Counterion Binding Research Articles

Effect of temperature and solvent compositions on the aggregation and thermodynamic properties of the polyvinyl alcohol + tetradecyltrimethylammonium bromide mixture in aqua-organic mixed media

The TTAB surfactant micelle formation in presence of PVA was detected by the evaluation of CMC from the conductivity plot against the concentration of surfactant. Micellar parameters, such as critical micelle concentration (CMC), the extent of counter ion binding (β), and thermodynamic properties (ΔG 0 m, ΔH 0 m and ΔS 0 m) of PVA + TTAB systems have been estimated. Values of CMC of the PVA + TTAB mixed system was achieved and found to reduce with enhancing PVA concentrations which designate the survival of interactions between TTAB and PVA. The values of CMC were found to undergo an increase in the mixed solvents in comparison to the values obtained in aqueous media, which might be attributed to the reduction of the dielectric constant as well as water cohesive energy. The values of free energy of micellisation () are negative for the PVA + TTAB system, suggesting a spontaneous aggregation phenomenon. The negative values of in H2O and 9% (w/w) mixed solvents follow the order: (H2O) > (water + AN) > (water + DO) > (water + DMF). The thermodynamic properties of transfer were also estimated for the move of PVA+ TTAB mixed system from water to aqua-organic mixture of solvents.

UV-responsive micellar systems and aqueous two-phase systems based on cationic ester-containing gemini surfactant and sodium trans-ortho-methoxycinnamate

Three ester-containing gemini surfactants (CmDEGs) were used to construct UV-responsive micellar systems with sodium trans-ortho-methoxycinnamate (trans-NaOMCA) as photo-sensitive additive. The effect of tail-chain length and spacer chain length on the UV-responsive ability was preliminarily explored. Longer tail chain and shorter spacer chain are favorable factors for enhancing UV-responsive ability. The addition of trans-NaOMCA into N,N′-bis(2-(dodecanoyloxy)ethyl)-N,N,N′,N′-tetramethyl-1,3-propane diammonium dibromide (C12DEG3) aqueous solution leads to a peak in zero-shear viscosity (η0) versus composition curve, and its further addition induces aqueous two-phase separation. For the C12DEG3/trans-NaOMCA/H2O mixed micellar systems, the UV responsiveness of significant decrease in η0 ascribes to microstructural transitions arising from the changes in counterion binding modes due to the trans-cis photoisomerization of NaOMCA. In comparison with the gemini surfactant 12-3-12, C12DEG3 has ester groups introduced in its tail chains. The introduction of ester groups leads to a significant effect on enhancing the photo-responsive ability in viscosity decrease of the constructed UV-responsive micellar systems. Furthermore, the effect of the addition of an amino acid–based surfactant sodium lauroylglutamate (SLGlu) into the C12DEG3/trans-NaOMCA/H2O mixed system on the UV-responsive behaviors was explored. In addition to UV-induced significant decrease in η0 and phase transition from aqueous two-phase systems (ATPS) to isotropic single-phase systems, the addition of SLGlu can also cause UV-induced increase in η0 and lead to richer UV-induced phase transition behaviors. The reason leading to these differences due to the presence of SLGlu was discussed based on 1H NMR spectra, molecular dynamics (MD) simulation, and molecular electrostatic potential (MEP) analysis.

Comparison of the interaction between propranolol hydrochloride (PPL) with anionic surfactant and cationic surface active ionic liquid in micellar phase

In this study, the interaction in binary mixtures comprising an amphiphilic drug (propranolol hydrochloride, PPL) and ionic surfactants (N-lauryl sarcosine sodium, NLS and 1-dodecyl-3-methylimidazolium bromide, SAIL) was investigated in micellar phase using conductometric technique in aqueous solution at 298.15 K. SAIL is a cationic surface-active ionic liquid with a specific critical micelle concentration(CMC). To identify the influence of polar head groups in interaction between components, the surfactants with the same alkyl chain length (C12) but with oppositely charged head groups were selected (NLS: anionic and SAIL: cationic). The deviation of experimental critical micelle concentration (CMCexp) from the corresponding ideal values of CMC (CMCid), the micellar compositions (X1 and X2), the mutual interaction parameter (βm), activity coefficients of the components in the mixed micelle (f1 and f2) and thermodynamic parameters have been calculated using different proposed theoretical models like Clint, Rubingh, and Motomura. The interaction parameter (βm) is negative values at all compositions for two systems (with two levels of values), showing attractive interactions between components. In comparison between the NLS/PPL and SAIL/PPL systems, the NLS/PPL system shows stronger micelle formation capability, smaller CMC values and stronger synergistic effect. The determined values of the micellar mole fraction of surfactant (X1) obtained from theoretical models signify the considerable contribution of surfactant in surfactant(1)/PPL(2) mixed micellization. Further, conductometry measurements indicate that the extent of counterion binding (α) of mixed micelles for SAIL/PPL system are higher than those found for NLS /PPL system.

Application of cationic-nonionic surfactant based nanostructured dye carriers: Mixed micellar solubilization

Most of organic compounds being hydrophobic in nature are insoluble or sparingly soluble in water. The improvement in solubility is one of the major challenges in their industrial applications. Said issue can be addressed using micellar solutions of surfactants. Surfactants, owing to their inherent amphiphilic nature, have invited the interest of many researchers. It has, however, been observed that the stability and solubilizing capability of a single surfactant-based colloidal system is not up to the mark. To overcome this problem, we have formulated and applied composite micelles of CTAB/TX-100 and CPC/TX-100 as carriers of direct red 28 molecules to aid dispersion, solubility and stability of the dye in aqueous medium. Herein, thermodynamics of micellization and degree of the dye partitioning have been quantified conductometrically and spectroscopically. Results suggest that blend of different surfactants act synergistically to augment the dye partitioning. Furthermore, it has also been noted that micellization of surfactants, counterion binding and the dye partitioning are spontaneous processes.

Hydration and counterion binding of aqueous acetylcholine chloride and carbamoylcholine chloride.

The hydration and Cl- ion binding of the neurot†ransmitter acetylcholine (ACh+) and its synthetic analogue, carbamoylcholine (CCh+), were studied by combining dilute-solution conductivity measurements with dielectric relaxation spectroscopy and statistical mechanics calculations at 1D-RISM and 3D-RISM level. Chloride ion binding was found to be weak but not negligible. From the ∼30 water molecules coordinating ACh and CCh+ only ∼1/3 is affected in its rotational dynamics by the cation, with the majority - situated close to the hydrophobic moieties - only retarded by a factor of ∼2.5. At vanishing solute concentration cations and the ∼3-4 H2O molecules hydrogen bonding to the CO group of the solute exhibit similar rotational dynamics but increasing concentration and temperature markedly dehydrates ACh+ and CCh+.

Counterion Binding in Adsorbed Surfactant Films Studied by Surface Tensiometry and Total Reflection XAFS Spectroscopy

Counterion Binding in Adsorbed Surfactant Films Studied by Surface Tensiometry and Total Reflection XAFS Spectroscopy

ITC for Characterization of Self-Assembly Process of Cationic Dendrons for siRNA Delivery.

siRNAs are emerging as promising therapeutic agents due to their ability to inhibit specific genes in many diseases. However, these tools require specific vehicles in order to be safely delivered to the targeted site. Among different siRNA delivery systems, self-assembled nanomicelles based on amphiphilic cationic dendrons (ACDs) have recently outperformed nanovectors based on covalent carriers. This chapter describes how isothermal titration calorimetry (ITC) can be exploited as one of the best techniques to investigate the self-assembly process of ACDs. Specifically, ITC can provide, as such or via specific analysis methods, a full thermodynamic characterization of these nanomicelles, including their critical micellar concentration, micelle aggregation number, degree of counterion binding, Gibbs free energy of micellization, and its enthalpic and entropic components.

Effect of head-group of cationic surfactants and structure of ionic groups of anionic polyelectrolyte in oppositely charged polymer-surfactant complexes

In this study, a detailed assessment of interactional conduct between different head-groups of cationic surfactants and different monomer fragments of anionic polyelectrolyte of aqueous media is reported. Tensiometry, conductometry, viscosimetry, dynamic light scattering have been employed to get insight into interactions among cationic surfactant and polyelectrolyte in interfacial region critical aggregation and micellization concentration, surface excess concentration, surface pressure at interface, minimum area occupied with the aid of one molecule of cationic surfactant at air-solvent interface, adsorption efficiency, surface tension at critical micelle concentration and the positive degree of counterion binding had been calculated. Thermodynamic parameters, i.e., standard Gibbs free energy of micellization and adsorption processes had been evaluated. Polyelectrolyte-surfactant interaction used to be studied in dependence on nature of head-group of cationic surfactant and polyelectrolyte chain and their influence on colloidal-chemical parameters of polyelectrolyte-surfactant complexes has been compared. Petrocollecting ability of these complexes in the waters of various mineralization degree was investigated.

Investigation the effect of sodium carboxymethylcellulose as polycounterion on cetirizine hydrochloride–sodium dodecyl sulphate mixed micelle

The aim of this research was to investigate the binding properties of sodium carboxymethylcellulose (NaCMCu) as polycounterions on mixed micelles of drug surfactants. Mixed micellization behavior of cetirizine hydrochloride (CTZ) and sodium dodecyl sulphate (SDS) was investigated in the absence and presence of NaCMCu using electrical conductivity, surface tension, fluorescence measurements, dynamic light scattering and UV measurements. The critical micelle concentration (CMC) in the aqueous and NaCMCu medium of CTZ + SDS mixed micelle was lower than the single micelle of CTZ and SDS. The presence of electrostatic interaction between NaCMCu and CTZ + SDS could increase the stability of mixed micelle from αSDS 1.0–0.0. The results showed that CTZ + SDS monomers could bind to the NaCMCu chains and form free mixed micelles in the solution, whereas no SDS / NaCMCu micelle-like complexes were found due to repulsive interaction. NaCMCu significantly decreased the CMC of CTZ. The values of counterion binding (B) from Corrin–Harkins approach and binding constant (Kb) indicated that the CTZ micelles bound to electrostatic interaction by –COO¯ ions of NaCMCu. UV absorbance data given a significant parameter, mean ion occupancy per micelle (i0) which estimated the occupancy per micelle of polycounterions for αSDS 1.0–0.0. However, the turbidity data and micellar size showed that the amount of NaCMCu increased, and the mixed micellar size also increased. Eventually, this system demonstrated that polyelectrolyte was used as an organic counterion to improve the micellar properties of amphiphilic drugs for the formulation of pharmaceutical medicinal products.

Interaction of metformin hydrochloride with ionic surfactants in aqueous and NaCl solution: Effect of temperatures and compositions

AbstractHerein, the interaction of metformin hydrochloride (MNH) with cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) has been investigated by the conductometric technique in aqueous medium as well as in the existence of NaCl over a range of temperatures. MNH, an antidiabetic drug that belongs to the biguanide group, is generally prescribed for the patients to manage type II diabetes. The micellar parameters such as critical micelle concentration (CMC), the extent of counterion binding (β), and different thermodynamic properties for MNH + surfactant systems were estimated and discussed elaborately. The CMC values of CTAB + MNH and SDS + MNH systems are dependent on the concentrations of NaCl at different temperatures. The significant decrease of CMC values in NaCl solution indicates that NaCl stabilizes MNH‐mediated surfactant micelles. The CMC values versus T plots show a nonlinear pattern for the CTAB + MNH system, whereas the CMC values almost monotonically decrease with increasing temperature for the SDS + MNH system. The values of ∆G0m were negative for both systems in all cases. Both ∆G0m and ∆G0m,t values indicate that the aggregation processes of MNH + surfactants mixture are spontaneous, which is also manifested in NaCl solution and with the change of temperatures in most of the cases. The obtained results proposed that surfactants may assist as a proficient drug delivery agent for antidiabetic drug, enhancing their bioavailability.

Analytical modeling of micelle growth. 4. Molecular thermodynamics of wormlike micelles from ionic surfactants: Theory vs. experiment

HypothesesThe aggregation number and length of spherocylindrical (rodlike, wormlike) micelles in solutions of an ionic surfactant and salt can be predicted knowing the molecular parameters and the input concentrations of the species. This can be achieved by upgrading the quantitative molecular thermodynamic model from the previous parts of this series with an expression for the electrostatic component of micelle scission energy that is the excess free energy of the spherical endcaps with respect to the cylindrical part of the micelle. TheoryThe thermodynamics of micellization is extended to the case of multicomponent system, which may contain several surfactants (both ionic and nonionic) and salts, taking into account the effect of counterion binding in the Stern layer on the micellar surface. Furthermore, the considerations are focused on a system that consists of single ionic surfactant plus salt. FindingsExcellent agreement was achieved between the theoretical model and experimental data for wormlike micelles from anionic and cationic surfactants at various concentrations of salt and temperatures. In accord with the experimental observations, at high salt concentrations, the model predicts loss of chemical equilibrium between the endcaps and cylindrical part of the wormlike micelles, which implies transition to self-assemblies of other, e.g. branched, morphology or the onset of crystallization and phase separation.

Interaction of tetradecyltrimethylammonium bromide with bovine serum albumin in different compositions: Effect of temperatures and electrolytes/urea

Herein, the interaction of a protein, bovine serum albumin (BSA), with tetradecyltrimethylammonium bromide (TTAB, a cationic surfactant), has been investigated using the conductivity measurement technique in pure water and some sodium salts (NaCl, Na2SO4, Na2CO3, and Na3PO4) solutions at temperature range of 295.15–320.15 K. Results reveal that, in the plot of specific conductivity versus the concentration of TTAB, only a single critical micelle concentration (cmc) was found for the TTAB + BSA mixed system in all solvents media studied. The addition of BSA in aqueous TTAB solution, the value of cmc undergoes a change from its pure form, which indicates the presence of strong interaction operating between the BSA and TTAB molecules. In aqueous system, the cmc values of the TTAB + BSA mixtures are obtained higher compared to the values found for single TTAB surfactant. However, the addition of salt decreases the cmc value of mixed TTAB + BSA system. The values of cmc of the BSA + TTAB mixed system at 310.15 K and 1.00 mmol·kg−1 ionic strength of salt followed the order: cmcNa2CO3 > cmcNa3PO4 > cmcNaCl > cmcNa2SO4. The cmc values of TTAB + BSA mixture were found to be lowered in urea solution within the concentrations studied. The values of degree of dissociation (α) and fraction of counter ion binding (β) were found to be dependent on additives and temperature. The free energy of micellization (∆ Gmo) is negative for all the systems, which manifests that the micellization phenomenon is energetically spontaneous. The enhancement of the negative value of ∆ Gmo in aqueous salt solutions reveals an increase of spontaneity of the TTAB + BSA micellization process. The values of ∆ Gmo also reveal that the spontaneity of micelle formation is enhanced at higher temperatures in all media studied. The values of free energy of transfer (∆ Gm, to) were also determined for numerous solvent media used in the present study and described with appropriate reasoning.

Chemical shifts-based similarity restraints improve accuracy of RNA structures determined via NMR.

Determination of structure of RNA via NMR is complicated in large part by the lack of a precise parameterization linking the observed chemical shifts to the underlying geometric parameters. In contrast to proteins, where numerous high-resolution crystal structures serve as coordinate templates for this mapping, such models are rarely available for smaller oligonucleotides accessible via NMR, or they exhibit crystal packing and counter-ion binding artifacts that prevent their use for the chemical shifts analysis. On the other hand, NMR-determined structures of RNA often are not solved at the density of restraints required to precisely define the variable degrees of freedom. In this study we sidestep the problems of direct parameterization of the RNA chemical shifts/structure relationship and examine the effects of imposing local fragmental coordinate similarity restraints based on similarities of the experimental secondary ribose 13C/1H chemical shifts instead. The effect of such chemical shift similarity (CSS) restraints on the structural accuracy is assessed via residual dipolar coupling (RDC)-based cross-validation. Improvements in the coordinate accuracy are observed for all of the six RNA constructs considered here as test cases, which argues for routine inclusion of these terms during NMR-based oligonucleotide structure determination. Such accuracy improvements are expected to facilitate derivation of the chemical shift/structure relationships for RNA.

Role of carbonate electrolytes on interaction of quinolone drug with anionic surfactant at various temperatures: A conductometric study

AbstractThe role of different carbonate salts on the interaction of anionic surfactant sodium dodecyl sulfate (SDS) with employed quinolone antibiotic drug (ciprofloxacin hydrochloride [CFH]) was explosively inspected through measuring specific conductivity (κ) of the investigated system. The drug, CFH, is an excellent antibiotic for the treatment of different bacterial infections like skin, urinary tract, and respiratory infections. The estimated critical micelle concentrations (cmc) of SDS were observed to be dwindled in the attendance of electrolytes and cmc reduction continues with the escalation of the electrolyte's concentration. The magnitudes of cmc for the SDS + CFH mixture were reduced with the elevation of temperature in K2CO3 and CaCO3 medium while increased with the rise of the temperature in the Na2CO3 medium. The magnitudes of counterion binding to micelles (β) were increased with the increase of the concentration of Na2CO3 and K2CO3 up to definite value and then reduced with the increase of successive rise of concentration of both salts at all temperatures while decreased monotonically with the rise of electrolyte concentration in CaCO3 medium. The values of standard free energy ( ) were achieved to be negative in each case suggesting spontaneous self‐assembly formation. The standard entropy change ( ) along with enthalpy change ( ) was also assessed and discussed elaborately.

Solvo-Driven Dimeric Nanoplasmon Coupling Under DNA Direction

Strong coupling is a prerequisite for nanoassemblies to deliver functions and applications unrealizable by noninteracting building units. DNA-Directed metamaterials, albeit highly programmable, oft...

Analytical modeling of micelle growth. 3. Electrostatic free energy of ionic wormlike micelles – Effects of activity coefficients and spatially confined electric double layers

Hypotheses: To correctly predict the aggregation number and size of wormlike micelles from ionic surfactants, the molecular-thermodynamic theory has to calculate the free energy per molecule in the micelle with accuracy better than 0.01 kT, which is a serious challenge. The problem could be solved if the effects of mutual confinement of micelle counterion atmospheres, as well as the effects of counterion binding, surface curvature and ionic interactions in the electric double layer (EDL), are accurately described.Theory: The electric field is calculated using an appropriate cell model, which takes into account the aforementioned effects. Expressions for the activity coefficients have been used, which vary across the EDL and describe the electrostatic, hard sphere, and specific interactions between the ions. New approach for fast numerical calculation of the electrostatic free energy is developed.Findings: The numerical results demonstrate the variation of quantities characterizing the EDL of cylindrical and spherical micelles with the rise of electrolyte concentration. The effect of activity coefficients leads to higher values of the free energy per surfactant molecule in the micelle as compared with the case of neglected ionic interactions. The results are essential for the correct prediction of the size of wormlike micelles from ionic surfactants. This study can be extended to mixed micelles of ionic and nonionic surfactants for interpretation of the observed synergistic effects.

Aggregation and adsorption properties of benzyldimethylhexadecylammonium tetrachloromanganate(II) metallosurfactant in water–ethylene glycol medium

The aggregation and adsorption properties of metallosurfactant, benzyldimethylhexadecylammonium tetrachloromanganate(II) (BDHA2[MnCl4], where BDHA represents benzyldimethylhexadecylammonium group) in binary aqueous mixtures of ethylene glycol (EG) were investigated by tensiometric, conductometric, dynamic light scattering (DLS) and transmission electron microscopy (TEM) methods at 298.15 K. The percentage of EG (by weight) was varied between 0 and 100%. The physicochemical properties determined and discussed include critical micelle concentration (cmc), counterion binding constant (β), Gibbs free energy of micellization (), surface excess at cmc (), minimum area per surfactant molecule (), surface pressure (πcmc), minimum free energies (G min) and size of aggregates. This study revealed that with increase in percentage of EG the cmc of BDHA2[MnCl4] metallosurfactant increases and the cmc of BDHA2[MnCl4] in EG is about 158 times higher than that in water. The counterion binding constant values increase with increase in percentage of EG from 10% to 70% and thereafter decrease. The adsorption of metallosurfactant at the air–solution interface decreases as the EG content in the bulk increases. The values were found to be negative and the negative value decreases with increase in percentage of EG. Gordon parameter and ratio of surface tension of medium to that of the metallosurfactant solution at cmc are used to represent solvophobicity of the medium. DLS measurements revealed that the hydrodynamic diameters (d H) of the micelles increase with increase in percentage of EG (in pure EG, d H = 28.3 nm). TEM measurements showed the presence of spherical micelles.

Electrostatic-driven structural transformation in the complexation of lysozyme and κ-carrageenan

Lysozyme (LYS) and κ-carrageenan (κ-CRG) are important components widely used in food and pharmaceutical products. In this work, we investigated the interactions in the aqueous mixtures of LYS and κ-CRG and the structural transformation of the LYS/κ-CRG complexes. When co-soluble polymers and soluble complexes are formed in near-neutral environment, insoluble complex coacervates are formed at lower pHs. Significant accumulation and size expansion of coacervate particles occur at pH = 4.0 where maximum interactions are presented at the mixing ratio of LYS/κ-CRG = 2:1. The coacervate system is flexible to rearrange to reach a charge balanced state by gradual protonation of LYS and κ-CRG. Addition of NaCl up to 50 mM weakens the electrostatic attractions among the aggregates through counterion binding. Thermal stability of LYS by forming complex coacervates differs from that in water, and effective protection of protein is achieved as the unfolding temperature is increased by 9 °C.

Polyelectrolyte in Electric Field: Disparate Conformational Behavior along an Aminopolysaccharide Chain.

Electrical signals are increasingly used in fabrication of hydrogels (e.g., based on aminopolysaccharide chitosan) to guide the emergence of complex and anisotropic structure; however, how an imposed electric field affects the polymer chain conformation and orientation during the self-assembly process is not understood. Here, we applied nonequilibrium all-atom molecular dynamics simulations to explore the response of a charged chitosan chain comprising 5- or 20-monomer units to a constant uniform electric field in water and salt solution. While no conformational or orientational response was observed for the polyelectrolyte (PE) chains under the small electric fields within the simulation time, a field strength of 400 mV/nm induced significant changes. In water, a 5-mer chain is found to be slightly bent and oriented parallel to the field; however, surprisingly, a 20-mer chain displays candy-cane-like conformations whereby one half of the chain is collapsed and flexible, while the other half of the chain is stretched along the electric field. In salt solution, the disparity remains between the two halves of the 20-mer chain, although the backbone is extremely flexible with multiple bent regions and non-native conformations occur near the chain center in one of the three trajectories. The disparate conformational response along the polyelectrolyte chain may be attributed to the balancing forces between chain dynamics, electric polarization, counterion binding, and hydrodynamic pressure as well as friction. These findings reconcile existing experiments and theoretical studies and represent an important step toward understanding the complex roles of electric field and salt in controlling the structure and properties of soft matter.

Effects of Halide Anions on the Solution Behavior of Double Hydrophilic Carboxy-Sulfobetaine Block Copolymers.

The solution behavior of the double polybetaine block copolymer poly(2-((2-(methacryloyloxy)ethyl)dimethylammonio)acetate)-block-poly(3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate (PGLBT-b-PSPE) in sodium halide aqueous solutions was investigated. In the presence of salt ions, the unimer-to-micelle transition of PGLBT-b-PSPE that originated by Coulombic attraction between PSPE motifs was suppressed and shifted to much lower temperatures. The transition was hindered more by increases in the salt concentration because of additional counterion binding on the ionized site of PGLBT-b-PSPE chains, which screens the dipole-dipole attractions. The specific ion effect was investigated on four different halides, Cl-, Br-, I-, and F-. Cl- and two chaotropes (Br- and I-) apparently prevented micelle formation, and the hindering effectiveness on the PSPE pairing followed the general Hofmeister series of anions: I- > Br- > Cl-. More chaotropic anions strongly maintained the polymer chains in a fully hydrated state when the same amount of salts was incorporated. However, F-, which is classified as a kosmotrope, only made a small contribution to lowering the transition point and led to abrupt transition without showing a gradual phase change prior to the transition. The variations of hydrodynamic radius and zeta potentials of unimers and micelles gave hints of the solvation state of salt-incorporated PGLBT-b-PSPEs in each state. These results suggest that chaotropic halides tend to exist in the vicinity of the diblock polybetaine chain surface and thus prominently influenced the thermoresponsive solution behavior, whereas kosmotropic F- prefers water molecules and causes minor changes in the PGLBT-b-PSPE aqueous solution.