Energy transfer and trapping in photosystem I.

Coordination and organometallic chemistry of metal-NO complexes.

▪ Abstract Photosystem I is the light-driven plastocyanin-ferredoxin oxidoreductase in the thylakoid membranes of cyanobacteria and chloroplasts. In recent years, sophisticated spectroscopy, molecular genetics, and biochemistry have been used to understand the light conversion and electron transport functions of photosystem I. The light-harvesting complexes and internal antenna of photosystem I absorb photons and transfer the excitation energy to P700, the primary electron donor. The subsequent charge separation and electron transport leads to the reduction of ferredoxin. The photosystem I proteins are responsible for the precise arrangement of cofactors and determine redox properties of the electron transfer centers. With the availability of genomic information and the structure of photosystem I, one can now probe the functions of photosystem I proteins and cofactors. The strong reductant produced by photosystem I has a central role in chloroplast metabolism, and thus photosystem I has a critical role in...

PHOTOSYSTEM I: Function and Physiology

Femtosecond spectroscopy of photosynthetic light-harvesting systems.

http://www.cchem.berkeley.edu/grfgrp/Papers/2003%20Yang%20BiophysJ85.pdf

Energy Transfer in Photosystem I of Cyanobacteria Synechococcus elongatus: Model Study with Structure-Based Semi-Empirical Hamiltonian and Experimental Spectral Density

Using low intensity femtosecond duration laser pulses at 708 nm, we have observed absorption transients associated with electron transfer through the primary electron acceptor A0 in the photosystem I (PSI) reaction center from spinach under nonreducing conditions. At this wavelength the electron donor P700 is excited directly, although some antenna chlorophylls are also excited. Using a nanosecond duration preflash of 690 nm to oxidize P700, and then measuring the absorption transients from the antenna alone, it is possible by subtraction to isolate the absorption transients arising from electron transfer. We discuss this method critically. The spectrum of A0- − A0 does not appear promptly but takes ∼3 ps to reach maximum intensity and resembles those spectra previously obtained from higher plants, with a maximum bleaching at 685 ± 2 nm and a shoulder in the region 670−675 nm. The decay time of the primary radical pair P700+A0- is calculated as 20 ps. Analysis of absorption transients indicates that the i...

Primary Charge Separation and Energy Transfer in the Photosystem I Reaction Center of Higher Plants

The para, meta, and ortho peripherally-molybdenated tetraphenylporphyrin complexes [5-{[Mo(NO)Tp*Cl]NHC6H4}-10,15,20-Ph3porphH2] [1−3, respectively; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; Ph3porphH2 = triphenylporphyrin] have been prepared by reaction of the corresponding 5-(aminophenyl)-10,15,20-triphenylporphyrin derivative with [Mo(NO)Tp*Cl2]. Cyclic voltammetry shows that most of these complexes undergo two oxidation processes (associated with the porphyrin) and three reduction processes (two associated with the porphyrin, and one with the molybdenum fragment). The redox potentials of the molybdenum fragment are little influenced by the presence of the macrocyclic ring, and vice versa. The ΔG° values for charge separation in 1−3 are close to 0 eV. Photochemical measurements have been made on 1−3, and they were all found to undergo photoinduced intramolecular electron transfer from the excited singlet state of the porphyrin macrocycle to the molybdenum moiety, yielding charge-separated states...

Nigel T. H. White

Papers

Primary Charge Separation and Energy Transfer in the Photosystem I Reaction Center of Higher Plants

Synthesis and photochemistry of amido-linked, peripherally-molybdenated tetraphenylporphyrins