Transformations of methyl orange dimers in aqueous–acid solutions, according to UV–Vis spectroscopy data


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The effect acidity has on the UV–Vis absorption spectra of azo dye methyl orange (MOD) in aqueous solutions of hydrochloric acid in the pH range of 1.7 to 7 and sulfuric acid in the 0.24 to 18 mol/L range of concentrations is investigated. The spectral transformations of MOD solutions are compared to the corresponding spectral transformations of solutions of dimethylaminoazobenzene (DAB), which is an azo dye akin to MOD. A close resemblance between the spectral transformations of MOD and dimers DAB2 is revealed. It is concluded that the ground state of MOD, like the ground state of DAB, consists of not individual molecules but of supramolecular dimers MOD2. It is found that dimers MOD2 in aqueous low-acidic solutions are reversibly protonated with the formation of di- and triprotonated forms, which reversibly dissociate into diprotonated monomers upon an increase in acidity. The structural formulas of the chromogenic groups responsible for the spectral transformations, and the mechanisms of their reversible transformations, are given.

作者简介

Yu. Mikheev

Emanuel Institute of Biochemical Physics

编辑信件的主要联系方式.
Email: mik@sky.chph.ras.ru
俄罗斯联邦, Moscow, 119334

L. Guseva

Emanuel Institute of Biochemical Physics

Email: mik@sky.chph.ras.ru
俄罗斯联邦, Moscow, 119334

Yu. Ershov

Bauman Moscow State Technical University

Email: mik@sky.chph.ras.ru
俄罗斯联邦, Moscow, 105005

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