The self-association of glycosyl phenylazo dyes (Yariv antigens)

Abstract

The aggregation of tris(4-glycosyloxyphenylazo)phloroglucinol compounds (Yariv antigens) where glyco = β-D-gluco, β-D-manno, β-D-galacto and α- D-galacto has been investigated by equilibrium sedimentation, the photoelectric scanning absorption optical system being utilized. The compounds have been shown to undergo a strong self-association in water and an analysis procedure employing Laplace transforms indicated a very wide distribution of species in the ultracentrifuge cell at equilibrium. To determine the type of association the concentration of monomer as a function of total weight concentration was calculated by using the recently developed Ω function. When the concentration of monomer is very low, as in the present case, the analysis is difficult because very slight curvature in the Ω-function plot has a large effect on the extrapolation to zero concentration.    

The results are best described by an isodesmic indefinite self- association. The β-glucoside Yariv antigen was the most extensively investigated and the most highly purified sample was shown to have an association constant of 2.5 x 10⁷ l. mol^-1. The order of the association constants of the Yariv compounds was found to be β-glucoside > β- galactoside > α-galactoside > β-mannoside. For the β-glucoside compound an increase in temperature favours species of lower molecular weight, and from the enthalpy change a positive entropy change for the association is indicated. The compounds are disaggregated by concentrated solutions of urea and guanidine hydrochloride. Spectral measurements on the β-glucoside compound indicate disaggregation by sodium dodecyl sulfate above the critical micelle concentration.