Helical superstructures and related spectral changes of bilayer membranes of a single-chain, phosphate amphiphile

Abstract

The aggregation behaviour and spectroscopic properties of a single-chain phoshateamphiphile possessing a chiral centre and an azobenzene chromophore have been examined. At neutral and alkaline pH, the bilayer dispersion contained helical structures and red-shifted (bathochromic) absorptions and enhanced CD spectra were observed under the conditions where this helical structure was formed. These morphological and spectral changes are explained in terms of ordering and hydrogen-bonded interactions at the bilayer surface. Effects of amines and metal-ion salts are similarly explained; in particular the strong binding of Ca²⁺ ions is thought to be due to the ordering of the surface phosphate groups.