Fluorescence probe studies of gelatin-sodium dodecyl sulfate interactions

The characteristics of sodium dodecyl sulfate (SDS) micelles bound to gelat in have been studied by fluorescence using 8-anilino-1-naphththalene sulfon ic acid (ANS) as probe. Like gelatin, ANS binds in the region of the micell e 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 fluores cence characteristics of ANS solubilized in the first micelle to bind to ge latin are very different from those exhibited in the second and third micel les to bind to the gelatin. This distinction arises because the first micel le to bind does so predominantly through an electrostatic interaction betwe en the anionic surfactant and cationic residues, leading to a highly hydrop hobic environment. Subsequent micelles bind through a combination of both e lectrostatic and hydrophobic interactions. We show that the bulk properties (principally viscosity) of the solution are intimately related to the (mic roscopic) structure of the palisade layer.