Electro-fluorescence studies of the binding of fluorescent dyes to sepiolite

Abstract

AbstractAqueous suspensions of sepiolite, tagged with fluorescent dyes, have been studied using electro-fluorescence polarization spectroscopy. The binding modes of some 37 fluorescent dyes and optical brightening agents to the rod-like sepiolite particles have been determined. Many of the dyes are found to bind with a degree of order to the clay particle's major axis. The binding geometries of the cationic dye molecules tested were found to be dependent upon molecular size. This supports the view that these cationic dye molecules are constrained within the channels which are characteristic of the mineral sepiolite. Results for uncharged and anionic dye molecules are also presented; no dependence of binding geometry upon molecular size was found. The anionic molecules are most likely to associate with the exterior cationic magnesium surface. The results indicate that some of the anionic dyes are too large to fit in the channels. Some of the uncharged molecules adopt a number of orientations upon binding which gives rise to an average geometry being observed for these dyes.