Regularities of homo- and heteroassociation of the pinacyanol cation in aqueous solution

Bromocresol purple in the processes of cation-anionic interactions in aqueous solutions: UV-Vis spectroscopy and computer simulation of dissimilar association

The formation of associates between single- or double-charged anions of bromocresol purple (3,3'-dimethyl-5,5'-dibromophenolsulfonephthalein) and single-charged cations of cyanines (quinaldine blue, quinaldine red) has been investigated. The equilibrium constants of the association have been determined on the basis of UV-Vis spectroscopy data. The energy of the cation-anion interaction (the standard enthalpy of formation of ions and associates), as well as the probable structure of associates, were established using the PM7 semiempirical method. The presented results can be useful in the development of new spectroscopic methods for the detection of organic additives in water (e.g. acetone) due to the spectral properties of dissimilar associates.

Hetero-association models of non-covalent molecular complexation

The present review discusses the current state-of-the-art in building models enabling the description of non-covalent equilibrium complexation of different types of molecules in solution, which results in the formation of supramolecular structures different in length and composition (hetero-association or supramolecular multicomponent co-polymerisation). The description is focused on standard physical and chemical quantities such as experimental observables and equilibrium parameters of interaction (equilibrium constants and concentrations). The major partial cases of the hetero-association models, such as finite and indefinite isodesmic and cooperative complexations, and Benesi-Hildebrand and Langmuir adsorption models are considered. Future challenges in the development of the hetero-association models are provided.

Dissimilar Associates of Dyes in Aqueous Solutions: Experimental Study and Computer Simulation

Dissimilar cation-anionic association of dyes («cyanine+oxyxanthene», «cyanine+sulfonepthalein») has been regularly investigated in aqueous solutions. Experimental (by spectrophotometry) and theoretical (by semiempirical) methods were used. The basic regularities of association processes have been discussed. It is shown that the change in the stability of associates has a systematic character both in the series of singly charged and doubly charged anions. The experimentally determined values (of equilibrium constant of association) and simulated values (of standard enthalpy of hydration of associates) are mutually consistent. The standard enthalpy of formation and the most probable structures of associates have been determined.