Diffusion in surfactant solutions

The diffusion coefficients in water of Triton X-100 and sodium dodecyl sulfate were measured as a function of concentration using the Taylor dispersion technique. For Triton X-100, a nonionic surfactant, the diffusion coefficient drops from 7.4 × 10^-7 cm²/sec at 0.45 g/liter to 6.45 x 10^-7 cm²/sec at 5 g/liter. The diffusion coefficient of methyl yellow solubilized in Triton X-100 is close to that of the surfactant. This behavior is quantitatively consistent with a chemical equilibrium between monomer and micelle. For sodium dodecyl sulfate, an anionic surfactant, the diffusion coefficient increases from 1.76 x 10^-6 cm²/sec at 0.01 M to 4.53 x 10^-6 cm²/sec at 0.125 M. The increase is less when 0.1 M NaCl is added. The diffusion coefficient of the methyl yellow solubilized by the SDS is significantly less than that of the surfactant, particularly at low ionic strength. This behavior can be quantitatively explained by including electrostatic coupling between monomer, micelle, and counterion.     

Diffusion Coefficients and Structure Properties of Triton X-100/ n-C6H13OH/H2O System

Abstract

The diffusion coefficients of Triton X-100 micelles with different shape are determined by cyclic voltammetry without any probe. The first CMC (3.2 × 10^?4 mol-L^minus;1) and the second CMC (1.3 × 10^minus;3 mol-L^minus;1) of Triton X-100 micelles arc obtained, and the mechanism of electrochemical reaction for Triton X-100 is deduced, When n-hexanol is added, the diffusion coefficient of Triton X-100 micelles with different shape increases, but the solubilization fraction of n-hexanol decreases in spherical micelles and is almost constant in rodlike ones. However, the micropolarity of micelles decreases in both spherical and rodlike micelles. Furthermore, the diffusion coefficient of Triton X-100 micelles with different shape increases with temperature and the diffusion activation energy increases with n-hexanol content.     

Effects of Triton X-100 on Properties of Hemoglobin and Controlled Release of Drug in Hemoglobin/Ribavirin/H2O System

Effects of Triton X-100 on the properties of hemoglobin (Hb) and on the controlled release of ribavirin were studied using the methods of UV-Vis spectrum, fluorescence spectrum, zeta potential, conductivity, high-performance liquid chromatographic (HPLC), and image morphology in Hb/ribavirin/H₂O system. With the increase of concentration of Triton X-100 in the system, the intrinsic fluorescence intensity, synchronous fluorescence intensity, fluorescence polarization, zeta potential, and morphology of Hb all changed gradually, and the ribavirin located on the Hb surface was dissociated and released out. When the concentration of Triton X-100 was higher than 1×10⁻⁵ mol·L⁻¹, the stronger interaction of Triton X-100 with Hb was predominant. Hb was unfolded and denaturized. A little Triton X-100 can protect Hb from the effects of ribavirin.     

Determination of the Micellar Properties of Triton X-100 by Voltammetry Method

ABSTRACT

The diffusion coefficient of the micelle, the first CMC and the second CMC of Triton X-100 are determined by cyclic voltammetry without any probe. The first CMC and the second CMC of Triton X-100 are 3.1x lO^?1 and 1.3× 10^?1 respectively. The viscosity of the micelle solution, the micellar aggregation number and the micellar size increase but the diffusion coefficient decreases with Triton X-100 concentration increasing. The mechanism of the electrochemical reaction of Triton X-100 at platinum electrode is deduced by measurements of conductivity, pH and cyclic voltammetry.     

Dynamic surface tensions of micellar Triton X-100 solutions

Considering surfactant solutions at concentrations exceeding the CMC, another relaxation process besides diffusion occurs, also affecting the dynamic surface tension. The latter equilibration process concerns a micellisation/demicellisation process, representing the disintegration of micelles into monomers. The micellisation kinetics are accounted for by adding a single source term to the diffusion equation of the free monomers.

In the present paper the integration of the diffusion equation is avoided by using the concept of the diffusion penetration depth. Nevertheless, when this approximation is made, good agreement is achieved between experiment and theory for micellar Triton X-100 solutions. Moreover, it follows that diffusion of micelles may not be neglected.     

Self-aggregation and supramolecular structure investigations of Triton X-100 and SDP2S by NOESY and diffusion ordered NMR spectroscopy

The self-aggregation and supramolecular micellar structure of two surfactants in aqueous solution, the anionic surfactant SDP2S (sodium dodecyl dioxyethylene-2 sulfate) and the nonionic surfactant Triton X-100 (octylphenol-polyoxyethylene ether with 9.5 ethoxy groups), were investigated by NMR spectroscopy. The critical micellar concentration (CMC), the size, and shape of the aggregates were determined by diffusion ordered NMR spectroscopy (DOSY), while 2D NOESY NMR spectra were used to study the mutual spatial arrangement of surfactant molecules in the aggregated state. A nonlinear increase of the micellar hydrodynamic radius, indicating possible sphere-to-rod shape transition, was found for SDP2S at higher surfactant concentrations. Triton X-100 micelles were found to be almost spherical at low surfactant concentrations, but formation of ellipsoid shaped particles and/or micellar aggregation was observed at higher concentrations. The NOESY data show that at low concentration Triton X-100 forms a two-layer spherical structure in the micelles, with partially overlapping internal and external layers of Triton X-100 molecules and no distinct hydrophilic-hydrophobic boundary.     

Oxidative degradation of non-ionic surfactant (TritonX-100) by chromium(VI)

Degradation of polyoxyethylene chain of non-ionic surfactant (TritonX-100) by chromium(VI) has been studied spectrophotometrically under different experimental conditions. The reaction rate bears a first-order dependence on the [Cr(VI)] under pseudo-first-order conditions, [TritonX-100]  [Cr(VI)] in presence of 1.16 mol dm⁻³ perchloric acid. The observed rate constant (k_obs) was 3.3 × 10⁻⁴ to 3.5 × 10⁻⁴ s⁻¹ and the half-life (t_1/2) was 33–35 min for chromium(VI). The effects of total [TritonX-100] and [H⁺] on the reaction rate were determined. Reducing nature of non-ionic TritonX-100 surfactant is found to be due to the presence of –OH group in the polyoxyethylene chain. It was observed that monomeric and non-ionic micelles of TritonX-100 were oxidized by chromium(VI). When [TritonX-100] was less than its critical micelle concentration (cmc) the k_obs values increased from 0.76 × 10⁻⁴ to 1.5 × 10⁻⁴ s⁻¹. As the [TritonX-100] was greater than the cmc, the k_obs values increases from 2.1 × 10⁻⁴ to 8.2 × 10⁻⁴ s⁻¹ in presence of constant [HClO₄] (1.16 mol dm⁻³) at 40 °C. A comparison was made of the oxidative degradation rates of TritonX-100 with different metal ion oxidants. The order of the effectiveness of different oxidants was as follows: permanganate > diperiodatoargentate(III) > chromium(VI) > cerium(IV).     

Fluorescence enhancement effect for the determination of DNA with calcein-cetyl trimethyl ammonium bromide system

A new spectrofluorimetric method was developed for the determination of trace amounts of DNA using the calcein as a fluorescent probe. In the presence of appropriate amounts of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), the anionic dye calcein dimerizes. The weak fluorescence intensity of the dimer was enhanced by adding DNA at pH 6–7. The interaction between calcein–CTAB and DNA was studied on the basis of this behavior and a new method was developed for determining DNA. Under the optimal conditions, the enhanced fluorescence intensity was in proportion to the concentration of DNA in the range of 4.0 × 10⁻⁶ to 8.0 × 10⁻⁵ g L⁻¹ for fsDNA and thermally denatured ctDNA (4.5 × 10⁻⁶ to 9.0 × 10⁻⁵ g L⁻¹). The detection limits (S/N = 3) were 2.0 × 10⁻⁶ and 2.2 × 10⁻⁶ g L⁻¹, respectively. This method was used for determining the concentration of DNA in synthetic samples with satisfactory results.     

Study on dynamic interfacial tension of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide at liquid/liquid interface

Dynamic interfacial tension between aqueous solutions of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R₁₂HTAB) and n-hexane were measured using the spinning drop method. The effects of the R₁₂HTAB concentration (the concentration below the CMC) and temperature on the dynamic interfacial tension have been investigated; the reason of the change of dynamic interfacial tension with time has been discussed. The effective diffusion coefficient, D_a, and the adsorption barrier, _a, have been obtained from the experimental data using the extended Word–Tordai equation. The results show that the dynamic interfacial tension becomes smaller while _a becomes higher with increasing R₁₂HTAB concentration in the bulk aqueous phase. D_a decreases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 0.87 × 10⁻¹² m⁻² s⁻¹ while _a increases from 5.41 kJ mol⁻¹ to 7.74 kJ mol⁻¹ with the increase of concentration in the bulk solution of R₁₂HTAB from 0.5 × 10⁻³ mol dm⁻³ to 4 × 10⁻³ mol dm⁻³. Change of temperature affects the adsorption rate through altering D_a and _a. The value of D_a increases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 13.98 × 10⁻¹² m⁻² s⁻¹ while that of _a decreases from 5.41 kJ mol⁻¹ to 5.07 kJ mol⁻¹ with temperature ascending from 303 K to 323 K. The adsorption of surfactant from the bulk phase into the interface follows a mixed diffusion–activation mechanism, which has been discussed in the light of interaction between surfactant molecules, diffusion and thermo-motion of molecules.     

Assembly properties of Triton X-100/phosphatidylcholine aggregates during liposome solubilization

The assembly properties of the nonionic surfactant Triton X-100 and phosphatidylcholine (PC) aggregates during the overall solubilization process of PC liposome were investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light scattered by liposome suspensions. A direct dependence was established between the bilayer/aqueous phase surfactant partition coefficients (K), the growth of vesicles and the leakage of entrapped CF in the initial interaction steps (surfactant to phospholipid molar ratioRe up to 0.2). These changes may be related to the increasing presence of surfactant molecules in the outer monolayer of vesicles. In theRe range 0.2–0.35 the coexistence of a low vesicle growth with a constant increase of CF release may be correlated with the decrease inK (increased rate of flip-flop of surfactant molecules). Furthermore, in theRe range between 0.64 and 2.0 (lytic levels) almost a linear dependence was detected between the composition of these aggregates (Re) and the decrease in both the surfactant-PC aggregate size and the static light scattered by the system. This dependence was not observed in the last solubilization steps (Re range 2.0–2.60) possibly due to the increased formation of mixed micelles in this interval. The fact that the free Triton X-100 concentration at sublytic and lytic levels showed respectively lower and similar values than its critical micelle concentration confirms that permeability alterations and solubilization were determined respectively by the action of surfactant monomer and by the formation of mixed micelles.Abbreviations PC phosphatidylcholine - PIPES piperazine-1,4 bis(2-ethanesulphonic acid) - T_X-100 Triton X-100 - CF 5(6)-carboxyflucrescein - Re enective surfactant/lipid molar ratio - Re _SAT effective surfactant/lipid molar ratio for bilayer saturation - Re _SOL enective surfactant/lipid molar ratio for bilayer solubilization - S _W surfanctant concentration in the aqueous medium - S _B surfactant concentration in the bilayers - S _T total surfactant concentration - K bilayer/aqueous phase surfactant partition coefficient - K _SAT bilayer/aqneous phase surfactant partition coefficient for bilayer saturation - K _SOL bilayer/aqueous phase surfactant partition coefficient for bilayer solubilization - PL phospholipid - TLC-FID thinlayer chromatography/flame ionization detection system - PI polydispersity index - CMC critical micellar concentration - r ² regression coefficient     

Adsorption of bovine serum albumin on fused silica: Elucidation of protein–protein interactions by single-molecule fluorescence microscopy

The adsorption of bovine serum albumin (BSA) on fused silica at pH 4.7 was studied at the single molecules level by total-internal-reflection fluorescence microscopy. This pH value was the isoelectric point of BSA. At low [BSA] of 20 pM, protein molecules adsorbed as monomers. At intermediate [BSA] of 500 pM, protein molecules adsorbed as clusters of about five monomers on average. Both monomers and clusters had adsorption rate coefficients of the order 10⁻⁷ m s⁻¹ and desorption rate coefficients of about 2 × 10⁻² s⁻¹. The respective steady-state coverage was about 10× higher than that at neutral pH, presumably because of the more favorable BSA–silica electrostatics. At pH 4.7 and with [BSA] higher than 100 nM, adsorption begot further adsorption to produce nonlinear isotherms. The coverage at 1 μM BSA was 2.5× that of the linearly extrapolated coverage. This suggests that at pH 4.7, solute–adsorbate affinity was the dominant factor that explains the enhanced adsorption observed in ensemble measurements.     

Magnetic Relaxation Probing of the State of Diheptyl Dithiophosphate Ions in Water and Aqueous Triton X-100 Solutions

The nuclear magnetic relaxation was used to study the state of diheptyl dithiophosphoric acid (D7DTP, L₇) anions in water and aqueous solutions of the nonionic surfactant, Ttiton X-100, at 298 K in the presence of paramagnetic probes, Mn²⁺ions. It was found that increase in the spin-lattice relaxation rate of water protons is caused by formation of simple and mixed (with surfactant) aggregates of D7DTP. Unlike the Mn²⁺–sodium dodecyl sulfate –Triton X-100 system, studied previously an influence of a probe concentration was found at surfactant concentration close to the CMC. It was suggested that two types of mixed species containing diheptyl dithiophosphate ions, Mn(II), and nonionic surfactant can be formed: micellar aggregates, {Mn(L₇)₂(TX)}, and polynuclear associates, [Mn _x (L₇) _y (tx) _z ]. The associates likely contain surfactant in the form of monomers (tx).     

Palladized aluminum electrode covered by Prussian blue film as an effective transducer for electrocatalytic oxidation and hydrodynamic amperometry of N-acetyl-cysteine and glutathione

The mediated oxidation of N-acetyl cysteine (NAC) and glutathione (GL) at the palladized aluminum electrode modified by Prussian blue film (PB/Pd–Al) is described. The catalytic activity of PB/Pd–Al was explored in terms of Fe^III[Fe^III(CN)₆]/Fe^III[Fe^II(CN)₆]¹⁻ system by taking advantage of the metallic palladium layer inserted between PB film and Al, as an electron-transfer bridge. The best mediated oxidation of NAC and GL on the PB/Pd–Al electrode was achieved in 0.5 M KNO₃ + 0.2 M potassium acetate of pH 2. The mechanism and kinetics of the catalytic oxidation reactions of the both compounds were monitored by cyclic voltammetry and chronoamperometry. The charge transfer-rate limiting step as well as overall oxidation reaction of NAC or GL is found to be a one-electron abstraction. The values of transfer coefficients α, catalytic rate constant k and diffusion coefficient D are 0.5, 3.2 × 10² M⁻¹ s⁻¹ and 2.45 × 10⁻⁵ cm² s⁻¹ for NAC and 0.5, 2.1 × 10² M⁻¹ s⁻¹ and 3.7 × 10⁻⁵ cm² s⁻¹ for GL, respectively. The modifying layers on the Pd–Al substrate have reproducible behavior and a high level of stability in the electrolyte solutions. The modified electrode is exploited for hydrodynamic amperometry of NAC and GL. The amperometric calibration graph is linear in concentration ranges 2 × 10⁻⁶–40 × 10⁻⁶ for NAC and 5 × 10⁻⁷–18 × 10⁻⁶ M for GL and the detection limits are 5.4 × 10⁻⁷ and 4.6 × 10⁻⁷ M, respectively.     

毛细管电泳-安培法测定复方磺胺甲噁唑片中的有效成分

采用毛细管电泳-安培法(CE-AD)同时分离测定了磺胺甲噁唑(sulfamethoxazole,SMZ)、磺胺嘧啶(sulfadiazine,SD)和抗菌增效剂甲氧苄胺嘧啶(trimethoprim,TMP)3种常用磺胺类抗菌药物成分,考察了实验参数对分离、检测体系的影响。在优化实验条件下,以300μm碳圆盘电极作为工作电极,检测电位为1050mV(vs.SCE),在Na2B4O7(13mmol/L)-KH2PO4(18mmol/L)(pH5.8)的缓冲溶液中,分离电压18kV,进样6s,3组分在14min内可实现基线分离。上述3组分浓度分别在5×10-4~5×10-2、5×10-4~0.1和5×10-4~5×10-2g/L范围内与其峰电流强度呈线性关系,检出限达5.1×10-5~8.0×10-5g/L(S/N=3)。该方法已成功应用于复方磺胺甲噁唑片中抗菌活性成分的含量测定,结果令人满意。     

Refining of nonionic surfactant micellization theory based on the law of mass action

Two approaches to determining critical micelle concentration (CMC) are assessed, i.e., from the inflection point in the curve for the concentration dependence of the degree of micellization and as K^1/(1–n), where K is the constant of the law of mass action and n is the aggregation number. The latter approach makes the theory simpler, while the former explicitly expresses the critical degree of micellization via the aggregation number. The concentrations of monomers and micelles are analyzed as functions of the overall concentration of a surfactant in a micellar solution. These functions look much simpler in the graphical form as compared with their complex exact analytical representation. This has resulted in derivation of simple analytical approximations for these functions, with these approximations being useful for calculations. The concentration dependence of the surfactant diffusion coefficient has been considered based on these approximations. It turned out that this dependence not only provides the known method for determining the diffusion coefficient of micelles, but also gives the possibility in principle to determine the aggregation number from the slope of the dependence of the diffusion coefficient on the inverse concentration (counted from the CMC in the CMC units). This new method for determining the aggregation number has been tested using the literature data on the diffusion coefficient of penta(ethylene glycol)-1-hexyl ether in an aqueous solution.     

Surface and volume properties of dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide: II. Volumetric properties of dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide

Density measurements were carried out for aqueous solutions of two cationic surfactants: dodecylethyldimethylammonium bromide (C₁₂(EDMAB)) and benzyldimethyldodecylammonium bromide (BDDAB). On the basis of the obtained results of the measurements the CMC and partial molar volumes of the surfactants studied were also determined. The obtained CMC values were also analyzed with those accounted on the basis of the surface tension data from the previous paper [J. Harkot, B. Jańczuk, J. Colloid Interface Sci. (2008), submitted for publication]. The values of CMC determined from the surface tension and density measurements for C₁₂(EDMAB) are equal to 9.9×10⁻³ and 1.5×10⁻² M and for BDDAB to 5.25×10⁻³ and 5.3×10⁻³ M, respectively. These obtained values are very similar. However, in the literature it is difficult to find the CMC values for C₁₂(EDMAB) and BDDAB determined by these two methods used by us—especially from the density measurements for BDDAB and surface tension measurements for C₁₂(EDMAB). In the case of the apparent molar volumes of C₁₂(EDMAB) there is a good agreement between the values obtained by us and those found in the literature. The CMC values for C₁₂(EDMAB) and BDDAB were also determined on the basis of their surface tension and free energy of electrostatic interactions between the polar heads of these surfactants and compared with those obtained from the surface tension and density measurements. It was found that the theoretically obtained CMC values were close to those determined from the density and surface tension data for the C₁₂(EDMAB) and that the ratios of the CMC values of the surfactants to their concentration at which the water surface tension decreased by about 20 mN/m proved that the presence of the aryl group in the BDDAB head instead of the methyl group caused that its micellization process was more inhibited in relation to its adsorption at air–water interface than that of C₁₂(EDMAB).     

Sensitive detection of potassium ion using Prussian blue nanotube sensor

A model K⁺ sensor using Prussian blue nanotubes is fabricated by electrochemical deposition of Prussian blue (PB) within the nanochannels of a porous metal-coated membrane with partially covered pore openings. The PB nanotube sensor exhibits excellent stability giving reproducible peak potentials up to 500 measurement cycles, a very low detection limit of 2.0 × 10⁻⁸ M and extremely wide logarithmic linear ranges between 5.0 × 10⁻⁸–7.0 × 10⁻⁴ M and 7.0 × 10⁻⁴–1.0 M. Negligible interferences by Na⁺, Mg²⁺ and Ca²⁺ are observed and a rapid analysis time of 30 s is readily achieved. The ease of electrodeposition, high stability of PB nanotubes and outstanding analytical performance which surpasses conventional PB voltammetric and potentiometric sensors demonstrates potential sensing applications including ion sensors and biosensors using PB and other metal hexacyanoferrate nanotubes.     

Indirect kinetic microdetermination of oxalate, citrate, and fluoride ions

An indirect catalytic method for the separate microdetermination of oxalate, citrate, and fluoride ions is described. The method is based on the inhibition action of oxalate, citrate, and fluoride ions on the catalytic oxidation reaction of 2,4-diaminophenol-hydrogen peroxide by iron(III).Procedures for the determination of 1.76 × 10⁻² to 17.6 × 10⁻² μg/ml for oxalate ion, 3.78 × 10⁻² to 30.24 × 10⁻² μg/ml for citrate ion, and 0.38 to 4.18 μg/ml for fluoride ion are given.Quantities of 1.76 × 10⁻² to 17.6 × 10⁻² μg/ml for oxalate ion, 3.78 × 10⁻² to 30.24 × 10⁻² μg/ml for citrate ion, and 0.38 to 4.18 μg/ml for fluoride ion could be determinated with a relative error of about 1–3.5% for oxalate and citrate ions and 1–2% for fluoride ion.     

A novel method for determination of peroxynitrite based on hemoglobin catalyzed reaction

A novel spectrofluorimetric method for the determination of peroxynitrite is proposed. The method is based on a mimetic enzyme catalyzed reaction with hemoglobin as the catalyst and l-tyrosine as the substrate. A new fluorescent substance is produced that might probably be the coupled dimmer of tyrosine, which, instead of nitryl-tyrosine, is likely to be a new marking substance of ONOO⁻ injury in vivo. Kinetics of the reaction is studied and the possible reaction mechanism is also recommended. The proposed method is simple and highly sensitive with a detection limit of 5.00 × 10⁻⁸ mol L⁻¹ of peroxynitrite. A liner calibration graph is obtained over the peroxynitrite concentration range 5.60 × 10⁻⁷ to 2.10 × 10⁻⁵ mol L⁻¹, with a correlation coefficient of 0.9983. Interferences from some amino acids and metal ions normally seen in biological samples, and also some anions structurally similar to ONOO⁻ are studied.     

Doxycycline-sensitized solid-phase fluorescence of europium on silica in the presence of surfactants

The effect of the second ligand and surfactant micelles on the solid-phase time-resolved fluorescence of europium sensitized by doxycycline on Silasorb 600 is studied. A procedure of the sorption-luminescence determination of doxycycline using micelles of Triton X-100 nonionic surfactant is developed; the detection limit is 1.1 × 10^?7. The analytical range for doxycycline is 3 × 10^?7 to 3 × 10^?5 M. The procedure is tested on a doxycycline pharmaceutical drug; RSD was no worse than 4%.