Degree Of Counterion Dissociation Research Articles

Counter-ion effect on surfactant–DNA gel particles as controlled DNA delivery systems

The ability to entrap drugs within vehicles and subsequently release them has led to new treatments for a number of diseases. Based on an associative phase separation and interfacial diffusion approach, we developed a way to prepare DNA gel particles without adding any kind of cross-linker or organic solvent. Among the various agents studied, cationic surfactants offered particularly efficient control for encapsulation and DNA release from these DNA gel particles. The driving force for this strong association is the electrostatic interaction between the two components, as induced by the entropic increase due to the release of the respective counter-ions. However, little is known about the influence of the respective counter-ions on this surfactant–DNA interaction. Here we examined the effect of different counter-ions on the formation and properties of the DNA gel particles by mixing DNA (either single- (ssDNA) or double-stranded (dsDNA)) with the single chain surfactant dodecyltrimethylammonium (DTA). In particular, we used as counter-ions of this surfactant the hydrogen sulfate and trifluoromethane sulfonate anions and the two halides, chloride and bromide. Effects on the morphology of the particles obtained, the encapsulation of DNA and its release, as well as the haemocompatibility of these particles are presented, using counter-ion structure and DNA conformation as controlling parameters. Analysis of the data indicates that the degree of counter-ion dissociation from the surfactant micelles and the polar/hydrophobic character of the counter-ion are important parameters in the final properties of the particles. The stronger interaction with amphiphiles for ssDNA than for dsDNA suggests the important role of hydrophobic interactions in DNA.

Cationic Micelles Modulated in the Presence of α,ω‐Alkanediols: A SANS, NMR and Conductometric Study

AbstractThe solution behavior of a typical cationic surfactant, tetradecyltrimethylammonium bromide, in mixed solvent systems composed of water and varying concentrations of α,ω‐alkanediols; 1,2‐ethanediol (ED), 1,4‐butanediol (BD), 1,6‐hexanediol (HD) and 1,8‐octanediol (OD) was examined via electrical conductance measurements, 13C‐NMR spectroscopy and small angle neutron scattering (SANS) measurements. The critical micelle concentration (CMC) values and degree of counterion dissociation (α) indicate that both ED and BD oppose micellization, whereas HD and OD enhance micelle formation. Changes in the 13C‐NMR chemical shifts (∆δ values) reveal that the short chain diols reside almost exclusively in the bulk phase and hence, affect the formation of micelles by altering the solvent properties in the bulk of the solution, whereas HD and OD partition between the pseudomicellar phase and the bulk phase. SANS studies indicated that both the micellar size and aggregation number (Nagg) decrease in the presence of all diols. ED and BD behave like cosolvents and increase the α and CMC values and decrease Nagg. We note that the effect of HD and OD on the properties of the micelles is concentration dependent; at low concentrations, these diols interact with the micelles and behave as cosurfactants (as evidenced by the trends in the micellar properties), while at higher concentrations, they enhance the surfactant solubility and behave as a cosolvent.

Aggregation behavior and intermicellar interactions of cationic Gemini surfactants: Effects of alkyl chain, spacer lengths and temperature

The aggregation behavior of the cationic Gemini surfactants C m H 2 m +1N(CH 3) 2(CH 2) S (CH 3) 2 N C m H 2 m +1,2Br − with m = 12, 14 and s = 2, 4 were studied by performing surface tension, electrical conductivity, pulsed field gradient nuclear magnetic resonance (PFG-NMR), and cyclic voltammetry (CV) measurements over the temperature range 298 K to 323 K. The critical micelle concentration (CMC), surface excess ( Г max), mean molecular surface area ( A min), degree of counter ion dissociation ( α), and the thermodynamic parameters of micellization were determined from the surface tension and conductance data. An enthalpy–entropy compensation effect was observed and all the plots of enthalpy–entropy compensation exhibit excellent linearity. The micellar self-diffusion coefficients ( D m ) and intermicellar interaction parameters ( k d ) were obtained from the PFG-NMR and CV measurements. These results are discussed in terms of the intermicellar interactions, the effects of the chain and spacer lengths on the micellar surface charge density, and the phase transition between spherical and rod geometries. The intermicellar interaction parameters were found to decrease slightly with increasing temperature for 14–4–14, which suggests that the micellar surface charge density decreases with increasing temperature. The mean values of the hydrodynamic radius, R h , and the aggregation number, N agg, of the Gemini surfactants’ m–4– m micelles were calculated from the micellar self-diffusion coefficient. Moreover, the N agg values were calculated theoretically. The experimental values of N agg increase with increases in the chain length and are in good agreement with both previous results and our theoretical results.

Cosolvent Effects on the Spontaneous Formation of Nanorod Vesicles in Catanionic Mixtures in the Rich Cationic Region

The aggregation behavior of cation-rich catanionic mixtures of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) was investigated in water-ethylene glycol (EG) solutions by performing surface tension, electrical conductivity, pulsed field gradient nuclear magnetic resonance, transmission electron microscopy, and cyclic voltammetry measurements. Different physicochemical properties such as the critical micelle concentration, degree of counterion dissociation (α), interfacial properties, aggregation numbers, morphology of aggregates, and interparticle interaction parameters were determined. Cosolvent effects on the interactions between the two surfactants CTAB and SDS were analyzed on the basis of regular solution theory, both for mixed monolayers at the air/liquid interface (β(δ)) and for mixed micelles. It was shown that an excess of cationic surfactant resulted in the formation of nonspherical vesicles. These were predominantly nanorod vesicles in water-EG mixed solvents. The interparticle interactions were assessed in terms of cosolvent effects on the micellar surface charge density, the sphere-to-rod morphology change, and the phase transition from vesicles to mixed micelles. Moreover, the variation of the repulsive electrostatic potential energy between two pairs of aggregates was investigated for two modes of nanostructural transition, namely the transition between spherical and rod-like micelles and the transition between rod-like micelles and nanorod vesicles.

Formation and Growth of Gemini Surfactant (12-s-12) Micelles as a Modulate by Spacers: A Thermodynamic and Small-Angle Neutron Scattering (SANS) Study

A series of symmetrical cationic gemini surfactants of the type N,N′-didodecyl-N,N,N′,N′-tetramethylalkane-α,ω-diammonium dibromide “12-s-12” (s = 2, 4, 6, 8, 10, and 12) are synthesized, and their micellization study in aqueous solution is systematically reported. Specific conductivity as a function of surfactant concentration was measured, and critical micelle concentration (CMC), degree of counterion dissociation (α) of the micelle, and thermodynamic parameters, namely, Gibbs energy (ΔGm), enthalpy (ΔHm), and entropy (ΔSm), of micellization were evaluated using this data at various temperatures. Surface tension studies at 298.15 K provided similar CMCs as given by conductometry along with information on the efficiency/effectiveness and the area occupied per molecule. Small-angle neutron scattering (SANS) inferred the presence of few morphological geometries ranging from spherical to rodlike micelles. Results are explained in terms of the hydrophobicity of spacer chain length along with the electrostati...

Micellization of a cationic gemini surfactant in aqueous solutions with different alkanols and alkanediols as additives: Effect of nonpolar chain and position of hydroxyl groups

The gemini surfactant N-N′bis(dimethyldodecyl)-1,4-butanediammonium dibromide (12-4-12) was synthesized and its critical micelle concentrations (CMCs) and degree of counterion dissociation ( α) in aqueous solutions in the presence of alkanols viz ethanol, isomeric butyl alcohols, 1-hexanol and alkanediols (ethanediol, 1,4-butanediol, 1,2-hexanediol, 2,5-hexanediol 1,6-hexanediol, and 1,8-octanediol) determined from electrical conductivity are reported. While ethanol, ethanediol, 1,4-butanediol showed an increase in CMC, a decrease was seen for isomeric butyl alcohols, 1-hexanol, isomeric hexanediols and 1,8-octanediol. For butyl alcohols the CMC decrease showed the trend 1° >2° > 3°; in C 6 diols, 1,2-hexanediol exerted more decrease as compared to 2,5-hexanediol and 1,6-hexanediol.The results are explained on the basis of the structure and hydrophobicity of alcohols that determine their effect as cosolvent or cosurfactant (partitioning in micelles). Two-dimensional nuclear overhauser enhancement spectroscopy (2D-NOESY) was used to examine the location for 1-butanol and 1,4-butanediol in micellar systems as representative additives from alkanols and alkanediols showing CMC decreasing and increasing effect respectively.

Micellization behaviour and thermodynamic parameters of 12-2-12 gemini surfactant in (water + organic solvent) mixtures

The effect of organic solvents on micellization behaviour and thermodynamic parameters of a cationic gemini (dimeric) surfactant, C 12H 25(CH 3) 2N +–(CH 2) 2–N +(CH 3) 2C 12H 25·2Br −, (12-2-12) was studied in aqueous solutions over the range of T = (293.15 to 323.15) K using the conductometric technique. Ethylene glycol (EG), dimethylsulfoxide (DMSO) and 1,4-dioxan (DO) were used as organic solvents with three different contents. The critical micelle concentration (cmc) and the degree of counter ion dissociation ( α) of micelles in the water and in the (water + organic solvent) mixtures including 10%, 20%, and 30% solvent contents were determined. The standard Gibbs free energy ( Δ G m ∘ ) , enthalpy ( Δ H m ∘ ) and entropy ( Δ S m ∘ ) of micellization were estimated from the temperature dependence of the cmc values. It was observed that the critical micelle concentration of the gemini surfactant and the degree of counter ion dissociation of the micelle increased as the volume percentage of organic solvent, and temperature increased. The standard Gibbs free energy of micellization was found to be less negative with the increase in the organic solvent content and temperature.

Effect of 1-alkanols/salt on the cationic surfactant micellar aqueous solutions—A dynamic light scattering study

The effect of 1-alkanols viz., ethanol, 1-butanol and 1-hexanol on five quaternary salts based cationic surfactants in water and in presence of 0.1 M salts has been systematically investigated by viscosity and dynamic light scattering (DLS) technique. The concentration for surfactant varying in non-polar tail, polar head and counterion was kept constant (∼50 mM) throughout. The viscosity data are less detailed, but confirm the general trend of micellar growth and transitions. Influence of 1-butanol on critical micelle concentration (CMC) and degree of counterion dissociation ( () was also investigated conductometrically. These measurements were done to supplement the role of counterions in exploring the binding phenomenon due to the effect of salt and alcohol during micellization. The effect of 1-alkanols upon the viscosity and micelle hydrodynamic diameter ( D h) of micelles in the presence of salt at varying concentration and temperature was also examined in detail to explain the hydrophobic interactions and electrostatic effects.

Aggregation of imidazolium based ionic liquids in binary methanol–water solvents: A linear solvation free energy relationship study

Aggregation behavior of an imidazolium based ionic liquid (IL), namely 1-dodecyl-3-methylimidazolium chloride [C 12mim][Cl] and a surfactant with the same aliphatic chain, dodecyl trimethylammonium chloride (DTAC), are studied and compared in different mole fractions of methanol–water binary solvents using conductometry. From the conductivity data, micellar parameters including critical micelle concentration (CMC), degree of counter ion dissociation (α) and Gibbs free energy of micellization (ΔG°mic) for both species were calculated as a function of methanol mole fraction. It was found that similar to the surfactant DTAC, the ionic liquid [C 12mim][Cl] forms micellar aggregation in pure water and methanol as well as in their binary mixtures. The CMC values for both compounds were increased up to a methanol mole fraction of 0.5 and then decreased at higher mole fractions. This was attributed to the preferential solvation and formation of methanol–water cluster in binary mixed solvents. The changes in CMC of [C 12mim][Cl] and DTAC as a function of methanol mole fraction were also described by changing in solvatochromic properties of solvents through linear solvation free energy relationship (LSFER) study. A linear relationship between log (CMC) and two solvatochromic Kamlet-Taff parameters including polarity/polarizability (π*) and hydrogen-bond basicity (β) was observed.

Effect of acetonitrile on the micellization and thermodynamic parameters of tetradecyltrimethylammonium bromide: Conductometric and fluorimetric studies

Micellization and related thermodynamic parameters of a conventional cationic surfactant tetradecyltrimethylammonium bromide (TTAB) in various compositions of water–acetonitrile (W–AN) mixed media have been studied at four temperatures ranging between 298.15 K and 323.15 K. We employed conductometric and fluorimetric experiments to obtain the parameters like critical micelle concentration ( cmc), degree of counterion dissociation ( α), and average aggregation number ( N agg). Assuming mass-action model for micelle formation, various thermodynamic parameters were also estimated from the temperature dependence of cmc values. The inclusion of AN caused an increase in cmc of TTAB and a decrease in N agg of micelles whereas the thermodynamic analysis shows that, although the micellization is not favorable compared to pure water, the process is spontaneous and exothermic.

Novel quaternary ammonium hydroxide cationic surfactants as corrosion inhibitors for carbon steel and as biocides for sulfate reducing bacteria (SRB)

A series of alkyl dimethylisopropylammonium hydroxide cationic surfactants (DEDIAOH, DODIAOH and HEDIAOH) was synthesized and characterized. The surface properties such as the critical micelle concentration (CMC), the effectiveness of surface tension reduction ( Π CMC), surface excess concentration ( Γ max) and surface area per molecule ( A min) have been determined by means of surface tension measurements. The degree of counter ion dissociation ( β) and the free energy of micellization (Δ G mic) were calculated. The corrosion inhibition of the synthesized cationic surfactants on carbon steel surface in 1 M HCl solution was investigated. For this purpose, a series of techniques such as gravimetric measurement, potentiodynamic polarization and scanning electron microscope (SEM) were used. The values of activation energy for carbon steel corrosion and the thermodynamic parameters such as adsorption equilibrium constant ( K ads), free energy of adsorption ( Δ G ads ° ) , adsorption heat ( Δ H ads ° ) and adsorption entropy ( Δ S ads ° ) values were evaluated. Results showed that HEDIAOH had better inhibition effect than DEDIAOH and DODIAOH of the corrosion of carbon steel in 1 M HCl solution and inhibition efficiency is higher than 96% after 24 h at 1 × 10 −2 M concentration of the inhibitor. The inhibition efficiency is discussed in terms of strong adsorption of the inhibitor molecules on the metal surface and formation of a protective film. Scanning electron microscope (SEM) showed a good surface coverage on the metal surface. The Biological activity was examined against sulfate reducing bacteria (SRB) by dilution method.

Studies on the Effect of Amino Acids/Peptide on Micellization of SDS at Different Temperatures

AbstractConductivities of (0.001–0.012) m sodium dodecyl sulfate have been determined in water and in the presence of 0.10 m aqueous glycine/alanine/glycylglycine at 298.15, 303.15, 308.15, and 313.15 K. From the specific conductivity data, the critical micellar concentration, degree of counter ion association, degree of counterion dissociation, free energy of transfer of hydrophobic chain from the medium to interior of the micelle, and surface contribution, standard free energy of micellization, standard enthalpy of micellization, and standard entropy of micellization of sodium dodecyl sulfate have been computed. The thermodynamic parameters of micellization and the effect of additives on these parameters have been used to study the interactions present in the micellar systems.

Effect of ethylene glycol on micellization and surface properties of Gemini surfactant solutions

Using surface tension and conductivity measurements, micellization of didodecyl dicationic dibromide Gemini surfactants of different methylene spacer lengths, 12- s-12, 2Br − (where s = 2, 4-methylene groups), is investigated in water–ethylene glycol (EG) mixtures with vol. percent of EG changing within the range of 0–30. Gibbs energy of mixed micellization ( Δ G m i c ° ) is obtained from the critical micelle concentration (CMC) and degree of counter-ion dissociation ( α) values. Differences in the Gibbs energies of micellization of Gemini surfactants between water and water–EG mixtures are calculated in order to monitor the influence of EG on the micellization process. We determine transfer free energy ( g tr ) micelle formation for Gemini surfactants in mixed solvents using the Flory interaction parameter. CMC and micellar ionization degree increase with increase in the vol. percent of EG. The surface excess concentration ( Γ max) decreases and the minimum area per surfactant molecule ( A min) increases with increase in the amount of EG present in the mixture.

Conductometry and Thermodynamics Study of Metal Dioctylsulfosuccinate in Aqueous Solution

The aggregation behavior of metal dioctylsulfosuccinate (MDSS) [Na+, Mg2+, Mn2+, Co2+, and Ni2+] in water has been studied by electrical conductivity (at 303.15 to 323.15 K) and surface tension method (at 303.15 K). Critical micelle concentration (CMCs), degree of counterion dissociation (β) evaluated from conductivity data. Using law of mass action, the thermodynamic parameters viz. Gibbs function (), enthalpy (), and entropy () were evaluated. The enthalpy of micellization decreases strongly with increasing temperature. ΔG is always negative (thermodynamically favored process), and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of counterion. The plots of differential conductivity (dk/dc) T,P , versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counerion.

Micellar Properties and Related Thermodynamic Parameters of the 14-6-14, 2Br− Gemini Surfactant in Water + Organic Solvent Mixed Media

Micellar parameters such as critical micelle concentration (cmc), degree of counterion dissociation (α), and aggregation number (Nagg) of the cationic gemini surfactant hexamethylene-1,6-bis(tetrad...

Conductometric studies of micellization of gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) in water and water–organic solvent mixed media

The micellization of gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) (14-5-14) has been investigated in water and water–organic solvent mixed media (organic solvents used: 1,4-dioxane (DO), dimethylformamide (DMF), ethylene glycol (EG)). The conductivity in water and in mixed media (water + organic solvent) as a function of surfactant concentration was measured at different temperatures and the data were used to find critical micelle concentration (cmc) and degree of counterion dissociation ( α) of the micelle. From the study, it is observed that the micellization tendency of the surfactant decreases in the presence of organic solvents and the increase in the cmc values is comparatively less below 20% (v/v) of organic solvents showing the predominance of water character in the bulk phase at lower compositions of the organic solvents. Thermodynamic parameters were also obtained from the temperature dependence of the cmc values. The standard free energy of micellization was found to be negative in all the cases that became less negative with the increase in the cosolvent content.

Study of Micellar Behavior of Crown Ether and Tetraethylammonium Bromide in Aqueous Media

Conductivity measurements have been carried out to study the micellar behavior of tetraethylammonium bromide in presence of 15‐crown‐5 in aqueous media. The measurements were carried out at 298.15 K as a function of surfactant concentration with varying concentrations of crown ether. The influence of this association on the micellar parameters, such as the cmc (critical micellization concentration) and β (degree of counterion dissociation) have been analyzed. Thermodynamics of the systems were discussed in terms of the change in free energy of micellisation, ΔG0m by applying the charged pseudo‐phase separation model. The trend shows that the micellization becomes less spontaneous in presence of crown ether. The influence of the presence of the inclusion complex on the micellization process of the surfactant has been studied.

Comparative study on the micelle properties of synthetic and dissolved organic matters

The conductivity of two synthetic surfactants and several natural surfactants, dissolved organic matters (DOMs), as well as their enhancement on phenanthrene solubility were measured in order to compare the formation of micelle by DOMs with synthetic surfactants, and their applicability for promoting hydrophobic organic pollutants’ mobility. The DOMs could form micelle structure, similar to the synthetic surfactants. The critical micelle concentration values of the DOMs are lower than those of the synthetic surfactants, and the enhancement of phenanthrene solubility by the DOMs is comparable to or more remarkable than the synthetic surfactants. The partitioning coefficient of phenanthrene to DOM micelles decreased at high DOM concentrations, which is attributed to the structure rearrangement of DOM macromolecules, while no such phenomenon was observed for simple synthetic surfactant micelles. There was an optimum concentration range when applying DOMs to enhance HOCs’ solubility and mobility. Synthetic surfactants gave a concentration dependent conductivity plot with two evident regimes, premicellar and postmicellar regimes, whereas the DOMs showed a gradual transition between the two regimes. The degree of counterion dissociation ( α) of the DOMs was remarkably higher than those of the synthetic ionic surfactants. These results provide insight into DOM micelle structure and micelle forming process with compared to synthetic surfactants, and valuable information on using natural surfactant-enhanced remediation technology.

Micellization of Cetyl Triphenyl Phosphonium Bromide Surfactant in Binary Aqueous Solvents

AbstractThe effect of the different binary aqueous organic solvents viz. 1,4‐dioxane, acetonitrile, dimethylsulfoxide, ethylene glycol, and methanol, on the micelle formation and thermodynamics of a cationic surfactant cetyl triphenyl phosphonium bromide has been studied conductometrically at 298–318 K. From the conductivity data critical micelle concentration, degree of counter ion dissociation (α) and thermodynamic parameters of micellization have been determined. It is observed that micellization tendency of the surfactant decreases in the presence of binary aqueous solvents. The entropies of micellization are all positive, and they compensate the enthalpies of the process.

Interactions of γ-Cyclodextrin with the Mixed Micelles of Anionic Surfactants and Their Inclusion Complexes Formation

Interactions of γ-cyclodextrin (γ-CD) with the single and mixed micelles of sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) have been studied at different concentrations of γ-CD by using conductivity measurements. From conductivity data, the pure and mixed critical micellar concentration (cmc), the equivalent ionic conductivities of the monomeric species (Λ m), the associated species (Λ assc) and the micelle (Λ mic), the degree of counterion dissociation (χ) in the presence of γ-CD have been evaluated from the slope of the conductivity versus concentration plots for the pure and binary mixture of surfactants. From the dependence of cmc of the surfactantson γ-CD concentration, we have deduced the association constant (K) of surfactant-γ-CD inclusion complexes assuming 2:1 stoichiometry. Theories of Clint, regular solution, and Motomura's have been used for the evaluation of ideality or nonideality of the mixed system. Mixed micelles were found to be rich in SDS content in the presence and the absence of γ-CD. The cmc values have been used to evaluate the transfer of standard free energy of micelles (ΔG0 M,tr) from the aqueous medium to additive medium.