Differential staining of polyanions according to critical electrolyte concentration principles in mixed solvents

Abstract

SUMMARYThree types of cationic reagent—cellulosic anion exchangers, cationic phthalocyanin dyes and detergents—formed insoluble complexes with the polyanions heparin, chondroitin‐4‐sulphate, hyaluronate, alginate and DNA. Dissociation of their complexes by MgCl2 was a critical phenomenon, occurring at a sharply defined concentration, the critical electrolyte concentration (CEC), in water and in water‐organic‐solvent mixtures. CECs of polysulphates were always higher than those of polycarboxylates or polyphosphates, especially in the presence of dimethyl sulphoxide or ethanol. The latter effect should improve biochemical fractionations and differential histochemical staining of polyanions.A general theoretical framework is proposed. Complex formation is promoted by electrostatic attractions, and results in a loss of polymer mixing energy. Electrolytes suppress the electrostatic interaction, thus preventing complex formation. More efficient suppression of the electrostatic interaction is required in a ‘worsening’ solvent, i.e. where a rise in CEC occurs. Plots of CEC against solvent composition are interpreted on these bases. Available data on electrolyte solutions account for specific ionic effects.The dissociation of phthalocyanin dye micelles in aqueous dimethyl sulphoxide, etc, was studied spectroscopically. The results support and extend the conclusions derived from the insoluble anion‐exchange celluloses.The general concepts serve as a bridge between biochemical and histochemical fractionations (i.e. specific staining of substrates).