Molecular Gels and their Fibrillar Networks - Soft Fibrillar Materials: Fabrication and Applications - page 17

OH

OH

O

16

100

L acid

50

350 400 450

0

λ (nm)

-50

D acid

-100

Figure 1.14 CD spectra of enantiomerically pure 16 in CCl 4 gels: 25.7 mmol L − 1 for the
L -acid; 35.7 mmol L − 1 for the D -acid. Reprinted with permission from Ref. [72]. Copyright
1979 Nature Publishing Group.

two different modes of crystallization. The analyses focused on the hydroxyl and
carbonyl stretching regions. Fitting the area of hydroxyl HB peaks to the Avrami
model [74] indicated (i) platelet-like crystals and sporadic nucleation (or spherulitic
crystals and instantaneous crystallization) at d:l ratios below 80 : 20 and (ii) fiber-like
crystal growth and sporadic nucleation at d:l ratios above 80 : 20. From analysis of
the carbonyl stretching region, it was found that equal amounts of cyclic and acyclic
dimers, formed between carboxylic acids, were present at d:l ratios below 80 : 20.
At d:l ratios higher than 80 : 20, significantly more cyclic dimers were present.
Based on this experimental characterization, the authors postulated that hydroxyl
groups are positioned on opposite sides of the cyclic dimers in gels of optically