Circular Dichroism Spectroscopy as a Test for the Chlorosome Antenna Structure

Abstract

Recently a novel model of tubular arranged six linear bacteriochlorophyll (BChl) chains with a low packing density, approximating that in vivo, and interchain distance of ~2nm has been proposed for chlorosomal antennae of green bacteria [1] (Fig. 1). This model is compatible with the key spectral features found by spectral hole-burning experiments [2]. Hole-burning spectroscopy determined the exciton level structure of a chlorosomal BChl aggregate. Namely, the position and the relative intensity of the lowest exciton level band was discovered. However, hole-burning spectra are almost insensitive to the spectral position of the highest exciton level, this second important structural feature of the aggregate. Circular dichroism (CD) spectroscopy is a suitable technique to control all the exiton levels of BChl c aggregate. But there are some difficulties in its use.