Dimerization of Cibacron Blue F3GA and other dyes: influence of salts and temperature

The monomer-dimer equilibria of Cibacron Blue F3GA (CB) and five other dyes (Levafix Brilliant Blue EB, Reactive Scarlet 017, Methyl Orange, Basic Blue 3 and Chicago Blue Sky) have been investigated in water and in the presence of KH2PO4. Aggregation of CB has been also examined in the presence of NaH2PO4, LiCl and KCl. When a new iterative approach, based on non-linear least-square (NLLSQ) fitting procedure was applied, it was found that the dimerization constants depend on the extension of organic molecules and the number of sulphonic groups. In the case of CB, cations had a greater effect on the equilibrium than anions. Analysis of the calculated spectra for monomer and dimer of Basic Blue 3 after deconvolution allowed us to specify the geometry of the dimer. (C) 2000 Elsevier Science Ltd. All rights reserved.