(31R)-bacteriochlorophyll (BChl) c solid aggregates with an absorbance around 740 nm were formed from BChl c dimers, and 2-D homonuclear 13C-13C radio frequency-driven dipolar recoupling as well as proton-driven spin diffusion dipolar correlation NMR spectra have been collected in ultrahigh magnetic field. Doubling of signals is observed for most carbons in the BChl c macrocycle, leading to two correlation networks. In this way, two major fractions denoted types A and B are identified. Some of the ring carbons show multiple resonances, revealing additional slight differences in microstructural environment. 2-D heteronuclear 1H-13C correlation data have been recorded using the frequency- and phase-switched Lee-Goldburg technique to assign the 1H response. 15N chemical shifts are assigned from 2-D heteronuclear 15N-13C correlation experiments using spectrally induced filtering in combination with cross polarization. Also the nitrogen atoms in the pyrrole rings I, II, and IV (NI, NII, and NIV, respectively) show two sets of resonances, each of which is connected to a single 13C correlation network A or B. The 13C chemical shifts are compared with the signals from antiparallel dimers in solution and with the response from chlorosomes previously reported. The data clearly show that the stacking in CH2Cl2-treated aggregates is different from the stacking in the chlorosomes and hexane-treated aggregates. Some degree of similarity with the antiparallel dimer form in solution transpires, in particular for the type A species. It is proposed that the CH2Cl2 precipitate represents a structural intermediate between the antiparallel dimer and the parallel stack as found in the chlorosome.
|ジャーナル||Journal of Physical Chemistry B|
|出版ステータス||Published - 2004 2 26|
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