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

Lovett, JE; Hoffmann, M; Cnossen, A; Shutter, ATJ; Hogben, HJ; Warren, JE; Pascu, SI; ... Anderson, HL; + view all (2009) Probing Flexibility in Porphyrin-Based Molecular Wires Using Double Electron Electron Resonance. J AM CHEM SOC , 131 (38) 13852 - 13859. 10.1021/ja905796z.

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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.

Type: Article
Title: Probing Flexibility in Porphyrin-Based Molecular Wires Using Double Electron Electron Resonance
DOI: 10.1021/ja905796z
Keywords: EPR DISTANCE MEASUREMENTS, PULSED ELECTRON, 2-PHOTON ABSORPTION, CONFORMATIONAL FLEXIBILITY, SPIN-RESONANCE, OLIGOMERS, PELDOR, SPECTROSCOPY, ARRAYS, BIOMACROMOLECULES
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > London Centre for Nanotechnology
URI: http://discovery.ucl.ac.uk/id/eprint/168715
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