Journal Article fragment molecular orbital method Cyclin-Dependent Kinase 2 EC 2.7.11.22 Ligands Proteins QM/MM DFT calculation RESP charge Research Support, Non-U.S. Gov't aza-Cope rearrangement cyclin-dependent kinase-2 inhibitors dispersion interaction dynamical average energy decomposition analysis host-guest interaction inter-fragment interaction energy minimum energy path molecular fragmentation pair interaction energy decomposition analysis peptide bond shape complementarity sp2 carbon atom supramolecular chemistry