, and sodium chloride concentration on the micelle diffusivity. Holographic interferometry was used to measure the gradient diffusion coefficient at three sodium chloride concentrations (0, 0.03, 0.10 M), three gel concentrations (0, 1, 2 wt%), and several surfactant concentrations. Time-resolved fluorescence quenching was used to measure aggregation numbers both in solution and gel. The micelle diffusivity increased linearly with surfactant concentration at the two larger sodium chloride concentrations and all gel concentrations. In general, the strength of this effect increased with decreasing sodium chloride concentration and increased with gel concentration. This behavior is evidence of decreasing micelle-micelle electrostatic interactions with increasing sodium chloride concentrations, and increasing excluded volume effects and hydrodynamic screening with increasing gel concentration, respectively. The only exception was at 0.1M sodium chloride and 2 wt% agarose, which showed a slight reduction in the slope compared to 1 wt% agarose. It was found that the concentration effect is quite strong for charged solutes: at a NaCl concentration of 0.03 M in a 2% agarose gel, in a solution with 3% SDS micelles by volume, the micelle diffusion coefficient is doubled relative to its value in the same gel at infinite dilution. The extrapolated, infinite-dilution diffusion coefficients and the rate at which the micelle diffusivity increased with surfactant concentration were compared with predictions of previously published theories in which the micelles are treated as charged, colloidal spheres and the gel as a Brinkman medium. The experimental data and theoretical predictions were in good agreement.     

Magnetic field and magnetic isotope effects on the recombination kinetics of covalently-linked ketyl-phenoxyl triplet radical pairs

The recombination kinetics of three photogenerated covalently-linked ketyl-phenoxyl triplet radical pairs,³[PhC^.(OD)C₆H₄O(CH₂) _n OC₆H₄C₆H₄O^.] (n=3, 6, and 10), and of the corresponding deuterated derivatives were examined by the laser flash technique under an external magnetic field (up to 0.2 T) in a CDCl₃/CD₃OD (21) mixture. In zero magnetic field, radical pairs (RPs) with small exchange interactions (n=6 and 10) are characterized by high values of the magnetic isotope effect (MIE), which reach 3 for pairs withn=10. Under strong magnetic fields (up to 0.2 T), the values of MIE decrease to 1.2 to 1.1. The photochemical behavior of covalently-linked RPs is compared with that of similar unlinked RPs in micelles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 442–446, March, 1995.The authors are grateful to V. F. Tarasov, A. I. Shushin (N. N. Semenov Institute of Chemical Physics, RAS) and V. A. Nadtochenko (Institute of Chemical Physics in Chernogolovka, RAS) for helpful discussions.     

Acid-base equilibria and dynamics in sodium dodecyl sulfate micelles: geminate recombination and effect of charge stabilization

The synthetic flavylium salt 4-carboxy-7-hydroxy-4'-methoxyflavylium chloride (CHMF) exhibits two acid-base equilibria in the range of pH 1-8 in both aqueous and micellar sodium dodecyl sulfate (SDS) solutions. The values of pK(a1) and pK(a2) for the cation-zwitterion (AH(2)(+) <--> Z + H(+)) and the zwitterion-base (Z <--> A(-) + H(+)) equilibria increase from 0.73 and 4.84 in water to 2.77 and 5.64 in SDS micelles, respectively. The kinetic study of the Z <--> A(-) + H(+) ground-state reactions in SDS points to the diffusion-controlled protonation of A(-) in the aqueous phase (k(p2w) = 4.2 x 10(10) M(-)(1) s(-)(1)) and in the micelle (k(p2m) = 2.3 x 10(11) M(-)(1) s(-)(1)). The deprotonation rate of Z did not significantly change upon going from water (k(d2) = 6.3 x 10(5) s(-)(1)) to SDS (k(d2) = 5.2 x 10(5) s(-)(1)), in contrast with the behavior of ordinary cationic flavylium salts, for which k(d2) strongly decreases in SDS micelles. These results suggest that deprotonation of the zwitterionic acid is not substantially perturbed by the micellar charge. Electronic excitation of the Z form of CHMF induces fast adiabatic deprotonation of the hydroxyl group of Z() (2.9 x 10(10) s(-)(1) in water and 8.4 x 10(9) s(-)(1) in 0.1 M SDS), followed by geminate recombination on the picosecond time scale. Interestingly, while recombination in water (k(rec) = 1.7 x 10(9) s(-)(1)) occurs preferentially at the carboxylate group, at the SDS micelle surface, recombination (k(rec) = 9.2 x 10(9) s(-)(1)) occurs at the hydroxyl group. The important conclusion is that proton mobility at the SDS micelle surface is substantially reduced with respect to the mobility in water, which implies that geminate recombination should be a general phenomenon in SDS micelles.     

Ionic quenching of naphthalene fluorescence in sodium dodecyl sulfate micelles

Micellar effects on luminescense of organic compounds or probes are well established, and here we show that quenching is highly favored in aqueous sodium dodecyl sulfate (SDS) micelles, which concentrate a naphthalene probe and cations of lanthanides, transition metals, and noble metals. Interactions have been studied by steady state and time-resolved fluorescence in examining the fluorescence suppression of naphthalene by metal ions in anionic SDS micelles. The quenching is collisional and correlated with the unit charge and the reduction potential of the metal ion. The rate constants, calculated in terms of local metal ion concentrations, are close to the diffusion control limit in the interior of SDS micelles, where the microscopic viscosity decreases the transfer rate, following the Stokes-Einstein relation.     

Anomalous solubilization behavior of dimyristoylphosphatidylcholine liposomes induced by sodium dodecyl sulfate micelles

The solubilization dynamics of dimyristoylphosphatidylcholine (DMPC) liposomes, as induced by sodium dodecyl sulfate (SDS), were investigated; this investigation was motivated by several types of atypical behavior that were observed in the solubilization in this system. The liposomes and surfactants were mixed in a microchip, and the solubilization reaction of each liposome was observed using a microscope. We found that solubilization occurred not only via a uniform dissolution of the liposome membrane, but also via a dissolution involving the rapid motion of the liposome, or via active emission of protrusions from the liposome surface. We statistically analyzed the distribution of these patterns and considered hypotheses accounting for the solubilization mechanism based on the results. When the SDS concentration was lower than the critical micelle concentration (CMC), the SDS monomers entered the liposome membrane, and mixed micelles were emitted. When the SDS concentration was higher than the CMC, the SDS micelles directly attacked the liposome membrane, and many SDS molecules were taken up; this caused instability, and atypical solubilization patterns were triggered. The size dependence of the solubilization patterns was also investigated. When the particle size was smaller, the SDS molecules were found to be homogeneously dispersed throughout the whole membrane, which dissolved uniformly. In contrast, when the particle size was larger, the density of SDS molecules increased locally, instability was induced, and atypical dissolution patterns were often observed.     

Inclusions of methylene blue and phenothiazine by β-cyclodextrin in sodium dodecyl sulfate micelles

The inclusions of methylene blue and phenothiazine by β-cyclodextrin (β-CD) in sodium dodecyl sulfate (SDS) micelles and SDS/n-C₅H₁₁OH mixed micelles are studied by fluorescence spectroscopy. β-CD molecules can include monomers of methylene blue only after they have included SDS at a ratio of 1:1. However, phenothiazine can be included in the β-CD cavities even with β-CD concentrations lower than the total SDS concentration in SDS micelles, but not for solutions with SDS/n-C₅H₁₁OH mixed micelles.     

Pyrene-assisted synthesis of size-controlled gold nanoparticles in sodium dodecyl sulfate micelles

Gold nanoparticles prepared by chemical reduction in sodium dodecyl sulfate (SDS) solution are size-controlled with the addition of pyrene. Micellar electrokinetic capillary chromatography (MEKC) is applied to the system to examine the size and polydispersity of gold nanoparticles and to show that pyrene has the extraordinary effect in decreasing the size and narrowing the dispersity of gold nanoparticles. The MEKC electropherograms further suggest that pyrene could be oxidized by the aqueous Au(III) complexes first. All the reduced Au complexes were then solubilized in the pyrene-SDS micelles. The growth of gold nanoparticles beyond the embryonic stage was subsequently inhibited by the encapsulating SDS and electrophilic pyrene.     

Chlorpromazine and sodium dodecyl sulfate mixed micelles investigated by small angle X-ray scattering

Small-angle X-ray scattering (SAXS) studies are reported on the interaction of chlorpromazine (CPZ) with micelles of anionic surfactant sodium dodecyl sulfate (SDS). Isotropic solutions of SDS (40 and 100 mM) at pH 4.0, 7.0, and 9.0 in the absence and presence of CPZ (2-25 mM) were investigated at the National Laboratory of Synchrotron Light (LNLS, Campinas, Brazil). The data were analyzed through the modeling of the micellar form factor and interference function. The results evidence a micellar shape transformation from prolate ellipsoid to cylinder accompanied by micellar growth and surface charge screening as the molar ratio CPZ : SDS increases in the complex. Small ellipsoids with axial ratio nu=1.5+/-0.1 at 40 mM SDS grow and reassemble into cylinder-like aggregates upon 5 mM drug incorporation (1 CPZ : 8 SDS monomers) with a decrease of the micelle surface charge. At 10 mM CPZ : 40 mM SDS cylindrical micelles are totally screened with an axial ratio nu approximately 2.5. The data also indicate the presence of small prolate ellipsoids (nu=1.7+/-0.1) in solutions of 100 mM SDS (no drug) and micellar growth (nu approximately 2.0 and 4.0) when 10 and 25 mM CPZ are added to the system. In the latter case, the aggregate is also better represented by a cylinder-like form. Therefore, our results demonstrate that the axial ratio and shape evolution of the surfactant : phenothiazine complex are both SDS concentration and drug : SDS molar ratio dependent. The drug location close to the SDS polar headgroup region without disrupting in a significant way both the paraffinic hydrophobic core and the polar shell thickness is inferred. SAXS data made it possible to obtain the shapes and dimensions of CPZ/SDS aggregates.     

Effect of sodium dodecyl sulfate micelles on peptide mass fingerprinting by matrix-assisted laser desorption/ionization mass spectrometry

Here we have examined the effect of sodium dodecyl sulfate (SDS) at various concentrations on matrix-assisted laser desorption/ionization (MALDI) peptide mass fingerprinting experiments. Several model proteins were digested with trypsin and then various amounts of SDS were added prior to MALDI mass spectrometry. Evaluation of the data was made by calculating the amino acid sequence coverage within each analysis. It was found that addition of 0.1-0.3% w/v SDS prior to MALDI analysis results in an increase in the number of tryptic peptides detected thereby improving the total sequence coverage of the analysis. The use of SDS at concentrations near its critical micelle concentration can improve sequence coverage from MALDI peptide mass fingerprinting analyses allowing for increased confidence in protein identification or additional opportunities to identify putative regions of posttranslational modification.     

Influence of the linking chain length on the recombination kinetics of covalently bonded triplet radical pairs and magnetic field effects

Nanosecond laser flash photolysis technique is used to study the formation and decay kinetics of covalently linked triplet radical pairs (RP) formed after photoinduced electron transfer in the series of 21 zinc porphyrin—chain—viologen (Pph—Sp_n—Vi²⁺) dyads, where the number of atoms (n) in the chain increases from 2 to 138. In poorly viscous polar solvents (acetone, CHCl₃—CH₃OH (1 : 1) mixture), the dependence of the rate constant of RP formation on n can be described by the equation k _e = k _e ⁰ n ^–a at k _e ⁰ = 2.95·10⁸ s^–1 anda = 0.8. In the zero magnetic field, the RP recombination rate constant (k _r(B = 0)) is significantly lower than k _e and ranges from 0.7·10⁶ to 8·10⁶ s^–1. The dependence of k _r(B = 0) on n is extreme. The dependence k _r(B = 0) reaches a maximum at n = 20. In the strong magnetic field (B = 0.21 T), the significant retardation of triplet RP recombination is observed. The chain length has an insignificant effect on k _r(B = 0.21 T), which ranges from 0.3·10⁶ to 0.9·10⁶ s^–1. The regularities found are discussed in terms of the interplay of molecular and spin dynamics.     

Enzymatic determination of some pharmaceuticals in direct and reversed sodium dodecyl sulfate micelles

The properties of horseradish peroxidase in sodium dodecyl sulfate (DDS) reversed micelles in benzene-pentanol-water solutions are studied. The potential of the analytical application of direct and reversed DDS micelles is demonstrated using newly developed methods for the determination of peroxidase substrates (hydrogen peroxide and cystein), inhibitor (sulfanylamide), and activator (imidazole) via the oxidation of o-dianisidine (o-D) with hydrogen peroxide.     

Structure of pravastatin and its complex with sodium dodecyl sulfate micelles studied by NMR spectroscopy

The aim of this work was to study the mechanisms of interaction between pravastatin and cell membranes using model membranes (sodium dodecyl sulfate micelles) by nuclear magnetic resonance spectroscopy methods. On the basis of the nuclear magnetic resonance experiments, it was established that pravastatin can form intermolecular complexes with sodium dodecyl sulfate micelles by the interaction of its hydrophilic groups with the polar surface of the micelle. Conformational features of pravastatin molecule were also studied. Copyright © 2014 John Wiley & Sons, Ltd.     

Separation and selectivity of benzophenones in micellar electrokinetic chromatography using sodium dodecyl sulfate micelles or sodium cholate modified mixed micelles

The separation and selectivity of nine benzophenones in micellar electrokinetic chromatography (MEKC) using sodium dodecyl sulfate (SDS) micelles or sodium cholate (SC) modified mixed micelles were investigated in the pH range 6.5-8.0. The results indicate that the combined effects of buffer pH and SC concentration can greatly affect the separation and selectivity of benzophenones, particularly for benzophenones possessing a hydroxyl substituent at the 4-position of the aromatic ring with respect to the carbonyl moiety when using SDS-SC mixed micelles. Better separability can be obtained with SDS-SC mixed micelles than with SDS micelles. Complete separation of nine benzophenones in MEKC can be achieved with an appropriate choice of buffer pH and the concentration of SDS micelles or SC modified mixed micelles. The dependence of the migration order of those benzophenones based on their structures and solute-micelle interactions is discussed.