A pulsed field gradient NMR diffusion investigation of enkephalin peptide-sodium dodecyl sulfate micelle association

Pulsed field gradient NMR (PFG-NMR) diffusion experiments were used to investigate the binding of leucine and methionine enkephalin peptides to anionic sodium dodecyl sulfate (SDS) micelles. The study was undertaken to investigate the mechanism of interaction between enkephalin peptides and SDS micelles and to determine if NMR-derived association constants, K(eq), can predict the elution order in electrokinetic chromatography (EKC). In EKC, peptides are separated on the basis of their interactions with micelles. The Leu-enkephalin peptide-micelle association constant increased from 130 +/- 8 to 1459 +/- 57 and 1744 +/- 64 M(-1), respectively, when an Arg or Lys was added to the C-terminus. The association constant of Leu-enkephalinamide was approximately equal to that of Leu-enkephalin-Arg. Substitution of Phe4 with a Trp or Gly2 with an Ala in the Leu-enkephalin peptides also increased the micelle binding affinity. These results confirm that the interaction of Leu-enkephalin peptides with SDS micelles is largely electrostatic and that the non-polar amino acid side chains interact with the hydrophobic micelle core. The peptide-micelle association constants for the cationic Met-enkephalin peptides were also greater than their zwitterionic counterparts. For example, the Met-enkephalin K(eq) value was 162 +/- 9 M(-1), while the association constants for Met-enkephalin-Arg, Met-enkephalin-Lys, and Met-enkephalinamide were, respectively, 674 +/- 31, 426 +/- 23, and 453 +/- 27 M(-1). In both Met-enkephalin and Met-enkephalinamide, replacing Gly2 with an Ala did not significantly increase the association constant. These results confirm that with the Met-enkephalin peptides, there was little or no interaction of the amino acid side chains with the micelle core. For both the Leu-enkephalin and Met-enkephalin peptides, the association constants were consistent with EKC results, in that the peptides with smaller K(eq) values were found to elute before those with larger association constants.     

Study of valsartan interaction with micelles as a model system for biomembranes

In this study, the interaction of valsartan (VAL), an angiotensin II receptor antagonist, with cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated. The effect of cationic micelles on spectroscopic and acid-base properties of VAL was carried out using UV spectrophotometry at physiological conditions (pH 7.4). The binding of VAL to CTAB micelles implied a shift in drug acidity constant (pK(a)(water)-pK(a)(micelle)=1.69) proving the great affinity of VAL dianion for the positively charged CTAB micelle surface. To quantify the degree of VAL/CTAB interaction, two constants were calculated by using mathematical models: micelle/water partition coefficient (K(x)) and drug/micelle binding constant (K(b)). The decrease of K(x) with VAL concentration, obtained by using pseudo-phase model, is consistent with an adsorption-like phenomenon. From the dependence of differential absorbance at lambda=295 nm on CTAB concentration, by using mathematical model that treats the solubilization of VAL dianion as its binding to specific sites in the micelles (Langmuir adsorption isotherm), the binding constant (K(b)=(2.50+/-0.49)x10(4)M(-1)) was obtained. Binding constant VAL/CTAB was also calculated using micellar liquid chromatography (MLC).     

Towards a general approach for the impurity profiling of drugs by micellar electrokinetic chromatography

A general micellar electrokinetic chromatographic (MEKC) strategy for the impurity profiling of drugs was developed involving a sodium dodecyl sulfate (SDS) and a cetyltrimethylammonium bromide (CTAB) MEKC system. With this combination, in principle, each sample component passes the detector in at least one of the two MEKC systems provided that separation buffers of the same pH are used in both systems. In order to select the proper MEKC systems, the electroosmotic flow (EOF) and micelle migration time (t(mc)) were determined for separation buffers of several pH values, containing various amounts of surfactant and organic modifier. The selectivity of the MEKC systems was studied using a mixture of compounds with a wide range of physico-chemical properties. The final selection of two adequate MEKC systems for this approach was based on the requirements that the t(mc) (i.e., analysis time) of both systems was below 20 min and that the t(mc)/t(eof) ratio was above 3 or 2 for the SDS and CTAB system, respectively. Furthermore, the systems should provide high efficiency, exhibit differences in selectivity and use moderate concentrations of modifier and surfactant, so that, if needed, further optimization is possible. The selected MEKC systems contained 60 mM SDS or 10 mM CTAB, respectively, in a phosphate buffer (pH 7.5) with 10% acetonitrile. Some test compounds with extreme mobilities were used to demonstrate the suitability of the MEKC approach to detect each component of a sample. The potential of the proposed MEKC combination for impurity profiling was demonstrated by the analysis of fluvoxamine with several impurities at the 0.1% level.     

Spectrophotometric study of interaction and solubilization of procaine hydrochloride in micellar systems

The interaction of Procaine hydrochloride (PC) with cationic, anionic and non-ionic surfactants; cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and triton X-100, were investigated. The effect of ionic and non-ionic micelles on solubilization of Procaine in aqueous micellar solution of SDS, CTAB and triton X-100 were studied at pH 6.8 and 29°C using absorption spectrophotometry. By using pseudo-phase model, the partition coefficient between the bulk water and micelles, K_x, was calculated. The results showed that the micelles of CTAB enhanced the solubility of Procaine higher than SDS micelles (K_x = 96 and 166 for SDS and CTAB micelles, respectively) but triton X-100 did not enhanced the solubility of drug because of weak interaction with Procaine. From the resulting binding constant for Procaine-ionic surfactants interactions (K_b = 175 and 128 for SDS and CTAB surfactants, respectively), it was concluded that both electrostatic and hydrophobic interactions affect the interaction of surfactants with cationic procaine. Electrostatic interactions have a great role in the binding and consequently distribution of Procaine in micelle/water phases. These interactions for anionic surfactant (SDS) are higher than for cationic surfactant (CTAB). Gibbs free energy of binding and distribution of procaine between the bulk water and studied surfactant micelles were calculated.      

孔雀绿与CTAB胶束的相互作用

以CTAB胶束模拟生命体系,用UV-Vis和荧光光谱等技术研究了孔雀绿与CTAB胶束的相互作用.结果表明,孔雀绿自发地定位于CTAB胶束栅栏层,使得胶束聚集数增加,胶束的微环境极性I1/I3下降.孔雀绿与CTAB胶束之间的结合常数K和孔雀绿在胶束相与水连续相之间的分配系数KD均随孔雀绿浓度增加而降低,表明孔雀绿与CTAB胶束之间的相互作用随孔雀绿浓度增加而降低.     

Distribution of emulsified monomers with different water solubility

The location and distribution of acrylic acid and styrene in emulsions made with a cationic surfactant, cetyltrimethylammonium bromide (CTAB), or an anionic surfactant, sodium dodecylsulfate (SDS), were determined with ultra-violet spectroscopy, conductivity, and potentiometry. In these systems, the acrylic acid remains in the aqueous phase near the micelle surface, whereas the styrene is located in the micelles or in emulsified droplets. In the absence of acrylic acid, some of the styrene is solubilized in the micelle interior and some is adsorbed at the micelle inner surface. Upon addition of acrylic acid, all the styrene is displaced to the center of the micelles. The interaction between acrylic acid and CTAB micelles is stronger than that between acrylic acid and SDS micelles. With CTAB, acrylic acid is adsorbed at the micelle surface, whereas with SDS, acrylic acid remains in the intermicellar solution. These differences can account for the differences reported in the emulsion copolymerization of acrylic acid and styrene using CTAB or SDS.     

Micelle formation of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide in aqueous solution and their influence on the aggregation of SDS and PEO-PPO-PEO copolymer micelles

The aggregation properties of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide were studied in aqueous solution and in the presence of SDS and SDS-polymer environments using UV-visible, surface tension, fluorescence and circular dichroism (CD) techniques. Both the peptides formed micelles. The cmc values obtained for dipeptide and tripeptide are 2×10(-5) and 4×10(-5) M, respectively in aqueous solution at 25°C. The presence of additives (SDS and polymer) hindered the micelle formation of peptides. The cmc values obtained by various methods are in good agreement with each other. Effect of peptides on the aggregation properties of SDS also was investigated. The cmc of SDS was decreased in presence of peptides and were reduced with increase in temperature. Using monophasic micellization concept, the association constant (K(A)) for the SDS-peptide mixed micellar systems was determined. Using biphasic model, the thermodynamic parameters viz; ΔG°(m), ΔH°(m) and ΔS°(m) for SDS-water and SDS-peptide-water mixed micellar systems, the standard free energy for transfer of SDS from aqueous to peptide additive environments were estimated at various temperatures. These results suggest that the SDS is more stable in micellized form in the SDS-water-peptide ternary systems compared to the situation in the corresponding SDS-water binary systems.     

Spectral studies of N-nonyl acridine orange in anionic, cationic and neutral surfactants

The spectroscopic and photophysical properties of N-nonyl acridine orange - a metachromatic dye useful as a mitochondrial probe in living cells - are reported in water and microheterogeneous media: anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral octylophenylpolyoxyethylene ether (TX-100). The spectral changes of N-nonyl acridine orange were observed in the presence of varying amount of SDS, CTAB and TX-100 and indicated formation of a dye-surfactant complex. The spectral changes were also regarded to be caused by the incorporation of dye molecules to micelles. It was proved by calculated values K(b) and f in the following order: K(bTX-100)>K(bCTAB)>K(bSDS) and f(TX-100)>f(CTAB)>f(SDS). NAO binds to the micelle regardless the micellar charge. There are two types of interactions between NAO and micelles: hydrophobic and electrostatic. The hydrophobic interactions play a dominant role in binding of the dye to neutral TX-100. The unexpected fact of the binding NAO to cationic CTAB can be explained by a dominant role of hydrophobic interactions over electrostatic repulsion. Therefore, the affinity of NAO to CTAB is smaller than TX-100. Electrostatic interactions play an important role in binding of NAO to anionic micelles SDS. We observed a prolonged fluorescence lifetime after formation of the dye-surfactant complex tau(SDS)>tau(TX-100)>tau(CTAB)>tau(water), the dye being protected against water in this environment. TX-100 is found to stabilize the excited state of NAO which is more polar than the ground state. Spectroscopic and photophysical properties of NAO will be helpful for a better understanding of the nature of binding and distribution inside mammalian cells.     

Study of sodium dodecyl sulfate-poly(propylene oxide) methacrylate mixed micelles

Sodium dodecyl sulfate (SDS)-poly(propylene oxide) methacrylate (PPOMA) (of molecular weight M(w) = 434 g x mol(-1)) mixtures have been studied using conductimetry, static light scattering, fluorescence spectroscopy, and 1H NMR. It has been shown that SDS and PPOMA form mixed micelles, and SDS and PPOMA aggregation numbers, N(ag SDS) and N(ag PPOMA), have been determined. Total aggregation numbers of the micelles (N(ag SDS) + N(ag PPOMA)) and those of SDS decrease upon increasing the weight ratio R = PPOMA/SDS. Localization of PPOMA inside the mixed micelles is considered (i) using 1H NMR to localize the methacrylate function at the hydrophobic core-water interface and (ii) by studying the SDS-PPO micellar system (whose M(w) = 400 g x mol(-1)). Both methods have indicated that the PPO chain of the macromonomer is localized at the SDS micelle surface. Models based on the theorical prediction of the critical micellar concentration of mixed micelles and structural model of swollen micelles are used to confirm the particular structure proposed for the SDS-PPOMA system, i.e., the micelle hydrophobic core is primarily composed of the C12 chains of the sodium dodecyl sulfate, the hydrophobic core-water interface is made up of the SDS polar heads as well as methacrylate functions of the PPOMA, the PPO chains of the macromonomer are adsorbed preferentially on the surface, i.e., on the polar heads of the SDS.     

Interaction of UO2 2+ with sodium dodecyl sulfate micelles: association of phenols to micelles through fluorescence quenching data

Time-resolved laser-induced fluorescence (TRLIF) has been used to study the interaction of uranyl ion with sodium dodecyl sulfate (SDS) micelles in H(3)PO(4) 1 M. The titration curve consists of two curved regions with different slopes, one of them more pronounced at low concentration of SDS and the other, with a less pronounced positive slope at larger [SDS] until a plateau is reached. The fluorescence quenching of uranyl ion by para-substituted phenol compounds was studied by TRLIF and steady-state emission intensity measurements. The results were interpreted in terms of binding of phenolic compounds to the micelle. The binding constant (K(Q)) as well as the entrance and exit rate constants were determined for all the quenchers used.     

Interaction of quinapril anion with cationic surfactant micelles of cetyltrimethylammonium bromide

In this study, the interaction of the anion of quinapril (QUIN), angiotensin converting enzyme (ACE) inhibitor, with cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated. The effect of cationic micelles on the spectroscopic and acid-base properties of QUIN was studied at pH 8. The binding of QUIN anion to CTAB micelles implied a shift in drug acidity constant (pK(a)(water)-pK(a)(micelle)=1.39) proving the great affinity of negatively charged QUIN ion for the positively charged CTAB micelle surface. The strong dependence of the partition coefficient K(x) on QUIN concentration, obtained by using pseudo-phase model, is consistent with an adsorption-like phenomenon. From the dependence of differential absorbance at lambda=272 nm on CTAB concentration, by using mathematical model that treats the solubilization of QUIN anion as its binding to specific sites in the micelles (Langmuir adsorption isotherm), the binding constant K(b)=(2.3+/-0.4)x10(3) mol(-1)dm(3) was obtained. QUIN-CTAB binding constant was also calculated from micellar liquid chromatography (MLC) and this method was found to be not accurate enough for its determination.     

Micellar effects on the electrochemistry of dopamine and its selective detection in the presence of ascorbic acid

The electrochemistry of dopamine (3-hydroxytyramine) was studied by cyclic voltammetry at a glassy carbon electrode in the presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) micelles at different pH. The anodic peak potential (E(pa)) and peak current (I(pa)) were found to be remarkably dependent on the charge and the concentration of the surfactant. The E(pa) and I(pa) change abruptly around the critical micellar concentration (CMC) of the surfactants and reach a plateau above the CMC. The E(pa) at the plateau shifts to more positive values in the cationic CTAB micellar solution, e.g. from 180 mV vs SCE in aqueous solution at pH 6.8 to 410 mV in CTAB micelle, whilst it shifts to less positive values in the anionic SDS micellar solution, e.g. 150 mV at pH 6.8. Therefore, the overlapped anodic peaks of dopamine and ascorbic acid in the mixture of the two compounds in aqueous solutions can be separated in CTAB micelles since the micelle shifts the E(pa) of ascorbic acid to less positive values. The two peaks are separated by ca. 400 mV at pH 6.8 in CTAB micelle, hence dopamine can be determined in the presence of 100 times excess of ascorbic acid. In SDS micelle and in the presence of ascorbic acid, the I(pa) of dopamine is greatly enhanced due to the catalytic oxidation of the latter that enables quantitative determination of both compounds.     

Anomalous association and fluorophore influence on the position of dimethylaniline in micelles: fluorescence quenching of 1,8-acridinedione

Fluorescence quenching of 9,10-dimethyl-3, 4,6,7,9,10-hexahydro-1,8(2H,5H) acridinedione (ADD) dye by N,N-dimethylaniline (DMA) in SDS and CTAB were studied by steady state fluorescence and time resolved techniques. The Stern-Volmer plots for the quenching of ADD by DMA is found to be linear and the Stern-Volmer constant K(SV) depends on the micellar concentration. The fluorescence quenching analysis reveals the binding of DMA with the micelles. The perturbation of the probe on the position of DMA molecule in micelle is inferred in the present investigation. The ADD fluorophore drives the DMA molecule into the non-polar region (core) of the micelle whereas other fluorophores like pyrene and rhodamine6G do not affect the position of DMA. In this report, the importance of the nature of fluorophores in determining the position and association of the quencher molecules in the aggregated systems is being discussed.     

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.     

The Self-Association and Mixed Micellization of an Anionic Surfactant,Sodium Dodecyl Sulfate,and a Cationic Surfactant,Cetyltrimethylammonium Bromide: Conductometric,Dye Solubilization,and Surface Tension Studies

In the present study, we investigate the self-association and mixed micellization of an anionic surfactant, sodium dodecyl sulfate (SDS), and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of SDS, CTAB, and mixed (SDS + CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), and A_min (the minimum area per surfactant molecule at the air/water interface)) of SDS, CTAB, and (SDS + CTAB) micellar/mixed micellar systems were evaluated. The thermodynamic parameters of the micellar (SDS and CTAB), and mixed micellar (SDS + CTAB) systems were evaluated.

A schematic representation of micelles and mixed micelles.     

聚(苯乙烯-co-甲基丙烯酸)自组装胶束假固定相电动色谱的特性

研究了两亲性无规共聚物聚(苯乙烯-co-甲基丙烯酸)(P(St-co-MAA))(单体摩尔比分别为6:4和7:3)自组装胶束的物理化学性质,及其作为假固定相(PSP)的胶束电动色谱性能。测定了聚合物胶束的临界胶束浓度(CMC),对胶束内核微环境的极性、表面电荷密度和流体力学直径等微结构参数进行了表征,对时间窗口、亚甲基选择性等电动色谱参数进行了测定,并与聚(甲基丙烯酸甲酯-co-甲基丙烯酸)(P(MMA-co-MAA))胶束、十二烷基硫酸钠(SDS)胶束体系进行了比较;利用线性溶剂化能关系(LSER)研究了聚合物PSP的选择性差异。结果表明:P(St-co-MAA)体系具有最小的CMC、最宽的时间窗口和最好的亚甲基选择性;LSER表明,疏水作用是决定聚合物PSP选择性的最主要因素,氢键酸度其次,特别是P(St-co-MAA)(单体摩尔比7:3)体系具有最高的作用参数,显示了该PSP具有较高的分离选择性。     

Mixed micelles of polyethylene glycol (23) lauryl ether with ionic surfactants studied by proton 1D and 2D NMR

(1)H NMR chemical shift, spin-lattice relaxation time, spin-spin relaxation time, self-diffusion coefficient, and two-dimensional nuclear Overhauser enhancement (2D NOESY) measurements have been used to study the nonionic-ionic surfactant mixed micelles. Cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as the ionic surfactants and polyethylene glycol (23) lauryl ether (Brij-35) as the nonionic surfactant. The two systems are both with varying molar ratios of CTAB/Brij-35 (C/B) and SDS/Brij-35 (S/B) ranging from 0.5 to 2, respectively, at a constant concentration of 6 mM for Brij-35 in aqueous solutions. Results give information about the relative arrangement of the surfactant molecules in the mixed micelles. In the former system, the trimethyl groups attached to the polar heads of the CTAB molecules are located between the first oxy-ethylene groups next to the hydrophobic chains of Brij-35 molecules. These oxy-ethylene groups gradually move outward from the hydrophobic core of the mixed micelle with an increase in C/B in the mixed solution. In contrast to the case of the CTAB/Triton X-100 system, the long flexible hydrophilic poly oxy-ethylene chains, which are in the exterior part of the mixed micelles, remain coiled, but looser, surrounding the hydrophobic core. There is almost no variation in conformation of the hydrophilic chains of Brij-35 molecules in the mixed micelles of the SDS/Brij-35 system as the S/B increases. The hydrophobic chains of both CTAB and SDS are co-aggregated with Brij-35, respectively, in their mixed micellar cores.     

表面活性剂在高效毛细管电泳中的作用

表面活性剂作为缓冲液添加剂已广泛用于高效毛细管电泳中,综述了阴离子、阳离子、两性离子、非离子及手性等多种表面活性剂在离子、中性分子、手性化合物、多肽和蛋白质分离等方面的作用,介绍了其作用机理与改善高效毛细管电泳分离的原理。     

Ultrafast photoinduced electron transfer from dimethylaniline to coumarin dyes in sodium dodecyl sulfate and triton X-100 micelles

The primary steps of photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to five coumarin dyes are studied in an anionic micelle [sodium dodecyl sulfate (SDS)] and a neutral micelle [triton X-100 (TX-100)] using femtosecond upconversion. The rate of PET in micelle is found to be highly nonexponential. In both the micelles, PET displays components much faster (approximately 10 ps) than the slow components (180-2900 ps) of solvation dynamics. The ultrafast components of electron transfer exhibit a bell-shaped dependence on the free energy change. This is similar to Marcus inversion. The rates of PET in TX-100 and SDS micelle are, in general, faster than those in cetyltrimethylammonium bromide (CTAB) micelle. In the SDS and TX-100 micelle, the Marcus inversion occurs at -DeltaG0 approximately 0.7 eV which is lower than that (approximately 1.2 eV) in CTAB micelle. Possible causes of variation of PET in different micelles are discussed.     

Capillary zone electrophoresis and micellar electrokinetic chromatography of solution of polyaniline particles

The behavior of two different fractions of the electrically conducting polymer polyaniline (PANI) was studied in order to characterize them using fast, simple, and cheap methods of capillary zone electrophoresis. In contradistinction to the expectations that the particles will bear a positive charge on their surface, in the milieu of electrolytes used for electrophoresis (0.01-0.05 M buffers of pH 4-8.5), the surface was demonstrated to be slightly negatively charged, which led to a slow migration to the anode. An evident charge was given to the particles after their interaction with micelles formed from surface active components, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). An active electrophoretic migration and full separation of the PANI fractions was achieved by micellar electrokinetic chromatography (MEKC) with negatively charged SDS micelles. With this method, a reliable qualitative as well as quantitative analysis was performed in the concentration range of 0.1-1.6 mg/mL with a reproducibility of migration times better than 1.5%.