Analytical micelles containing amphiphilic aminoanthraquinone solvatochromic reporter receptor

Аннотация

The feasibility of using an amphiphilic photoactive derivative of aminoanthraquinone (C18) as both a local solvatochromic probe reporting its position in a micelle and a component of an analytical supramolecular unit in mixed micelles based on a nonionic surfactant, Triton X100, has been considered. The solvatochromism of the 1,8-anthraquinone derivative (C18) has, for the first time, been investigated. Dipole moments of C18 molecules have been determined within the frameworks of the Lippert–Mataga, Kawski, and Reichardt approaches. It has been found that the Δμ values, as calculated with the help of the first two approaches and the Onsager radius, which is, for C18, equal to 5.8 Å, are markedly higher than the value obtained in terms of the Reichardt model. Possible reasons for discrepancies, which arise between experimental data and theoretical predictions when analyzing the solvatochromic properties of dyes, have been briefly discussed. C18 has been employed as an example to show that, for chromophores capable of donor–acceptor interactions, the use of protic solvents is more reasonable, because they ensure realization of a wider spectrum of interactions with a probe, among which the van der Waals interactions play an important role. Therewith, polarization effects, rather than charge separation, make a substantial contribution. In the case of amphiphilic chromophores, “enveloping” of polar groups with hydrocarbon chains decreases the local dielectric permittivity and the probability of intermolecular donor–acceptor interactions (hydrogen bonding). The character of the microenvironment of C18 reporter in micelles has been determined with the use of the “relative polarity parameter” proposed in this work. This parameter makes it possible to compare results obtained for different models of solvatochromism. It has been shown that the characteristics of C18 microenvironment in micelles correspond to those of water–alcohol solutions, with the chromophoric moieties of dye molecules located in the polar region of a micelle, this region being formed by hydrated ethylene-oxide chains of Triton X100. Polar receptor groups of C18, which face the aqueous phase, complete the hydrophilic shell of a micelle, while hydrocarbon chains of both components compose its hydrophobic core. This structure of the normal micelle and the markedly higher intensity of fluorescence of the micellar system than that of an aqueous C18 solution make possible the analytical determination of metal ions in aqueous media.