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THE CHLOROPHYLL a AGGREGATE ABSORBING NEAR 685 nm IS SELECTIVELY FORMED IN AQUEOUS TETRAHYDROFURAN *
Author(s) -
Uehara Kaku,
Hioki Yuko,
Mimuro Mamoru
Publication year - 1993
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.1751-1097.1993.tb04913.x
Subject(s) - tetrahydrofuran , aqueous solution , chemistry , dimer , monomer , solvent , molecule , j aggregate , chlorophyll , chlorophyll a , raman spectroscopy , photochemistry , stereochemistry , organic chemistry , polymer , optics , biochemistry , physics
An aqueous solution of 2–12% (vol/vol) tetrahydrofuran (THF) induced the selective aggregation of chlorophyll a (Chl a ) to form a novel species, A‐685, absorbing near 685 nm. The formation of A‐685 was closely correlated with a decrease in water activity of the solution. A Raman spectrum of the Chl a species formed in the presence of 6% THF suggests a unique interaction among Chl a , solvent THF and water molecules to give a stacked aggregate (Chl a .THF.H 2 O.THF.Chl a ). The circular dichroic spectrum of the Chl a species formed in the 6% THF aqueous solution showed an intense signal that had negative and positive wings with about 100‐fold larger molar ellipticity for the A‐685 than for monomer. However, Chl a ', the C10 epimer of Chl a , and chlorophyllide, with a phytyl chain replaced by an ethyl group, did not form A‐685 in 6% THF. These clearly indicate that 10‐methylcarboxylate and the phytyl chain have a significant role in stabilizing A‐685. A possible structure for A‐685 is proposed as a novel in vitro model for the P‐680 Chl a dimer.