The torsion angles of flexible bonds in each candidate when in complex with H1 and N1 are summarized in Figure 8 . In Xylopine_2, all monitored bonds were stable in H1 except for e ( Figure 8A ). The fluctuations could be attributed to the attraction between the amine group H atoms and Asp 103. When bound to N1, b was the primary location for torque changes in Xylopine_2. The recorded torsion angle changes at b support our previous speculation that the unattached xylopine moiety is a key source of instability for Xylopine_2. Torsion angle fluctuations of Rosmar-icine_14 in both H1 and N1 were mainly due to rotations at g and j ( Figure 8B ). Such changes are expected as the H atoms on the amine group continuously rotate to form H-bonds with key amino acids. Bonds in Rosmaricine_15 ( Figure 8C ) exhibited similar characteristics to those in Rosmaricine_14. Rapid rotations at the amine groups l and o are visualized by the recorded angle trajectories. NAG ( Figure 8D ) and Tamiflu ( Figure 8E ) both have relatively stable intermolecular torsion changes. This indicates that the lower stability of NAG and Tamiflu in H1 and N1, respectively, are not due to instability of their ligand structures, but may be attributed to weaker or unstable ligand-protein affinities.