Peptide Orientation at Emulsion Nanointerfaces Dramatically Different from Flat Surfaces

The adsorption of protein to nanoparticles plays an important role in toxicity, food science, pharmaceutics, and biomaterial science. Understanding how proteins bind to nanophase surfaces is instrumental for understanding and, ultimately, controlling nanoparticle (NP) biochemistry. Techniques probing the adsorption of proteins at NP interfaces exist; however, these methods have been unable to determine the orientation and folding of proteins at these interfaces. For the first time, we probe in situ with sum frequency scattering vibrational spectroscopy the orientation of model leucine-lysine (LK) peptides adsorbed to NPs. The results show that both α-helical and β-strand LK peptides bind the particles in an upright orientation, in contrast to the flat orientation of LKs binding to planar surfaces. The different binding geometry is explained by Coulombic forces between peptides across the particle volume.