A Cytochrome c Oxidase Model Catalyzes Oxygen to Water Reduction Under Rate-Limiting Electron Flux

Collman, James P.; Devaraj, Neal K.; Decréau, Richard A.; Yang, Ying; Yan, Yi‐Long; Ebina, Wataru; Eberspacher, Todd A.; Chidsey, Christopher E. D.

doi:10.1126/science.1135844

Cited by 502 publications

(530 citation statements)

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“…The selectivity is significantly better with the FeCuPhOH catalyst, which shows only 6 Ϯ 1% PROS (Table 1), i.e., 94% selectivity. This is consistent with previous results obtained from RRDE (32). The PROS formed by using the FeFe (Fig.…”

Section: Resultssupporting

confidence: 93%

“…In the past, we have reported several functional synthetic model complexes of CcO (32,39). These functional FeCu CcO models provided insights into important issues such as reversible inhibition by NO and CN Ϫ poisoning (43).…”

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confidence: 99%

“…In this technique, a ring (Pt or Au) is held at a potential where it specifically oxidizes/reduces the product/byproduct of the electrocatalytic reaction occurring on the Au disc electrode it encircles. A common application has been detection of partially reduced oxygen species (PROS) like superoxide (O 2 Ϫ ) or hydrogen peroxide (H 2 O 2 ) leaked during electrocatalytic reduction of O 2 (32,(37)(38)(39). However, this technique has limited collection efficiencies (CE, i.e., percentage of the PROS generated being detected on the ring).…”

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confidence: 99%

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O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

Collman

Dey

Yang

et al. 2009

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

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O2 reactivity of a functional NOR model is investigated by using electrochemistry and spectroscopy. The electrochemical measurements using interdigitated electrodes show very high selectivity for 4e O2 reduction with minimal production of partially reduced oxygen species (PROS) under both fast and slow electron flux. Intermediates trapped at cryogenic temperatures and characterized by using resonance Raman spectroscopy under single-turnover conditions indicate that an initial bridging peroxide intermediate undergoes homolytic OOO bond cleavage generating a trans heme/nonheme bis-ferryl intermediate. This bis ferryl species can oxygenate 2 equivalents of a reactive substrate.C ytochrome c oxidase (CcO) and nitric oxide reductase (NOR) belong to the heme copper oxidase superfamily of enzymes (1, 2). CcO is the terminal enzyme in the respiratory chain of higher organisms, located in their mitochondrial membrane, that reduces O 2 to H 2 O as source of energy. The O 2 reduction process in CcO generates a pH gradient across the bilayer membrane, which provides the driving force for ATP synthesis. The bimetallic active site of CcO has a heme ligated to the protein by a proximal histidine ligand and a distal Cu B site coordinated by 3 histidine ligands ( Fig. 1) (3). In addition to the bimetallic site, there is a conserved tyrosine ligand covalently attached to one of the histidines coordinated to Cu B (4, 5). The NORs are the older member of the family and are found in bacteria using NO 3 Ϫ as source of energy instead of O 2 (2, 6, 7). Although there are no high-resolution crystal structures of NOR, biochemical studies and computer modeling indicate that these enzymes have a histidine-ligated heme, quite like the CcOs, and a distal Fe B , unlike Cu B in CcO, coordinated by 3 histidines ( Fig. 1) (8-10). NORs do not have the conserved tyrosine residue of CcO but have a few conserved key glutamate residues (11,12). Although the NOR enzymes are proposed to have specific proton channels, they are probably not involved in generating proton gradients (13-16).These 2 enzymes exhibit complementary reactivity toward 2 very significant diatomic molecules in nature; O 2 and NO. In eukaryotes CcO (aa 3 type) reduces O 2 to H 2 O and is reversibly but strongly inhibited by [17][18][19][20]. Several other CcOs (ba 3 , caa 3 , cbb 3 ) are reported to exhibit limited (Ͻ1%) NOR activity, i.e., reduce NO to N 2 O (7, 21). On the other hand, NORs that reduce NO to N 2 O are reversibly but strongly inhibited by O 2 , and some of them show modest (Ϸ10%) O 2 reduction activity (12). The parallels in their reactivities toward O 2 and NO and similarities in their secondary structures have led to a hypotheses regarding NOR's and CcO's similar evolutionary origins (6,22).Electrochemistry is a very powerful technique that can provide fundamental insights into reaction mechanisms of redox catalysts (23-27). Conventionally, a catalyst is deposited on a conducting electrode material (e.g., graphite); however, this approach does not allow site isola...

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Section: Resultssupporting

confidence: 93%

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confidence: 99%

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confidence: 99%

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O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

Collman

Dey

Yang

et al. 2009

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

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“…29 Additionally, enhanced reactivity of some porphyrin electrocatalysts is observed when the second coordination site is empty or replaced with an appropriate Lewis acidic metal ion. 17,[30][31][32] …”

Section: Oxygen Reduction By Cobalt Pacman Complexesmentioning

confidence: 99%

Role of Proton‐Coupled Electron Transfer in O—O Bond Activation

Rosenthal

Nocera

2007

ChemInform

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The selective reduction of oxygen to water requires four electrons and four protons. The design of catalysts that promote oxygen reduction therefore requires the management of both electron and proton inventories. Pacman and Hangman porphyrins provide a cleft for oxygen binding, a redox shuttle for oxygen reduction, and functionality for tuning the acid-base properties of bound oxygen and its intermediates. With proper control of the proton-coupled electron transfer events, O-O bond breaking of oxygen, and more generally oxygenated substrates, may be achieved with high efficiencies. The rule set developed for oxygen reduction may be applied to a variety of other small molecule activation reactions of consequence to energy conversion.

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“…Furthermore, the use of platinum-based electrocatalysts in direct methanol fuel cells is blocked by the methanol crossover effect. To date, extensive efforts have been devoted to overcome these problems by using Pt-based alloys, [184][185][186][187][188][189] non-noble metals, [190][191][192][193] and enzymes 194,195 to replace Pt-based electrocatalysts. Nitrogen-doped graphene has also been reported to have high electrocatalytic activities and durability, because of its atom-thick 2D structure and high conductivity.…”

Section: Catalystsmentioning

confidence: 99%

Graphene/polymer composites for energy applications

Sun

Shi

2012

J Polym Sci B Polym Phys

236

120

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Graphene has wide potential applications in energyrelated systems, mainly because of its unique atom-thick twodimensional structure, high electrical or thermal conductivity, optical transparency, great mechanical strength, inherent flexibility, and huge specific surface area. For this purpose, graphene materials are frequently blended with polymers to form composites, especially when fabricating flexible devices. Graphene/polymer composites have been explored as electrodes of supercapacitors or lithium ion batteries, counter electrodes of dye-sensitized solar cells, transparent conducting electrodes and active layers of organic solar cells, catalytic electrodes, and polymer electrolyte membranes of fuel cells. In this review, we summarize the recent advances on the synthesis and applications of graphene/polymer composites for energy applications. The challenges and prospects in this field have also been discussed. V C 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 231-253 KEYWORDS: composites; energy; fuel cell; graphene; lithium ion battery; redox polymers; solar cell; supercapacitor; synthesis INTRODUCTION Energy is one of the most important recent topics of concern to human society. To replace conventional fossil fuels, clean and renewable energies based on sunlight, wind, new chemicals, and biofuels are urgently demanded. Therefore, materials that can directly convert or store renewable energies are being extensively studied. Among them, graphene has recently attracted a great deal of attention because of its unique atom-thick two-dimensional (2D) structure 1,2 and excellent electrical, 2 thermal, 3 optical, and mechanical properties. 4,5 Graphene is a promising material for applications in various energy-related systems such as supercapacitors, 6-9 secondary batteries, 10-14 solar cells, 15-17 and fuel cells. [18][19][20] For this purpose, graphene materials are frequently blended with polymers to form functional composites. [21][22][23] The polymer component can improve the processability and/or flexibility of graphene materials, and also possibly provide them with new functions. To date, various graphene composites with insulating or conducting polymers (CPs) have been prepared through noncovalent 22 or covalent approaches. 24 They have also been applied as electrodes for supercapacitors and lithium ion batteries (LIBs), 25-29 counter electrodes of dye-sensitized solar cells (DSSCs), 15,30,31 and transparent conducting electrodes (TCEs) 32,33 or active layers of organic solar cells, 34 catalytic electrodes, and polymer electrolyte membranes of fuel cells. [35][36][37] This review focuses on summarizing the recent advances in the synthesis of graphene/polymer composites and their energy applications.

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A Cytochrome c Oxidase Model Catalyzes Oxygen to Water Reduction Under Rate-Limiting Electron Flux

Cited by 502 publications

References 41 publications

O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

Role of Proton‐Coupled Electron Transfer in O—O Bond Activation

Graphene/polymer composites for energy applications

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A Cytochrome c Oxidase Model Catalyzes Oxygen to Water Reduction Under Rate-Limiting Electron Flux

Cited by 502 publications

References 41 publications

O 2 reduction by a functional heme/nonheme bis-iron NOR model complex

O 2 reduction by a functional heme/nonheme bis-iron NOR model complex

Role of Proton‐Coupled Electron Transfer in O—O Bond Activation

Graphene/polymer composites for energy applications

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O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex