Of
course, the distribution of dihedral angle
∠NQ− CQ− C−NAand ∠CQ−CQ−NA−C can make
a distinction between the chirality of 2a and 2b . From
Figure 7, it can be seen that the angle peaks of
∠NQ−CQ−C−NA at ±10° for
(P)-2a /(M)-2b .
The angle peaks of
∠NQ−CQ−C−NA for2a/2b are less than that in 1a/1b , it due to two
three-center hydrogen bonds O–H−NA and
NQ–H−NA improve the coplanar of
∠NQ−CQ−C−NA(Figure 8). Based on above analysis, it shows that atomic chirality is
the main factor on the helical selection of β -pinene-derived
pyridyine
Figure 7. The
three-center hydrogen bond in 2b. Figure 8. The frequency of
occurrence for
NQ−CQ−C−NA in2a and 2b
substituted foldamer at C-terminal, and hydrogen bond just enhance the
stable of foldamers 2a/2b . However, the experimental found that
the N-terminal substituted foldamers have better helical selection than
C-terminal substituted foldamers. What is the intrinsic reason?
2.3Helix-handedness bias ofβ‑pinene-derived pyridyl carboxylic acid-substituted oligomers
3a/3b at N-terminal