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- Title
Coordination-Driven Dimerization of Zinc Chlorophyll Derivatives Possessing a Dialkylamino Group.
- Authors
Watanabe, Hiroaki; Kamatani, Yusuke; Tamiaki, Hitoshi
- Abstract
Zinc chlorophyll derivatives Zn-1- 3 possessing a tertiary amino group at the C31 position have been synthesized through reductive amination of methyl pyropheophorbide- d obtained from naturally occurring chlorophyll- a. In a dilute CH2Cl2 solution as well as in a dilute 10 %(v/v) CH2Cl2/hexane solution, Zn-1 possessing a dimethylamino group at the C31 position showed red-shifted UV/Vis absorption and intensified exciton-coupling circular dichroism (CD) spectra at room temperature owing to its dimer formation via coordination to the central zinc by the 31-N atom of the dimethylamino group. However, Zn-2/3 bearing 31-ethylmethylamino/diethylamino groups did not. The difference was dependent on the steric factor of the substituents in the tertiary amino group, where an increase of the carbon numbers on the N atom reduced the intermolecular N⋅⋅⋅Zn coordination. UV/Vis, CD, and 1H NMR spectroscopic analyses including DOSY measurements revealed that Zn-1 formed closed-type dimers via an opened dimer by single-to-double axial coordination with an increase in concentration and a temperature decrease in CH2Cl2, while Zn-2/3 gave open and flexible dimers in a concentrated CH2Cl2 solution at low temperature. The supramolecular closed dimer structures of Zn-1 were estimated by molecular modelling calculations, which showed these structures were promising models for the chlorophyll dimer in a photosynthetic reaction center.
- Subjects
COORDINATE covalent bond; DIMERIZATION; ZINC compounds; CHLOROPHYLL; AMINO group
- Publication
Chemistry - An Asian Journal, 2017, Vol 12, Issue 7, p759
- ISSN
1861-4728
- Publication type
Article
- DOI
10.1002/asia.201700015