Temperature-dependent spectral changes of self-aggregates of zinc chlorophylls esterified by different linear alcohols at the 17-propionate

Abstract

Systematically synthetic zinc 3-hydroxymethyl-131-oxo-chlorins esterified by different linear alcohols (methanol, 1-propanol, 1-hexanol, 1-dodecanol and 1-octadecanol) at the 17-propionate were self-assembled in the presence of cetyltrimethylammonium bromide in an aqueous solution. These zinc chlorins exhibited red-shifted Q y absorption bands and circular dichroism (CD) signals in the corresponding Q y region after incubation for 17 h, indicating that the zinc chlorins formed self-aggregates like those in natural chlorosomes of green photosynthetic bacteria. Visible absorption and CD spectra of self-aggregates of the zinc chlorins depended on the length of their esterifying alcohols. Zinc chlorins esterified by shorter alcohols gave larger changes in their visible absorption and CD spectra after incubation above 40°C, whereas zinc chlorins esterified by longer alcohols afforded smaller changes. These results indicate that hydrophobic interaction among esterifying chains of chlorin molecules as well as that between the esterifying chains and peripheral surfactants or lipids play an important role in the stability of chlorosomal self-aggregates.