Excited-State Electronic Asymmetry of the Special Pair in Photosynthetic Reaction Center Mutants:  Absorption and Stark Spectroscopy†

Biochemistry ◽  
1999 ◽  
Vol 38 (37) ◽  
pp. 11949-11960 ◽  
Author(s):  
Laura J. Moore ◽  
Huilin Zhou ◽  
Steven G. Boxer
Keyword(s):  
Excited State ◽  
Reaction Center ◽  
Photosynthetic Reaction Center ◽  
Stark Spectroscopy ◽  
Special Pair

Co-facial magnesium porphyrin dimer complexed with fullerene: photosynthetic reaction center model of 'special pair' self-assembled to electron acceptor

2008 ◽  
Vol 12 (07) ◽  
pp. 857-865 ◽  
Author(s):  
Atula S. D. Sandanayaka ◽  
Navaneetha K. Subbaiyan ◽  
Raghu Chitta ◽  
Yasuyuki Araki ◽  
Osamu Ito ◽  
...  
Keyword(s):  
Reaction Center ◽  
Electron Acceptor ◽  
Photosynthetic Reaction Center ◽  
Ammonium Cation ◽  
Model Systems ◽  
Spectral Studies ◽  
Special Pair ◽  
Self Assembled ◽  
Alkyl Ammonium ◽  
Porphyrin Dimer

Using a self-assembled supramolecular approach, a closer model for the photosynthetic reaction center 'special pair' assembled with an electron acceptor conjugate, is reported. As the 'special pair' donor, magnesium meso-(benzo-15-crown-5)porphyrin was self-assembled with K + to form a highly stable Mg porphyrin dimer with a co-facial geometry arrangement, which is a better electron donor since it is nearly 130 mV easier to oxidize compared to the earlier reported Zn porphyrin dimer analog. Further, pyridine and alkyl ammonium cation-functionalized fullerene was attached via axial coordination and crown ether-alkyl ammonium cation complexation to form the four-fold, donor-acceptor complex. The self-assembled supramolecular complex, constructed using this approach, possesses defined geometry and orientation. Efficient charge separation from the singlet excited state of the Mg porphyrin dimer to the fullerene entity and a relatively slow charge recombination, were revealed by time-resolved emission and nanosecond transient absorption spectral studies, supporting the impending exploitation of these novel biomimetic model systems for light energy harvesting applications.

scholarly journals Primary processes in the bacterial reaction center probed by two-dimensional electronic spectroscopy

2018 ◽  
Vol 115 (14) ◽  
pp. 3563-3568 ◽  
Author(s):  
Andrew Niedringhaus ◽  
Veronica R. Policht ◽  
Riley Sechrist ◽  
Arkaprabha Konar ◽  
Philip D. Laible ◽  
...  
Keyword(s):  
Excited State ◽  
Reaction Center ◽  
Charge Separation ◽  
Purple Bacteria ◽  
Electronic Spectroscopy ◽  
Reaction Centers ◽  
Purple Bacterium ◽  
Absorption Bands ◽  
Sequential Reaction ◽  
Special Pair

In the initial steps of photosynthesis, reaction centers convert solar energy to stable charge-separated states with near-unity quantum efficiency. The reaction center from purple bacteria remains an important model system for probing the structure–function relationship and understanding mechanisms of photosynthetic charge separation. Here we perform 2D electronic spectroscopy (2DES) on bacterial reaction centers (BRCs) from two mutants of the purple bacterium Rhodobacter capsulatus, spanning the Qy absorption bands of the BRC. We analyze the 2DES data using a multiexcitation global-fitting approach that employs a common set of basis spectra for all excitation frequencies, incorporating inputs from the linear absorption spectrum and the BRC structure. We extract the exciton energies, resolving the previously hidden upper exciton state of the special pair. We show that the time-dependent 2DES data are well-represented by a two-step sequential reaction scheme in which charge separation proceeds from the excited state of the special pair (P*) to P+HA− via the intermediate P+BA−. When inhomogeneous broadening and Stark shifts of the B* band are taken into account we can adequately describe the 2DES data without the need to introduce a second charge-separation pathway originating from the excited state of the monomeric bacteriochlorophyll BA*.

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