Protolytic equilibria in aqueous sodium deoxycholate solutions

Protolytic equilibria taking place in aqueous solutions of sodium deoxycholate (DCNa) have been studied at 25°C using 0.5M NaCl as ionic medium. Electromotive force measurements of a galvanic cell were carried out by means of a glass electrode.The reagent necessary to change the acidity of the solutions was produced in situ by supplying a constant small current.Solubility and acid constant of deoxycholic acid (HDC) have been determined for the chosen experimental conditions. Experimental data obtained in less acid solutions have been explained by assuming the presence of the species H(DC)₂. The relative stability constant has been determined. At higher deoxycholate concentration the presence of a polymeric micellar species has been assumed.

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Protolytische Gleichgewichte in wäßrigen Natriumdesoxycholat-Lösungen

Zusammenfassung Die Protonierung von Natrium-Desoxycholat (DCNa) in wäßrigen Lösungen mit 0.5M NaCl wurde bei 25°C mit Hilfe von E.M.K. Messungen mit einer Glaselektrode untersucht.Das notwendige Reagens für die Umwandlung der Säure in den untersuchten Lösungen wurde in situ durch einen konstanten schwachen Strom erzeugt.Löslichkeit und Dissoziationkonstante von Desoxycholsäure (HDC) wurden unter den gewählten experimentellen Bedingungen bestimmt. Die experimentellen Daten in schwach sauren Lösungen konnten mit der Annahme der Existenz von H(DC)₂ erklärt werden. Die entsprechende Konstante wurde bestimmt. Zur Erklärung der Daten in stärker konzentrierten Lösungen von Desoxycholat ist die Annahme einer polynuklearen Spezies nötig.

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Symbols H analytical excess of hydrogenions, if negative it corresponds to OH^–; - h free concentration of hydrogen ions; - A total concentration of deoxycholate; - a free concentration of deoxycholate; - K _a acid constant of deoxycholic acid (HDC) defined as follows: [HDC]K _a =ha; - _q,p stability constant of a speciesH _p (DC) _q defined as follows: [H _p (DC) _q ]= _q,p h ^p a ^q ; - C ⁰ solubility of HDC; - formation function representing the average number of H⁺ bonded to deoxycholate.     

Micellization and intermicellar interactions in aqueous sodium dodecyl benzene sulfonate solutions

Quasielastic light scattering was used to investigate the size and shape of sodium dodecyl benzene sulfonate (SDBS) micelles in aqueous solutions. Measurements were made as a function of temperature and NaCl and SDBS concentrations. Light scattering data indicate that the micelles are spherocylinders with a semiminor axis of 22 Å. The length of the micelles increases strongly with salt concentration and decreases with temperature. The minimum micelle has an aggregation number of n⁰ = 28 and a hydrodynamic radius of R = 22 Å. Diffusion coefficient and intensity data were analyzed using a thermodynamic theory of micellar aggregation and a model based on DLVO theory of interactions.     

Effect of sodium salicylate, sodium oxalate, and sodium chloride on the micellization and adsorption of sodium deoxycholate in aqueous solutions

The salicylate ion increases the rate of bile flow (choleretic effect) and bile salts are known to affect the colonic absorption of oxalate. Owing to this physiological relevance of salicylate and oxalate ions, critical micelle concentration (cmc) values of sodium deoxycholate (NaDC) were determined in aqueous sodium oxalate, sodium salicylate, and sodium chloride solutions by using surface tension, fluorescence, and EMF methods. The results indicate, besides a counterion effect, the influence of coanions on the cmc. In the range from 25 to 40 °C, cmc increases almost linearly with temperature. In the temperature range from 30 to 40 °C, the counterion binding constant β of NaDC micelles has the same value (0.17±0.01) in the presence of sodium chloride and sodium salicylate. On the other hand, in sodium oxalate solution β=0.05±0.02 when oxalate concentration is less than or equal to c* and β=0.48±0.04 above c*, where c*≈0.038 mol kg(-1). EMF measurements also supported this type of counterion binding to NaDC micelles in sodium oxalate solutions. In sodium oxalate solution, at c* a change in the shape of deoxycholate micelles is expected to take place. Salicylate, oxalate, and chloride coanions have a similar effect on the adsorption of NaDC. This study reveals that the choleretic effect of salicylate is not due to the influence of salicylate ions on the micellization of NaDC.     

Micellization in solutions of ionic liquids

This review is devoted to the problem of aggregation in solutions of ionic liquids (ILs) and the results of relevant studies published in recent years. To a great extent, this problem remains urgent, because the ability to self-organization extends the possibilities of the practical application of ILs. The fields of IL application in which their amphiphilicity is of importance in connection with widening the spectrum of objects under investigation are discussed. The results of studying the aggregation behavior of different systems are briefly considered, including IL solutions in water, water-organic, and organic solvents; aqueous solutions of IL-classical surfactant mixtures; and solutions in which one IL plays the role of a solvent, while another IL or a classical surfactant serves as an amphiphilic solute. Some experimental results are analyzed, and thermodynamic aspects of micellization and problems of molecular-thermodynamic simulation are discussed.     

Micellization of dodecylpyridinium chloride in water-ethanol solutions

Micellar properties of dodecylpyridinium chloride (DPC) were investigated by means of electrical conductometry with emphasis on the influences of cosolvent-water content and temperature. Ethanol was used as a cosolvent. Conductivity measurements gave information about critical micelle concentration and micellar ionization degree of the water-ethanol micellar solutions at different temperatures. In all solvent mixtures, it was observed that the critical micelle concentration of DPC and the degree of the counterion dissociation increase with an increasing concentration of ethanol and increasing temperature. Micellar and thermodynamics data were obtained from the temperature dependence of critical micelle concentrations in various aqueous mixtures of ethanol. In order to explain the effect of the cosolvent, the differences in the Gibbs energies of micellization of DPC between water and binary cosolvent were determined. The standard free energy (ΔG°_mic) of micellization was found to be negative as the concentration of the solvent increases, but it is roughly independent of temperature. Although the enthalpic contribution was found to be larger than the entropic one, in particular at lower temperatures, an entropy-enthalpy compensation effect was observed for all systems. Also, enthalpy (ΔH°_mic) and entropy (ΔS°_mic) of micellization are strongly temperature dependent and decrease with increasing temperature and cosolvent content. The text was submitted by the authors in English.     

Micellization and surface activity ofn-alkyldimethylaminopropanesulfonates in aqueous solutions

Surface tension experiments were performed on severaln-alkyldimethylaminopropanesulfonate aqueous solutions at 15°, 25°, and 35°C. The critical micellar concentrations have been obtained and the surface properties calculated. The enthalpic and entropic contributions to either micellization and adsorption processes have been discussed. The observed properties have been related to the zwitterionic character of these surfactants.     

Bilirubin conformational enantiomer selection in sodium deoxycholate chiral micelles

Intramolecularly hydrogen-bonded, bichromophoric tetrapyrrole pigments, bilirubin-IX and mesobilirubin-XIII, adopt either of two enantiomeric conformations which are in dynamic equilibrium in solution. InpH 8 aqueous sodium deoxycholate solutions, chiral micelles preferentially select one conformational enantiomer, and the solutions exhibit a bisignate circular dichroism Cotton effect in the vicinity of the bilirubin long wavelength electronic transition. Exciton coupling theory indicates a predominance of the left-handed (or negative) chirality bilirubin conformational enantiomer.     

Micellization in aqueous solutions of mixed surfactants containing alkylpolyglucosides

Tensometry is used to find the dependences of critical micelle concentration in aqueous solutions on the composition of mixed systems comprising anionic surfactants (alkyl sulfates and individual sodium soaps) and alkylpolyglucosides. Mixed micellization is revealed and the compositions of micelles and the parameters of intermolecular interaction are calculated. The average hydrodynamic diameter of micelles is measured by dynamic light scattering.     

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.     

Interaction between bilirubin and sodium deoxycholate and their adsorption from mixed solutions on the surface of silica sorbents

The interaction between the bile pigment bilirubin and sodium deoxycholate is studied in aqueous buffer solutions at pH 7.4. It is established that bilirubin forms strong complexes with deoxycholate trimers. The complexation constant is determined by spectrophotometry. The adsorption of bilirubin and sodium deoxycholate from their mixed solutions on the surface of a hydrophilic and two hydrophobic silica sorbents is investigated. It is shown that bilirubin is adsorbed on the surface of all these sorbents only in the free state. Sodium deoxycholate is adsorbed in the forms of monomers and trimers. The affinity of all adsorbed particles is higher for hydrophobic silica sorbents. The binding constants of bilirubin, as well as monomers and trimers of deoxycholate, with the surfaces of all examined sorbents are determined.     

Micellization in solutions of anionic surfactants with two ionogenic groups

Conductometry is employed to measure the critical micellization concentrations of homologous sodium monoalkyl sulfosuccinates with double-charged surface-active anions and alkyl radicals R containing 10–14 carbon atoms (ROOCCH₂CH(SO₃Na)COONa). The degrees of counterion binding with micelles and the Gibbs energy ΔG ^m of micellization are calculated. The incorporation of an additional ionogenic group into a surfactant molecule somewhat decreases ΔG ^m. For the examined series of surfactants, the increment of ΔG ^m due to one methylene group is ?4.44 kJ/mol.     

Disaggregation of amphotericin B by sodium deoxycholate micellar aggregates

Amphotericin B (AmB) is present as aggregates in aqueous media. Sodium deoxycholate (NaDC) is known to cause disaggregation of AmB and to form monomers, as is observed by the increase of absorbance at 414 nm. By following the fluorescence intensity at 472 nm (lambda(ex) 335 nm), it was found that with increasing NaDC concentration there is a progressive disaggregation of AmB leading to increase in both monomeric and dimeric forms. Although the presence of dimeric AmB form in NaDC micellar media is known, observation of the growth of the dimeric species is novel. Studies in fluorescence lifetime and steady state fluorescence anisotropy also support this conclusion. As NaDC (at ca. 10 mM) is the preferred choice of medium for AmB delivery and AmB aggregation has been implicated for its toxicity, the observation of dimeric AmB at these NaDC concentrations assumes significance.     

Water vapor adsorption behavior of sodium deoxycholate anhydrous forms

Pseudopolymorphism of sodium deoxycholate (NaDC) was investigated. Intact NaDC (dihydrate) was dried at 60 degrees C under reduced pressure resulting an anhydrous amorphous phase. On the other hand, intact NaDC was altered to an anhydrous crystalline form by heating at 200 degrees C. The water vapor adsorption and desorption isotherms of dehydrated NaDCs were determined using an automatic gravimetric water vapor adsorption analyzer. In the case of NaDC dehydrated at 60 degrees C, the weight was increased in rising relative humidity and it was transformed into the NaDC tetrahydrate above 60% RH, which was identified by TG/DTA and powder X-ray diffraction. During the water vapor adsorption process of the sample dehydrated at 200 degrees C, the NaDC dihydrate was obtained in the range of 50 to 70% RH and then transformed into the NaDC octahydrate above 85% RH. The NaDC octahydrate was characterized by TG/DTA and powder X-ray diffraction for the first time. During the desorption process, the octahydrate was changed to the tetrahydrate between 80 and 40% RH.     

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.     

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.     

Micellization of sodium dodecyl sulfate and polyoxyethylene dodecyl ethers in solution

The effect of polyoxyethylene type nonionic surfactants (C₁₂E _n n = 3, 4, 5, 6, 7 and 8) on the aqueous solution of sodium dodecyl sulfate (SDS) in absence and presence of NaCl was examined using small-angle neutron scattering (SANS), dynamic light scattering (DLS), and viscosity measurements. Upon addition of C₁₂E _n , micellar size of SDS was found to increase significantly, and such micellar elongation was further enhanced in the presence of NaCl. Micellar growth is most significant in presence of shorter moieties of C₁₂E _n (e.g., n = 3, 4) as compared to higher ethereal oxygen content. The results of structural investigations with SANS and DLS to confirm this assumption are reported. The cloud point of C₁₂E _n has increased upon addition of SDS and decrease with NaCl, and a typical behavior is observed when both SDS and NaCl were present.     

Micellization of decyl- and dodecyldimethylbenzylammonium bromides at various temperatures in aqueous solutions

Electrical conductivity and density measurements of aqueous solutions of decyl- and dodecyldimethylbenzylammonium bromides have been determined at various temperatures. From these data the critical micelle concentration (cmc) and the degree of ionization of the micelles were determined. The standard free energy of the micellization process and the minima of the temperature dependent values of the cmc were estimated. From the density data the apparent molal volumes of the monomeric and micellized surfactants as well as the contributions of the methylene and phenylene groups were estimated.     

Tunable size and spectral properties of fluorescent nanoGUMBOS in modified sodium deoxycholate hydrogels

Microstructures of sodium deoxycholate hydrogels were altered considerably in the presence of variable tris(hydroxymethyl)aminomethane (TRIS) concentrations. These observations were confirmed by use of X-ray diffraction, polarized optical microscopy, rheology, and differential scanning calorimetry measurements. Our studies reveal enhanced gel crystallinity and rigidity with increasing TRIS concentrations. The tunable hydrogel microstructures obtained under various conditions have been successfully utilized as templates to synthesize cyanine-based fluorescent nanoGUMBOS (nanoparticles from a group of uniform materials based on organic salts). A systematic variation in size (70-200 nm), with relatively low polydispersity and tunable spectral properties of [HMT][AOT] nanoGUMBOS, was achieved by use of these modified hydrogels. The gel microstructures are observed to direct the size as well as molecular self-assembly of the nanomaterials, thereby tuning their spectral properties. These modified hydrogels were also found to possess other interesting properties such as variable morphologies ranging from fibrous to spherulitic, variable degrees of crystallinity, rigidity, optical activity, and release profiles which can be exploited for a multitude of applications. Hence, this study demonstrates a novel method for modification of sodium deoxycholate hydrogels, their applications as templates for nanomaterials synthesis, as well as their potential applications in biotechnology and drug delivery.