Binding of chrysophenine G by methyl cellulose and poly(vinyl alcohol)

Abstract

SynopsisEquilibrium constants ( n K ) for the binding of Chrysophenine G by methyl cellulose (MC) and poly(viny1 alcohol) (PVA) were determined spectrophotometrically in the temperature range 15-40°C. The polymer chains of PVA extended by the dye binding but those of MC shrank slightly. The enthalpy change and the entropy change for the binding by MC were negative and positive, respectively, whereas those for the binding by PVA were both negative. When the dye was bound to the extended polymer chains, the contribution of the entropy term to the binding increased. The rate of the dye bindings was studied by means of the temperature jump method. For the dye binding to PVA, the whole relaxation process finished in a very rapid step. On the other hand, for dye binding to MC, the initial rapid step was followed by two successive slower steps; the relaxation times for the slower steps were independent of the polymer concentration The results were interpreted in terms of the stiffness of polymer chain of MC; the conformational change of the stiff chains to accommodate the dye in stable states seems to be the rate determining step in each slow relaxation.