3. Conclusion
In conclusion, using the metadynamic methods, we prove an experiment
results that the β -pinene connects with quinoline oligomers at
N-terminal has the better helical induction than at C-terminal. However,
the intrinsic reason is rather electronic delocalization and steric
effect than hydrogen-bond effect. Especially, β -pinene is chiral
group of huge steric hindrance, which can induce the helix preference of
foldamer, but the chiral delivery of chiral atom is affected by steric
hindrance and delocalized effect. When the β ‑pinene connects with
oligomer units at the C-terminal, the dihedral angle
∠NQ−CQ−C−NA is far away
from chiral carbon of pinene, which cannot effectively induce the helix
bias of foldamer. Even an additional hydrogen bond is added at
C-terminal, which still no obviously improve the helical selection. That
is, for foldamer 1 and 2 with β ‑pinene
derivative at C-terminal, the hydrogen bonds rarely affect the helical
selection of foldamer. When the β ‑pinene connects with it at
N-terminal, chiral carbon of β ‑pinene can form the conjugated
bond with NQ−CQ−C−NAbond, it is benefit for the delivery of chirality. The chiralβ ‑pinene forms the more hydrogen bonds with quinoline oligoamide,
the foldamers are more stable. Therefore, the free-energy profiles
(FEPs) of 1–4 show that there is a small free energy barrier
between P and M for foldamers 1 and 2 , but in FEPs of3 and 4, free-energy has large difference between P
and M, the foldamer 4a with more hydrogen bond has the bigger
free-energy gap between P helix and M than 3a has.