Physicochemical characteristics of patent blue violet dye

Physicochemical data for patent blue violet dye (I) are reported. The pKa for protonation of the first diethylanilino group was 2.78 +/- 0.03. The absorptivity values calculated for a 1% (w/v) solution of previously dried I at pH 7.4 were 1650, 170, and 250 at 638, 412, and 309 nm, respectively. A table of wavelength maxima and observed solution color as a function of pH and Ho and five spectra of I at certain pH and Ho values are included. The solution chemistry of I is explained, and a scheme showing its two protonated carbonium ions and its triphenylcarbinol derivative is presented. The distribution coefficients of I in n-octanol or chloroform and pH 7.4 phosphate buffer systems were 0.013 and 0.12, respectively. The approximate solubilities at 25 degrees of I in six organic solvents and the solubility analysis of I in distilled water are reported. Results of the latter analysis suggest that I forms a lyotropic mesophase in high aqueous concentrations. Compound I is poorly lipid soluble. Samples of 1.000% I in 0.9% NaCl, formulated with and without 1% (v/v) benzyl alcohol and autoclaving, varied not more than 5% from the initial I content during storage in the dark and under constant fluorescent light at 25 +/- 5 degrees for 20 months. Data from the TLC of I in several eluents indicated a high degree of purity of the dye. The half-lives for the loss of color in 5 X 10(-4)% I solutions in potassium hydroxide solutions of pH 13.7, 12.7, 11.3, and 10.0 were 1.2 hr, 17.0 hr, 9.5 days, and 180 days, respectively. The fraction of I bound to 4% (w/v) human serum albumin at 37 degrees and pH 7.4 ranged from 0.05 to 0.83, corresponding to unbound I in the postdialysis concentration range of 1.7 X 10(-4) to 2.0% (w/v). A Scatchard plot of the albumin binding data of I revealed one high-affinity binding site, K = 6235 M-1, and five low-affinity sites, with average affinity constants of 33 M-1. The data support the fact that the spectrophotometric determination of I at 639 +/- 2 nm appears to comprise a stability-indicating assay.