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Probing Flexibility in Porphyrin-Based Molecular Wires Using Double Electron Electron Resonance.
- Source :
-
Journal of the American Chemical Society . 9/30/2009, Vol. 131 Issue 38, p13852-13859. 8p. - Publication Year :
- 2009
-
Abstract
- A series of butadiyne-linked zinc porphyrin oligomers, with one, two, three, and four porphyrin units and lengths of up to 75 A, have been spin-labeled at both ends with stable nitroxide TEMPO radicals. The pulsed EPA 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 pyndine). 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. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00027863
- Volume :
- 131
- Issue :
- 38
- Database :
- Academic Search Index
- Journal :
- Journal of the American Chemical Society
- Publication Type :
- Academic Journal
- Accession number :
- 44600339
- Full Text :
- https://doi.org/10.1021/ja905796z