The mechanism for proton–coupled electron transfer from tyrosine in a model complex and comparisons with Y
            Z
            oxidation in photosystem II

In the water–oxidizing reactions of photosystem II (PSII), a tyrosine residue plays a key part as an intermediate electron–transfer reactant between the primary donor chlorophylls (the pigment P 680 ) and the water–oxidizing Mn cluster. The tyrosine is deprotonated upon oxidation, and the coupling between the proton reaction and electron transfer is of great mechanistic importance for the understanding of the water–oxidation mechanism. Within a programme on artificial photosynthesis, we have made and studied the proton–coupled tyrosine oxidation in a model system and been able to draw mechanistic conclusions that we use to interpret the analogous reactions in PSII.

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Design and synthesis of benzimidazole phenol-porphyrin dyads for the study of bioinspired photoinduced proton-coupled electron transfer

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424619501189 ◽

2019 ◽

Vol 23 (11n12) ◽

pp. 1336-1345

Author(s):

S. Jimena Mora ◽

Daniel A. Heredia ◽

Emmanuel Odella ◽

Uma Vrudhula ◽

Devens Gust ◽

...

Keyword(s):

Electron Transfer ◽

Excited State ◽

Photosystem Ii ◽

Proton Transfer ◽

Water Oxidation ◽

Oxidation Catalyst ◽

Design And Synthesis ◽

Proton Coupled Electron Transfer ◽

Anchoring Groups ◽

High Redox Potential

Benzimidazole phenol-porphyrin dyads have been synthesized to study proton-coupled electron transfer (PCET) reactions induced by photoexcitation. High-potential porphyrins have been chosen to model P680, the photoactive chlorophyll cluster of photosynthetic photosystem II (PSII). They have either two or three pentafluorophenyl groups at the meso positions to impart the high redox potential. The benzimidazole phenol (BIP) moiety models the Tyr[Formula: see text]-His190 pair of PSII, which is a redox mediator that shuttles electrons from the water oxidation catalyst to P680[Formula: see text]. The dyads consisting of a porphyrin and an unsubstituted BIP are designed to study one-electron one-proton transfer (E1PT) processes upon excitation of the porphyrin. When the BIP moiety is substituted with proton-accepting groups such as imines, one-electron two-proton transfer (E2PT) processes are expected to take place upon oxidation of the phenol by the excited state of the porphyrin. The bis-pentafluorophenyl porphyrins linked to BIPs provide platforms for introducing a variety of electron-accepting moieties and/or anchoring groups to attach semiconductor nanoparticles to the macrocycle. The triads thus formed will serve to study the PCET process involving the BIPs when the oxidation of the phenol is achieved by the photochemically produced radical cation of the porphyrin.

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Faculty Opinions recommendation of The possible role of proton-coupled electron transfer (PCET) in water oxidation by photosystem II.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1098463.554539 ◽

2007 ◽

Author(s):

Vincent Pecoraro

Keyword(s):

Electron Transfer ◽

Photosystem Ii ◽

Water Oxidation ◽

Proton Coupled Electron Transfer

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Proton-Coupled Electron Transfer in a Model for Tyrosine Oxidation in Photosystem II

Journal of the American Chemical Society ◽

10.1021/ja803574n ◽

2008 ◽

Vol 130 (25) ◽

pp. 8108-8108 ◽

Cited By ~ 1

Author(s):

Claudio Carra ◽

Nedialka Iordanova ◽

Sharon Hammes-Schiffer

Keyword(s):

Electron Transfer ◽

Photosystem Ii ◽

Proton Coupled Electron Transfer ◽

Tyrosine Oxidation

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Energetics of Proton-Coupled Electron Transfer in High-Valent Mn2(μ-O)2Systems: Models for Water Oxidation by the Oxygen-Evolving Complex of Photosystem II

Journal of the American Chemical Society ◽

10.1021/ja9626906 ◽

1996 ◽

Vol 118 (45) ◽

pp. 11325-11326 ◽

Cited By ~ 84

Author(s):

Michael J. Baldwin ◽

Vincent L. Pecoraro

Keyword(s):

Electron Transfer ◽

Photosystem Ii ◽

Water Oxidation ◽

Oxygen Evolving Complex ◽

Proton Coupled Electron Transfer ◽

High Valent ◽

Oxygen Evolving

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Electrostatics and proton transfer in photosynthetic water oxidation

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2002.1137 ◽

2002 ◽

Vol 357 (1426) ◽

pp. 1407-1418 ◽

Cited By ~ 93

Author(s):

Wolfgang Junge ◽

Michael Haumann ◽

Ralf Ahlbrink ◽

Armen Mulkidjanian ◽

Jürgen Clausen

Keyword(s):

Electron Transfer ◽

Proton Transfer ◽

Water Oxidation ◽

Bound Water ◽

Bohr Effect ◽

Primary Donor ◽

Mn Cluster ◽

Electron Proton Transfer ◽

Photosynthetic Water Oxidation ◽

Hydrogen Bonded

Photosystem II (PSII) oxidizes two water molecules to yield dioxygen plus four protons. Dioxygen is released during the last out of four sequential oxidation steps of the catalytic centre (S 0 ⇒ S 1 , S 1 ⇒ S 2 , S 2 ⇒ S 3 , S 3 ⇒ S 4 → S 0 ). The release of the chemically produced protons is blurred by transient, highly variable and electrostatically triggered proton transfer at the periphery (Bohr effect). The extent of the latter transiently amounts to more than one H + /e – under certain conditions and this is understood in terms of electrostatics. By kinetic analyses of electron–proton transfer and electrochromism, we discriminated between Bohr–effect and chemically produced protons and arrived at a distribution of the latter over the oxidation steps of 1 : 0 : 1 : 2. During the oxidation of tyr–161 on subunit D1 (Y Z ), its phenolic proton is not normally released into the bulk. Instead, it is shared with and confined in a hydrogen–bonded cluster. This notion is difficult to reconcile with proposed mechanisms where Y Z acts as a hydrogen acceptor for bound water. Only in manganese (Mn) depleted PSII is the proton released into the bulk and this changes the rate of electron transfer between Y Z and the primary donor of PSII P + 680 from electron to proton controlled. D1–His190, the proposed centre of the hydrogen–bonded cluster around Y Z , is probably further remote from Y Z than previously thought, because substitution of D1–Glu189, its direct neighbour, by Gln, Arg or Lys is without effect on the electron transfer from Y Z to P + 680 (in nanoseconds) and from the Mn cluster to Y ox Z .

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