Klovak V. Hydrophobically modified reagent systems for fluorescence determination of organic compounds of ionic nature

The thesis is devoted to systematic research and evaluation of the combined effect of charge, nature, and hydrophobicity of organic reagents and surfactants on the fluorescent signal of the latter in solutions, identification of supramolecular matching effects in the association of reagents with surfactants, and development of practical recommendations for rational fluorescent determination of hydrophobic organic compounds of ionic nature, in particular proteins. The main factors influencing the analytical signal of the ionic surfactants in two-component reagent – surfactant associates are clarified. The combined effect of the hydrophobicity parameters of the associate components, the fluorescence intensity of the reagent, and the contrast of the association reaction on the analytical signal of the surfactants in solutions has been established. The different nature of the formed two-component systems depending on the ratio of reagent and surfactant charges has been shown. As a result, the investigated associates were distributed depending on the ability of the reagents to exhibit electrostatic attraction with the surfactant ion. Anionic reagents that make an electrostatic contribution to the formation of reagent-surfactant systems are characterized by greater stability of the associates and give a greater analytical signal. The evaluation of electrostatic and hydrophobic contributions to the free energy of the associate formation showed the dominant effect of hydrophobic interactions enhanced by electrostatic attraction between the interacting particles. The nature of the multidirectional change of the analytical signal of surfactants in the association reactions with the fluorescent reagents has been investigated. The stepwise nature of the reagents and ionic surfactants associates with the formation of stoichiometric, substoichiometric, and solubilized associates with different ratios of components has been shown. It has been found that a decrease in the intensity of the ionic surfactants fluorescent signal is observed in the formation of hydrophobic stoichiometric associates, and an increase in the signal is associated with solubilization processes at surfactant concentrations above the critical micelle concentration. The study of the analytical signal of anionic and cationic surfactants in two-component associates with fluorescent reagents revealed the effects of «charge» and «spatial-hydrophobic» matching, which are manifested in the increase of the surfactant signal. The influence of charge and hydrophobicity of reagents and ionic surfactants in the micellar medium of non-ionic surfactant Triton X 100 on the spectral changes of stoichiometric and solubilized associates was studied. It has established that the maximum analytical signal of the ionic surfactant in reaction with reagents of different charge and hydrophobicity in Triton X 100 solutions is registered under the conditions of «charge» matching between the electroneutral particle of luminol and nonionic surfactant. The «spatial-hydrophobic» matching effect between the components of the solubilized associate reagent – ionic surfactant in solutions of nonionic surfactant is preserved. At the same time, a decrease in the effect of hydrophobicity of alkylpyridinium cationic surfactants on the analytical signal in the Triton X 100 medium has registered. Based on the studied regularities of reagent – ionic surfactants associate in aqueous solutions and Triton X 100 medium, the main factors of influence and recommendations for rational creation of modified reagent systems for fluorescent determination of hydrophobic organic compounds of ionic nature are formulated. Thus, the design of the reagent system should take into account the contrast of the association of the organic reagent with the surfactant, fluorescence intensity and hydrophobicity of the reagent, the presence of electrostatic attraction between oppositely charged components of the associate, «charge» and «spatial-hydrophobic» matching between interacting particles in the determination of specific surfactants. The analytical signal of organic compounds of cationic nature and proteins in the reaction with Al(III) – lumagalion and Mo(VI) – bromopyrohalol red complexes by the methods of fluorescence, spectrophotometry, and colorimetry has been studied. Possibilities of purposeful use of a hydrophobic modification of metal-reagent systems at the determination of organic cations by methods of molecular spectroscopy for improvement of metrological characteristics and quality of the analytical signal of analyte have been revealed. Based on the studied patterns of association of two- and three-component reagent – ionic surfactant and reagent – ionic surfactant – nonionic surfactant systems, respectively, purposeful hydrophobization of reagent systems and generalizations developed methods of fluorescent determination of hydrophobic organic compounds of ionic nature, in particular proteins.