Oligonuclear ferrocene amides: mixed-valent peptides and potential redox-switchable foldamers

Chemistry. 2011 Apr 11;17(16):4540-51. doi: 10.1002/chem.201002101. Epub 2011 Jan 27.

Abstract

Trinuclear ferrocene tris-amides were synthesized from an Fmoc- or Boc-protected ferrocene amino acid, and hydrogen-bonded zigzag conformations were determined by NMR spectroscopy, molecular modelling, and X-ray diffraction. In these ordered secondary structures orientation of the individual amide dipole moments approximately in the same direction results in a macrodipole moment similar to that of α-helices composed of α-amino acids. Unlike ordinary α-amino acids, the building blocks in these ferrocene amides with defined secondary structure can be sequentially oxidized to mono-, di-, and trications. Singly and doubly charged mixed-valent cations were probed experimentally by Vis/NIR, paramagnetic ¹H NMR and Mössbauer spectroscopy and investigated theoretically by DFT calculations. According to the appearance of intervalence charge transfer (IVCT) bands in solution, the ferrocene/ferrocenium amides are described as Robin-Day class II mixed-valent systems. Mössbauer spectroscopy indicates trapped valences in the solid state. The secondary structure of trinuclear ferrocene tris-amides remains intact (coiled form) upon oxidation to mono- and dications according to DFT calculations, while oxidation to the trication should break the intramolecular hydrogen bonding and unfold the ferrocene peptide (uncoiled form).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amides / chemical synthesis
  • Amides / chemistry*
  • Ferrous Compounds / chemical synthesis
  • Ferrous Compounds / chemistry*
  • Magnetic Resonance Spectroscopy
  • Metallocenes
  • Models, Molecular*
  • Molecular Conformation
  • Molecular Structure
  • Oxidation-Reduction
  • Peptides / chemistry*

Substances

  • Amides
  • Ferrous Compounds
  • Metallocenes
  • Peptides
  • ferrocene