Comparative study of the interaction of some meso-substituted anionic cyanine dyes with human serum albumin

Spectral-fluorescent properties of the meso-substituted anionic cyanine dye 3,3'-di-(γ-sulfopropyl)-4,5,4',5'-dibenzo-9-methylthiacarbocyanine betaine (DMC) were studied in solutions and in the presence of human serum albumin (HSA). The properties of DMC were compared with those of the previously studied meso-substituted anionic dyes 3,3'-di(γ-sulfopropyl)-4,5,4',5'-dibenzo-9-ethylthiacarbocyanine betaine (DEC), 3,3'-di-(γ-sulfopropyl)-9-methylthiacarbocyanine betaine (MTC) and 3,3'-di-(γ-sulfopropyl)-5,5'-diphenyl-9-ethyloxacarbocyanine betaine (OCC), which were studied here in more detail. In aqueous solutions, DMC, like DEC, is prone to dimerization; it also forms H- and J-aggregates. The noncovalent interaction of DMC with HSA leads to decomposition of the dimers with a shift in the cis-trans isomeric equilibrium toward the trans-monomer complexed with HSA, which is accompanied by a significant increase in fluorescence. The spectral-fluorescent data were used to estimate the binding constants of the dyes with HSA and other characteristics of the dyes, which are important when used as probes for HSA. The effect of structural rearrangements of HSA upon denaturation by urea on the spectral-fluorescent properties of the dyes was studied. Molecular docking of the dye-HSA systems was performed. A comparative assessment of the prospects for the use of the dyes as spectral-fluorescent probes for HSA in vitro was carried out.