Interactions between amino acid and carboxyl-functionalized C60 cage

Glycine is employed as the simplest representative of a backbone unit of a protein to examine the interaction between amino acid and carboxyl-functionalized C60 cage (C60C3H5COOH). The B3LYP/6-31G(d) DFT calculations show that the interaction between glycine and C60C3H5COOH forms two strong hydrogen bonds, resulting in stable complexes. The bonding of the carboxyl group of C60C3H5COOH to the carboxyl and amino groups of glycine produces the most and the least stable complexes with stabilization energies of 17.1 and 5.6 kcal/mol, respectively. Those results predict that the introduction of carboxyl-functionalized C60 cages into bio-system (such as human body) may affect the structures of proteins.