Amino Acids Trapped Inside C₁₀₀: A Computational Study

The feasibility of the C₁₀₀ fullerene as a nanocontainer for glycine, alanine, and serine has been investigated using density functional theory (B3LYP-D3), second-order Møller-Plesset perturbation theory, and the domain-based local pair natural orbital-coupled cluster singles doubles and perturbative triples (DLPNO-CCSD(T)) method. The interaction energies for glycine@C₁₀₀, alanine@C₁₀₀, and serine@C₁₀₀ are calculated to be -47.8, -45.5, and -43.8 kcal mol^-1, respectively, for their most stable conformers, at the DLPNO-CCSD(T) level, indicating favorable host-guest interactions. Furthermore, encapsulation leads to substantial stabilization of both the intramolecular hydrogen-bonded and nonhydrogen-bonded conformers of the amino acids. Vibrational frequency analysis shows a blueshift for most of the vibrational modes, indicative of restricted motion due to the confined space. However, the OH-stretch mode, especially for the intramolecular hydrogen-bonded conformers, exhibits a large redshift upon encapsulation, suggesting a strengthening of the hydrogen bond due to confinement. The results of the dipole moment calculations reveal a significant reduction in the dipole moment after encapsulation, indicating an effective screening of the dipole by the C₁₀₀ cage. ¹H NMR chemical shift calculations reveal a large downfield shift, consistent with the deshielding effects experienced by the encapsulated molecules due to the unique electronic environment within the fullerene cavity.