Spectroscopy of proflavine adsorbed on clays

Abstract

The ion exchange of monoprotonated proflavine on Wyoming bentonite, Camp Berteau montmorillonite and a synthetic mica-type montmorillonite, Barasym SSM-100, results in the presence of monoprotonated and diprotonated proflavine and dimers on the surface after freeze-drying. On Barasym SSM-100, below a loading of 500 µmol g^–1, the molecules are exclusively adsorbed on the external surface. For the other minerals the interlamellar surface is also available for adsorption. Protonation to the diprotonated proflavine is favoured the higher the negative charge density of the minerals: BS > CB > WB. The extent of dimerization is proportional to the available surface area, but sets in far below monolayer coverage. These three different species of proflavine on the surface have been characterized by their typical absorption and fluorescence spectra. For the first time fluorescence of the proflavine dimers has been detected at 580 nm. The fluorescence intensity is quenched by Fe^III, by protonation to diprotonated proflavine and by dimerization.