Micellization of AOT in aqueous sodium chloride, sodium acetate, sodium propionate, and sodium butyrate media: a case of two different concentration regions of counterion binding

Critical micelle concentrations of AOT in water in the presence of sodium chloride, sodium acetate, sodium propionate, and sodium butyrate were determined at 25 degrees C by the surface tension method. The co-ions do not have any effect on the value of critical micelle concentration. The surface density of AOT at the air-water interface increases in the presence of added electrolyte and attains a maximum value of 2.5+/-0.1 mol m-2 at a particular electrolyte concentration which is different for sodium chloride and the other three electrolytes. From the Corrin-Harkins plot it has been found that for AOT micelles the counterion binding constant has values 0.40 and 0.82 below and above approximately 0.015 mol kg-1 electrolyte concentration (c*), respectively. Measurement of sodium ion activity from the EMF method has confirmed such a shift in the counterion binding constant of AOT at c*. The higher value of the counterion binding constant for AOT has been reported for the first time. From fluorescence spectroscopy it has been found that the aggregation number of AOT is 22 in water and its average aggregation numbers in the presence of electrolytes are about 34 and 136 below and above c*, respectively. The increase by a factor of 2 in the counterion binding constant is shown to be due to a change in the shape of the AOT micelles around c*. The shape of AOT micelles in the electrolyte concentration range c* is inferred to be oblate spheroid and a change from this shape appears to occur above c*. A sudden increase in the polarity of the micelle-solution interface is also observed above c*.     

Thermodynamics of demicellization of mixed micelles composed of sodium oleate and bile salts

Isothermal titration calorimetry (ITC) was used to determine the critical micelle concentration (cmc) and the thermodynamic parameters associated with the demicellization of sodium oleate (NaO) and mixed micelles composed of the bile salt (BS) sodium cholate (NaC) or sodium deoxycholate (NaDC), respectively, and NaO at a molar ratio of 5:2. The influence of the ionic strength (pure water and 0.1 M NaCl at pH 7.5) as well as that of the temperature (10-70 degrees C) were analyzed. For NaO, two cmc's were detected, indicating a two-step aggregation process, whereas only one cmc was observed for the two BSs. A single aggregation mechanism is also evident for the demicellization of mixed micelles (BS/NaO 5:2). Increasing the ionic strength induces the well-known decrease of the cmc. The cmc shows a minimum at room temperature. The cmc(mix) of the mixed micelles was analyzed using models assuming an ideal or nonideal mixing behavior of both detergents. The thermodynamic parameters describing the enthalpy (deltaHdemic), entropy (deltaSdemic), and Gibbs energy change (deltaGdemic), as well as the change in heat capacity (deltaCp,demic) for demicellization, were obtained from one ITC experiment. From the temperature dependence of deltaHdemic, the change of the hydrophobic surface area of the detergents from the micellar into the aqueous phase was derived. In all cases, the deltaCp,demic values are positive. In addition, the temperature dependence of the size of the formed aggregates was studied by dynamic light scattering (DLS). DLS indicated two populations of aggregates in the mixed system, small primary micelles (0.5-2 nm), and larger aggregates with a hydrodynamic radius in the range of 50-150 nm.     

Small-angle neutron scattering study of sodium cholate and sodium deoxycholate interacting micelles in aqueous medium

Small angle neutron scattering (SANS) measurements of D₂O solutions (0.1 M) of sodium cholate (NaC) and sodium deoxycholate (NaDC) were carried out atT= 298 K. Under compositions very much above the critical micelle concentration (CMC), the bile salt micelle size growths were monitored by adopting Hayter-Penfold type analysis of the scattering data. NaC and NaDC solutions show presence of correlation peaks atQ = 0.12 and 0.1 ?_-1 respectively. Monodisperse ellipsoids of the micelles produce best fits. For NaC and NaDC systems, aggregation number (9.0, 16.0), fraction of the free counterions per micelle (0.79, 0.62), semi-minor (8.0 ?) and semi-major axes (18.4, 31.7 ?) values for the micelles were deduced. Extent of micellar growth was studied using ESR correlation time measurements on a suitable probe incorporating NaC and NaDC micelles. The growth parameter (axial ratio) values were found to be 2.3 and 4.0 for NaC and NaDC systems respectively. The values agree with those of SANS.     

SIMULTANEOUS DETERMINATION OF MICELLAR DISSOCIATION CONCENTRATION AND CRITICAL MICELLAR CONCENTRATION OF BILE SALTS BY pH MEASUREMENTS

This paper demonstrates a method of using a pH meter to determine the micellar dissociation concentration (mdc) and the. critical micellar concentration (cmc) of eight bile salt samples: sodium cholate (NaC), sodium deoxycholate (NaDC), sodium glycocholate (NaGC), sodium glycodeoxycholate (NaGDC), sodium glyco-chenodeoxycholate (NaGCDC), sodium taurocholate (NaTC), sodium taurodeoxycholate (NaTDC) and sodium taurochenodeoxycholate (NaTCDC). The experiments were performed by diluting the bile salt solutions with freshly distilled water and following the pH changes with a hydrogen ion electrode at 25°C. One break appears in most of the pH-concentration plots of the bile salt solutions, signifying mdc. However, two breaks appear for NaC and NaDC samples, signifying mdc and cmc. The mdc and cmc values are in good agreement with values determined by surface tension and turbidity methods and with data reported in the literature. The method described in this paper is quick, simple and requiring no sample purification. It is the only method which can be used to determine mdc and cmc simultaneously.     

Effect of sodium deoxycholate and sodium cholate on DPPC vesicles: A fluorescence anisotropy study with diphenylhexatriene

Effects of two bile salts, namely sodium deoxycholate (NaDC) and sodium cholate (NaC), on DPPC small unilamellar vesicles have been investigated using the steady-state fluorescence anisotropy (r _ss ) of diphenylhexatriene (DPH) as a tool. It was found that the variation of r _ss is sensitive enough to monitor different stages of interaction of bile salts with DPPC vesicles. NaDC induced significant changes in the membrane well below its CMC (6 mM). Even at 4 mM, which is still lower than the CMC, the phospholipids were completely solubilised by the NaDC micelles. The effect of NaC on DPPC vesicles, however, was much less significant, especially in the sub-micellar concentration regime. Being more hydrophilic NaC does not interact with the membrane efficiently. Complete solubilisation of phospholipids took place only when the concentration of NaC was above its CMC (16 mM). The experiments also showed that the bile salt-induced changes of vesicle structure were strongly dependent on the concentration of the bile salt and not on the molar ratio of lipid and bile salt.     

Micellization in sodium deoxycholate solutions

NMR self-diffusion, tensiometry, and measurement of solubilization capacity are employed to comparatively study micellization in aqueous solutions of a facial amphiphilic compound, sodium deoxycholate (NaDC), and a conventional micelle-forming sodium dodecyl sulfate. Based on the two-state model, which is commonly used to analyze the data of NMR diffusometry, a method is proposed for determining variable sizes of NaDC micelles. It is shown that, in the concentration range from the critical micelle concentration to 0.1 M, the sizes of NaDC micelles monotonically increase. At comparable sizes of molecules of the examined surfactants, NaDC micelles are characterized by noticeably smaller aggregation numbers and solubilization capacity than sodium dodecyl sulfate due to the rigid structure of NaDC molecules, their facial amphiphilicity, and a low value of hydrophilic-lipophilic balance.     

Aqueous sodium dehydrocholate-sodium deoxycholate mixtures at low concentration

The behavior of the sodium dehydrocholate (NaDHC)-sodium deoxycholate (NaDC) mixed system was studied by a battery of methods that examine effects caused by the different components of the system: monomers, micelles, and both components. The behavior of the mixed micellar system was studied by the application of Rubingh's model. The obtained results show that micellar interaction was repulsive when the aggregates were rich in NaDHC. The gradual inclusion of NaDC in micelles led to a structural transformation in the aggregates and the interaction became attractive. The bile salts' behavior in mixed monolayers at the air-solution interface was also investigated. Mixed monolayers are monotonically rich in NaDC, giving a stable and compact adsorbed layer. Results have shown that the interaction in both micelles and monolayer is not ideal and such behavior is assumed to be due to a structural factor in their hydrocarbon backbone.     

Co‐ and Counterion Effect on the Micellization Characteristics of Dodecylpyridinium Chloride

Micellization parameters, critical micelle concentration (cmc), degree of counterion dissociation (α), aggregation number (n), critical packing parameter, and hydrophobic core volume of Dodecylpyridinium chloride (DPC) micelles were determined in presence of varying concentrations of sodium chloride (NaCl), sodium acetate (SAc), sodium propionate (SPr), ethylammonium chloride (EACl), diethylammonium chloride (DEACl), tetraethylammonium chloride (TEACl), and propylammonium chloride (PACl) through conductometric investigations at 298.15 K. The resulting data suggests that both counter and coions affect the cmc values‐cmc depressing tendency of the salts varies in order PACl≈NaCl>EACl>DEACl>TEACl>SPr>SAc, while the degree of counterion dissociation is dependent on the nature and concentration range of the added salt. Increasing salt concentration increases the relative hydrophobic volume of the micelles and coion has not much effect on aggregation number.     

Aggregation and adsorption of sodium dioctylsulfosuccinate in aqueous ammonium chloride solution: role of mixed counterions

The critical micelle concentration (cmc) of sodium dioctylsulfosuccinate (AOT) was determined at 25 °C from surface tension and fluorescence methods in aqueous NH(4)Cl solution for assessing the influence of mixed counterions on the special counterion binding behavior (SCB) of AOT. The SCB of AOT refers to a sudden twofold increase in the value of the counterion binding constant (β) in aqueous medium when the concentration (c(*)) of the added 1:1 sodium salt is about 0.015 mol kg(-1), and it has been tested so far for sodium ion only. In the presence of sodium and ammonium mixed counterions also the SCB of AOT exist, but with lower c(*) (0.009 mol kg(-1) NH(4)Cl). Synergism in the cmc occurs due to mixed counterions. In the case of inorganic counterions, unlike the case with organic counterions, the cmc is dependent on the total counterion concentration in solution and negligibly on the specific type of counterion. Na(+) and NH(4)(+) bind almost equally to the micelle in the region of low β (below c(*)), but in the region of high β (above c(*)) NH(4)(+) binds predominantly. It has been shown that the theoretical expression for the surface excess of ionic surfactant+electrolyte system containing a single counterion can also be used to evaluate the surface excess in the presence of mixed counterions if the two counterions are considered to undergo Henry-type adsorption at the air-solution interface.     

Mixed Micellization of Dodecyldimethylamine Oxide with Bile Salts in Aqueous Solutions

Micellar behavior of dodecyldimethylamine oxide (DMDAO) with bile salts [sodium deoxycholate (NaDC) and sodium cholate (NaC)] with and without NaCl was studied by surface tension. Interaction parameters of the mixed micelles were estimated using Rubingh's theory. Strong synergism observed for each mixed system, which is a common feature shown by anionic-cationic mixtures. The mixed solutions remained clear even at equimolar ratio. Different behavior of the two bile salts is explained on the basis of their orientation in cationic micelles.     

“Three-in-one” Complexes Formed by Anionic Guests and Monosubstituted Cationic Alkyldiamino β-Cyclodextrin Derivatives

The effect of electrostatic interactions on the complexation of ionic guests by charged β-cyclodextrin (βCD) derivatives is reviewed. Special attention is paid to the numerous studies concerning the effect of electrostatic interactions on (i) the complexation of fluorescent and UV probes; (ii) the catalytic and chiral recognition properties of βCD derivatives; and (iii) the complexation of two bile salts (sodium cholate, NaC, and sodium deoxycholate, NaDC). The formation of three-in-one complexes between NaC and alkyldiamino βCD derivatives is also presented.     

Temperature dependence of the interaction of cholate and deoxycholate with fluid model membranes and their solubilization into mixed micelles

The interaction of bile salts with model membranes composed of soybean phosphatidylcholine (SPC) and synthetic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was investigated using high sensitivity isothermal titration calorimetry (ITC). The partitioning and incorporation of the bile salts sodium cholate (NaC) and sodium deoxycholate (NaDC) from an aqueous phase (pure water or 0.1 M NaCl) into fluid bilayer vesicles was studied as a function of temperature and ionic strength. The thermodynamic parameters of partitioning were determined with a model taking electrostatic interactions into account. In addition, the solubilization of SPC and POPC vesicles with NaC and NaDC as a function of temperature was also studied by ITC and the phase diagrams for the vesicle to micelle transition at two different temperatures were established. Unsaturated phospholipids require higher amounts of detergent to be transformed into micelles compared to saturated phospholipids. In addition, the width of the coexistence region of mixed micelles and mixed vesicles is larger for phosphatidylcholines with unsaturated chains. A comparison of NaDC with NaC shows the higher solubilization effectiveness of NaDC in agreement with its lower cmc. Furthermore, increasing the ionic strength decreases the amount of bile salt necessary for the formation of mixed micelles, which is also expected from the decrease of the cmc with ionic strength due to the shielding of the charges of the bile salts.     

The interaction of Co ions and sodium deoxycholate micelles

To mimic the interaction between divalent metal ions and bile slats in vivo, two groups of coordination complex compounds, crystalline and gel-like, were synthesized in vitro by mixing the aqueous solutions of CoCl₂ with sodium deoxycholate (NaDC) at various concentrations. Structures and compositions of the compounds were investigated using FT-IR, EXAFS, XRD as well as elemental and ICP analysis, respectively. Then the interaction of Co²⁺ with deoxycholate in solution was observed by laser light scattering (LLS), Transmission electronic microscope techniques and ICP analysis. Conclusions are (1) the crystalline complexes, Co (DC)₂·3H₂O were obtained by reaction of Co²⁺ with mono-molecules of NaDC, and the gel-like complexes, Na_nCo_m(DC)_n+2m formed by reaction of Co²⁺ with NaDC micelles. The gel-like complexes exhibit the non-stoichiometric character; (2) the coordination structures of carboxyl groups with Co²⁺ were different between the crystalline and gel-like complexes. In Co(DC)₂·3H₂O complex, the carboxyl groups of deoxycholate coordinated with Co²⁺ in chelating and pseudo-chelating modes, but that in bridge mode in the case of Na_nCo_m(DC)_n+2m complexes. The non-stoichiometric complexes of Na_nCo_m(DC)_n+2m are formed with a macromolecular structure through the Co²⁺ bridges; (3) NaDC can increase the solubility of Co(DC)₂·3H₂O in aqueous solution, and larger micelles (30-80 nm diameter) formed in the supernate. It is a mixed micelle formed by Co²⁺ ions bridges connecting with NaDC simple micelles. So these micelles are a new kind of micelle containing two kinds of metal ions; (4) these results are in agreement with those formed under physiological conditions in that the different states such as gel, precipitate, micelles of various structures are present in bile of gallbladder. An ideal model of the interaction between Co²⁺ and bile salts in vivo has been proposed.     

H＋对水溶液中脱氧胆酸钠聚集体的影响

运用pH滴定、傅立叶变换红外光谱、紫外可见光谱、激光光散射谱、ICP和元素分析等方法研究了H＋的加入对水溶液中脱氧胆酸钠（NaDC）聚集体的影响.结果表明,浓度大于cmc的NaDC水溶液具有一定的缓冲能力,NaDC浓度越高,缓冲能力越大;随溶液中H＋浓度的增加,首先形成质子化胶团,质子化胶团通过酸盐结构的氢键作用使NaDC初级胶团长大,形成较大的高级胶团,甚至形成凝胶体,最终形成HnNam(DC)n＋m沉淀.     

Micellization of bile salts in aqueous medium: a fluorescence study

Owing to the physiological importance of the micellization process of bile salts, the critical micelle concentration (CMC) becomes a fundamental parameter in the evaluation of their biological activities. The present study suggests fluorescence probing, using 1,6-diphenylhexatriene (DPH), as a simple, convenient, sensitive and economic method for monitoring the micellization process of bile salts in aqueous medium. Three independent parameters: fluorescence intensity, anisotropy and lifetime of DPH have been employed successfully for determining the CMC of two bile salts, sodium deoxycholate (NaDC) and sodium cholate (NaC), in aqueous medium. The CMC values reported by all the above three parameters of DPH are found to be same and it is 16 mM for NaC and 6 mM for NaDC at 25 degrees C in unbuffered solution. The effect of temperature and ionic strength on the micellization process has also been investigated employing DPH as a fluorescent probe. Increasing temperature leads to the formation of fluffier micelles with less rigid interior for both NaC and NaDC. The micelle core of NaC is less perturbed by the presence of NaCl whereas in case of NaDC, the aggregates provide DPH a more nonpolar and rigid environment in presence of NaCl than that in absence of salt.     

Counterion binding behaviour of micelles of sodium dodecyl sulphate and bile salts in the pure state,in mutually mixed states and mixed with a nonionic surfactant

The counterion binding behaviour of micelles of sodium dodecyl sulphate (SDS) and several bile salts in the pure state have been studied, as well as in mutually mixed states, and in a mixed state with polyoxyethylene sorbitan monolaurate (PSML) as a nonionic surfactant. Electrochemical measurements have shown no counterion binding by the pure bile salt micelles and their mixtures with PSML; they can bind counterions when mixed with SDS, whereas the surfactant anions of SDS micelles bind counterions in the pure state and/or in mixed states with PSML. In the SDS-PSML and SDS-bile salts combinations, the counterion association is decreased by the increased proportions of the second component. The extent of counterion binding by the different systems is presented.     

Effect of submicellar concentrations of conjugated and unconjugated bile salts on the lipid bilayer membrane

The interaction of submicellar concentrations of various physiologically important unconjugated [sodium deoxycholate (NaDC), sodium cholate (NaC)] and conjugated [sodium glycodeoxycholate (NaGDC), sodium glycocholate (NaGC), sodium taurodeoxycholate (NaTDC), sodium taurocholate (NaTC)] bile salts with dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) small unilamellar vesicles in solid gel (SG) and liquid crystalline (LC) phases was investigated using the excited-state prototropism of 1-naphthol. Steady-state and time-resolved fluorescence of the two excited-state prototropic forms of 1-naphthol indicate that submicellar bile salt concentration induces hydration of the lipid bilayer membrane into the core region. This hydration effect is a general phenomenon of the bile salts studied. The bilayer hydration efficiency of the bile salt follows the order NaDC > NaC > NaGDC > NaTDC > NaGC > NaTC for both DPPC and DMPC vesicles in their SG and LC phases.     

Identification of Coexisting Pentose,Hexose, and Disaccharides with Preliminary Separation through Hydrophilic Interaction on Silica HPTLC Plate Using Aqueous Sodium Deoxycholate-Acetonitrile Mobile Phase System

JPC – Journal of Planar Chromatography – Modern TLC - Aqueous micellar bile salt, sodium deoxycholate (NaDC) solution as additive in acetonitrile (ACN) in the ratio (1:5 v/v) was...     

Effect of Sodium Alkanoates on Micellization of Dodecylbenzyldimethylammonium Chloride in Aqueous Medium

The present study deals with the interaction of sodium alkanoates viz. sodium acetate, sodium propionate, sodium butanoate, sodium hexanoate and sodium benzoate on the micellization of dodecylbenzyldimethylammonium chloride using conductometeric and flourscence quenching experiments carried out at 25°C. The analysis has been made through study of variation of critical micelle concentration (cmc), degree of counterion binding (β), aggregation number (N), and micropolarity with the concentration of these hydrophobic salts. The differentiation between the effects of hydrophobic and inorganic salts was made by comparing the above results with the influence of NaCl on cmc, β, and N.