IGC studies of binary cationic surfactant mixtures

Inverse gas chromatography (IGC) has been used to measure the interaction parameter between two twin-tailed cationic surfactants. Didodecyldimethylammonium (DDAB) and dioctadecyldimethylammonium (DODAB) bromides and their mixtures were used as stationary phases. IGC and DSC techniques have been used for the determination of the temperature zone of working. The activity coefficients at infinite dilution (on a mole fraction basis) were calculated for eleven probe solutes on each pure surfactant column. Values of interaction parameter between surfactants obtained at four weight fractions of the mixtures and at five temperatures are positive and suggested that the interactions is more unfavourable with the increment of DODAB concentration in the mixture. The results are interpreted on the basis of partial miscibility between DDAB and DODAB.     

Spectroscopic study on the inherent binding information of cationic perfluorinated surfactant with bovine serum albumin

UV-vis, FT-IR, fluorescence and synchronous fluorescence spectra are applied to discuss the inherent binding information of model protein bovine serum albumin (BSA) with perfluorinated surfactant trimethyl-1-propanaminium iodide (FC-134). According to the results analyzed from Stern-Volmer equation, FC-134 can quench the fluorescence intensity of BSA via a dynamic quenching mechanism with complex formation. The thermodynamic parameters are calculated, revealing that hydrophobic force is the main interaction driven force. The binding constants and number of binding sites are also obtained. With the aid of site markers—warfarin and ibuprofen, we first report that FC-134 primarily binds to tryptophan residue Trp-214 of BSA within site I (sub-domain IIA).     

Kinetics of membrane raft formation: fatty acid domains in stratum corneum lipid models

The major barrier to permeability in skin resides in the outermost layer of the epidermis, the stratum corneum (SC). The major SC lipid components are ceramides, free fatty acids, and cholesterol. Ternary mixtures containing these constituents are widely used for physicochemical characterization of the barrier. Prior X-ray diffraction and IR spectroscopy studies have revealed the existence of ordered lipid chains packed in orthorhombic subcells. To monitor the kinetics of formation of regions rich in fatty acids, the current study utilizes a modification of the method (J. Phys. Chem. 1992, 96, 10008) developed to monitor component demixing in n-alkane mixtures. The approach is based on changes in the scissoring or rocking mode contours in the IR spectra of (orthorhombically packed) ordered chains. In the current study, equimolar mixtures of ceramides (either non-hydroxy fatty acid sphingosine ceramide or alpha-hydroxy fatty acid sphingosine ceramide) with chain perdeuterated fatty acids (either palmitic or stearic acid) and cholesterol reveal a time evolution of the scissoring contour of the deuterated fatty acid chains following quenching from relatively high temperatures where random mixing occurs. Segregation of domains enriched in the fatty acid component is observed. The kinetics of segregation are sensitive to the quenching temperature and to the chemical composition of the mixture. The kinetic regimes are conveniently catalogued with a power law of the form P=Ktalpha where P is a (measured) property related to domain composition. The time scales for demixing in these experiments are similar to times observed in several studies that have tracked the restoration of the in vivo permeability barrier following nonthermal challenges to SC integrity. Further evidence for the physiological importance of the current measurements is the detection of these phases in native SC. The current work constitutes the first direct, structure-based determination of the kinetics of barrier formation in relevant skin lipid barrier models.     

Spontaneous aggregate transition in mixtures of a cationic gemini surfactant with a double-chain cationic surfactant

Controllable aggregate transitions were realized by mixing two kinds of cationic surfactants, hexylene-1,6-bis(dodecyldimethylammonium bromide) (C(12)C(6)C(12)Br(2)) and didodecyldimethylammonium bromide (DDAB). It was found that two parameters are the main factors determining the aggregation behavior of the mixed system, the total concentration of DDAB and C(12)C(6)C(12)Br(2) (C(T)), and the mole fraction of DDAB in the mixtures of DDAB and C(12)C(6)C(12)Br(2) (X(DDAB)). How these two parameters act on the aggregate transitions was studied in detail by various measurements including surface tension, turbidity, electrical conductivity, ζ potential, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, and (1)H NMR. When C(T) was constant, spontaneous vesicle-to-micelle transitions were found with decreasing X(DDAB) at high C(T). When X(DDAB) was constant, aggregate transitions were generated by gradually increasing C(T), depending on different X(DDAB) ranges. At X(DDAB) < 0.6, small spherical aggregates formed first and then transferred to vesicles, and finally the vesicles transitioned to micelles. At X(DDAB) ≥ 0.6, the progressive increase in C(T) led to aggregate transitions on the order of the arising of vesicles, the continuous growth of vesicles, the disruption of vesicles into micelles, and the final coexistence of vesicles and micelles. The hydrophobic interaction and electrostatic repulsion between DDAB and C(12)C(6)C(12)Br(2) together with the related degree of ionization and hydration of the surfactants were gradually adjusted by changing the ratio and the total concentration of these two surfactants, which should be responsible for the complicated aggregation behavior.     

Contribution to the mechanism of liquid membrane oscillators involving cationic surfactant

It is shown that liquid membrane oscillators with cationic surfactants have more complex oscillation patterns than observed previously. The actual details of the oscillations depend strongly on the nature of the membrane material, disclosing even the presence of parallel molecular events. It appears that sampling topology also has a great influence on the observed oscillatory behavior. Variation of oscillation patterns with diffusion path length in the membrane demonstrated the decisive role played by the actual timing of molecular events. The new evidences produced complete usefully the actual views concerning the mechanism of oscillations.     

Use of marker ion and cationic surfactant plastic membrane electrode for potentiometric titration of cationic polyelectrolytes

A plasticized poly (vinyl chloride) (PVC) membrane electrode sensitive to stearyltrimethylammonium (STA) ion is applied to the determination of cationic polyelectrolytes such as poly (diallyldimethylammonium chloride) (Cat-floc) by potentiometric titration, using a potassium poly (vinyl sulfate) (PVSK) solution as a titrant. The end-point of the titration is detected as the potential change of the plasticized PVC membrane electrode caused by decrease in the concentration of STA ion added to the sample solution as a marker ion due to the ion association reaction between the STA ion and PVSK. The effects of the concentration of STA ion, coexisting electrolytes in the sample solution and pH of the sample on the degree of the potential change at the end-point were examined. A linear relationship between the concentration of cationic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 2×10⁻⁵ to 4×10⁻⁴ N for Cat-floc, glycol chitosan, and methylglycol chitosan.     

Analysis of electron spin resonance spectra of alkyl spin labels in excised guinea pig dorsal skin, its stratum corneum, delipidized skin and stratum corneum model lipid liposomes

The electron spin resonance (ESR) spectra of alkyl spin labels were observed in the excised guinea pig dorsal skin, its stratum corneum, delipidized skin and stratum corneum model lipid liposomes. The spectrum of 5-doxylstearic acid (5-NS) in the stratum corneum and order parameter obtained from the spectrum, indicated that the spin label was present in highly ordered lipid lamella. On the other hand, the spectrum of methyl ester of 5-NS (5-NMS) and its apparent rotational correlation time calculated from the spectrum, showed only a weakly immobilized component in the stratum corneum as well as in the whole excised skin. The ester spin label seemed to be scarcely present in the rigid lipid lamella, but mainly in the relatively fluid environment. On the other hand, cationic alkyl spin labels showed quite different spectra depending on their alkyl chain lengths. Long-chain 4-(N,N-dimethyl-N,-pentadecyl)ammonium-2,2,6,6-tetramethylpiperidine-1-oxyl (CAT-15) seemed to be present in the protein region of the stratum corneum as we recently reported, whereas hydrophilic quaternary ammonium spin label 4-trimethylammonium-2,2,6,6-tetramethylpiperidine-1-oxyl (CAT-1) seemed to be present in the bulk water of the skin, even in delipidized skin. These findings indicated that the different interaction and different localization of the alkyl spin labels depended on their electronic charge as well as their alkyl chain lengths.     

The effects of transdermal permeation enhancers on thermotropic phase behaviour of a stratum corneum lipid model

This study evaluates the interactions of a model stratum corneum (SC) lipid system based on ceramide AP (N-(2-hydroxystearoyl)phytosphingosine) with three selected permeation enhancers including urea, oleic acid (OA), and N-lauroylglycine lauryl ester (12G12) using temperature-dependent small-angle X-ray diffraction measurements. As a first step, the thermotropic phase behaviour of the control SC lipid membrane, i.e. without enhancer, was characterized. The system shows two separated phases at 32 °C, which mix into another phase at around 45 °C. This phase is stable till 70 °C when the repeat distance starts to decrease. After cooling, only one phase is visible which shows two phase transitions at 45 and 70 °C again. Based on these results, the effects of the permeation enhancers were studied. The permeation enhancers influence the phase behaviour of the system. Urea and 12G12 cause a concentration-dependent shift of the phase transition temperatures while OA induces a phase separation. The results from this simple model system may provide basis for studies on more complex systems or real SC.     

Surface complexation of DNA with a cationic surfactant

We have studied the surface complexation of DNA with a cationic surfactant (DTAB) using a combination of methods: dynamic surface tension, ellipsometry and Brewster angle microscopy. Below the surfactant critical aggregation concentration (cac), complexation occurs only at the surface, and the results are consistent with neutralization of the surfactant charges by the free polymer ions. Above the cac, surfactant starts to bind cooperatively to DNA in the bulk, and adsorption of the preformed hydrophobic surfactant DNA aggregate is now possible, leading to thick surface layers. At still higher concentrations of surfactant (still below saturation of binding in the bulk), there is decrease in adsorption due to competition with bulk aggregates. Finally, as surfactant concentration is increased still further, bulk aggregates become less soluble and large amounts are adsorbed, forming a surface layer, which is solid-like and brittle.     

Interaction of water-soluble cationic porphyrin with anionic surfactant

The interaction of a cationic water-soluble porphyrin, 5,10,15,20-tetrakis [4-(3-pyridiniumpropoxy)phenyl]porphyrin tetrakisbromide (TPPOC3Py), with anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous solution has been studied by means of UV-vis, (1)H NMR, fluorescence, circular dichroism (CD) spectra and dynamic laser light scattering (DLLS), and it reveals that TPPOC3Py forms porphyrin-surfactant complexes (aggregates), including ordered structures J- and H-aggregates, induced by association with surfactant monomers below the SDS critical micelle concentration (cmc), and forms micellized monomer upon the cmc, respectively. The position of TPPOC3Py in the micelle is determined, which is not in the micelle core instead of intercalated among the SDS chains, most likely with the pyridinium group extending into the polar headgroup region of the micelle.     

Interaction of sodium ions with cationic surfactant interfaces

The thermodynamically stable microemulsion and lamellar phases in the didodecyldimethylammonium bromide/water/n-decane ternary system were explored in the presence of NaBr to gain information on sodium ion-interface interactions. Experimental results, obtained by different NMR techniques, strongly suggest accumulation of sodium ions at the cationic interface. This apparently counterintuitive result is explained by invoking the dispersion potential experienced by the ions near the interface. A mechanism is proposed that can account for the dramatic shrinkage of the microemulsion phase region when an electrolyte is added.     

Solubilizing interactions of octylphenol surfactants with liposomes modeling the stratum corneum lipid composition

 The interaction of a series of polyethoxylated octylphenols (ethylene oxide units average 8.5–20.0) with liposomes modeling the stratum corneum (SC) lipid composition (40% ceramides, 25% cholesterol, 25% palmitic acid and 10% of cholesteryl sulfate) was investigated. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous-phase partition coefficients (K) were determined by monitoring the changes in the static light scattering of the system during solubilization. The fact that free concentration for each surfactant tested was always similar to its critical micelle concentration (CMC) indi-cates that the liposome solubilization was mainly ruled by the formation of mixed micelles. The Re and K para-meters for liposome saturation fell as the surfactant HLB increased. Thus, at this interaction step the higher the surfactant HLB, the higher the ability of these surfactants to saturate SC liposomes and the lower their degree of partitioning into liposomes. However, the maximum solubilizing ability was achieved at intermediate HLB values. Thus, the octylphenols with 20 and 12.5 ethylene oxide units showed, respectively, the highest power of saturation and solubilization of SC structures in terms of the total surfactant amounts needed to produce these effects. Different trends in the interaction of these surfactants with SC liposomes were observed when comparing the Re and K parameters with those reported for PC ones. Thus, whereas the SC liposomes were more resistant to the surfactant action, the affinity of these surfactants with these bilayer structures was higher in all cases. Received: 3 March 1997 Accepted: 22 May 1997     

Spectroscopic studies of model polar stratospheric cloud films

Fourier transform infrared (FTIR) spectroscopy has been used to study nitric acid/ice films representative of type I polar stratospheric clouds (PSCs). These studies reveal that in addition to amorphous nitric acid/ice mixtures, there are three stable stoichiometric hydrates of nitric acid—nitric acid monohydrate (NAM), dihydrate (NAD) and trihydrate (NAT). Two distinct crystalline forms of the trihydrate were also observed. These two forms appear to differ in their concentration of crystalline defects, but not in their chemical composition. In addition to probing the composition of type I PSCs, we have also used FTIR spectroscopy to characterize laboratory surfaces on which measurements of heterogeneous reaction rates are performed. Our studies suggest that “water-rich NAT” is a two-phase system with separate ice and NAT crystalline regimes. Finally, we have used FTIR spectroscopy to determine the desorption kinetics for evaporation of model PSC films. Ice evaporation was found to follow zero-order desorption kinetics with a desorption barrier of 12±2 kcal/mol and a preexponential factor of 10^30.5±1.5 molec/cm²-s.     

Interactions of temperature-responsive anionic polyelectrolytes with a cationic surfactant

The interactions of temperature-responsive copolymers of sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS) and N-isopropylacrylamide (NIPAM) with a cationic surfactant, dodecyltrimethylammonium chloride (DTAC), have been studied. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol%. The surface activity was higher for the polymers with lower AMPS content. It was found that DTAC undergoes association with the polymer chain, forming mixed polymer-surfactant micelles. The values of cac for the polymers were found in fluorescence studies using pyrene as the fluorescent probe. They were in the range 0.9-3.6x10(-3) M and were lower for polymers with higher AMPS content. An increase in DTAC concentration up to about its cmc results in a decrease of the LCST (lower critical solution temperature) of the copolymers, while further increase above the cmc results in an increase of the LCST. The minimum value of LCST in the presence of the surfactant is lower than the LCST of NIPAM homopolymer.     

Fabrication of positively charged catanionic vesicles from ion pair amphiphile with double-chained cationic surfactant

In this study, a pseudodouble-chained ion pair amphiphile, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), was prepared from a mixture of cationic surfactant, hexadecyltrimethylammonium bromide, and anionic surfactant, sodium dodecylsulfate. Positively charged catanionic vesicles were then successfully fabricated from HTMA-DS with the addition of cationic surfactants, dialkyldimethylammonium bromide (DXDAB), including ditetradecyldimethylammonium bromide (DTDAB), dihexadecyldimethylammonium bromide, and dioctadecyldimethylammonium bromide (DODAB), with a mechanical disruption approach. The control of charge characteristic and physical stability of the catanionic vesicles through the variations of DXDAB molar fraction and alkyl chain length was then explored by size, zeta potential, and Fourier transform infrared analyses. It was found that the molecular packing and/or molecular interaction of HTMA-DS with DXDAB rather than the electrostatic repulsion between the charged vesicles dominated the physical stability of the mixed HTMA-DS/DXDAB vesicles. The presence of DTDAB, which possesses short alkyl chains, could adjust the packing of the unmatched chains of HTMA⁺ and DS^? and promote the vesicle formation. However, the weak molecular interaction due to the short chains of DTDA⁺ could not maintain the vesicle structures in long-term storage. With increasing the alkyl chain length of DXDAB, it was possible to improve the vesicle physical stability through the enhanced molecular interaction in the vesicular bilayer. However, the long alkyl chains of DODAB unmatched with those of HTMA-DS, resulting in the vesicle disintegration in long-term storage. For the formation of stable charged catanionic vesicles of HTMA-DS/DXDAB, a good match in hydrophobic chains and strong molecular interaction were preferred for the vesicle-forming molecules.     

Spectrophotometric studies of anionic dye-cationic surfactant interactions in mixture of cationic and nonionic surfactants

The interaction between an anionic dye C.I. Reactive Orange 16 (RO16) and a cationic surfactant dodecylpyridinium chloride (DPC) in mixtures of DPC and nonionic surfactants poly(oxyethylene)ethers (C(m)POE(n); m = 12, 16 and 18, n = 4, 10 and 23) are investigated spectrophotometrically in a certain micellar concentration range. The spectrophotometric measurements of dye-surfactant systems are carried out as function of mole fraction of surfactant at four different temperatures. For this reason, a typical system was occurred at 1.0 x 10(-2) mol l(-1) for surfactants and at 1.0 x 10(-4) mol l(-1) for dye concentrations. The formation of DPC-RO16 complex in the C(m)POE(n) solutions of different mole fractions in its micellar concentration range have been determined and compared to those obtained in the binary mixtures. From the spectrophotometric measurements has been observed that the addition of nonionic surfactant in to the mixture of DPC-RO16, causes a significant increase of the value of absorbance. This increase explains that the stability of DPC-RO16 complex is reduced in the presence of nonionic surfactant micelles. It can be seen from results; in mixed surfactant solutions, there are DPC-C(m)POE(n) and RO16-C(m)POE(n) interactions in addition to DPC-RO16 interaction. Since the solubilizaton of the DPC-RO16 complex has been appeared in the C(m)POE(n) solution, our results support the conclusion that adding C(m)POE(n) influences the hydrophobic-hydrophilic balance of the studied complex. Furthermore effect of the alkyl chain length and the number of poly(oxyethylene) in nonionic surfactant on values of absorbance have been investigated.     

Adsorption of organic anions from aqueous solutions by layered silicates modified with cationic surfactant

The interaction of anionic organic dyes with layered silicates (kaolinite and hydromica) both natural and modified with a cationic surfactant (cetylpyridinium bromide) is studied by adsorption and spectral methods. The adsorption of organic anions by modified silicates is proved to proceed via the formation of ionic associates of these adsorbates with the modifier. It is found that the interaction of large organic anions with the modifier results in the desorption of the latter, followed by its secondary adsorption in the form of ionic associates with the adsorbates. The selectivity of layered silicates modified with the cationic surfactant to organic anionic dyes is determined by the stability of the formed dye/modifier ionic associates and their affinity to the surface. These factors depend on the sizes of the hydrocarbon moieties of both components of the associates. Therefore, the selection of a suitable modifier allows one to control the selectivity of modified minerals to different organic anions. Using long-chain organic cations as modifiers, organic anions of any sizes can be extracted from aqueous solutions.     

Ionic rectification properties of a bipolar interface consisting of a cationic surfactant and cation-exchange membrane

A novel bipolar interface that consists of cationic surfactant and cation-exchange membrane was successfully prepared in an aqueous electrolyte system. This bipolar interface shows a ionic rectification behavior similar to that observed in bipolar membranes. However, different from bipolar membranes, this system has a total rectification behavior, where we cannot observe the occurrence of a water-splitting phenomenon, which always occurs in the bipolar membrane process under reverse bias conditions.