Optical spectroscopic study of (Chl a.H2O)2 according to the proposed C2 symmetrical molecular structure for the P700 photoactive aggregate in photosynthesis

Fong, Francis K.; Koester, Vaughn J.; Polles, J. S.

doi:10.1021/ja00436a068

Cited by 28 publications

(5 citation statements)

References 3 publications

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“…Ab initio 6-31G* charge distributions make noncovalent interactions possible where solvent molecules form 1:1 or 1:2 complexes with chlorophylls and bacteriochlorophylls in solution, suggested in several spectroscopic studies. − Self-aggregation of bacteriochlorophylls may occur via magnesium and oxygen atoms of the adjacent chromophores via electrostatic interactions. In particular, the O13 1 atom of bacteriochlorophylls may easily, without any steric hindrance, bind noncovalently to the positively charged Mg atom of the next bacteriochlorophyll forming a dimer or a larger aggregate. − Other negatively charged oxygen atoms, especially OR3, OR7, OR7, and O13 2 may have a role in aggregation processes. , Furthermore aggregates, where chlorophylls or bacteriochlrophylls are linked by solvent molecules may be formed in many ways with and without the oxygen atoms of the porphyrin ring being involved. − …”

Section: Discussionmentioning

confidence: 99%

Spectroscopic Properties of Mg−Chlorin, Mg−Bacteriochlorin, and Bacteriochlorophylls a, b, c, d, e, f, g, and h Studied by Semiempirical and Ab Initio MO/CI Methods

Linnanto

Korppi-Tommola

2001

J. Phys. Chem. A

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The semiempirical PM3 method has been used to calculate fully optimized structures of bacteriochlorophylls a, b, c, d, e, f, g, and h, magnesium−chlorin, and magnesium−bacteriochlorin. Several configuration interaction (CI) methods, the PM3 (5,5) CIS and CISD, ZINDO/S CIS (n,n) with 2 < n <30, and ab initio CIS (5,5)/6-31G* methods, were tested for their predictive power in estimation of spectroscopic properties of bacteriochlorophylls. The ZINDO/S CIS (15,15) method turned out the best results for overall simulation of absorption spectra. Both the transition energies and relative intensities of the Q y , Q x , and Soret bands were correctly predicted. The effect of solvent coordination on the transition energies and oscillator strengths was also studied. The calculations predict solvent-induced spectroscopic shifts of the Q x and Soret bands, whereas the Q y transitions remain practically unshifted, in accord with experimental findings. The shifts are due to solvent-induced energy level shifts and charge redistribution of the magnesium atom in the excited states of bacteriochlorophylls. The results are discussed with reference to spectroscopic properties of bacteriochlorophylls in solution, in aggregates, and in photosynthetic light harvesting antenna.

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Section: Discussionmentioning

confidence: 99%

Spectroscopic Properties of Mg−Chlorin, Mg−Bacteriochlorin, and Bacteriochlorophylls a, b, c, d, e, f, g, and h Studied by Semiempirical and Ab Initio MO/CI Methods

Linnanto

Korppi-Tommola

2001

J. Phys. Chem. A

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“…2B) coincides with the absorption bands of Chl a dimer in solution reported by Fong et al (24). From the independent spectral evidence (22,24), we are led to assume that in TSF-I particles poised at -625 mV and at low temperature, the 1-msec decay component of the light-induced absorbance § We note that when a 65-nm laser pulse was used for excitation, formation of -1-msec triplet state of chlorophyll absorbing at 680 nm was observed, in agreement with previous work (13). difference spectrum reflects a photochemical charge separation between P-700 and a ChI a dimer (acceptor Al).…”

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confidence: 99%

Spectral and kinetic evidence for two early electron acceptors in photosystem I

Шувалов

Dolan

1979

Proc. Natl. Acad. Sci. U.S.A.

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Triton-fractionated photosystem-I particles poised at -625 mV, where the two bound iron-sulfur proteins are reduced, have been studied by optical and electron paramagnetic resonance spectroscopies from 293 to 5 K. At 5-9 K, these particles exhibit two decay components with lifetimes of 1.3 and 130 msec in the laser pulse-induced absorption and electron paramagnetic resonance signal changes. Spectral properties of the 130-msec decay component reflect the charge separation between P-700 and some iron-sulfur center having a broad optical absorbance in the 400-to 550-nm region and a previously reported electron paramagnetic resonance signal with g = 1.78, 1.88, and 2.08. Spectral properties of the 1-msec decay component indicate photoinduced charge separation between P-700 and a chlorophyll a dimer having absorption bands at 420, 450, and 700 nm. It is assumed that these two acceptors participate in the electron transfer from P-700* to the bound iron-su fur proteins.Since the discoveries of a spectral species, P-430, by flash-kinetic spectroscopy (1) and of chloroplast membrane-bound ironsulfur protein(s) by electron paramagnetic resonance (EPR) spectroscopy (2) as candidates for the primary electron acceptor in photosystem I in 1971, extensive investigations and developments on this subject have taken place. Currently available evidence based on kinetic (3-6) and spectral (7,8) correlation and on correlation of their redox behavior (9-13) supports the identity of P-430 with an iron-sulfur protein. It was subsequently found, however, that some reversible photooxidation of the primary donor P-700 could still be observed even when the bound iron-sulfur proteins were chemically reduced prior to illumination (14, 15). Under illumination, the chemically reduced photosystem-I particles yielded a new, reversible EPR signal (g values 2.08, 1.88, and 1.78), in parallel with the reversible P-700+ signal. These results pointed to the existence of an earlier electron acceptor, X, in photosystem I. In an attempt to determine the redox potential of this more primary acceptor, Ke et al. (16) performed a reductive titration over a range more negative than that of the bound iron-sulfur proteins and monitored the attenuation of the light-induced EPR signal of P-700+ at 15 K with decreasing potential. These experimental data also suggested the existence of a more primary acceptor, with a midpoint potential near -735 mV.More recently, Sauer et al. (17,18) investigated laser flashinduced P-700 absorbance changes in photosystem-I particles in which the acceptors were selectively reduced beforehand. With redox potentials more negative than that of the bound iron-sulfur proteins, more rapid decays of the P-700 absorbance change were observed. These results were interpreted in terms of two intermediary electron acceptors Al and A2: P-700-Al-A2-P-430.In this note, we report spectroscopic and kinetic data obtained by optic and EPR spectroscopies which appear to substantiate and complement the proposal of two earlier electron accepto...

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“…The presence of the C9 keto and CIO carbomethoxy carbonyls in ring V and the C7 propionic ester carbonyl in ring IV of the chlorophyll a molecule gives rise to several possible self-aggregating interactions between monomeric units of Journal of the American Chemical Society / 99:7 / March is the ratio of the transition intensities (D) of the a (red) and ß (far red) exciton components (see ref 3). The angle , subtended by the transition moments of the two Chi a molecules, has been calculated from according to eq 4 of ref 3.…”

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confidence: 99%

“…It has also been pointed out that the = 180°value for B is responsible for the single Gaussian component observed for the Qy transition in B. 3 The observed features of the spectral analysis of A and B are listed in Table I. Also listed in Table I are corresponding properties derived from published16 light-minus-dark absorption change spectra of the in vivo P700 reaction center.17…”

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confidence: 99%

Endo and exo carbomethoxy carbonyl bonding in hydrated chlorophyll a dimers. Experimental criteria for the determination of the P700 structure in photosynthesis

Fong¹,

Koester²,

Galloway³

1977

J. Am. Chem. Soc.

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Optical spectroscopic study of (Chl a.H2O)2 according to the proposed C2 symmetrical molecular structure for the P700 photoactive aggregate in photosynthesis

Cited by 28 publications

References 3 publications

Spectroscopic Properties of Mg−Chlorin, Mg−Bacteriochlorin, and Bacteriochlorophylls a, b, c, d, e, f, g, and h Studied by Semiempirical and Ab Initio MO/CI Methods

Spectroscopic Properties of Mg−Chlorin, Mg−Bacteriochlorin, and Bacteriochlorophylls a, b, c, d, e, f, g, and h Studied by Semiempirical and Ab Initio MO/CI Methods

Spectral and kinetic evidence for two early electron acceptors in photosystem I

Endo and exo carbomethoxy carbonyl bonding in hydrated chlorophyll a dimers. Experimental criteria for the determination of the P700 structure in photosynthesis

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