Stabilization and Structure of the cis Tautomer of a Free-Base Porphyrin.
Kolle E ThomasLaura J McCormickHugo Vazquez-LimaAbhik GhoshPublished in: Angewandte Chemie (International ed. in English) (2017)
Single-crystal X-ray analysis of the β-heptakis(trifluoromethyl)-meso-tetrakis(p-fluorophenyl)porphyrin, H2 [(CF3 )7 TpFPP], has revealed the first example of a stable cis tautomer of a free-base porphyrin, the long-postulated intermediate of porphyrin tautomerism. The stability of the unique molecule appears to reflect a dual origin: a strongly saddled porphyrin skeleton, which alleviates electrostatic repulsion between the two NH protons, and two polarization-enhanced, transannular N-H⋅⋅⋅O-H⋅⋅⋅N hydrogen bond chains, each involving a molecule of water. DFT calculations suggest that the observed tautomer has a lower energy than the alternative, doubly hydrated trans tautomer by some 8.3 kcal mol-1 . A fascinating prospect thus exists that H2 [(CF3 )7 TpFPP]⋅2 H2 O and cognate structures may act as supramolecular synthons, which, given their chirality, may even be amenable to resolution into optically pure enantiomers.
Keyphrases
- photodynamic therapy
- metal organic framework
- energy transfer
- electron transfer
- cystic fibrosis
- density functional theory
- molecular dynamics simulations
- molecular dynamics
- single cell
- single molecule
- quantum dots
- room temperature
- magnetic resonance
- mass spectrometry
- capillary electrophoresis
- crystal structure
- electron microscopy