Switching "on" and "off" the expression of chirality in peptide rotaxanes

M Asakawa, G Brancato, M Fanti, DA Leigh, T Shimizu, Alexandra Martha Zoya Slawin, JKY Wong, F Zerbetto, S Zhang

Research output: Contribution to journalArticlepeer-review

103 Citations (Scopus)

Abstract

The hydrogen-bond-directed synthesis, X-ray crystal structures, and optical properties of the first chiral peptide rotaxanes are reported. Collectively these systems provide the first examples of single molecular species where the expression of chirality in the form of a circular dichroism (CD) response can selectively be switched "on" or "off", and its magnitude altered, through controlling the interactions between mechanically interlocked submolecular components. The switching is achievable both thermally and through changes in the nature of the environment. Peptido[2]rotaxanes consisting of an intrinsically achiral benzylic amide macrocycle locked onto various chiral dipeptide (Gly-L-Ala, Gly-L-Leu, Gly-L-Met, Gly-L-Phe, and Gly-L-Pro) threads exhibit strong (10-20k deg cm(2) dmol(-1)) negative induced CD (theta) values in nonpolar solvents (e.g. CHCl3), where the intramolecular hydrogen bonding between thread and macrocycle is maximized. In polar solvents (e.g., MeOH), where the intercomponent hydrogen bonding is weakened, or switched off completely, the elliptical polarization falls close to zero in some cases and can even be switched to large positive values in others. Importantly, the mechanism of generating the switchable CD response in the chiral peptide rotaxanes is also determined: a combination of semiempirical calculations and geometrical modeling using the continuous chirality measure (CCM) shows that the chirality is transmitted from the amino acid asymmetric center on the thread via the macrocycle to the C-terminal stopper of the rotaxane. This understanding could have important implications for other areas where chiral transmission from one chemical entity to another underpins a physical or chemical response, such as the seeding of supertwisted nematic liquid crystalline phases or asymmetric synthesis.

Original languageEnglish
Pages (from-to)2939-2950
Number of pages12
JournalJournal of the American Chemical Society
Volume124
DOIs
Publication statusPublished - 27 Mar 2002

Keywords

  • BENZYLIC AMIDE <2>CATENANE
  • MM3 FORCE-FIELD
  • DIFFERENTIAL-OVERLAP TECHNIQUE
  • MAGNETIC CIRCULAR-DICHROISM
  • MOLECULAR MECHANICS
  • INTERMEDIATE NEGLECT
  • SUPRAMOLECULAR CHIRALITY
  • ENERGY MINIMIZATION
  • HYDROCARBONS
  • SHUTTLE

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