REDOX CONTROL OF HELICAL CHIRALITY

James W. Canary
Department of Organic Chemistry
New York University
New York, NY 10003



Certain metal ion complexes of tripodal ligands exhibiting conformational enantiomerism can be biased to adopt single enantiomer, propeller-like structures when a chiral center is incorporated into the ligand scaffold.1 Since the ligand conformation is fluxional and dependent upon metal ion coordination, chiroptical spectra (e.g., circular dichroism) of the ligand are highly dependent upon the identity and oxidation state of the metal ion, as well as upon the coordination of counter ions of varied size and shape. Several complexes have been prepared and studied in order to prototype novel strategies for the development of metal ion sensors2 and redox-switched chiroptical materials3,4

This lecture will focus on amino acid derivatives that demonstrate inversion of circular dichroism spectra upon one-electron redox change.3 The spectral changes are attributed to ligand exchange at the metal center that results in inversion of a propeller-like helical asymmetry of the ligand through a gearing mechanism.

 

References:
  1. Canary, J. W.; Zahn, S.; Chiu, Y.-H.; dos Santos, O.; Liu, J.; Zhu, L. Enantiomer 2000, 5, 397-403.
  1. Castagnetto, J. M.; Canary, J. W. J. Chem. Soc., Chem. Commun. 1998, 203-4.
  1. Zahn, S.; Proni, G.; Spada, G. P.; Canary, J. W. Chem. Eur. J. 2000, 7, 88-93.
  1. Zahn, S.; Canary, J. W. Science 2000, 288, 1404-7.