Interactions between mucin and alkyl sodium sulfates in solution. A light scattering study

The properties of negatively charged mucin in aqueous solutions and its interaction with anionic sodium alkyl sulfates with different hydrocarbon chain lengths were studied by means of dynamic light scattering. It was observed that mucin forms aggregates in aqueous solutions with a hydrodynamic radius above 500 nm. These aggregates dissolve when sodium dodecyl sulfate or sodium decyl sulfate is present at sufficiently high concentration, above about 0.2 cmc (critical micellar concentration). On the other hand, sodium octyl sulfate is not very effective in dissolving the mucin aggregates. The hydrodynamic radius of the dissolved mucin, decorated with some associated surfactant, is found to be in the range of 40-90 nm. The observation that the dissolving power of the sodium alkyl sulfates decreases with decreasing surfactant chain length suggests that the association between the surfactant and mucin is hydrophobically driven. The kinetics of the dissolution process depends on the surfactant concentration, a higher surfactant concentration giving rise to a more rapid dissolution of the aggregates. It was also observed that when the ionic strength is increased, the surfactant concentration needed to dissolve the mucin aggregates decreases. This can be explained by reduction of repulsive electrostatic forces by the salt.