Effect of terbium(iii) on the binding of aromatic guests with sodium taurocholate aggregates

Abstract

The effect of binding Tb³⁺ to sodium taurocholate aggregates containing polyaromatic hydrocarbon guests was examined using pyrene and 1-ethylnaphthalene as guests that bind to the primary aggregate, and 1-naphthyl-1-ethanol as a secondary aggregate guest. Time-resolved fluorescence quenching studies were used to study the binding site properties, while laser flash photolysis quenching studies provided information on the dynamics of the guest-aggregate system. Both the primary and secondary aggregate binding sites became more compact in the presence of bound Tb³⁺, while only the primary aggregate became more accessible to anionic molecules. The binding dynamics for the guest-primary aggregate system became faster when Tb³⁺ was bound to the aggregate. In contrast, for the guest-secondary aggregate the presence of Tb³⁺ resulted in a small decrease in the dissociation rate constant. The influence of bound Tb³⁺ on the primary and secondary bile salt aggregates is significantly different, which affects how these aggregates can be used as supramolecular host systems to modify guest reactivity.