Premicellar and micelle formation behavior of aqueous anionic surfactants in the presence of triphenylmethane dyes: protonation of dye in ion pair micelles

Abstract

The premicellar and micelle formation behaviors of four cationic triphenylmethane dyes, viz, Pararosaniline (RN), Crystal violet (CV), Ethyl violet (EV), and Malachite green (MG), in aqueous anionic surfactant solutions of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium dodecyl sulfonate (SDSN) have been studied by spectral and surface tension measurements. The study was carried out within a pH range where the dyes are stable in their quinoid forms. The dyes have been found to form dye–surfactant ion pairs (DSIPs) with the surfactants, at the surfactant concentrations well below their critical micelle concentration, CMC*. The DSIPs behave like nonionic surfactants and form an air–water interfacial monolayer. The DSIPs have a lower critical micelle concentration (CMCIP), greater efficiency, and lower effectiveness than the corresponding pure surfactants. As the surfactant concentration is increased below the CMC*, the DSIPs start forming micelles of their own where the dye gets protonated and exists as a protonated dye–surfactant ion pair (PDSIP) in the ion pair micelles. As the concentration of the surfactant exceeds the CMC* of the pure surfactant, the protonation reverses gradually with the dye remaining in the micelles in solubilized form and the DSIPs in the air–water interfacial monolayer are replaced by pure surfactants. The distorted helical isomeric form (isomer B) of the dyes is favored in the PDSIPs. Copyright © 2009 John Wiley & Sons, Ltd.

Protolytic properties of dyes embedded in gelatin films

“…In aqueous SDS micellar solutions, in accordance with the report of Dutta and associates, 51 practically no changes in malachite green absorbance in time were registered. The pK a app value 11.62 ± 0.09 was determined at dye concentration 1.00 × 10 -5 mol L -1 in 0.01 mol L -1 SDS solutions; I = 0.05 mol L -1 (phosphate buffer solution + NaCl), 2 h after preparation of working solutions.…”

Specific interactions of anions and pre-micelles in the alkaline fading of crystal violet carbocation

“…At higher surfactant concentrations (but below the CMC of the pure surfactant), the nonionic ion-pair surfactants are transformed into cationic surfactant on protonation of the dye in the ion pair. In another similar study [23] involving cationic triphenylmethane dyes with a few anionic surfactants in aqueous medium same type of ion pair was reported to be formed. Spectral changes in the presence of surfactants were related to specific interactions or some changes in the microenvironment.…”

“…Dye-surfactant interactions are now a days being widely investigated [20,23,24]. Since crystal violet exists as a carbocation it may be expected that there will be interaction between CV + and anionic surfactants.…”

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

“…Assuming the interaction to be of 1:1 stoichiometry, the interaction can be represented as follows [26,[33][34][35]:…”

“…The type of interactions depends mostly on the chemical structure and nature of both of the interacting compounds [31]. Surface tensiometric studies showed that some ionic surfactants exhibit two distinct CMC's in the presence of some oppositely charged dyes where the dye-surfactant ion pairs behave like nonionic surfactants in the submicellar concentration range [32][33][34][35].…”