Special-pair singlet excited state

The primary reaction of bacterial photosynthesis - an electron transfer via several prosthetic groups in the so-called reaction center - proceeds extremely rapid on the time-scale of picoseconds. A series of recent experiments gave the following picture of this charge transfer process (data taken for reaction centers from Rhodobacter (Rb.) sphae-roides /1-4/) After excitation of the lowest excited singlet state of the primary electron donor (a "special pair" of bacteriochlorophyll molecules) the excited electronic state P lives for approximately 3.5ps. The decay of P is related with the electron transfer away from P. From several time-resolved experiments it was concluded that this first charge transfer carries the electron directly to the bacterio-pheophytin H /I,2/. Only very recently we could demonstrate the existence of an additional short-lived intermediate prior to the reduction of the bacteriopheophytin H /4/. We interpreted this intermediate as P+B , i.e. the state where the electron from the special pair P has reduced the monomeric bacteriochlorophyll B to the anion radical B . In the final picosecond reaction the electron arrives (with a time constant of 200 ps) at the quinone Qa. It is the purpose of this paper to present additional experimental data supporting a sequential electron transfer via the accessory bacteriochlorophyll. 

We have produced a reaction center mutant with enhanced symmetry between the L and M polypeptide chains in the vicinity of the special pair. This mutant is capable of charge separation with high yield and grows photosynthetically. The mutation does not radically alter the transition energy between the ground state and the lowest excited singlet state of P. However, it does alter the shape of the Qy absorbance band of P. 

Here p is the probability of the molecule i to be in the excited state, N is the number of antenna molecules in PSU, is the time of excitation decay due to all the losses in the antenna, except quenching by RC, is the charge separation time in RC. In this model, RC functions merely as a shallow trap for singlet excitations of antenna pigments. Part of the excitations reaching RC move back to the antenna, part of them initiate the photo-oxidation of a special pair of pigment molecules in RC, which in normal conditions... 

In spite of the structural symmetry, the RC is functionally highly asymmetric Absorption of a photon or energy transfer from light-harvesting complexes in the membrane raises the special pair D to its first excited singlet state, D, which is the starting point for a series of electron transfer reactions across the membrane, leading to and Qb- In the first step D+Oa is formed from D Oa with a... 

The exciting discovery of super-conductivity in metallic fiillerencs (f) leads us to inquire whether the classic mechanism for superconductivity, namely, effective electron-electron attraction via the interaction of electrons with vibrations of the ions, is applicable here as well. Associated with this is the question of whether the direct electron-electron repulsion in FuUerenes can suppress conventional singlet pairing. In this paper we exploit the special nature of cluster compounds to derive a particularly simple expression for electron-vibrational coupling from which parameters of the superconducting state of fuUerenes are easily calculated. Further, we present arguments why the effective repulsions in fuUerenes are no different than in conventional metals. 

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