Fluorescence Probe Studies Of Gelatin-Sodium Dodecyl Sulfate Interactions

The characteristics of sodium dodecyl sulfate (SDS) micelles bound to gelatin have been studied by fluorescence using 8-anilino-1-naphththalene sulfonic acid (ANS) as probe. Like gelatin, ANS binds in the region of the micelle occupied by the hydrated headgroups, the palisade layer. The gelatin used in this study can bind an average of up to three SDS micelles. The fluorescence characteristics of ANS solubilized in the first micelle to bind to gelatin are very different from those exhibited in the second and third micelles to bind to the gelatin. This distinction arises because the first micelle to bind does so predominantly through an electrostatic interaction between the anionic surfactant and cationic residues, leading to a highly hydrophobic environment. Subsequent micelles bind through a combination of both electrostatic and hydrophobic interactions. We show that the bulk properties (principally viscosity) of the solution are intimately related to the (microscopic) structure of the palisade layer.