Langmuir aggregation of Evans blue on cetyltrimethylammonium bromide and on proteins and its application

The microphase adsorption-spectral correction (MPASC) technique is described and applied to the study of the interactions of Evans blue (EB) with cetyltrimethylammonium bromide (CTAB) and with four proteins: bovine serum albumin (BSA), myoglobin (Mb), hemoglobin (Hb) and ovalbumin (OVA). EB can be adsorbed on a cationic surfactant and on protein by electrostatic force and the aggregation obeys the Langmuir isotherm. Results have shown that the products are formed as follows: monomer aggregate EB·CTAB, micellar aggregate (EB·CTAB)₇₈ and protein aggregates (EB₆₈·BSA), (EB₁₄·OVA), (EB₁₂₆·Mb) and (EB₅₈·Hb). The adsorption constant of the aggregates are calculated to be K_EB·CTAB=2.95×10⁶, K_EB68·BSA=3.40×10⁴, K_EB14·OVA=5.20×10², K_EB126·Mb=6.81×10² and K_EB58·Hb=5.73×10², respectively. The aggregation of EB in proteins is sensitive in the presence of CTAB and selective in the presence of EDTA and it has been applied to the analysis of samples with satisfactory results.