Abstract
The stacking of the bacteriochlorophyll (BChl) c and the role of water in forming an aggregate, in chlorosome, were examined by 13C-NMR and 25Mg-NMR spectroscopies and X-ray diffraction: (1) "The weakly-overlapped dimers forming displaced layers" was selected out of six different stackings so far identified in the smaller aggregates of isomeric BChl c and the solid aggregate of an isomeric mixture of BChl c. The selection was based on the comparison between the intermolecular 13C magnetic-dipole correlations and the nearest-neighbor carbon-to-carbon close contacts. (2) The crucial role of water in stabilizing the aggregate was shown by tracing the dehydration processes and by comparison with the solid-aggregate X-ray diffraction pattern. Possible binding sites of water were located by structural simulation. (3) The dimer-based stacking was evidenced by 25Mg-NMR, which exhibited a pair of signals showing different quadrupole couplings, due to the presence or absence of water in the axial position.