Abstract
Chlorobium limicola contains an antenna complex called ‘chlorosomes’ consisting of a higher aggregate of BChl c isomers. We found that the solid artificial aggregate was an assembly of the ‘piggy-back dimers’ of BChl c by means of solid-state NMR and electronic-absorption spectroscopies. In chlorosomes, the set of data suggested that chlorosomes also were based on the ‘piggy-back dimers’.
Solid-state NMR spectroscopy can detect only short-range interactions, whereas electronic-absorption spectroscopy can detect only long-range interactions among transition dipoles. However, X-ray powder diffraction can systematically detect from short-range to long-range interactions. This method provides informations on the relative positions of macrocycles in a column as well as the arrangement of such columns. Thus, we propose the following structure of the solid artificial aggregate and chlorosomes; the former is in a two-dimensioned crystalline form, while the latter is in a spiral cylinder, both consisting of arrangement of columns of stacked piggy-back dimers.
