Bacteriochlorophyll c monomers, dimers, and higher aggregates in dichloromethane, chloroform, and carbon tetrachloride

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Abstract
Bacteriochlorophyll c in vivo is a mixture of at least 5 homologs, all of which form aggregates in CH2Cl2, CHCl3 and CCl4. Three homologs exist mainly in the 2-R-(1-hydroxyethyl) configuration, whereas the other two homologs, 4-isobutyl-5-ethyl and 4-isobutyl-5-methyl farnesyl bacteriochlorophyll c, exist mainly in the 2-S-(1-hydroxyethyl) configuration (Smith KM, Craig GW, Kehres LA and Pfennig N (1983) J. Chromatograph. 281: 209–223). In CCl4 the S-homologs form an aggregate of 2–3 molecules whose absorption (747 nm maximum) and circular dichroism spectra resemble those of the chlorosome. In CH2Cl2, CHCl3 and CCl4 the 4-n-propyl homolog (R-configuration) forms dimers absorbing at ca. 680 nm and higher aggregates absorbing at 705–710 nm. In CCl4 the dimerization constant is approx. 10 µM−1 (1000 times that for chlorophyll a). The difference between the types of aggregates formed by the 4-n-propyl and 4-isobutyl homologs is attributed to the difference between the R- and S-configurations of the 2-(1-hydroxyethyl) groups in each chlorophyll.

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