Premium
Coordination‐Driven Dimerization of Zinc Chlorophyll Derivatives Possessing a Dialkylamino Group
Author(s) -
Watanabe Hiroaki,
Kamatani Yusuke,
Tamiaki Hitoshi
Publication year - 2017
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201700015
Subject(s) - dimer , chemistry , zinc , crystallography , steric effects , photosynthetic reaction centre , supramolecular chemistry , circular dichroism , methyl group , stereochemistry , phenyl group , photochemistry , crystal structure , group (periodic table) , organic chemistry , alkyl , electron transfer , halogen
Zinc chlorophyll derivatives Zn‐1 – 3 possessing a tertiary amino group at the C3 1 position have been synthesized through reductive amination of methyl pyropheophorbide‐ d obtained from naturally occurring chlorophyll‐ a . In a dilute CH 2 Cl 2 solution as well as in a dilute 10 %(v/v) CH 2 Cl 2 /hexane solution, Zn‐1 possessing a dimethylamino group at the C3 1 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 3 1 ‐N atom of the dimethylamino group. However, Zn‐2/3 bearing 3 1 ‐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 1 H 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 CH 2 Cl 2 , while Zn‐2/3 gave open and flexible dimers in a concentrated CH 2 Cl 2 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.