Design, synthesis, and crystal structure of self-assembling norbornene (NBE)-supported two-helix bundles: A unique example of Janus helicity in the solid-state structure of NBE(Aib5)2
✍ Scribed by Darshan Ranganathan; Sunita Kurur; Isabella L. Karle
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2000
- Tongue
- English
- Weight
- 223 KB
- Volume
- 54
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Norbornene-supported bis-helical peptides with the general structure NBE(Aib n ) 2 (NBE: 2,3-trans-norbornene dicarbonyl unit; Aib: ␣,␣Ј-dimethyl glycine unit; n ϭ 4,5) have been synthesized and examined for self-assembly preferences in the solid state. An x-ray study has revealed a phenomenon of Janus helicity in the solid state structure of NBE(Aib 5 ) 2 . The lower homologue NBE(Aib 4 ) 2 , however, shows an identical screw sense for both the helical arms. The difference in the handedness of left and right arms is reflected in the self-assembly patterns. Thus, while the NBE(Aib 4 ) 2 molecule self-assembles to form an infinite hydrogen-bonded superhelical ladder, the Janus molecule NBE(Aib 5 ) 2 crystallizes as individual units surrounded by water molecules. The structures of Z-Aib 4 -OMe and Z-Aib 5 -OMe are also presented to compare their conformations with the helical arms of the title compound and also to the already known structures of other X-Aib n -Y compounds. The helices in all the molecules are the 3 10 -type.