Supramolecular complex induced by the binding of sodium dodecyl sulfate to PAMAM dendrimers

Isothermal titration calorimetry (ITC) and dynamic light scattering (DLS) were employed to study the spontaneous supramolecular complexation of amine terminated PAMAM dendrimer (G3[EDA] PAMAM-NH2) induced by the binding of an anionic surfactant, sodium dodecyl sulfate (SDS). At pH <= 2, SDS molecules bound to protonated amines on the outer rims of G3[EDA] PAMAM-NH2 driven by electrostatic interaction, which induced the formation of PAMAM/SDS supramolecular complex via hydrophobic association between bound SDS molecules. The complex with radius of similar to 37 nm was observed at SDS concentration as low as 0.02 mM (in 0.2 mM PAMAM). The size of the complex increased progressively with increasing SDS concentration and precipitated when the SDS concentration exceeded 15 mM. At pH of similar to 7.4, the formation of PAMAM/SDS complex was observed at higher SDS concentration (0.1 mM in 0.2 mM PAMAM), and it resolubilized with further increase of SDS concentration to similar to 18 mM due to weaker electrostatic interaction at higher pH. At pH >= 10, the electrostatic binding ceased because the deprotonated PAMAM dendrimer was uncharged, and hence the surfactant-induced supramolecular assembly could not be formed.