Probing Flexibility in Porphyrin-Based Molecular Wires Using Double Electron Electron Resonance

Janet E. Lovett*, Markus Hoffmann, Arjen Cnossen, Alexander T. J. Shutter, Hannah J. Hogben, John E. Warren, Sofia I. Pascu, Christopher W. M. Kay, Christiane R. Timmel, Harry L. Anderson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

60 Citations (Scopus)

Abstract

A series of butadiyne-linked zinc porphyrin oligomers, with one, two, three, and four porphyrin units and lengths of up to 75 angstrom, have been spin-labeled at both ends with stable nitroxide TEMPO radicals. The pulsed EPR technique of double electron electron resonance (DEER) was used to probe the distribution of intramolecular end-to-end distances, under a range of conditions. DEER measurements were carried out at 50 K in two types of dilute solution glasses: deutero-toluene (with 10% deutero-pyridine) and deutero-o-terphenyl (with 5% 4-benzyl pyridine). The complexes of the porphyrin oligomers with monodentate ligands (pyridine or 4-benzyl pyridine) principally adopt linear conformations. Nonlinear conformations are less populated in the lower glass-transition temperature solvent. When the oligomers bind star-shaped multidentate ligands, they are forced to bend into nonlinear geometries, and the experimental end-to-end distances for these complexes match those from molecular mechanics calculations. Our results show that porphyrin-based molecular wires are shape-persistent, and yet that their shapes can deformed by binding to multivalent ligands. Self-assembled ladder-shaped 2:2 complexes were also investigated to illustrate the scope of DEER measurements for providing structural information on synthetic noncovalent nanostructures.

Original languageEnglish
Pages (from-to)13852-13859
Number of pages8
JournalJournal of the American Chemical Society
Volume131
Issue number38
DOIs
Publication statusPublished - 30 Sept 2009

Keywords

  • EPR DISTANCE MEASUREMENTS
  • PULSED ELECTRON
  • 2-PHOTON ABSORPTION
  • CONFORMATIONAL FLEXIBILITY
  • SPIN-RESONANCE
  • OLIGOMERS
  • PELDOR
  • SPECTROSCOPY
  • ARRAYS
  • BIOMACROMOLECULES

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