induces a different enantiomeric axial chirality at the polyene backbone
and opposite responses in CD. The low energy barrier between the left- and
right-handed helical senses makes the dual behaviour of the polymer easy, thus
M +
metal
scavenger resin
NH
O
O
NH
O
O
NH
O
O
M +
induced by monovalent metal cations
poly-(R)-2
poly-(R)-2
-10
10
-5
0
5
240
500
300
400
Wavelength [nm]
-25
25
-20
-10
0
10
20
240
500
300
400
Wavelength [nm]
-25
25
-20
-10
0
10
20
240
500
300
400
Wavelength [nm]
poly-(R)-2
poly-(R)-2/M
+2
poly-(R)-2/M
+
Negative
Cotton effect
M 2+
metal
scavenger resin
NH
O
O
NH
O
O
NH
O
O
poly-(R)-2/M
+ complex
poly-(R)-2/M
+2 complex
induced by divalent metal cations
NH
O
O
NH
O
O
M 2+
Positive
Cotton effect
Null CD
("racemic")
Fig. 5 Selection of the helical sense and chiral amplification by metal ion complexation on poly(R)-2. Representative CD spectra are shown
130
F. Freire et al.