ELECTRIC DICHROISM - THE EFFECT OF DIALYSIS ON THE COLOR OF CRYSTAL VIOLET ADSORBED TO MONTMORILLONITE

Electric dichroism was measured in aqueous suspensions of Na-montmoril lonite which had been treated with ZnCl2 and stained with crystal viol et(CV+). Salt had to be removed by dialysis in order to reduce ionic c onductivity. On dialysis, new absorption bands of CV appeared simultan eously at 435 nm (weak) and 665 nm (strong), at the expense of metachr omic bands beta and gamma. The new bands were attributed to CVH2+, pro tonated during dialysis by hydrolyzed water adjacent to Zn2+. CV+ has chiral D-3 symmetry and two overlapping absorption bands at 590 nm. Th e bands would separate by the action of a force of lower symmetry than that of the molecule. The exceptionally large separation of the new b ands indicated that the extra proton was attached at an apex of the mo lecule, i.e., an amine group. Our MO calculations showed that protonat ion alone could not account for the observed band splitting and a tilt of a phenylamine ring was essential. The hydrolyzed samples were stab le for months, unlike those acidified with HCl. Electric dichroism rev ealed that the absorption dipoles of the CV+ cations which yield bands alpha and beta, as well as those of CVH2+, were parallel to the alumi nosilicate layers of the montmorillonite. In contrast, the absorption dipoles of aggregated CV, which was trapped in the interparticle space of a flee of the clay and which yielded band gamma, were not parallel to the layers of the clay mineral.