Host-guest interaction between tyrosine and β-cyclodextrin: Molecular modeling and nuclear studies

Host-guest interactions of tyrosine with β-cyclodextrin have been investigated by the semiempirical methods PM7, PM6 and its modern variants, PM6-DH2, PM6-D3H4, and the ONIOM2 hybrid approach and density functional theory with the B3LYP functional. Two models were assessed for the encapsulation of tyrosine in the cavity of β-cyclodextrin. The results obtained with semiempirical models clearly indicate that the complexation process with the A model (Tyrosine enters into the cavity of β-CD from its wide side by hydroxyl phenolic group) is energetically favored than that of the B model (Tyrosine penetrates the β-CD cavity from its wide side by carboxylic group), the preference is greater in the case of ONIOM2 calculations. In addition, NBO analysis reveals that mutual interactions between donor and acceptor orbital of tyrosine and β-CD play an important role to the stabilization of such complex. Finally, 1H Nuclear Magnetic Resonance (NMR) chemical shifts of free and complexed tyrosine were calculated by the gauge-including atomic orbital (GIAO) method and compared with available experimental data.