Submicellar Concentration Range Research Articles

Stabilization of diketo tautomer of curcumin by premicellar anionic surfactants: UV–Visible, fluorescence, tensiometric and TD-DFT evidences

A newly observed UV band of aqueous curcumin, a biologically important molecule, in presence of anionic surfactants, viz., sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and sodium dodecylsulfonate (SDSN) in buffered aqueous solutions has been studied experimentally and theoretically. The 425nm absorption band of curcumin disappears and a new UV-band is observed at 355nm on addition of the surfactants in the submicellar concentration range which is reversed as the surfactant concentration approaches the critical micelle concentration (CMC). The observed spectral absorption, fluorescence intensity and surface tension behavior, under optimal experimental conditions of submicellar concentration ranges of the surfactants in the pH range of 2.00–7.00, indicate that the new band is due to the β-diketo tautomer of curcumin stabilized by interactions between curcumin and the anionic surfactants. The stabilization of the diketo tautomer by submicellar anionic surfactants described here as well as by submicellar cationic surfactant, reported recently, is unique as this is the only such behavior observed in presence of submicellar surfactants of both charge types. The experimental results are in good agreement with the theoretical calculations using ab initio density functional theory combined with time dependent density functional theory (TD-DFT) calculations.

C.I. Reactive Orange 16-dodecylpyridinium chloride interactions in electrolytic solutions

The effect of electrolytes on the interaction between an anionic dye and a cationic surfactant was investigated spectrophotometrically in submicellar concentration range at certain temperature. The spectral change of the azo dye C.I. Reactive Orange 16 (RO16) exhibits a high sensitivity to the polarity of dye's environment. Dodecylpyridinium chloride (DPC) affects the electronic absorption spectra of dye solution that is dye–surfactant interaction results formation of complex and therefore a decrease in maximum absorption spectra (1.577 at 494 nm). The electrolyte cations cause an increase of the absorbance of DPC–RO16 ion-pair complex in the following order: Ca 2+ > Na + > NH 4 + > K + > Mg 2+, also for electrolyte anions Br − > Cl − > SO 4 2−. Furthermore, this order can be changeable with increasing electrolyte concentration. The increase on absorbance value with increasing electrolyte concentration is explained as charge screening. The increase or decrease on absorption spectra of RO16–DPC solution depends on concentration range of the electrolyte added. As an increase on absorbance value with increasing electrolyte concentration is explained as charge screening, a decrease in this value for higher concentration of electrolyte is attributed as the charge of micelle shape.

Effect of the spacer length on the association and adsorption behavior of dissymmetric gemini surfactants

A series of dissymmetric gemini surfactants with the general formula [C 12H 25(CH 3) 2N(CH 2) s N(CH 3) 2C 14H 29]Br 2 designed as 12– s–14, where s = 2 , 6, and 10, were synthesized and their physicochemical properties investigated. The effect of spacer length on Krafft temperature, adsorption at the air/solution interface, and association in aqueous solution was studied by tensiometry, conductometry, and cryo-transmission electron microscopy. The Krafft temperature was found to increase linearly with spacer length. In the submicellar concentration range the dissymmetric 12– s–14 surfactants display ion pairing and premicellar association. Adsorption at air/solution interfaces and micellization in aqueous solution are similar to the behavior of their symmetric counterparts and depend strongly on spacer length.

Use of cholate derivatives with submicellar concentration for controlling selectivity of proteins in hydrophobic interaction chromatography

Hydrophobic interaction chromatography (HIC) of proteins using a phenyl column has been performed in the presence of various surfactants with micellar and submicellar concentration ranges. Most surfactants were effective for a decrease in the retention of proteins in both concentration ranges. However, the use of anionic cholate derivatives increased the retention of the proteins with high isoelectric point, such as lysozyme, cytochrome c, and trypsin, in submicellar concentration range, and then decreased it above the critical micellar concentration, while the retention of the other proteins was monotonously decreased. The results of frontal chromatographic analysis of the surfactant and capillary electrophoresis for the proteins in the presence of surfactant show that in the submicellar concentration range, cholate derivatives allowed to be adsorbed on the stationary phase, while they exhibited no interactions with the proteins. Thus, it appeared that the increase in the retention of basic proteins was due to the electrostatic attraction between the proteins and cholate-modified stationary phase. We have applied the unique property of cholate to the separation of ovalbumin and lysozyme in egg white sample using hydrophobic chromatography.

Chromatographic behaviour in reversed-phase high-performance liquid chromatography with micellar and submicellar mobile phases

Micellar HPLC can be used to separate non-ionic analytes in reversed-phase systems with aqueous mobile phases containing surfactants in concentrations higher than critical micellar concentrations (CMC). Ionic analytes are often separated by ion-pair reversed-phase chromatography in aqueous-organic mobile phases containing lower concentrations of ionic surfactants. The objective of the present work was to compare chromatographic behaviour of non-ionic solutes in micellar mobile phases and in mobile phases containing surfactants in concentrations lower than CMC (submicellar mobile phases). CMC were measured for several cationic and anionic surfactants on an octysilica column. The Langmuir isotherm was modified to describe the distribution of the surfactants between the stationary and the mobile phases in the submicellar concentration range. Retention behaviour of polar solutes with low retention in reversed-phase systems was measured in aqueous mobile phases containing surfactants in concentrations lower and higher than CMC. According to the form of the dependence of their retention on the concentration of the surfactant in the submicellar and micellar range of mobile phase compositions, the analytes were classified into four different classes. Equations describing the retention in dependence on the concentration of surfactant in submicellar and micellar mobile phases were derived and experimentally verified. The forms of the equations are the same for all analytes, but the meanings of the equation constants depend on the compound class. The selectivity of separation of a number of polar compounds is better in submicellar than in aqueous-organic mobile phases and the efficiency of separation is improved with respect to the micellar HPLC. Further, the sensitivity of non-specific detection, e.g. with refractive index detectors, is significantly better in submicellar than in micellar mobile phases. Submicellar HPLC has been applied to separation of various types of compounds, such as lower alcohols, barbiturates, phenols and nitriles of carboxylic acids used as the intermediates in production of some herbicides.

Dye–Surfactant Interaction in Submicellar Concentration Range

Abstract Interactions of cationic dyes, viz., phenosafranine (PSF), safranine O (SFO) and safranine T (SFT) with anionic surfactants, viz., sodium dodecyl sulfate (SDS) and sodium octyl sulfate (SOS) in submicellar concentration ranges have been investigated spectroscopically. The interaction has been shown to be an induced protonation of the dye in the dye–surfactant ion pair. Even though the opposite charges on the dye and the surfactant are the primary requirements for the ion pair formation, it is the hydrophobicity of the surfactant as well as of the dye which induces the protonation. The spectroscopic and thermodynamic parameters show that the orders of effectiveness of the dyes and the surfactants for the interaction are, SFO > SFT > PSF and SDS >> SOS.

Use of the surfactant 3-(3-cholamidopropyl)-dimethyl-ammoniapropane sulfonate in hydrophobic interaction chromatography of proteins

Isocratic hydrophobic interaction chromatography of five proteins has been carried out using mobile phases containing the surfactant 3-(3-cholamidopropyl)-dimethylammoniopropane sulfonate (CHAPS). Linear relationships were found between log k′ and ammonium sulfate concentrations for all the proteins with CHAPS in the submicellar concentration range. The slope of such a plot decreases monotonically as CHAPS concentration is increased. To a first approximation, the effect of CHAPS on the protein retention can be explained in terms of a competitive binding model. However, CHAPS does show differential effects on the elution of proteins, substantially altering selectivity. The use of a normalized capacity factor, k′/k′ 0, proves useful for comparing retention times of different proteins as a function of CHAPS concentration. The magnitudes of k′/k′ 0 were found to be inversely correlated with the slopes of plots of log k′ vs. ammonium sulfate concentration in the absence of CHAPS. Adsorption isotherms for CHAPS were determined over the working range of ammonium sulfate. The binding of CHAPS to the SynChropak Propyl stationary phase and its effects on retention were found to be readily reversible. For each protein, plots of k′/k′ 0 vs. surface concentration of CHAPS were superposable for data obtained at different salt concentrations. These findings support a competitive binding model. A simple geometric argument for stationary phase occupancy provides a qualitative explanation for the observed surfactant selectivity.

The Association and Hydration of Sodium Dodecyl Sulfate in the Submicellar Concentration Range

The Association and Hydration of Sodium Dodecyl Sulfate in the Submicellar Concentration Range