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OPTICAL ABSORPTION AND ELECTRON SPIN RESONANCE SPECTRA OF CATION RADICALS OF DIMERIC CHLOROPHYLL a IN LOW‐TEMPERATURE MATRICES
Author(s) -
Hoshino Mikio,
Ikehara Kiyoshi,
Imamura Masashi,
Seki Hiroshi,
Hama Yoshimasa
Publication year - 1981
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1981.tb08964.x
Subject(s) - chemistry , electron paramagnetic resonance , radical , absorption (acoustics) , absorption spectroscopy , photochemistry , absorption band , monomer , p700 , spectral line , analytical chemistry (journal) , nuclear magnetic resonance , materials science , photosystem i , photosynthesis , photosystem ii , polymer , biochemistry , physics , organic chemistry , quantum mechanics , astronomy , optics , composite material , chromatography
Abstract— A chlorophyll (Chl) a solution in 3‐methylpentane at 77 K exhibits an absorption spectrum with a distinct peak at 706 nm in the red‐band region. The formation of the 706 nm absorbing species (S706) was reversible with respect to temperature change; no chemical change was observed. γ‐Irradiation of the rigid 3‐methylpentane solution at 77 K yields an absorption spectrum which can be ascribed to S706 + and S706 − . When carbon tetrachloride, an electron scavenger, was added to the solution, the absorption of S706 + survived, which has peaks at 850 and 956 nm. It is assumed that the S706 is hydrogen‐bonded dimeric Chi a , which may be regarded as a model of P700 in photosynthesis. Cation radicals of monomeric Chi a were formed in a γ‐irradiated sec ‐butyl chloride solution at 77 K, and an absorption spectrum with peaks at 730 and 813 nm was recorded. ESR spectra of the cation radicals of S706 and monomeric Chi a are of a similar shape but their linewidths are 7.5 and 11.0 Gauss, respectively. The linewidth narrowing observed for S706 + is clear evidence for the assumption that S706 is dimeric Chi a. Comparison was made of the absorption spectrum of S706 + with the light‐induced spectrum of P700 reported earlier.