Abstract
Ionic equilibrium of 22 hydroxyxanthenes, including halogen and nitro derivatives of fluorescein, and their thio- and aza analogues, were studied spectrophotometrically in micellar solutions of cetyltrimethylammonium chloride at ionic strength of the bulk phase 4.0 M KCl. This micellar pseudophase is characterized by the electrostatic surface potential of +(15–16) mV and the ETN value of 0.623. In the case of dyes bearing the COOH group, colorless lactone is the predominant tautomer of the molecular form H2R. A new classification of fluoresceins is developed. The dyes were divided into four groups based on the nature of tautomerism of the anions. In the case of the fluorescein type, the monoanions HR− exist predominantly as “carboxylate” tautomers, with ionized carboxylic and non–ionized hydroxylic group. For the dyes of the eosin type, the situation is opposite, while for the intervening type of compounds, the concentrations of the two tautomers are comparable. Dyes capable of forming lactone anions HR− were classified as the fourth type. For some of them, even the dianion R2− exists as a lactone. The relationship between the stepwise ionization constants, Ka1/Ka2, varies from 1.3 to 1.07 × 105 and is determined by the state of tautomeric equilibrium of molecules and ions.
Highlights
Micellar surfactant solutions in water are widely used in photochemistry, chromatography, chemical analysis, micellar catalysis, nanoparticle synthesis, etc
From colloidal point of view, surfactant micelles, drops of microemulsions, macromolecules of polymers, aggregates formed by dendrimers, calixarenes, cyclodextrins, etc., are lyophilic, or thermodynamically stable reversible ultramicroheterogeneous dispersions with extremely high specific surface area
We present the results ofofa fluorescein spectrophotometric study of fluorescein dyes in cetyltrimethylammonium-based at high ionic strength of the bulk
Summary
Micellar surfactant solutions in water are widely used in photochemistry, chromatography, chemical analysis, micellar catalysis, nanoparticle synthesis, etc Such systems are a popular and very promising type of liquid media. From colloidal point of view, surfactant micelles, drops of microemulsions (including reverse ones), macromolecules of polymers, aggregates formed by dendrimers, calixarenes, cyclodextrins, etc., are lyophilic, or thermodynamically stable reversible ultramicroheterogeneous dispersions with extremely high specific surface area. Such organized solutions, and among them first of all micelles of self-assembled surfactants, are reduced models of more complicated systems studied in biochemistry and biophysics. Variations in the properties of micellar pseudophases can be achieved by modifying solutions of self-assembled surfactants using various additives [8]
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