A Structural Analysis of Chlorosomes by Solid-State NMR, Electronic-Absorption and Circular Dichroism Spectroscopies

Abstract

  Concerning the structure of chlorosomes, two kinds of models have been proposed; one is ‘the monomer-based stacking’ and the other is ‘the dimer-based stacking’. We tried to determine the structures of BChl c artificial aggregates and chlorosomes by the use of solid-state NMR, electronic-absorption and circular dichroism spectroscopies.
  In the case of BChl c artificial aggregate, we measured the 2D spin-diffusion spectra which can detect through-space ¹³C–¹³C correlations. The through-space correlations experimentally determined were compared with those simulated by intermolecular distances in the models. The structure of BChl c artificial aggregates could be explained not by the monomer-based stacking but by the dimer-based stacking; in which the macrocycles are stacked like a stair case. This structure realizes the red-shift of the Q_y absorption as observed spectroscopically.
  In chlorosomes, the CD spectral pattern was simulated only by the left-handed cylindrical arrangement of dimers.