Investigating the effects of amino acid-based surface modification of carbon nanoparticles on the kinetics of insulin amyloid formation

Surface functionality of nanoparticles has been pivotal in defining interactions of nanoparticles and biomolecules. To explore various functionalities on the surface of nanoparticle through a facile procedure, various carbon-based nanoparticles, modified with a specific natural amino acid, were synthesized; the amino acids were chosen in order that almost all classes of amino acids were included. After characterizations of the nanoparticles using several spectroscopic methods, the effects of surface modification of nanoparticles were examined against amyloid formation, exploiting insulin as a model amyloidogenic polypeptide. Although most amino acids afforded carbon nanoparticles, only glycine, glutamine, and asparagine containing nanoparticles demonstrated significant inhibition of amyloid formation. These bioactive nanoparticles displayed low toxicity, and they allowed higher cell viability when mixed with the amyloid fibrils. The mechanism of the inhibition was investigated by monitoring conformational changes, and intermediates in the presence of bioactive nanoparticles. All in all, the results indicated that flexibility and the amide functionality can be considered as two main factors that enhance inhibitory roles of the modified nanoparticles likely through making networks of hydrogen bonding via functionalized surface of nanoparticles.