Fluorescence detected magnetic resonance of monomers and aggregates of bacteriochlorophylls of green sulfur bacteria Chlorobium sp.

Fluorescence detected magnetic resonance (FDMR) was used to study the lowest triplet state of bacteriochlorophylls (BChls) c and d in Chlorobium (Chl.) tepidum and Chl. vibrioforme, respectively. These pigments were studied both in the oligomeric form (in whole cells) and in the monomeric form (after conversion using a 1% 1-hexanol treatment). Fluorescence spectra show the presence of lower-state aggregates, apart from monomers, in samples treated with 1-hexanol. Values of the zero field splitting (ZFS) parameter D, obtained from FDMR spectra, were found to decrease with an increasing aggregate size. The observed ZFS trends are explained by a delocalization of the triplet spins, including a charge resonance (CR) contribution, over the aggregate. A simple model is presented relating the changes of D and E as a result of monomer aggregation to the aggregate geometry. Application of this model to BChls c and d indicates approximately diagonal stacking of the monomers in the dimer. Results for oligomeric BChl c and d were compared with those previously obtained for oligomeric BChl e. FDMR transitions of BChls c, d and e differ both in frequencies and in signs. The D and E values of Car's and BChl a (in whole cells) agree well with those reported for Chl. phaeobacteroides and Chl. limicola

Fast Exciton Dynamics and Coherent Oscillations Revealed by Coherent 2D Spectroscopy in Chlorosomes

In this study ultrafast energy transfer dynamics in chlorosomes from sulphur bacterium Chlorobaculum tepidum were explored by means of coherent electronic two-dimensional spectroscopy. Observed sub-100 fs dynamics were attributed to incoherent downhill excitation diffusion between disordered domains within chlorosomes. At the same time vibrational coherent oscillations were investigated on the longer timescales

Slow Slip and Tremor Detected at the Northern Costa Rica Seismogenic Zone

EOS Transactions, American Geophysical Unio