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bola-Type Ala-Ala Dipeptides: Odd-Even Effect in Molecular Packing Structures
Cheng Zheng1, Shuwei Lin1, Yuanli Chen2
1Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application, Department of Polymer Science and Engineering, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science , Soochow University , Suzhou 215123 , P. R. China.
Abstract:
A series of bola-type Ala-Ala dipeptides with different alkylene bridges (n = 10-15) were synthesized. In methanol, the molecules with even-numbered carbon bridges self-assembled into twisted nanoribbons, while those with odd-numbered carbon bridges self-assembled into straight belts. The morphology displays a pronounced odd-even dependence upon the number of carbons (n) in the connecting alkylene bridge. The circular dichroism spectra of the self-assemblies showed that molecules with even- and odd-numbered carbon bridges stacked in different structures. FT-IR spectra indicated that the dipeptides with even-numbered carbon bridges formed hydrogen bonds between the amide group and carboxyl ester group, while those with odd-numbered carbon bridges formed hydrogen bonds only between the amide groups. X-ray diffraction patterns revealed that molecules with odd- and even-numbered carbon bridges stacked in monoclinic and triclinic structures, respectively.
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