Highly efficient stabilisation of meta-ethynylpyridine polymers with amide side chains in water by coordination of rare-earth metals

Abstract

An amphiphilic meta-ethynylpyridine polymer with chiral amide side chains was developed. The polymer was prepared by sequential Sonogashira reactions, and the product was soluble in polar and apolar solvents. The additive effects of metal salts on the polymer were examined in water and aqueous EtOH on the basis of UV-vis and CD spectra. The enhancement of the positive Cotton effect and hypochromism around 360 nm occurred by the addition of various metal salts, indicating the coordination of the cations to the amide side chains of the polymer to stabilise the helical structure. Among them, rare-earth metal salts, especially Sc(OTf)₃ showed more efficient additive effects probably because of its strong coordination ability even in water. Positive cooperativity was observed for the coordination of Sc(OTf)₃ to the polymer in aqueous EtOH.