Coupled electron transfers in artificial photosynthesis

Hammarström, Leif; Styring, Stenbjörn

doi:10.1098/rstb.2007.2225

Cited by 66 publications

(59 citation statements)

References 47 publications

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“…For instance, the light–harvesting [Ru(bpy) 3 ] 2+ moiety was used as the replacement for P680; Mn complexes, such as a Mn(II,II) dimer (Figure 4(c)), were incorporated in the assemblies to mimic the OEC (Abrahamsson et al, 2002; Lomoth et al, 2006). Light induced accumulative electron transfer from the Mn(II,II) dimer to the photooxidized Ru center resulted in the formation of a Mn(III,IV) complex (Hammarström and Styring, 2008; Huang et al, 2002). The researchers also introduced a tyrosine link between the Ru center and the Mn dimer.…”

Section: Artificial Photosynthesismentioning

confidence: 99%

Energy Conversion in Natural and Artificial Photosynthesis

McConnell

Brudvig

2010

Chemistry & Biology

391

311

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Summary Modern civilization is dependent upon fossil fuels, a nonrenewable energy source originally provided by the storage of solar energy. Fossil fuel dependence has severe consequences including energy security issues and greenhouse gas emissions. The consequences of fossil fuel dependence could be avoided by fuel-producing artificial systems that mimic natural photosynthesis, directly converting solar energy to fuel. This review describes the three key components of solar energy conversion in photosynthesis: light harvesting, charge separation, and catalysis. These processes are compared in natural and artificial systems. Such a comparison can assist in understanding the general principles of photosynthesis and in developing working devices including photoelectrochemical cells for solar energy conversion.

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Section: Artificial Photosynthesismentioning

confidence: 99%

Energy Conversion in Natural and Artificial Photosynthesis

McConnell

Brudvig

2010

Chemistry & Biology

391

311

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“…Phenols were used as EPT donors in these experiments because of their enhanced acidities upon oxidation. For tyrosine, pK a decreases from 10 to −2 in the radical cation (33).…”

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confidence: 95%

Direct observation of light-driven, concerted electron–proton transfer

Gagliardi

Wang

Dongare

et al. 2016

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

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The phenols 4-methylphenol, 4-methoxyphenol, and N-acetyl-tyrosine form hydrogen-bonded adducts with N-methyl-4, 4′-bipyridinium cation (MQ+) in aqueous solution as evidenced by the appearance of low-energy, low-absorptivity features in UV-visible spectra. They are assigned to the known examples of optically induced, concerted electron–proton transfer, photoEPT. The results of ultrafast transient absorption measurements on the assembly MeOPhO-H---MQ+ are consistent with concerted EPT by the instantaneous appearance of spectral features for MeOPhO·---H-MQ+ in the transient spectra at the first observation time of 0.1 ps. The transient decays to MeOPhO-H---MQ+ in 2.5 ps, accompanied by the appearance of oscillations in the decay traces with a period of ∼1 ps, consistent with a vibrational coherence and relaxation from a higher υ(N-H) vibrational level or levels on the timescale for back EPT.

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“…Efficient catalysis of transformations of energy consequence (7-13) mandates the coupling of electron transfer (ET) to proton transfer (PT) in proton-coupled electron transfer (PCET) reactions (14)(15)(16)(17)(18)(19)(20). In the absence of PCET, intermediates possessing equilibrium potentials that are prohibitively large depreciate the storage capacity offered by the solarto-fuels conversion process.…”

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confidence: 99%

Role of pendant proton relays and proton-coupled electron transfer on the hydrogen evolution reaction by nickel hangman porphyrins

Bediako

Solis

Dogutan

et al. 2014

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

181

204

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The hangman motif provides mechanistic insights into the role of pendant proton relays in governing proton-coupled electron transfer (PCET) involved in the hydrogen evolution reaction (HER). We now show improved HER activity of Ni compared with Co hangman porphyrins. Cyclic voltammogram data and simulations, together with computational studies using density functional theory, implicate a shift in electrokinetic zone between Co and Ni hangman porphyrins due to a change in the PCET mechanism. Unlike the Co hangman porphyrin, the Ni hangman porphyrin does not require reduction to the formally metal(0) species before protonation by weak acids in acetonitrile. We conclude that protonation likely occurs at the Ni(I) state followed by reduction, in a stepwise proton transfer-electron transfer pathway. Spectroelectrochemical and computational studies reveal that upon reduction of the Ni(II) compound, the first electron is transferred to a metal-based orbital, whereas the second electron is transferred to a molecular orbital on the porphyrin ring.renewable | solar fuels | electrocatalysis S olar-to-fuels conversions provide a path to harnessing the ubiquitous albeit intermittent renewable energy resource offered by the sun (1-6). Efficient catalysis of transformations of energy consequence (7-13) mandates the coupling of electron transfer (ET) to proton transfer (PT) in proton-coupled electron transfer (PCET) reactions (14)(15)(16)(17)(18)(19)(20). In the absence of PCET, intermediates possessing equilibrium potentials that are prohibitively large depreciate the storage capacity offered by the solarto-fuels conversion process. The coupling of protons to changes in electron equivalency offers the possibility of restricting the equilibrium potentials of the redox steps to a more narrow potential range, thereby minimizing the overpotential required to sustain catalysis at a desired turnover rate. Thus, the exploitation of PCET pathways to permit potential-leveling effects is a crucial prerequisite for the efficient catalytic conversion reactions of energy relevant molecules.PCET reactions may be classified into stepwise and concerted pathways (14,16,20,21). Stepwise PCET may involve ET first followed by PT (ETPT), or PT followed by ET (PTET). In concerted proton-electron transfers (CPET), the proton and electron traverse a common transition state. Whereas concerted pathways avoid the formation of thermodynamically costly intermediates, CPET reactions may incur kinetic penalties associated with the requirements for proton tunneling (19,20,22). The competition between these dynamics during catalysis determines the most efficient route of reaction. Studies that explore the interplay between these factors are crucial to designing catalytic reactions of high efficiency. Along these lines, the incorporation of proton relays in the second coordination sphere of molecular catalysts has emerged as a useful tool in optimizing PCET transformations (23-29). We have focused on the synthesis and mechanistic investigation of a class of me...

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Coupled electron transfers in artificial photosynthesis

Cited by 66 publications

References 47 publications

Energy Conversion in Natural and Artificial Photosynthesis

Energy Conversion in Natural and Artificial Photosynthesis

Direct observation of light-driven, concerted electron–proton transfer

Role of pendant proton relays and proton-coupled electron transfer on the hydrogen evolution reaction by nickel hangman porphyrins

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