Fluorescence polarisation studies on the interaction of cellulose polycations with polyanions

Abstract

The interaction of two commercially available cellulose-based polycations, Polymer JR-400 and Celquat L200, with polyacrylates (PAA-Na) and polyvinylsulphonates (PVS-Na) of various molecular weights was investigated by covalently labelling the polycations with dansyl hydrazine and then studying the fluorescence polarisation of the dansyl group. Celquat L200 was shown to form complexes that were more stoichiometric than the complexes formed by Polymer JR-400 at pH 6·1. This was attributed to the higher charge density and lower average molecular weight of the Celquat L200. At pH 3·5, no complex formation was observed with any of the samples of PAA-Na; PVS-Na samples did form complexes with the polycations and the ones with Polymer JR-400 were more stoichiometric than the complexes formed at pH 6·1. The critical electrolyte concentration (C.E.C.) of each of the complexes was studied using sodium chloride as the electrolyte. The C.E.C. values for Polymer JR-400 complexes were in the order: PAA-Na (230 000)>PVS-Na (15 000)>PAA-Na (90 000)>PVS-Na (4300)>PAA-Na (5000). For complexes of Celquat L200, the order was: PAA-Na (230 000)>PVS-Na (15 000)=PVS-Na (4300)>PAA-Na (90 000)>PAA-Na (5000). The numerical values of the C.E.C. for complexes of Celquat L200 were found to be greater than the values for complexes of Polymer JR-400, thus implying that Celquat L200 binds more strongly to the polyanions. The order of binding indicated that, for a given molecular weight, the complexes formed by the polyvinylsulphonates are stronger than those formed by the polyacrylates.