A associação do corante catiônico indoeptametinocianina com vários corantes aniônicos (quatro sulfonaftaleínas e cinco xantinas) em solução aquosa foi investigada usando espectroscopia de absorção no visível. Os valores das constantes de associação estão na faixa de 10 4 a 7 × 10 7 mol -1 L. Em todos os casos, um efeito hipocrômico significativo foi observado para a banda de absorção do cátion (λ max = 737 nm). O mesmo foi observado para a interação do cátion indotrimetínio (λ max = 540 nm) com espécies aniônicas. Interações eletrostáticas, de Van der Waals e hidrofóbicas são identificadas como as forças que dirigem esta associação. A adição de surfatantes iônicos destrói os compostos de associação do corante, primeiramente devido à interação com os íons de corante com carga oposta. Este processo é acompanhado pela restauração dos espectros de absorção visível dos corantes aniônico e catiônico.The association of the cationic dye indoheptamethine cyanine with various anionic dyes (four sulfonephthaleins and five xanthenes) in aqueous solutions was detected using the Vis-spectroscopic method. The values of the association constants are within the range (10 4 to 7×10 7 mol -1 L). In all the cases a substantial hypochromic effect is observed for the Vis absorption band of the cation (λ max = 737 nm). The interaction of indotrimethinium cation (λ max = 540 nm) with anionic species manifests itself in analogous manner. Electrostatic, Van der Waals, and hydrophobic interactions are regarded as driving forces of the association. Addition of ionic surfactants destroys the dye associates, primarily due to interactions with the oppositely charged dye ions. This process is accompanied by the restoration of the initial Vis absorption bands of both the cationic and the anionic dye.
A strong interaction between chmmophores of cationic and anionic components was found based on the analysis of electronic absorption spectra of aqueous solutions of mixtures of cationic indopolycarbocyanines with anionic cyanines. Strong dissimilar 1 : 1 associates are formed. Association constants were estimated spectrophotometrically. The main factors determining the degree of interaction of ehromophores were revealed.
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