Sodium Dodecyl Sulfate Micellar Solutions Research Articles

Magnetic Isotope Effect on Kinetic Parameters and Quantum Beats of Radical Pairs in Micellar Solution Studied by Optically Detected ESR Using Pulsed Microwave

We investigated the quantum beats, the oscillation between singlet and triplet states of radical pairs induced by the microwave field resonant to one of the component radicals. They were observed as the alternation of the yields of the component radicals by a nanosecond time-resolved optical absorption with the X-band (9.15 GHz) resonant microwave pulse. This technique was applied to the photochemical reaction of benzophenone, benzophenone-d(10), and benzophenone-carbonyl-(13)C in a sodium dodecylsulfate micellar solution with a step-by-step increase of the resonant microwave pulse width. The yields of the component radicals showed alternation with an increase of the microwave pulse width. This indicates that the radical pair retains spin coherence in the micellar solution. The magnetic isotope effect on the amplitude of the quantum beat was observed. The MW effect on the quantum beat of BP-(13)C decreases from 80% to 60% of that of BP by irradiation of the pi-pulse MW due to spin-locking. The kinetic parameters were also determined using the X- or Ku-band (17.44 GHz) region. They are almost similar to each other except for the intersystem recombination rate in the system of BP-(13)C, which may be slightly higher than those in other systems.

Determination of atenolol by the micelle‐stabilized room‐temperature phosphorescence methodology

A micellar-stabilized room-temperature phosphorescence (MS-RTP) method for the determination of atenolol has been developed in micellar solutions of sodium dodecylsulphate (SDS) in the presence of thallium(I) as a heavy atom and sodium sulphite as an oxygen scavenger. The effects of thallium(I) nitrate, SDS and sodium sulphite concentrations on atenolol MS-RTP intensity were studied. Optimized conditions to obtain maximum sensitivity were 0.015 mol/L thallium(I) nitrate, 0.1 mol/L SDS and 0.0075 mol/L sodium sulphite. The maximum phosphorescence signal was completely developed in 10 min and the intensity was measured at lambda(ex) = 272 nm and lambda(em) = 412 nm. The linear range of application obtained was 2.01-16.00 microg/mL. The detection limit estimated from the least-squares regression analysis was 0.86 microg/mL and the relative standard deviation of 10 replicates was 1.7%. The proposed method was applied to the determination of atenolol in a pharmaceutical formulation. The quantitation was carried out by means of standard calibration, standard-additions calibration and Youden calibration. These three experiments were necessary to evaluate the presence of constant and proportional errors due to the matrix.

Analytical Studies on Photochemical Behavior of Phototoxic Substances; Effect of Detergent Additives on Singlet Oxygen Generation

Monitoring of reactive oxygen species (ROS) generation from photoirradiated compounds would be effective for the prediction of the phototoxic potential. The aim of this investigation was to clarify the possible role of biomimetic vehicle systems on the photochemical properties of phototoxic compounds, focusing on the singlet oxygen generation. Nine phototoxic and one non-phototoxic compounds (200 microM), dissolved in Tween 20, sodium laurate, or sodium dodecyl sulfate (SDS) micellar solution, were exposed to UVA/B light (250 W/m2), and singlet oxygen generation was monitored by RNO bleaching methodology. Photochemical properties of photosensitizers were also evaluated by UV measurement, and the interaction of photosensitizers with surfactant micelles was assessed by Z-potential and NMR spectroscopic analyses. All phototoxic compounds tended to generate singlet oxygen under light exposure in the all micellar solutions tested. There appeared to be some differences in photoreactivity of both cationic and anionic photosensitizers among the micelles tested, whereas ROS data on anthracene, dissolved in three micellar solutions, were found to be quite similar. Photosensitizers exhibited no significant changes in UV spectral patterns among the dissolving micellar solutions. Addition of cationic photosensitizer at the final concentration of 100 microM into 100 mM SDS solution resulted in the 20 mV increase of zeta potential and transition of NMR spectral pattern, which would reflect the electrostatic interaction with anionic micelles. Based on the data obtained, the photoreactivity of photosensitizing molecules, especially cationic and anionic photosensitizers, strongly depends on the physicochemical properties of the microenvironment.

Importance of Micellar Lifetime and Sub-micellar Aggregates in Detergency Processes

Abstract Micelles are known to be dynamic entities, rapidly breaking and reforming continuously. Micellar dynamics can be manipulated by the addition of non-ionic or oppositely charged cosurfactant to a sodium dodecyl sulfate solution. Using filtration through nanoporous membranes we have shown that sodium dodecyl sulfate micellar solutions are not only made up of micelles and monomers, but also contain a high concentration of sub-micellar aggregates. The concentration of sub-micellar aggregates decreases as the micellar stability increases. We have investigated the role of micellar stability and sub-micellar aggregates in cleaning of fabrics and hard surfaces such as porcelain dishes. After careful observation, it was determined that more stable micelles and lower concentrations of sub-micellar aggregates lead to more efficient detergency. In summary, it is desirable to have relatively stable micelles and the least number of sub-micellar aggregates for efficient detergency.

The electrical double layer of micelles in ionic surfactant solutions in the presence of a background electrolyte: 2. Moderately concentrated micellar solutions of sodium dodecyl sulfate

To continue previous studies [1], a model is developed for calculating electrostatic potentials 1ψ0 and 1ψd corresponding to the surface of micelle core and the Stern layer, respectively, and the degree 1β of binding of counterions in moderately concentrated micellar solutions of ionic surfactants. By the example of sodium dodecyl sulfate micellar solutions, dependences of 1ψ0 and 1ψd on overall concentration n varying over the range from 0.1 to 0.9 M are determined at different NaCl concentrations in the system. The absolute values of 1ψ0 and 1ψd potentials are found to grow with a rise in the degree of micellization and a reduction in the average intermicellar distances. This growth is greatly pronounced at a low content of the background electrolyte, whereas, in concentrated NaCl solutions (of approximately 0.1 M), potentials 1ψ0 and 1ψd remain practically constant. Dependence 1 − 1β(n) is monotonically decreasing function.

Osmotic pressure of micellar sodium dodecyl sulfate solutions in the presence of NaCl

The concentration dependence of osmotic pressure πs of micellar solutions of an ionic surfactant in the presence of a background electrolyte is theoretically considered in terms of the Debye-Huckel theory with due regard for the premicellar association and interaction of micelles. On the basis of the quasi-chemical theory of micellization, the system composition is determined and the thickness of the electrical double layer of micelles is calculated. Within the framework of a cell model and the ideas of the molecular and ion-electrostatic interaction of micelles, which varies in relation to the degree of micellization, osmotic pressure in a sodium dodecyl sulfate-0.01 M NaCl system is calculated during variations in the overall surfactant concentrations. The results obtained are in good qualitative and quantitative agreement with available experimental data. At the same time, the results of calculating πs values in terms of the Debye-Huckel theory without consideration for the interaction of micelles do not allow explanation of the experimental regularities.

Structure and Dynamics of Surfactin Studied by NMR in Micellar Media

The NMR structure of the cyclic lipopeptide surfactin from Bacillus subtilis was determined in sodium dodecyl sulfate (SDS) micellar solution. The two negatively charged side chains of surfactin form a polar head opposite to most hydrophobic side chains, accounting for its amphiphilic nature and its strong surfactant properties. Disorder was observed around the fatty acid chain, and 15N relaxation studies were performed to investigate whether it originates from a dynamic phenomenon. A very large exchange contribution to transverse relaxation rate R(2) was effectively observed in this region, indicating slow conformational exchange. Temperature variation and Carr-Purcell-Meiboom-Gill (CPMG) delay variation relaxation studies provided an estimation of the apparent activation energy around 35-43 kJ x mol(-1) and an exchange rate of about 200 ms(-1) for this conformational exchange. 15N relaxation parameters were also recorded in dodecylphosphocholine (DPC) micelles and DMSO. Similar chemical exchange around the fatty acid was found in DPC but not in DMSO, which demonstrates that this phenomenon only occurs in micellar media. Consequently, it may either reflect the disorder observed in our structures determined in SDS or originate from an interaction of the lipopeptide with the detergent, which would be qualitatively similar with an anionic (SDS) or a zwitterionic (DPC) detergent. These structural and dynamics results on surfactin are the first NMR characterization of a lipopeptide incorporated in micelles. Moreover, they provide a model of surfactin determined in a more biomimetic environment than an organic solvent, which could be useful for understanding the molecular mechanism of its biological activity.

Application of a partial filling technique to electrophoretic analysis on microchip with T-cross channel configuration

To achieve a high performance sample injection, we designed microchips with both T- and cross-type channel geometry (T-cross chip), which enables two sample solutions to be introduced into a separation channel simultaneously with desired volumes by a combination of gated and pinched injection techniques. The developed microchips were applied to microchip micellar electrokinetic chromatography (MCMEKC) using a partial filling (PF) technique. In the PF technique, to suppress the increase in the background noise due to the presence of a pseudostationary phase (PSP), e.g., ionic surfactant micelles in MCMEKC with mass spectrometric (MS) detection, in a background solution (BGS), the separation channel is partially filled with a PSP while the rest of the channel including the detection point is filled with the BGS without a PSP. As a result, both sodium dodecyl sulfate (SDS) micellar and sample solutions were simultaneously injected into the separation channel on the T-cross chip with a good repeatability of the injection lengths by applying programmed voltages, and a baseline separation of rhodamine derivatives was achieved within 40 s by MCMEKC, in which the micellar zone was partially injected with the PF technique. It was confirmed that the detection could be performed without any influence of SDS by the fluorescence imaging measurements. These results demonstrated that the developed T-cross chips will allow a combination of the MCMEKC separation with the MS detection by employing the PF technique for high performance analysis of biogenic compounds. In the PF–MCMEKC analysis, furthermore, the resolution of two rhodamines clearly increased from 1.30 to 1.73 with the increase of the injection length of PSP from 0.16 to 0.89 mm, whereas at the injection length of 1.47 mm the resolution decreased. Therefore, the selection of an optimal injection length on the T-cross chip is very important and the effects of the injection length on the separation processes in PF–MCMEKC were discussed on the basis of theoretical calculations.

Receptor properties of calix[4]resorcinarenes toward tetramethylammonium and choline cations in micellar solutions of sodium dodecyl sulfate

Concentration range of solubilization of calix[4]resorcinarene (H8L) in sodium dodecyl sulfate (SDS) micelles was found. The interaction of the deprotonated form of H8L (tetraanions [H4L]4−) with tetramethylammonium (TMA) and choline cations in micellar solutions of SDS was studied by pH-metry and NMR spectroscopy. The concentration dependences of the change in the cloud point in a multicomponent system TMA (choline)-[H4L]4-SDS-tetrabutylammonium bromide were determined. A correlation of these dependences with host-guest binding processes was found. The sharp change in the cloud points of the corresponding micellar solutions in concentration regions of TMA (0-5·10−4 mol L−1) and choline (0–1.1· 10−3 mol L−1) is caused by the formation of inclusion complexes TMA (choline)-[H4L]4− at the interface of the aqueous and micellar pseudophases.

Magnetic field effects on the reaction of a triplet-born radical pair consisting of two equivalent sulphur-centre radicals under ultrahigh fields of up to 28 T

A water-cooled pulsed magnet having a room temperature bore of diameter 20 mm was constructed. Magnetic field effects on a triplet sensitization reaction of p-aminophenyl disulfide (APDS) with xanthone (Xn) were studied in a sodium dodecylsulfate (SDS) micellar solution by a nanosecond laser flash photolysis technique under ultrahigh magnetic fields of up to 28 T. Upon irradiation of the SDS micellar solution containing APDS and Xn, triplet radical pairs of p-aminophenylthiyl radicals were generated. The yield of the escaped p-aminophenylthiyl radical was found to decrease by 6 ± 2% at 28 T compared with that at 0 T.

The Quantitative Characterization of Chemical Modification of Sodium Dodecyl Sulphate Micellar Solutions and Retention Model in Micellar Liquid Chromatography

Abstract The micelle solutions of sodium dodecyl sulphate (NaDS) modified by simultaneously presence of different aliphatic alcohols and an inorganic salt have been quantitatively characterized by the values of critical micelle concentrations, the degrees of counter-ion binding and electrostatic potentials of surface. The obtained characteristics of hybrid micelles and the coefficients of modifier distribution between aqueous solution and micellar pseudophase were used to develop a conceptual retention model in micellar liquid chromatography (MLC). The new retention model takes into account the microenvironment changes of an analyte when it goes from the hybrid micellar eluent to a modified surface of alkyl-bounded sorbent.

Anomalous Magnetic Field Effects Interpreted by the Relaxation Mechanism under Ultrahigh Fields of up to 28 T

Abstract Magnetic field effects on the triplet sensitization reaction of p-aminophenyl disulfide were studied in a sodium dodecylsulfate micellar solution by a nanosecond laser flash photolysis technique under ultrahigh magnetic fields of up to 28 T. The yield of the escaped p-aminophenyl thiyl radical decreased by 6 ± 2% at 28 T compared with that at 0 T.

A study of the non-electrostatic interaction micelle/charged ligand: A comparison of the results obtained by two different methods

A kinetic study of the reaction between [Fe(CN) 6] 4− (hexacyanoferrate (II)) and [Co(en) 2Cl 2] + ( trans-dichlorobis cobalt(III) bis(ethylenediammine)) has been carried out in sodium dodecyl sulphate (SDS) micellar solutions containing NaCl. The results are discussed by using an approach based on the pseudophase model. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants ([Co(en) 2Cl] + in the present Letter) to the micelles, which depends on the surface potential of the micelles. The electrostatic and non-electrostatic components of the free energy of binding are determined by two different methods and the results of these determinations are compared.

Oxidation of methyl linoleate in micellar solutions induced by the combination of iron(II)/ascorbic acid and iron(II)/H 2O 2

The oxidation of methyl linoleate (ML) was studied in the presence of Fe(II) alone and its combination with either ascorbic acid (AsAH 2) or hydrogen peroxide (H 2O 2) at different molar ratios. Reactions were carried out in micellar solutions of TTAB (tetradecyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate), respectively, and were monitored by UV spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Fe(II) alone was able to catalyze the oxidation of ML in micellar solutions of TTAB, but not in those of SDS. The combination of H 2O 2 with Fe(II) showed catalytic effect only in the TTAB medium, leading to different ML and Fe(II) oxidation kinetics compared to the Fe(II)-only catalyzed reactions. The AsAH 2/Fe(II) combination demonstrated to be a good catalyst for the oxidation of ML in SDS micellar solutions, but not in TTAB micellar solutions; the activity of the catalyst was dependent on the AsAH 2/Fe(II) molar ratio. The obtained results confirm that, for the ML oxidation to be initiated, the presence of a Fe(II)/Fe(III) couple is essential, which is related to the pH of micellar solutions. The catalytic properties of the AsAH 2/Fe(II) combination were explained by taking into account the anti-oxidant and pro-oxidant properties of AsAH 2, as well as the possible formation of an iron/ascorbate complex as the initiator of the ML oxidation.

Dielectric spectroscopy by differential measurements in transmission lines on sodium dodecyl sulfate micelles in water

A sodium dodecyl sulfate micellar solution in water was studied by Broad Band Dielectric Spectroscopy to investigate the relaxation processes. The experimental complex permittivity vs. frequency was analyzed by fitting the experimental data to three different models. The simplest one uses two Debye relaxation processes, one for bulk water and one for micelles contribution. The second model uses a Debye relaxation process for water and a Cole–Cole one for micelles, the third uses two Debye relaxation processes instead of the Cole–Cole one. Step amplitudes and relaxation time constants were obtained for the different processes. The sample Ohmic conductivity was also studied.

Micellar solubilization of ibuprofen: influence of surfactant head groups on the extent of solubilization

An important property of micelles with particular significance in pharmacy is their ability to increase the solubility of poorly soluble drugs in water, thus increasing their bioavailability. In this work, the solubilization of ibuprofen (IBU) was studied in micellar solutions of three surfactants possessing the same hydrocarbon tail but different hydrophilic head groups, namely sodium dodecyl sulphate (SDS), dodecyltrimethylammonium bromide (DTAB), and n-dodecyl octa(ethylene oxide) (C12EO8). The results showed that, irrespective of the surfactant type, the solubility of IBU increased linearly with increasing surfactant concentration, as a consequence of the association between the drug and the micelles. The 80 mM DTAB and the 80 mM C12EO8 micellar solutions resulted in a 16-fold increase in solubility of IBU when compared to the buffer solution, whereas the 80 mM SDS micellar solution resulted in a 5.5-fold increase in IBU solubility. The highest value of molar solubilization capacity (chi) was obtained with DTAB, chi = 0.97, followed by C12EO8 ,chi = 0.72, and finally SDS, chi = 0.23. However, due to the stronger tendency of the nonionic surfactant in forming micelles in solution, at the same surfactant concentration, we obtained the same solubility of IBU in both DTAB and C12EO8.

Slow Water Diffusion in Micellar Solutions

Slowly diffusing water molecules were found by quasi-elastic neutron scattering (QENS) in a sodium dodecyl sulfate (SDS) micellar solution, and both their diffusion coefficient (4.33 x 10(-6) cm2 x s(-1)) and mole fraction (0.057) were determined. After successfully checking the mean slowing down of solvent molecules by the gradient compensated stimulated spin-echo (GCSTE) pulse sequence NMR method, a similar effect was observed with this technique in the solvent phase of dodecyl trimethylammonium bromide (DTAB) and differing chain length (X = 12, 20, 30, and 40) ethoxylated nonyl phenol (9NX) micellar systems. Following the literature, the experimental results are qualitatively explained by assuming that, apart from ionic hydration, H-bonds may form between the solvent molecules and the O or N atoms present in the hydrophilic (head)groups of the micelle-forming monomers.

Kinetics and mechanism of bimolecular electron transfer reaction in quinone-amine systems in micellar solution

Photoinduced electron transfer (ET) reactions between anthraquinone derivatives and aromatic amines have been investigated in sodium dodecyl sulphate (SDS) micellar solutions. Significant static quenching of the quinone fluorescence due to high amine concentration in the micellar phase has been observed in steady-state measurements. The bimolecular rate constants for the dynamic quenching in the present systems k(q) (TR), as estimated from the time-resolved measurements, have been correlated with the free energy changes DeltaG(0) for the ET reactions. Interestingly it is seen that the k(q) (TR) vs DeltaG(0) plot displays an inversion behavior with maximum k(q) (TR) at around 0.7 eV, a trend similar to that predicted in Marcus ET theory. Like the present results, Marcus inversion in the k(q) (TR) values was also observed earlier in coumarin-amine systems in SDS and TX-100 micellar solutions, with maximum k(q) (TR) at around the same exergonicity. These results thus suggest that Marcus inversion in bimolecular ET reaction is a general phenomenon in micellar media. Present observations have been rationalized on the basis of the two-dimensional ET (2DET) theory, which seems to be more suitable for micellar ET reactions than the conventional ET theory. For the quinone-amine systems, it is interestingly seen that k(q) (TR) vs DeltaG(0) plot is somewhat wider in comparison to that of the coumarin-amine systems, even though the maxima in the k(q) (TR) vs DeltaG(0) plots appear at almost similar exergonicity for both the acceptor-donor systems. These observations have been rationalized on the basis of the differences in the reaction windows along the solvation axis, as envisaged within the framework of the 2DET theory, and arise due to the differences in the locations of the quinones and coumarin dyes in the micellar phase.

The ion-pair formation between dodecylsulfate and ammine-complexes of copper(II), nickel(II), zinc(II), palladium(II) and platinum(II), and the extraction behavior of the ammine-complexes by using sodium dodecylsulfate

A micellar solution of sodium dodecylsulfate (SDS) exhibits the property of being separated into two phases due to a temperature change or the addition of salts. The ammine-complexes of copper(II), nickel(II) and palladium(II) reacted with the dodecylsulfate anion to form the corresponding ion-pair, and were extracted into the SDS gel phase. The SDS plays the roles of a pairing-ion for the ammine-complexes and of an extraction medium. The ion-pair extraction mechanism was investigated; the extractability of metals was given by the function of the solubility products of the ion-pairs. This method was applied to the mutual separation of Ni(II)/Cu(II) and Pd(II)/Pt(II). The driving force for the extraction was an electrostatic interaction between the cationic complex and the surfactant anion. The use of the SDS gel as ion-exchanger is also expected.

Structural Characterization of Micellar Aggregates in Sodium Dodecyl Sulfate/Aluminum Nitrate/Urea/Water System in the Synthesis of Mesoporous Alumina

The mechanism of templated synthesis of ordered mesoporous alumina according to the recipe proposed by Yada et al. (Yada, M.; Machida, M.; Kijima, T. Chem. Commun. 1996, 769) using sodium dodecyl sulfate (SDS) as template, has been investigated by NMR self-diffusion and spin and fluorescence probe techniques. In the precursor solutions urea was found to produce a substantial shortening of the long entangled cylindrical aggregates characteristic of the SDS micellar solutions with aluminum salt in large excess. The formation of mesostructured hexagonal alumina was followed using spin probes incorporated in the SDS aggregates. No structural changes were observed during urea hydrolysis, before the onset of the precipitation. In the precipitate, the presence of the surfactant template is demonstrated as well as its interaction with the aluminum species. Time evolution of this interaction is also observed. Finally, the influence of the composition of the precursor system on the structure and thermal stability of as-synthesized alumina has been studied. It appears that hexagonally structured alumina is formed over a large range of compositions of the starting solution, with the dimension of the unit cell being almost constant. A model of precipitation is proposed that is based on the analogy with the formation of the hexagonal crystalline Al-DS precipitate in the ternary SDS/Al(NO3)3/water system.