DFT-ONIOM study of the dopamine-β-CD complex: NBO and AIM analysis

In this work, we conducted a systematic search of the minimum energy of a dopamine-beta-cyclodextrin complex via different ONIOM approaches using both mixed (DFT-HF) and nonmixed (DFT-DFT) combinations. Different density functionals were employed: B3LYP, MPW1PW91, M05-2X, M06-2X, and omega B97X-D. Two different basis sets were used on the dopamine-beta-cyclodextrin complex; a lower basis set (3-21G*) is used on beta-cyclodextrin and a higher basis set (6-31G(d)) is used on dopamine. To fulfill this task, complexation and deformation energies were determined. The relative performance of these functionals was compared with that obtained with the DFT method at the M06-2X/6-31G(d) level that is chosen as a reference method. Although we did not clearly establish an assessment of the relative performance of these density functionals, the efficacy of the ONIOM combination (DFT-HF) is shown compared with a nonmixed ONIOM combination (DFT-DFT). The intermolecular hydrogen bond interactions of the complex obtained with the full M06-2X/6-31G(d) have been analyzed with the atoms-in-molecules and natural bond rrbital methodologies.