A synthetic biomimetic model of special pair bacteriochlorophyll a

Wasielewski, Michael R.; Smith, Ursula; Cope, B. T.; Katz, Joseph

doi:10.1021/ja00454a054

Cited by 51 publications

(23 citation statements)

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“…Considering the fact that zinc bacteriochlorin had a larger coordinated ability than zinc chlorin , the steric hindrance at the B‐ring would disturb the production of the tightly folded conformer. The redshift of ethylene bis(bacteriochlorophyllide‐ a ) (=Mg analog of 2B with 13 2 ‐COOMe) in water‐saturated benzene was reported to be 370 cm −1 , which was comparable to the present value.…”

Section: Resultssupporting

confidence: 87%

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin, Chlorin, and Bacteriochlorin π‐Systems

Tamiaki

Fukai

Shimazu

et al. 2013

Photochem & Photobiology

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Zinc complex of pyropheophorbide-b, a derivative of chlorophyll-b, was covalently dimerized through ethylene glycol diester. The synthetic homo-dyad was axially ligated with two methanol molecules from the β-face and both the diastereomerically coordinating methanol species were hydrogen bonded with the keto-carbonyl groups of the neighboring chlorin in a complex. The resulting folded conformer in a solution was confirmed by visible, (1) H NMR and IR spectra. All the synthetic zinc chlorin homo- and hetero-dyads consisting of pyropheophorbides-a, b and/or d took the above methanol-locked and π-π stacked supramolecules in 1% (v/v) methanol and benzene to give redmost (Qy) electronic absorption band(s) at longer wavelengths than those of the corresponding monomeric chlorin composites. The other zinc chlorin and bacteriochlorin homo-dyads completely formed similar folded conformers in the same solution, while zinc inverse chlorin and porphyrin homo-dyads partially took such supramolecules. The J-type aggregation to folded conformers and the redshift values of composite Qy bands were dependent on the electronic and steric factors of porphyrinoid moieties in dyads.

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Section: Resultssupporting

confidence: 87%

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin, Chlorin, and Bacteriochlorin π‐Systems

Tamiaki

Fukai

Shimazu

et al. 2013

Photochem & Photobiology

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“…5), which is similar to models proposed earlier (46,47,49), is characterized as follows. (i) The equivalence of the two halves of the dimer is assured by adopting a model with C2 symmetry.…”

mentioning

confidence: 93%

Structural studies of the primary donor cation radical P ₈₇₀ ^+· in reaction centers of Rhodospirillum rubrum by electron-nuclear double resonance in solution

Lubitz

Lendzian

Scheer

et al. 1984

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

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The light-induced cation radical of the primary electron donor, Ps70, in photosynthetic reaction centers from Rhodospirillum rubrum G-9, has been investigated by electron-nuclear double resonance (ENDOR) in liquid aqueous solution. The measured hyperfine coupling constants are assigned to specific molecular positions by partial deuteration.Comparison with the bacteriochlorophyll a cation radical shows different reduction factors of the individual coupling constants deviating from the value 2.0 reported in earlier investigations in frozen solutions. The average of the coupling constants is, however, reduced by a factor very close to 2.0. EPR simulations using the ENDOR coupling constants support a dimer model for PsO with C2 symmetry, where the two macrocycles are close enough to form a supermolecular orbital resulting in a different distribution of the unpaired electron, compared with the monomeric bacteriochlorophyll a cation radical. Molecular orbital calculations were used to obtain structural information about this dimer.In bacterial photosynthesis, the light-induced charge separation starts with the fast donation of an electron from an excited singlet primary donor P to an electron-transport chain in the reaction center protein (RC) (1-5). RCs offer a convenient system for the investigation of the cation and anion radicals formed in this process. Much of our present knowledge about the various species and their interactions in RCs has evolved from the application of paramagnetic resonance methods (3, 6). The dimeric nature of the primary donor cation radical P8t,0 in some bacteria was originally proposed by Norris et al. (7) to explain the observed narrowing of the EPR line by a reduction factor (RF) of \/2 compared with the monomeric bacteriochlorophyll a cation radical (BChl-a+ ) (Fig. 1). Further support for this model came from electron-nuclear double resonance (ENDOR) at low temperatures in which a reduction of the hyperfine coupling constants (hfcs) by a factor of two was deduced when going from BChl-a+ to P8+70 (8)(9)(10)(11)(12)(13)(14). The detailed structure of the suggested dimer is still controversial (3,4,14), but its geometry is of prime importance for basic understanding of the primary act of light-induced charge separation in photosynthesis.ENDOR in solution has been used to elucidate the electronic structure of the various isolated pigment radicals and has provided an almost complete set of isotropic hfcs (15)(16)(17)(18)(19)(20). Liquid-state ENDOR is superior to frozen-solution EN-DOR (10, 21, 22) because the linewidths are smaller due to the absence of anisotropic broadening so that hfcs from all magnetic nuclei in the radical can often be obtained (23,24). However, most of the ENDOR studies of photosynthesis thus far were carried out in frozen matrices (8)(9)(10)(11)(12)(13)). An EN-DOR in solution study on RC [Rhodopseudomonas (Rp.) sphaeriodes R-26] in water at room temperature has been reported only recently (25). In those experiments, the additional application of electron...

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“…A nearly perpendicular orientation of the BChl planes for the B2 with Dr. Tiede's present address is Chemistry Division D-200, Argonne National Laboratory, Argonne, Ill 60439. respect to the membrane surface is shown by the fact that a plane formed by both the optical Qx, Qy (12)(13)(14)(15) and spin-polarized triplet magnetic X, Y axes is found to be tilted at 10-20o from the membrane normal (16,17). A well-supported model suggests that the B2 is composed of a staggered pair of parallel BChl molecules, overlapping along the Y (pyrrole ring I-III) direction (18)(19)(20). The linear dichroism of oriented membranes has shown that the B2 Qy transition lies nearly parallel to the membrane plane (12)(13)(14)(15).…”

Section: Introductionmentioning

confidence: 99%

Geometry for the Primary Electron Donor and the Bacteriopheophytin Acceptor in Rhodopseudomonas viridis Photosynthetic Reaction Centers

Tiede¹,

Choquet²,

Breton³

1985

Biophysical Journal

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The tetrapyrrole electron donors and acceptors (bacteriochlorophyll, BCh; bacteriopheophytin, BPh) within the bacterial photosynthetic reaction center (RC) are arranged with a specific geometry that permits rapid (picosecond time scale) electron tunneling to occur between them. Here we have measured the angle between the molecular planes of the bacteriochlorophyll dimer (primary donor), B(2), and the acceptor bacteriopheophytin, H, by analyzing the dichroism of the absorption change associated with H reduction, formed by photoselection with RCs of Rhodopseudomonas viridis. This angle between molecular planes is found to be 60 degrees +/- 2. This means that the ultrafast electron tunneling must occur between donors and acceptors that are fixed by the protein to have a noncoplanar alignment. Nearly perpendicular alignments have been determined for other electron tunneling complexes involving RCs. These geometries can be contrasted with models proposed for heme-heme electron transfer complexes, which have emphasized that mutually parallel orientations should permit the most kinetically facile transfers.

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A synthetic biomimetic model of special pair bacteriochlorophyll a

Cited by 51 publications

References 2 publications

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin, Chlorin, and Bacteriochlorin π‐Systems

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin, Chlorin, and Bacteriochlorin π‐Systems

Structural studies of the primary donor cation radical P ₈₇₀ ^+· in reaction centers of Rhodospirillum rubrum by electron-nuclear double resonance in solution

Geometry for the Primary Electron Donor and the Bacteriopheophytin Acceptor in Rhodopseudomonas viridis Photosynthetic Reaction Centers

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A synthetic biomimetic model of special pair bacteriochlorophyll a

Cited by 51 publications

References 2 publications

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin, Chlorin, and Bacteriochlorin π‐Systems

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin, Chlorin, and Bacteriochlorin π‐Systems

Structural studies of the primary donor cation radical P 870 +· in reaction centers of Rhodospirillum rubrum by electron-nuclear double resonance in solution

Geometry for the Primary Electron Donor and the Bacteriopheophytin Acceptor in Rhodopseudomonas viridis Photosynthetic Reaction Centers

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Structural studies of the primary donor cation radical P ₈₇₀ ^+· in reaction centers of Rhodospirillum rubrum by electron-nuclear double resonance in solution