Covalently linked zinc chlorophyll dimers as a model of a chlorophyllous pair in photosynthetic reaction centers.
A heterodimer, where zinc pyropheophorbide-a was linked with zinc pyropheophorbide-d through ethylene glycol diester, was prepared, as well as the corresponding homodimers. The synthetic dimers were complexed with methanol in benzene to give folded dimers by mutual Zn...O(Me)-H...O=C13(1) bonding. Such complexes had furthest red (Qy) absorption bands at longer wavelengths than the monomeric species. These red-shifts were ascribable to excitonic coupling of the Qy transition states in the chlorin pi-pi stacking conformer. In the heterodimeric system, a minor band was observed at the shorter wavelength side of the main Qy band. This observation can be explained by an additional contribution of Qy vibronic state to the exciton-coupled states. Based on the experimental results, a pair of chlorophyll(Chl)-d with Chl-a as well as a Chl-d homopair were proposed as dimers in reaction centers of Chl-d dominating cyanobacteria.
Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan. tamiaki@se.ritsumei.ac.jp
Hitoshi
H
Tamiaki
Kazuhiro
K
Fukai
Hideki
H
Shimazu
Katsunori
K
Nishide
Yutaka
Y
Shibata
Shigeru
S
Itoh
Michio
M
Kunieda
D002734:Chlorophyll / Q000737:chemistry*; D000458:Cyanobacteria / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D004952:Esters / Q000737:chemistry; D005026:Ethylene Glycols / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry*
D004952:Esters; D005026:Ethylene Glycols; D009942:Organometallic Compounds; D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; D015032:Zinc