Is There Elliptic Distortion in the Light Harvesting Complex 2 of Purple Bacteria?

TL;DR

This study investigates whether elliptic distortion explains the spectral features of LH2 in purple bacteria, using simulations to compare models of symmetry modulation and disorder effects.

Contribution

The paper demonstrates that uniform k=2 symmetry modulation cannot account for observed spectral data, proposing alternative disorder models that better fit the experimental results.

Findings

Uniform k=2 symmetry modulation fails to explain SMS data.

Disorder models with k=1 and k=2 symmetry correlation fit the data well.

Lower major peak may be an average of k=1 and k=0 states.

Abstract

Single molecule spectroscopy (SMS) revealed unusually large gap between two major exciton peaks of the B850 unit of light harvesting complex 2 (LH2), which could be explained assuming elliptic distortion or k=2 symmetry modulation in the site excitation energy. On the basis of extensive simulation of the SMS data and ensemble lineshape, we found that uniform modulation of k=2 symmetry cannot explain the dependence of intensity ratios on the gap of the two major peaks, which are available from SMS, nor the ensemble lineshape. Alternative models of disorder with k=1 and k=2 symmetry correlation are shown to reproduce these data reasonably well and can even explain the gap distribution when it is assumed that the lower major peak in the SMS lineshape is an intensity weighted average of k=1- and k=0 states.