Adsorption of amino acids by fullerenes and fullerene nanowhiskers

Abstract

We have investigated the adsorption of some amino acids and an oligopeptide by fullerene (C₆₀) and fullerene nanowhiskers (FNWs). C₆₀ and FNWs hardly adsorbed amino acids. Most of the amino acids used have a hydrophobic side chain. Ala and Val, with an alkyl chain, were not adsorbed by the C₆₀ or FNWs. Trp, Phe and Pro, with a cyclic structure, were not adsorbed by them either. The aromatic group of C₆₀ did not interact with the side chain. The carboxyl or amino group, with the frame structure of an amino acid, has a positive or negative charge in solution. It is likely that the C₆₀ and FNWs would not prefer the charged carboxyl or amino group. Tri-Ala was adsorbed slightly by the C₆₀ and FNWs. The carboxyl or amino group is not close to the center of the methyl group of Tri-Ala. One of the methyl groups in Tri-Ala would interact with the aromatic structure of the C₆₀ and FNWs. We compared our results with the theoretical interaction of 20 bio-amino acids with C₆₀. The theoretical simulations showed the bonding distance between C₆₀ and an amino acid and the dissociation energy. The dissociation energy was shown to increase in the order, Val < Phe < Pro < Asp < Ala < Trp < Tyr < Arg < Leu. However, the simulation was not consistent with our experimental results. The adsorption of albumin (a protein) by C₆₀ showed the effect on the side chains of Try and Trp. The structure of albumin was changed a little by C₆₀. In our study Try and Tyr were hardly adsorbed by C₆₀ and FNWs. These amino acids did not show a different adsorption behavior compared with other amino acids. The adsorptive behavior of mono-amino acids might be different from that of polypeptides.