Diastereoselective Control of Bacteriochlorophyll e Aggregation. 3-S-BChl e Is Essential for the Formation of Chlorosome-Like Aggregates

Abstract

We have investigated supramolecular bacteriochlorophyll (BChl) e aggregates in four different solvent systems. Aggregates of HPLC-purified BChl e species, 31-R-8-ethyl-12-ethyl BChl e, 31-R-8-propyl-12 ethyl BChl e, 31-S-8-propyl-12-ethyl BChl e, and 31-S-8-isobutyl-12-ethyl BChl e, in cyclohexane, n-hexane, H2O/monogalactosyldiglyceride, or H2O/lecithin, indicate two different aggregate structures, as judged from absorption, circular dichroism, infrared, and resonance Raman spectroscopies. Aggregates of 31-R-BChl (R-BChl) e were characterized by a 706 nm absorption band and broad C-131 carbonyl stretching bands at 1650−1680 cm-1. In contrast, aggregates of 31-S-BChl (S-BChl) e displayed a Qy band maximum at 717 nm and a carbonyl stretching band at 1650 cm-1 only. All measurements indicated that the aggregates of S-8-isobutyl-12-ethyl BChl (S[IE]BChl) e mimicked the supramolecular aggregates in intact chlorosomes of Chlorobium phaeobacteroides much better than did the R-8-ethyl-12-ethyl BChl (R[EE]BChl) e...