Adsorption of amino acids by fullerenes and fullerene nanowhiskers

We have investigated the adsorption of some amino acids and an oligopeptide by fullerene (C(60)) and fullerene nanowhiskers (FNWs). C(60) 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 C(60) or FNWs. Trp, Phe and Pro, with a cyclic structure, were not adsorbed by them either. The aromatic group of C(60) 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 C(60) and FNWs would not prefer the charged carboxyl or amino group. Tri-Ala was adsorbed slightly by the C(60) 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 C(60) and FNWs. We compared our results with the theoretical interaction of 20 bio-amino acids with C(60). The theoretical simulations showed the bonding distance between C(60) 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 C(60) showed the effect on the side chains of Try and Trp. The structure of albumin was changed a little by C(60). In our study Try and Tyr were hardly adsorbed by C(60) 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.