Self-assembly and hydrophobic clusters of amphiphilic polysaccharides

The objective of this work was to synthesize and characterize new polymeric surfactants deriving from natural polymers and designed for membrane protein solubilization. For this purpose, a set of hydrophobically-modified pullulans (HMCMPs) of moderate molar mass and differing in hydrophobic modification ratio, charge ratio and the nature of the hydrophobic chains introduced, were prepared. Their behaviour in aqueous dilute solutions was investigated by surface tension measurement and with a polarity probe, the Coomassie Brilliant Blue dye. Two distinct critical concentrations were evidenced, demonstrating the complex behaviour of HMCMPs. Amphiphilic pullulan derivatives may indeed establish hydrophobic associations in bulk solution while adsorbing at the air ∣ water interface. The structural parameters of the polymers influence their aqueous behaviour. Self-assembly of HMCMPs occurs at smaller concentrations when the hydrophobic modification ratio or the alkyl hydrophobic chain length increases. It seems to be governed by the concentration of hydrophobic grafts, rather than by polymer concentration. Probably because of steric hindrance, 3-phenylpropyl grafts do not favour self-assembly, and lead to HMCMPs that preferentially adsorb at the air ∣ water interface.