Semiequilibrium Dialysis Method Research Articles

Determining binding of polycyclic aromatic hydrocarbons to CTABr micelles using semi-equilibrium dialysis techniques

Micellar enhanced ultrafiltration (MEUF) has been shown to be an effective removal technique for a variety of trace contaminants in wastewater, especially for water soluble low molecular weight organic contaminants. In MEUF, contaminants first partition into surfactant micelles prior to removal by ultrafiltration, where the contaminants are below the molecular weight cut-off of the ultrafiltration membrane but the micelles are above the cut-off. Binding constants of selected Polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, phenanthrene, pyrene and fluorene have been determined in order to examine the removal efficiency of MEUF for PAHs with Cetyltrimethylammonium bromide (CTABr) using a semi equilibrium dialysis method. PAHs show strong binding with CTABr because of hydrophobic interactions. Our results enabled us to develop a relationship between binding constant (log KB) and log KOW for neutral compounds, which will be useful for predicting MEUF performance for PAHs removal from waste water. The range of our reported binding constant values are from 2.61 to 5.07.

Determining binding of sulfonamide antibiotics to CTABr micelles using semi-equilibrium dialysis

Abstract Membrane filtration processes such as ultrafiltration are increasingly employed in industrial and municipal wastewater treatment. However, these filtration processes are usually poor for removing low molecular weight organic and inorganic contaminants. Micellar enhanced ultrafiltration (MEUF), where contaminants first partition into micellar phases prior to removal by ultrafiltration, has been shown to be an effective removal technique for a variety of trace contaminants in wastewater. To characterize or predict the removal efficiency of MEUF, it is important to have a quantitative measure of the extent to which a species is able to bind to a micelle as well as to develop an understanding of the dynamics of the binding interactions. Herein, we report micellar binding constants for a series of sulfonamide antibiotics (sulfadoxine, sulfathiazole, sulfamethoxazole, sulfamerazine, sulfadiazine, sulfamethazine, sulfacetamide, sulfaguanidine, and sulfanilamide) with cetyltrimethylammonium bromide (CTABr) micelles, as determined using a semi-equilibrium dialysis method. Sulfadoxine, sulfathiazole and sulfamethoxazole exhibited the strongest tendency to bind to CTABr micelles, indicating that they possessed greater potential for removal via MEUF than did sulfanilamide or sulfaguanidine, which displayed little affinity for binding with CTABr micelles. Linear free energy plots of Log KB (in CTABr) versus Log KOW and pKa2 values indicated that there was a weak correlation between binding and Log KOW and a stronger correlation with pKa2 for these compounds, likely reflecting the stronger binding of ionizable sulfonamide molecules in the anionic form by the cationic micelles.

VOLATILITY AND SOLUBILIZATION OF SYNTHETIC FRAGRANCES BY PLURONIC P-85

ABSTRACT The volatility of synthetic fragrances (benzyl formate, benzyl acetate, benzyl propionate) from pluronic P-85 aqueous solution has been investigated by the dynamic headspace method The experimental results showed that the volatility of a more hydrophobic fragrance was strongly controlled by pluronic P-85. This volatile behavior was explained by the solubilization constants of fragrances between the micelle and bulk phase by semiequilibrium dialysis method.

A modified semiequilibrium dialysis method for studying solubilization in surfactant micelles: testing the semiequilibrium assumption

The detailed analysis of data obtained with the semiequilibrium dialysis (SED) method for studying solubilization in surfactant micelles requires accounting for the formation of micelles in the permeate compartment and for the presence of solubilized organic solute in these micelles. An extension of the SED method is proposed in which the concentration of surfactant is maintained well above the critical micelle concentration (cmc) in both compartments of the dialysis cell. Under these conditions, it is shown that the validity of the «semiequilibrium» assumption, viz., that the organic solute reaches equilibrium simultaneously with both surfactant solutions be demonstrated for solutions of small organic molecules and typical ionic surfactants

Solubilization of Perfume Compounds by Pure and Mixtures of Surfactants

The solubilization of two perfume compounds, 2-phenylethanol (PEA) and benzyl acetate (BA), was studied by using an anionic surfactant (sodium dodecyl sulfate, SDS), a nonionic surfactant (hexadecyl polyoxyethylene ether, C 16POE 20), and mixed anionic-nonionic micelles (SDS/C 16POE 20). In order to study the distribution of perfume compounds between the micelle and bulk phases, the solubilization equilibrium constants (distribution constant) were determined as functions of the intramicellar mole fraction of perfume compounds by using the semi-equilibrium dialysis method. The results of the present study show that (1) two or three surfactant molecules may on the average provide a location for the attachment of a PEA molecule in the single surfactant system, (2) BA molecules presumably bind somewhat more weakly to water and other polar groups in the hydrophilic group region of the single surfactant micelle, and (3) the solubilization equilibrium constants for the mixed surfactant system are smaller than predicted by linear or additive mixing rules applied to the single-component surfactant equilibrium constants, indicating that the compactness of the hydrophilic region of the mixed micelle may reduce the number of solubilization sites for the solutes in the micelle as a result of the hydrophilic interaction between the oxygen atoms of anionic surfactant and the ethylene oxide chains of nonionic surfactant.

An equilibrium model for ligand-modified micellar-enhanced ultrafiltration using a water-insoluble ligand

The semiequilibrium dialysis method has been used to investigate the ionic equilibria occurring in a ligand-modified micellar-enhanced ultrafiltration (LM-MEUF) process. With attachment of a C[sub 12]-hydrocarbon group to an iminodiacetic acid group and incorporation of this ligand in a cationic micelle, it is possible to bind Cu[sup 2+] selectively to the ligand in the retentate and expel Ca[sup 2+] into the permeate. An ion equilibrium model has been developed to predict the concentrations of the divalent ions in the permeate from known concentrations in the retentate and known experimental parameters, including the binding constants of the divalent metal ion/ligand complexes. In contrast with other micellar-enhanced ultrafiltration processes, addition of salt increases the retention of the bound metal ion. The model explains both the enhanced retention of Cu[sup 2+] and variations in the extent of expulsion of Ca[sup 2+] caused by changing the added salt concentration. 25 refs., 4 figs., 2 tabs.

Substituent group effects on the solubilization of polar aromatic solutes (phenols, anilines, and benzaldehydes) by N-hexadecylpyridinium chloride

Solubilization isotherms of polar aromatic solutes (phenols, anilines, and benzaldehydes) in N-hexadecylpyridinium chloride micelles have been determined at 25{degree}C by using the semiequilibrium dialysis method. Effects of various substituent groups (H, F, Cl, Br, CH{sub 3}O, NO{sub 2}, CH{sub 3}, Et, i-Pr, and CF{sub 3}) have been studied for the solubilization of phenol, aniline, and benzaldehyde derivatives in aqueous solutions of the surfactant. Both hydrophobic and electrostatic effects are shown to be important in influencing the solubilization behavior. The simple expression, K = K{sub 0}(1 {minus} BX){sup 2}, is used to correlate the solubilization equilibrium constant (K) with the mole fraction of solute in the micelles (X). Linear free energy relationships can be used to correlate the solubilization results for the different classes of compounds.

Effects on the micellar solubilization of organic compounds by surfactant micelles. I. Length of carboxylic side chains in aromatic acids

The semiequilibrium dialysis method has been used to determine solubilization equilibrium constants and activity coefficients of benzoic, phenylacetic, and hydrocinnamic acids (solubilizate) in micelles of the cationic surfactant hexadecylpyridinum chloride (cetylpyridinium chloride) in 0.1M HCl aqueous solutions. Methods described previously were employed to infer the concentrations of monomeric organic solute and surfactant on both sides of the dialysis cell. Values of the apparent solubilization constant K of the neutral acids have been correlated with mole fractions of the acid in the micelle XA, where K=XA/[monomeric acid]. The activity coefficients of both acid and surfactant were obtained, consistent with the Gibbs-Duhem equation. The solubilization constants of all three acids are nearly the same, indicating that there is no significant effect owing to the presence of one or more methylene groups between the carboxylate and the phenyl groups of benzoic acid. The solubilization constants also decrease appreciably, and the activity coefficients of the acids increase, as the mole fraction of the acid in the micelle increases.

Solubilization of cresols by 1-hexadecylpyridinium chloride micelles and removal of cresols from aqueous streams by micellar-enhanced ultrafiltration

In micellar-enhanced ultrafiltration (MEUF), solubilization of organic solutes in micelles, combined with ultrafiltration of these micellar solutions, leads to the removal of dissolved, low molecular weight organic compounds from water. The permeate from MEUF contains the organic solute at concentrations equal to the unsolubilized solute concentration in the rejected (retentate) solution. Therefore, the equilibrium solubilization of the solute dictates the permeate purity or rejection of the solute by the membrane. The semiequilibrium dialysis method has been used to investigate the equilibrium solubilization of o-, m-, and p-cresol by aqueous solutions of 1-hexadecylpyridinium chloride, throughout a range of concentrations of the cresols and the surfactant. The apparent solubilization constant, K = X/sub c//(concentration of unsolubilized cresol), has been correlated with X/sub c/, the mole fraction of cresol in the micelle.

Use of the semi-equilibrium dialysis method in studying the thermodynamics of solubilization of organic compounds in surfactant micelles. Systemn-hexadecylpyridinium chloride-phenol-water

The semi-equilibrium dialysis method has been used to infer solubilization equilibrium constants or, alternatively, activity coefficients of solutes solubilized into micelles of aqueous surfactant solutions. Methods are described for inferring the concentrationa of monomers of the organic solute and of the surfactant on both sides of the dialysis membrane, under conditions where the organic solute is in equilibrium with both the high-concentration (retentate) and low-concentration (permeate) solutions. By using a form of the Gibbs-Duhem equation, activity coefficients of both phenol (the solubilizate) and n-hexadecylpyridinium chloride (the surfactant) are obtained for aqueous solutions at 25°C throughout a wide range of relative compositions of surfactant and solubilizate within the micelle. The apparent solubilization constant, K=[solubilized phenol]/([monomeric phenol][micellar surfactant]), is found to decrease significantly as the mole fraction of phenol in the micelle increases.