Res. Chem. Intermed.
, Vol. 33, No. 1–2, pp. 161–168 (2007)
Also available online - www.brill.nl/rci
Self-aggregation of synthetic zinc
-oxo-17,18-cis-chlorin in a non-polar
, TAKUYA WATANABE and MICHIO KUNIEDA
Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan
University, Kusatsu, Shiga 525-8577, Japan
Received 4 September 2003; accepted 22 January 2004
Abstract—Zinc methyl 3
-demethyl-17,18-cis-bacteriopheophorbide-d was prepared as a model of
naturally occurring bacteriochlorophyll-d. From the absorption spectral analysis, the synthetic cis-
chlorin self-aggregated in a non-polar organic solvent to give an oligomer possessing red-shifted and
broadened peaks, compared to the non-aggregated form. The red-shifted values by self-aggregation
were smaller than those observed in the corresponding trans-isomer, indicating that self-aggregates of
the cis-isomer took on more disordered supramolecular structures than those of the trans-isomer.
Keywords: Bacteriochlorophyll; dihydroporphyrin; self-aggregate; stereoisomer; visible spectrum.
Bacteriochlorophyll (BChl)-d (see left drawing in Fig. 1 as a molecular structure
in one of the homologs) self-aggregates without any assistance of peptides to form
the core part of the main light-harvesting antennas (= chlorosomes) in some green
sulfur photosynthetic bacteria [1–3]. Isolated BChls-d also self-aggregated in
non-polar organic solvents to give oligomers possessing similar supramolecular
structures with natural systems [4, 5]. As model compounds, zinc 3
-oxo-chlorins (see middle drawing in Fig. 1 as a typical model) were prepared
by modifying naturally occurring chlorophylls, and their self-aggregation in non-
polar organic solvents was investigated by visible absorption spectroscopy; the
self-aggregates had red-shifted and broadened peaks compared with the monomeric
species [6 – 15]. All of the natural and artiﬁcial chlorophylls examined so far have
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