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Tuning Helical Chirality in Polycyclic Ladder Systems
Author(s) -
Rickhaus Michel,
Unke Oliver T.,
Mannancherry Rajesh,
Bannwart Linda M.,
Neuburger Markus,
Häussinger Daniel,
Mayor Marcel
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201503202
Subject(s) - racemization , circular dichroism , oligomer , crystallography , helix (gastropod) , chirality (physics) , chemistry , enantiomer , stereochemistry , materials science , physics , ecology , nambu–jona lasinio model , chiral symmetry breaking , organic chemistry , quantum mechanics , snail , biology , quark
Conceptually and experimentally, a new set of helical model compounds is presented herein that allow correlations between structural features and their expression in the secondary structure to be investigated. A cross‐linked oligomer with two strands of mismatching lengths connected in a ladder‐type fashion serves as a model system. Compensation for the dimensional mismatch leads to the adoption of a helical arrangement. A strategically placed relay ensures the continuity and uniformity of the helix. Upon exchanging the heteroatomic linkage, the helix responds by increasing or decreasing the torsion of the backbone. Inversion of the relay’s substitution pattern causes a distortion of the structure, while maintaining the directionality of the helix. Based on a short synthetic protocol with a modular precursor, four closely related “Geländer” oligomers (Geländer is the German word for bannister) were accessed and fully characterized. XRD analysis for one representative of each helical arrangement and complementary computational studies for the remaining derivatives allowed the impact of the alterations on the secondary structures to be studied. Isolation of pure enantiomers of all new Geländer oligomers provided insight into the racemization kinetics and estimation of the racemization barrier. In silico simulation of the electronic circular dichroism spectra of the model compounds enabled the helicity of the isolated samples to be assigned.