Mesomorphic solid-like structures of sulfated extra-cellular polysaccharide-C_nTAB compounds

Complexes formed by a partially sulfated polysaccharide (from the unicellular micro alga Porphyridium sp.) and surfactant homologues of alkyltrimethylammonium bromide were investigated using various techniques, such as small and wide angle X-ray scattering, optical phase interference microscopy and ²H nuclear magnetic resonance (NMR). The scattering data suggest an average regular ordering at both microscopic and mesoscopic length scales, the second of which varies with the surfactant tail length. The ²H NMR spectrum, however, reveals a large variation of structural features around this average. The dynamics of the surfactant molecules, inferred from the NMR spectrum and relaxation times, resemble those found in crystalline surfactant phases. Transparent self-standing 'biofilms' were also processed from the complex; the microstructure seems to be largely invariant whether the complex is in powder or in film form.