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Cheng MH, Way R, Fresa K, Catandi GD, Carnevale E, Chicco AJ, Chen TW. IMSIS: An instrumented microphysiological system with integrated sensors for monitoring cellular metabolic activities. Biosens Bioelectron 2024; 263:116595. [PMID: 39098284 DOI: 10.1016/j.bios.2024.116595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2024] [Revised: 07/02/2024] [Accepted: 07/18/2024] [Indexed: 08/06/2024]
Abstract
Well plates are widely used in biological experiments, particularly in pharmaceutical sciences and cell biology. Its popularity stems from its versatility to support a variety of fluorescent markers for high throughput monitoring of cellular activities. However, using fluorescent markers in traditional well plates has its own challenges, namely, they can be potentially toxic to cells, and thus, may perturb their biological functions; and it is difficult to monitor multiple analytes concurrently and in real-time inside each well. This paper presents a fully instrumented microphysiological system with integrated sensors (IMSIS) with a similar well format. Each well in the microphysiological system has a set of sensors for monitoring multiple metabolic analytes in real-time. The IMSIS platform is supported by integrated bioelectronic circuits and a graphical user interface for easy user configuration and monitoring. The system has integrated microfluidics to maintain its microphysiological environment within each well. The IMSIS platform currently incorporates O2, H2O2, and pH sensors inside each well, allowing up to six wells to perform concurrent measurements in real-time. Furthermore, the architecture is scalable to achieve an even higher level of throughput. The miniaturized design ensures portability, suitable for small offices and field applications. The IMSIS platform was successfully used to monitor in real-time the mitochondrial functions of live bovine embryos in O2 consumption, H2O2 release as an indication of ROS production, and extracellular acidity changes before and after the introduction of external substrates.
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Affiliation(s)
- Ming-Hao Cheng
- Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, CO, USA
| | - Ryan Way
- Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, CO, USA
| | - Kyle Fresa
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
| | - Giovana D Catandi
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
| | - Elaine Carnevale
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
| | - Adam J Chicco
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
| | - Thomas W Chen
- Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, CO, USA; School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA.
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2
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Gibbs CA, Ghazi N, Tao J, Warren JJ. An Investigation of the Influence of Tyrosine Local Interactions on Electron Hopping in a Model Protein. Molecules 2024; 29:350. [PMID: 38257263 PMCID: PMC10818705 DOI: 10.3390/molecules29020350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 01/04/2024] [Accepted: 01/05/2024] [Indexed: 01/24/2024] Open
Abstract
Multi-step electron transfer reactions are important to the function of many cellular systems. The ways in which such systems have evolved to direct electrons along specific pathways are largely understood, but less so are the ways in which the reduction-oxidation potentials of individual redox sites are controlled. We prepared a series of three new artificial variants of Pseudomonas aeruginosa azurin where a tyrosine (Tyr109) is situated between the native Cu ion and a Ru(II) photosensitizer tethered to a histidine (His107). Arginine, glutamine, or methionine were introduced as position 122, which is near to Tyr109. We investigated the rate of CuI oxidation by a flash-quench generated Ru(III) oxidant over pH values from 5 to 9. While the identity of the residue at position 122 affects some of the physical properties of Tyr109, the rates of CuI oxidation are only weakly dependent on the identity of the residue at 122. The results highlight that more work is still needed to understand how non-covalent interactions of redox active groups are affected in redox proteins.
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Affiliation(s)
| | | | | | - Jeffrey J. Warren
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
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3
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McGuinness KN, Fehon N, Feehan R, Miller M, Mutter AC, Rybak LA, Nam J, AbuSalim JE, Atkinson JT, Heidari H, Losada N, Kim JD, Koder RL, Lu Y, Silberg JJ, Slusky JSG, Falkowski PG, Nanda V. The energetics and evolution of oxidoreductases in deep time. Proteins 2024; 92:52-59. [PMID: 37596815 DOI: 10.1002/prot.26563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 07/06/2023] [Indexed: 08/20/2023]
Abstract
The core metabolic reactions of life drive electrons through a class of redox protein enzymes, the oxidoreductases. The energetics of electron flow is determined by the redox potentials of organic and inorganic cofactors as tuned by the protein environment. Understanding how protein structure affects oxidation-reduction energetics is crucial for studying metabolism, creating bioelectronic systems, and tracing the history of biological energy utilization on Earth. We constructed ProtReDox (https://protein-redox-potential.web.app), a manually curated database of experimentally determined redox potentials. With over 500 measurements, we can begin to identify how proteins modulate oxidation-reduction energetics across the tree of life. By mapping redox potentials onto networks of oxidoreductase fold evolution, we can infer the evolution of electron transfer energetics over deep time. ProtReDox is designed to include user-contributed submissions with the intention of making it a valuable resource for researchers in this field.
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Affiliation(s)
- Kenneth N McGuinness
- Department of Natural Sciences, Caldwell University, Caldwell, New Jersey, USA
- Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey, USA
| | - Nolan Fehon
- Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, USA
| | - Ryan Feehan
- Computational Biology Program, The University of Kansas, Lawrence, Kansas, USA
| | - Michelle Miller
- Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, USA
| | - Andrew C Mutter
- Department of Physics, The City College of New York, New York, New York, USA
| | - Laryssa A Rybak
- Department of Physics, The City College of New York, New York, New York, USA
| | - Justin Nam
- Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey, USA
| | - Jenna E AbuSalim
- Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey, USA
| | - Joshua T Atkinson
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas, USA
| | - Hirbod Heidari
- Department of Chemistry, University of Texas at Austin, Austin, Texas, USA
| | - Natalie Losada
- Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey, USA
| | - J Dongun Kim
- Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, USA
| | - Ronald L Koder
- Department of Physics, The City College of New York, New York, New York, USA
| | - Yi Lu
- Department of Chemistry, University of Texas at Austin, Austin, Texas, USA
| | - Jonathan J Silberg
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas, USA
| | - Joanna S G Slusky
- Computational Biology Program, The University of Kansas, Lawrence, Kansas, USA
- Department of Molecular Biosciences, The University of Kansas, Lawrence, Kansas, USA
| | - Paul G Falkowski
- Environmental Biophysics and Molecular Ecology Program, Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, USA
- Department of Earth and Planetary Sciences, Rutgers University, New Brunswick, New Jersey, USA
| | - Vikas Nanda
- Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey, USA
- Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, New Jersey, USA
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Mitchell KE, Wenner BA, Lee C, Park T, Socha MT, Kleinschmit DH, Firkins JL. Supplementing branched-chain volatile fatty acids in dual-flow cultures varying in dietary forage and corn oil concentrations. I: Digestibility, microbial protein, and prokaryotic community structure. J Dairy Sci 2023; 106:7530-7547. [PMID: 37532627 DOI: 10.3168/jds.2022-23165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2022] [Accepted: 03/17/2023] [Indexed: 08/04/2023]
Abstract
Branched-chain amino acids are deaminated by amylolytic bacteria to branched-chain volatile fatty acids (BCVFA), which are growth factors for cellulolytic bacteria. Our objective was to determine the dietary conditions that would increase the uptake of BCVFA by rumen bacteria. We hypothesized that increased forage would increase cellulolytic bacterial abundance and incorporation of BCVFA into their structure. Supplemental polyunsaturated fatty acids, supplied via corn oil (CO), should inhibit cellulolytic bacteria growth, but we hypothesized that additional BCVFA would alleviate that inhibition. Further, supplemental BCVFA should increase neutral detergent fiber degradation and efficiency of bacterial protein synthesis more with the high forage and low polyunsaturated fatty acid dietary combination. The study was an incomplete block design with 8 dual-flow continuous cultures used in 4 periods with 8 treatments (n = 4 per treatment) arranged as a 2 × 2 × 2 factorial. The factors were: high forage (HF) or low forage (LF; 67 or 33%), without or with supplemental CO (3% dry matter), and without or with 2.15 mmol/d (which included 5 mg/d of 13C each of BCVFA isovalerate, isobutyrate, and 2-methylbutyrate). The isonitrogenous diets consisted of 33:67 alfalfa:orchardgrass pellet, and was replaced with a concentrate pellet that mainly consisted of ground corn, soybean meal, and soybean hulls for the LF diet. The main effect of supplementing BCVFA increased neutral detergent fiber (NDF) degradability by 7.6%, and CO increased NDF degradability only in LF diets. Supplemental BCVFA increased bacterial N by 1.5 g/kg organic matter truly degraded (6.6%) and 0.05 g/g truly degraded N (6.5%). The relative sequence abundance decreased with LF for Fibrobacter succinogenes, Ruminococcus flavefaciens, and genus Butyrivibrio compared with HF. Recovery of the total 13C dose in bacterial pellets decreased from 144 µg/ mg with HF to 98.9 µg/ mg with LF. Although isotope recovery in bacteria was greater with HF, BCVFA supplementation increased NDF degradability and efficiency of microbial protein synthesis under all dietary conditions. Therefore, supplemental BCVFA has potential to improve feed efficiency in dairy cows even with dietary conditions that might otherwise inhibit cellulolytic bacteria.
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Affiliation(s)
| | - B A Wenner
- Elanco Animal Health, Greenfield, IN 46140
| | - C Lee
- Department of Animal Sciences, The Ohio State University, Wooster, OH 44691
| | - T Park
- Department of Animal Science and Technology, Chung-Ang University, Anseong, Gyeonggi-do, Korea 17546
| | - M T Socha
- Zinpro Corporation, Eden Prairie, MN 55344
| | | | - J L Firkins
- Department of Animal Sciences, The Ohio State University, Columbus, OH 43035
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Rietmann SJ, Gäbel G, Dengler F. The intraruminal redox potential is stabilised by opposing influences during fermentation. J Anim Physiol Anim Nutr (Berl) 2023; 107:53-61. [PMID: 35238079 PMCID: PMC10078661 DOI: 10.1111/jpn.13697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2021] [Revised: 12/09/2021] [Accepted: 02/04/2022] [Indexed: 01/10/2023]
Abstract
An optimal fermentation process in the forestomach is pivotal for the wellbeing and performance of ruminants. Complex carbohydrates are broken down into short-chain fatty acids (SCFA) which form the major energy source for the animal. A strong interrelationship of this process with intraruminal pH and redox potential (Eh) exists. These parameters can be measured with intraruminal sensors, but the interpretation of the measurements, especially of Eh, and their meaning for intraruminal homeostasis is not completely clear. In this study, factors influencing intraruminal Eh were elucidated. We hypothesised that intraruminal Eh is influenced by the fermentation process as such, but not by its end products SCFA. We measured Eh and pH in ruminal fluid from fasting cannulated sheep after the addition of 0.06 m Na-acetate, -propionate, -butyrate or glucose in vitro. Furthermore, we assessed the interrelation of pH and Eh. Basal Eh and pH values were -120 ± 41 mV and 7.0 ± 0.3, respectively, in native ruminal fluid in vitro. While the addition of SCFA did not induce any changes, glucose addition caused a significant decrease in both pH and Eh compared to the values before the addition (paired Student's t-test, p < 0.05). We attribute the decrease in Eh to an increased production of H2 in the process of generating SCFA, predominantly acetate. By titrating both native and particle-free ruminal fluid to more acidic and basic pH values (4.5-8.5), we found a non-linear inverse correlation of pH and Eh, counteracting the H2 -driven decrease of Eh during fermentation. Thus, the intraruminal Eh is influenced by pH and H2 output during SCFA formation. The opposed character of these factors stabilises the intraruminal homeostasis which might help maintain symbiotic microbiota in the rumen. Understanding, monitoring, and supporting this system will be an essential part of modern cattle production.
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Affiliation(s)
- Stefan J Rietmann
- Institute of Veterinary Physiology, University of Leipzig, Leipzig, Germany
| | - Gotthold Gäbel
- Institute of Veterinary Physiology, University of Leipzig, Leipzig, Germany
| | - Franziska Dengler
- Institute of Veterinary Physiology, University of Leipzig, Leipzig, Germany.,Unit of Physiology, Pathophysiology and Experimental Endocrinology, Department of Biomedical Sciences, University of Veterinary Medicine Vienna, Vienna, Austria
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Nilsen-Moe A, Rosichini A, Glover SD, Hammarström L. Concerted and Stepwise Proton-Coupled Electron Transfer for Tryptophan-Derivative Oxidation with Water as the Primary Proton Acceptor: Clarifying a Controversy. J Am Chem Soc 2022; 144:7308-7319. [PMID: 35416654 PMCID: PMC9052761 DOI: 10.1021/jacs.2c00371] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Concerted electron-proton transfer (CEPT) reactions avoid charged intermediates and may be energetically favorable for redox and radical-transfer reactions in natural and synthetic systems. Tryptophan (W) often partakes in radical-transfer chains in nature but has been proposed to only undergo sequential electron transfer followed by proton transfer when water is the primary proton acceptor. Nevertheless, our group has shown that oxidation of freely solvated tyrosine and W often exhibit weakly pH-dependent proton-coupled electron transfer (PCET) rate constants with moderate kinetic isotope effects (KIE ≈ 2-5), which could be associated with a CEPT mechanism. These results and conclusions have been questioned. Here, we present PCET rate constants for W derivatives with oxidized Ru- and Zn-porphyrin photosensitizers, extracted from laser flash-quench studies. Alternative quenching/photo-oxidation methods were used to avoid complications of previous studies, and both the amine and carboxylic acid groups of W were protected to make the indole the only deprotonable group. With a suitably tuned oxidant strength, we found an ET-limited reaction at pH < 4 and weakly pH-dependent rates at pH > ∼5 that are intrinsic to the PCET of the indole group with water (H2O) as the proton acceptor. The observed rate constants are up to more than 100 times higher than those measured for initial electron transfer, excluding the electron-first mechanism. Instead, the reaction can be attributed to CEPT. These conclusions are important for our view of CEPT in water and of PCET-mediated radical reactions with solvent-exposed tryptophan in natural systems.
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Affiliation(s)
- Astrid Nilsen-Moe
- Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden
| | - Andrea Rosichini
- Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden
| | - Starla D Glover
- Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden
| | - Leif Hammarström
- Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden
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7
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Abstract
The pathway of activationless proton transfer induced by an electron-transfer reaction is studied theoretically. Long-range electron transfer produces highly nonequilibrium medium polarization that can drive proton transfer through an activationless transition during the process of thermalization, dynamically altering the screening of the electron-proton Coulomb interaction by the medium. The cross electron-proton reorganization energy is the main energy parameter of the theory, which exceeds in magnitude the proton-transfer reorganization energy roughly by the ratio of the electron-transfer to proton-transfer distance. This parameter, which can be either positive or negative, is related to the difference in pKa values in two electron-transfer states. The relaxation time of the medium is on the (sub)picosecond time scale, which establishes the characteristic time for activationless proton transfer. Microscopic calculations predict substantial retardation of the collective relaxation dynamics compared to the continuum estimates due to the phenomenology analogous to de Gennes narrowing. Nonequilibrium medium configuration promoting proton transfer can be induced by either thermal or photoinduced charge transfer.
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Affiliation(s)
- Dmitry V Matyushov
- School of Molecular Sciences and Department of Physics, Arizona State University, P.O. Box 871504, Tempe, Arizona 85287-1504, United States
| | - Marshall D Newton
- Chemistry Department, Brookhaven National Laboratory, P.O. Box 5000, Upton, New York 11973-5000, United States
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Al-Zahrani S, Astudillo-Calderón S, Pintos B, Pérez-Urria E, Manzanera JA, Martín L, Gomez-Garay A. Role of Synthetic Plant Extracts on the Production of Silver-Derived Nanoparticles. PLANTS (BASEL, SWITZERLAND) 2021; 10:1671. [PMID: 34451715 PMCID: PMC8400420 DOI: 10.3390/plants10081671] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 08/05/2021] [Accepted: 08/11/2021] [Indexed: 02/04/2023]
Abstract
The main antioxidants present in plant extracts-quercetin, β-carotene, gallic acid, ascorbic acid, hydroxybenzoic acid, caffeic acid, catechin and scopoletin-are able to synthesize silver nanoparticles when reacting with a Ag NO3 solution. The UV-visible absorption spectrum recorded with most of the antioxidants shows the characteristic surface plasmon resonance band of silver nanoparticles. Nanoparticles synthesised with ascorbic, hydroxybenzoic, caffeic, and gallic acids and scopoletin are spherical. Nanoparticles synthesised with quercetin are grouped together to form micellar structures. Nanoparticles synthesised by β-carotene, were triangular and polyhedral forms with truncated corners. Pentagonal nanoparticles were synthesized with catechin. We used Fourier-transform infrared spectroscopy to check that the biomolecules coat the synthesised silver nanoparticles. X-ray powder diffractograms showed the presence of silver, AgO, Ag2O, Ag3O4 and Ag2O3. Rod-like structures were obtained with quercetin and gallic acid and cookie-like structures in the nanoparticles obtained with scopoletin, as a consequence of their reactivity with cyanide. This analysis explained the role played by the various agents responsible for the bio-reduction triggered by nanoparticle synthesis in their shape, size and activity. This will facilitate targeted synthesis and the application of biotechnological techniques to optimise the green synthesis of nanoparticles.
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Affiliation(s)
- Sabah Al-Zahrani
- Research Group FiVe-A, Plant Physiology Unit, Faculty of Biology, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain; (S.A.-Z.); (S.A.-C.); (B.P.); (E.P.-U.); (L.M.)
| | - Sergio Astudillo-Calderón
- Research Group FiVe-A, Plant Physiology Unit, Faculty of Biology, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain; (S.A.-Z.); (S.A.-C.); (B.P.); (E.P.-U.); (L.M.)
| | - Beatriz Pintos
- Research Group FiVe-A, Plant Physiology Unit, Faculty of Biology, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain; (S.A.-Z.); (S.A.-C.); (B.P.); (E.P.-U.); (L.M.)
| | - Elena Pérez-Urria
- Research Group FiVe-A, Plant Physiology Unit, Faculty of Biology, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain; (S.A.-Z.); (S.A.-C.); (B.P.); (E.P.-U.); (L.M.)
| | - José Antonio Manzanera
- Research Group FiVe-A, College of Forestry and Natural Environment, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040 Madrid, Spain;
| | - Luisa Martín
- Research Group FiVe-A, Plant Physiology Unit, Faculty of Biology, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain; (S.A.-Z.); (S.A.-C.); (B.P.); (E.P.-U.); (L.M.)
| | - Arancha Gomez-Garay
- Research Group FiVe-A, Plant Physiology Unit, Faculty of Biology, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain; (S.A.-Z.); (S.A.-C.); (B.P.); (E.P.-U.); (L.M.)
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Roman-Garcia Y, Mitchell KE, Denton BL, Lee C, Socha MT, Wenner BA, Firkins JL. Conditions stimulating neutral detergent fiber degradation by dosing branched-chain volatile fatty acids. II: Relation with solid passage rate and pH on neutral detergent fiber degradation and microbial function in continuous culture. J Dairy Sci 2021; 104:9853-9867. [PMID: 34147227 DOI: 10.3168/jds.2021-20335] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 05/02/2021] [Indexed: 11/19/2022]
Abstract
To support improving genetic potential for increased milk production, intake of digestible carbohydrate must also increase to provide digestible energy and microbial protein synthesis. We hypothesized that the provision of exogenous branched-chain volatile fatty acids (BCVFA) would improve both neutral detergent fiber (NDF) degradability and efficiency of microbial protein synthesis. However, BCVFA should be more beneficial with increasing efficiency of bacterial protein synthesis associated with increasing passage rate (kp). We also hypothesized that decreasing pH would increase the need for isobutyrate over 2-methylbutyrate. To study these effects independent from other sources of variation in vivo, we evaluated continuous cultures without (control) versus with BCVFA (0 vs. 2 mmol/d each of isobutyrate, isovalerate, and 2-methylbutyrate), low versus high kp of the particulate phase (2.5 vs. 5.0%/h), and high versus low pH (ranging from 6.3 to 6.8 diurnally vs. 5.7 to 6.2) in a 2 × 2 × 2 factorial arrangement of treatments. Diets were 50% forage pellets and 50% grain pellets administered twice daily. Without an interaction, NDF degradability tended to increase from 29.7 to 35.0% for main effects of control compared with BCVFA treatments. Provision of BCVFA increased methanogenesis, presumably resulting from improved NDF degradability. Decreasing pH decreased methane production. Total volatile fatty acid (VFA) and acetate production were decreased with increasing kp, even though true organic matter degradability and bacterial nitrogen flow were not affected by treatments. Decreasing pH decreased acetate but increased propionate and valerate production, probably resulting from a shift in bacterial taxa and associated VFA stoichiometry. Decreasing pH decreased isobutyrate and isovalerate production while increasing 2-methylbutyrate production on a net basis (subtracting doses). Supplementing BCVFA improved NDF degradability in continuous cultures administered moderate (15.4%) crude protein diets (excluding urea in buffer) without major interactions with culture pH and kp.
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Affiliation(s)
- Y Roman-Garcia
- Department of Animal Sciences, The Ohio State University, Columbus 43210
| | - K E Mitchell
- Department of Animal Sciences, The Ohio State University, Columbus 43210
| | - B L Denton
- Department of Animal Sciences, The Ohio State University, Columbus 43210
| | - C Lee
- Ohio Agricultural Research and Development Center, Wooster 44691
| | - M T Socha
- Zinpro Corporation, Eden Prairie, MN 55344
| | - B A Wenner
- Department of Animal Sciences, The Ohio State University, Columbus 43210
| | - J L Firkins
- Department of Animal Sciences, The Ohio State University, Columbus 43210.
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10
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Noodleman L, Han Du WG, McRee D, Chen Y, Goh T, Götz AW. Coupled transport of electrons and protons in a bacterial cytochrome c oxidase-DFT calculated properties compared to structures and spectroscopies. Phys Chem Chem Phys 2021; 22:26652-26668. [PMID: 33231596 DOI: 10.1039/d0cp04848h] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
After a general introduction to the features and mechanisms of cytochrome c oxidases (CcOs) in mitochondria and aerobic bacteria, we present DFT calculated physical and spectroscopic properties for the catalytic reaction cycle compared with experimental observations in bacterial ba3 type CcO, also with comparisons/contrasts to aa3 type CcOs. The Dinuclear Complex (DNC) is the active catalytic reaction center, containing a heme a3 Fe center and a near lying Cu center (called CuB) where by successive reduction and protonation, molecular O2 is transformed to two H2O molecules, and protons are pumped from an inner region across the membrane to an outer region by transit through the CcO integral membrane protein. Structures, energies and vibrational frequencies for Fe-O and O-O modes are calculated by DFT over the catalytic cycle. The calculated DFT frequencies in the DNC of CcO are compared with measured frequencies from Resonance Raman spectroscopy to clarify the composition, geometry, and electronic structures of different intermediates through the reaction cycle, and to trace reaction pathways. X-ray structures of the resting oxidized state are analyzed with reference to the known experimental reaction chemistry and using DFT calculated structures in fitting observed electron density maps. Our calculations lead to a new proposed reaction pathway for coupling the PR → F → OH (ferryl-oxo → ferric-hydroxo) pathway to proton pumping by a water shift mechanism. Through this arc of the catalytic cycle, major shifts in pKa's of the special tyrosine and a histidine near the upper water pool activate proton transfer. Additional mechanisms for proton pumping are explored, and the role of the CuB+ (cuprous state) in controlling access to the dinuclear reaction site is proposed.
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Affiliation(s)
- Louis Noodleman
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
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11
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Sjödin M, Hjelm J, Rutherford AW, Forster R. Reprint of "Proton-coupled electron transfer from an interfacial phenol monolayer". J Electroanal Chem (Lausanne) 2020. [DOI: 10.1016/j.jelechem.2020.114760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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12
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Melin F, Hellwig P. Redox Properties of the Membrane Proteins from the Respiratory Chain. Chem Rev 2020; 120:10244-10297. [DOI: 10.1021/acs.chemrev.0c00249] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Frederic Melin
- Chimie de la Matière Complexe UMR 7140, Laboratoire de Bioelectrochimie et Spectroscopie, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67070 Strasbourg, France
| | - Petra Hellwig
- Chimie de la Matière Complexe UMR 7140, Laboratoire de Bioelectrochimie et Spectroscopie, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67070 Strasbourg, France
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13
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Sjödin M, Hjelm J, Rutherford AW, Forster R. Proton-coupled electron transfer from an interfacial phenol monolayer. J Electroanal Chem (Lausanne) 2020. [DOI: 10.1016/j.jelechem.2020.113856] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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14
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Janssen RH, Canelli G, Sanders MG, Bakx EJ, Lakemond CMM, Fogliano V, Vincken JP. Iron-polyphenol complexes cause blackening upon grinding Hermetia illucens (black soldier fly) larvae. Sci Rep 2019; 9:2967. [PMID: 30814530 PMCID: PMC6393531 DOI: 10.1038/s41598-019-38923-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 12/20/2018] [Indexed: 02/02/2023] Open
Abstract
Insects are a promising alternative protein source. One of the bottlenecks in applying insects in food is the fast darkening initiated during grinding. Besides enzymatic browning, non-enzymatic factors can cause off-colour formation, which differs between species. This study investigates the impact of iron, phenoloxidase, and polyphenols on off-colour formation in insect larvae. Hermetia illucens showed a blackish colour, whereas Tenebrio molitor turned brown and Alphitobius diaperinus remained the lightest. This off-colour formation appeared correlated with the iron content in the larvae, which was 61 ± 9.71, 54 ± 1.72 and 221 ± 6.07 mg/kg dw for T. molitor, A. diaperinus and H. illucens, respectively. In model systems, the formation of iron-L-3,4-dihydroxyphenylalanine (L-DOPA) bis- and tris-complexes were evidenced by direct injection into ESI-TOF-MS, based on their charges combined with iron isotope patterns. The reversibility of the binding of iron to phenolics, and thereby loss of blackening, was confirmed by EDTA addition. Besides complex formation, oxidation of L-DOPA by redox reactions with iron occurred mainly at low pH, whereas auto-oxidation of L-DOPA mainly occurred at pH 10. Tyrosinase (i.e. phenoloxidase) activity did not change complex formation. The similarity in off-colour formation between the model system and insects indicated an important role for iron-phenolic complexation in blackening.
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Affiliation(s)
- Renske H Janssen
- Food Quality and Design, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands
- Laboratory of Food Chemistry, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands
| | - Greta Canelli
- Laboratory of Food Chemistry, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands
| | - Mark G Sanders
- Laboratory of Food Chemistry, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands
| | - Edwin J Bakx
- Laboratory of Food Chemistry, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands
| | - Catriona M M Lakemond
- Food Quality and Design, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands
| | - Vincenzo Fogliano
- Food Quality and Design, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands
| | - Jean-Paul Vincken
- Laboratory of Food Chemistry, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands.
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15
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Saxena M, Loza-Rosas SA, Gaur K, Sharma S, Pérez Otero SC, Tinoco AD. Exploring titanium(IV) chemical proximity to iron(III) to elucidate a function for Ti(IV) in the human body. Coord Chem Rev 2018; 363:109-125. [PMID: 30270932 PMCID: PMC6159949 DOI: 10.1016/j.ccr.2018.03.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Despite its natural abundance and widespread use as food, paint additive, and in bone implants, no specific biological function of titanium is known in the human body. High concentrations of Ti(IV) could result in cellular toxicity, however, the absence of Ti toxicity in the blood of patients with titanium bone implants indicates the presence of one or more biological mechanisms to mitigate toxicity. Similar to Fe(III), Ti(IV) in blood binds to the iron transport protein serum transferrin (sTf), which gives credence to the possibility of its cellular uptake mechanism by transferrin-directed endocytosis. However, once inside the cell, how sTf bound Ti(IV) is released into the cytoplasm, utilized, or stored remain largely unknown. To explain the molecular mechanisms involved in Ti use in cells we have drawn parallels with those for Fe(III). Based on its chemical similarities with Fe(III), we compare the biological coordination chemistry of Fe(III) and Ti(IV) and hypothesize that Ti(IV) can bind to similar intracellular biomolecules. The comparable ligand affinity profiles suggest that at high Ti(IV) concentrations, Ti(IV) could compete with Fe(III) to bind to biomolecules and would inhibit Fe bioavailability. At the typical Ti concentrations in the body, Ti might exist as a labile pool of Ti(IV) in cells, similar to Fe. Ti could exhibit different types of properties that would determine its cellular functions. We predict some of these functions to mimic those of Fe in the cell and others to be specific to Ti. Bone and cellular speciation and localization studies hint toward various intracellular targets of Ti like phosphoproteins, DNA, ribonucleotide reductase, and ferritin. However, to decipher the exact mechanisms of how Ti might mediate these roles, development of innovative and more sensitive methods are required to track this difficult to trace metal in vivo.
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Affiliation(s)
- Manoj Saxena
- Department of Chemistry, University of Puerto Rico Río Piedras, San Juan, PR 00931
| | - Sergio A. Loza-Rosas
- Department of Chemistry, University of Puerto Rico Río Piedras, San Juan, PR 00931
| | - Kavita Gaur
- Department of Chemistry, University of Puerto Rico Río Piedras, San Juan, PR 00931
| | - Shweta Sharma
- Department of Environmental Sciences, University of Puerto Rico Río Piedras, San Juan, PR 00931
| | - Sofia C. Pérez Otero
- Department of Chemistry, University of Puerto Rico Río Piedras, San Juan, PR 00931
| | - Arthur D. Tinoco
- Department of Chemistry, University of Puerto Rico Río Piedras, San Juan, PR 00931
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16
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Glover SD, Tyburski R, Liang L, Tommos C, Hammarström L. Pourbaix Diagram, Proton-Coupled Electron Transfer, and Decay Kinetics of a Protein Tryptophan Radical: Comparing the Redox Properties of W 32• and Y 32• Generated Inside the Structurally Characterized α 3W and α 3Y Proteins. J Am Chem Soc 2017; 140:185-192. [PMID: 29190082 DOI: 10.1021/jacs.7b08032] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Protein-based "hole" hopping typically involves spatially arranged redox-active tryptophan or tyrosine residues. Thermodynamic information is scarce for this type of process. The well-structured α3W model protein was studied by protein film square wave voltammetry and transient absorption spectroscopy to obtain a comprehensive thermodynamic and kinetic description of a buried tryptophan residue. A Pourbaix diagram, correlating thermodynamic potentials (E°') with pH, is reported for W32 in α3W and compared to equivalent data recently presented for Y32 in α3Y ( Ravichandran , K. R. ; Zong , A. B. ; Taguchi , A. T. ; Nocera , D. G. ; Stubbe , J. ; Tommos , C. J. Am. Chem. Soc. 2017 , 139 , 2994 - 3004 ). The α3W Pourbaix diagram displays a pKOX of 3.4, a E°'(W32(N•+/NH)) of 1293 mV, and a E°'(W32(N•/NH); pH 7.0) of 1095 ± 4 mV versus the normal hydrogen electrode. W32(N•/NH) is 109 ± 4 mV more oxidizing than Y32(O•/OH) at pH 5.4-10. In the voltammetry measurements, W32 oxidation-reduction occurs on a time scale of about 4 ms and is coupled to the release and subsequent uptake of one full proton to and from bulk. Kinetic analysis further shows that W32 oxidation likely involves pre-equilibrium electron transfer followed by proton transfer to a water or small water cluster as the primary acceptor. A well-resolved absorption spectrum of W32• is presented, and analysis of decay kinetics show that W32• persists ∼104 times longer than aqueous W• due to significant stabilization by the protein. The redox characteristics of W32 and Y32 are discussed relative to global and local protein properties.
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Affiliation(s)
- Starla D Glover
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania 19104, United States.,Department of Chemistry, Ångström Laboratory, Uppsala University , Box 523, SE-75120 Uppsala, Sweden
| | - Robin Tyburski
- Department of Chemistry, Ångström Laboratory, Uppsala University , Box 523, SE-75120 Uppsala, Sweden
| | - Li Liang
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania 19104, United States
| | - Cecilia Tommos
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine , Philadelphia, Pennsylvania 19104, United States
| | - Leif Hammarström
- Department of Chemistry, Ångström Laboratory, Uppsala University , Box 523, SE-75120 Uppsala, Sweden
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17
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Friedman N, Shriker E, Gold B, Durman T, Zarecki R, Ruppin E, Mizrahi I. Diet-induced changes of redox potential underlie compositional shifts in the rumen archaeal community. Environ Microbiol 2016; 19:174-184. [PMID: 27696646 DOI: 10.1111/1462-2920.13551] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 09/26/2016] [Indexed: 11/30/2022]
Abstract
Dietary changes are known to affect gut community structure, but questions remain about the mechanisms by which diet induces shifts in microbiome membership. Here, we addressed these questions in the rumen microbiome ecosystem - a complex microbial community that resides in the upper digestive tract of ruminant animals and is responsible for the degradation of the ingested plant material. Our dietary intervention experiments revealed that diet affects the most abundant taxa within the microbiome and that a specific group of methanogenic archaea of the order Methanomicrobiales is highly sensitive to its changes. Using metabolomic analyses together with in vitro microbiology approaches and whole-genome sequencing of Methanomicrobium mobile, a key species within this group, we identified that redox potential changes with diet and is the main factor that causes these dietary induced alternations in this taxa's abundance. Our genomic analysis suggests that the redox potential effect stems from a reduced number of anti-reactive oxygen species proteins coded in this taxon's genome. Our study highlights redox potential as a pivotal factor that could serve as a sculpturing force of community assembly within anaerobic gut microbial communities.
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Affiliation(s)
- Nir Friedman
- The Department of Life Sciences & the National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel.,Department of Ruminant Science, Institute of Animal Sciences, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel.,The Porter School of Environmental Studies, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Eran Shriker
- The Department of Life Sciences & the National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel.,Department of Ruminant Science, Institute of Animal Sciences, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel.,The Porter School of Environmental Studies, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Ben Gold
- The Department of Life Sciences & the National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel
| | - Thomer Durman
- The Department of Life Sciences & the National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel
| | - Raphy Zarecki
- Center for Bioinformatics and Computational Biology & Department of Computer Science, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Eytan Ruppin
- The Sackler School of Medicine, Tel Aviv University, Tel Aviv, 69978, Israel.,Blavatnik School of Computer Sciences, Tel Aviv University, Tel Aviv, 69978, Israel.,Department of Computer Science and Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD, 20742, USA
| | - Itzhak Mizrahi
- The Department of Life Sciences & the National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel
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18
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Dongare P, Maji S, Hammarström L. Direct Evidence of a Tryptophan Analogue Radical Formed in a Concerted Electron−Proton Transfer Reaction in Water. J Am Chem Soc 2016; 138:2194-9. [DOI: 10.1021/jacs.5b08294] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Prateek Dongare
- Department of Chemistry,
Ångström Laboratory, Uppsala University, Box 523, Uppsala SE-751 20, Sweden
| | - Somnath Maji
- Department of Chemistry,
Ångström Laboratory, Uppsala University, Box 523, Uppsala SE-751 20, Sweden
| | - Leif Hammarström
- Department of Chemistry,
Ångström Laboratory, Uppsala University, Box 523, Uppsala SE-751 20, Sweden
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19
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Warren JJ, Shafaat OS, Winkler JR, Gray HB. Proton-coupled electron hopping in Ru-modified P. aeruginosa azurin. J Biol Inorg Chem 2016; 21:113-9. [PMID: 26790882 DOI: 10.1007/s00775-016-1332-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 01/04/2016] [Indexed: 10/22/2022]
Abstract
We constructed two artificial multiple-step electron transfer (hopping) systems based on Pseudomonas aeruginosa azurin where a tyrosine (YOH) is situated between Ru(2,2'-bipyridine)2(imidazole)(histidine) and the native copper site: RuH107YOH109 and RuH124-YOH122. We investigated the rates of Cu(I) oxidation by flash-quench generated Ru(III) over a range of conditions that probed the role of proton-coupled oxidation/reduction of YOH in the reaction. Rates of Cu(I) oxidation were enhanced over single-step electron transfer by factors between 3 and 80, depending on specific scaffold and buffer conditions.
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Affiliation(s)
- Jeffrey J Warren
- Beckman Institute, California Institute of Technology, Pasadena, CA, 91125, USA. .,Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
| | - Oliver S Shafaat
- Beckman Institute, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Jay R Winkler
- Beckman Institute, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Harry B Gray
- Beckman Institute, California Institute of Technology, Pasadena, CA, 91125, USA.
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20
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Bonin J, Costentin C, Robert M, Routier M, Savéant JM. Proton-Coupled Electron Transfers: pH-Dependent Driving Forces? Fundamentals and Artifacts. J Am Chem Soc 2013; 135:14359-66. [DOI: 10.1021/ja406712c] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Julien Bonin
- Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d’Electrochimie
Moléculaire, Unité Mixte de Recherche Université
- CNRS no. 7591, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
| | - Cyrille Costentin
- Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d’Electrochimie
Moléculaire, Unité Mixte de Recherche Université
- CNRS no. 7591, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
| | - Marc Robert
- Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d’Electrochimie
Moléculaire, Unité Mixte de Recherche Université
- CNRS no. 7591, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
| | - Mathilde Routier
- Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d’Electrochimie
Moléculaire, Unité Mixte de Recherche Université
- CNRS no. 7591, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
| | - Jean-Michel Savéant
- Université Paris Diderot, Sorbonne Paris Cité, Laboratoire d’Electrochimie
Moléculaire, Unité Mixte de Recherche Université
- CNRS no. 7591, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
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21
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Gunner MR, Amin M, Zhu X, Lu J. Molecular mechanisms for generating transmembrane proton gradients. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1827:892-913. [PMID: 23507617 PMCID: PMC3714358 DOI: 10.1016/j.bbabio.2013.03.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Revised: 01/28/2013] [Accepted: 03/01/2013] [Indexed: 01/02/2023]
Abstract
Membrane proteins use the energy of light or high energy substrates to build a transmembrane proton gradient through a series of reactions leading to proton release into the lower pH compartment (P-side) and proton uptake from the higher pH compartment (N-side). This review considers how the proton affinity of the substrates, cofactors and amino acids are modified in four proteins to drive proton transfers. Bacterial reaction centers (RCs) and photosystem II (PSII) carry out redox chemistry with the species to be oxidized on the P-side while reduction occurs on the N-side of the membrane. Terminal redox cofactors are used which have pKas that are strongly dependent on their redox state, so that protons are lost on oxidation and gained on reduction. Bacteriorhodopsin is a true proton pump. Light activation triggers trans to cis isomerization of a bound retinal. Strong electrostatic interactions within clusters of amino acids are modified by the conformational changes initiated by retinal motion leading to changes in proton affinity, driving transmembrane proton transfer. Cytochrome c oxidase (CcO) catalyzes the reduction of O2 to water. The protons needed for chemistry are bound from the N-side. The reduction chemistry also drives proton pumping from N- to P-side. Overall, in CcO the uptake of 4 electrons to reduce O2 transports 8 charges across the membrane, with each reduction fully coupled to removal of two protons from the N-side, the delivery of one for chemistry and transport of the other to the P-side.
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Affiliation(s)
- M R Gunner
- Department of Physics, City College of New York, New York, NY 10031, USA.
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22
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Irebo T, Zhang MT, Markle TF, Scott AM, Hammarström L. Spanning four mechanistic regions of intramolecular proton-coupled electron transfer in a Ru(bpy)3(2+)-tyrosine complex. J Am Chem Soc 2012; 134:16247-54. [PMID: 22909089 DOI: 10.1021/ja3053859] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Proton-coupled electron transfer (PCET) from tyrosine (TyrOH) to a covalently linked [Ru(bpy)(3)](2+) photosensitizer in aqueous media has been systematically reinvestigated by laser flash-quench kinetics as a model system for PCET in radical enzymes and in photochemical energy conversion. Previous kinetic studies on Ru-TyrOH molecules (Sjödin et al. J. Am. Chem. Soc. 2000, 122, 3932; Irebo et al. J. Am. Chem. Soc. 2007, 129, 15462) have established two mechanisms. Concerted electron-proton (CEP) transfer has been observed when pH < pK(a)(TyrOH), which is pH-dependent but not first-order in [OH(-)] and not dependent on the buffer concentration when it is sufficiently low (less than ca. 5 mM). In addition, the pH-independent rate constant for electron transfer from tyrosine phenolate (TyrO(-)) was reported at pH >10. Here we compare the PCET rates and kinetic isotope effects (k(H)/k(D)) of four Ru-TyrOH molecules with varying Ru(III/II) oxidant strengths over a pH range of 1-12.5. On the basis of these data, two additional mechanistic regimes were observed and identified through analysis of kinetic competition and kinetic isotope effects (KIE): (i) a mechanism dominating at low pH assigned to a stepwise electron-first PCET and (ii) a stepwise proton-first PCET with OH(-) as proton acceptor that dominates around pH = 10. The effect of solution pH and electrochemical potential of the Ru(III/II) oxidant on the competition between the different mechanisms is discussed. The systems investigated may serve as models for the mechanistic diversity of PCET reactions in general with water (H(2)O, OH(-)) as primary proton acceptor.
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Affiliation(s)
- Tania Irebo
- Photochemistry and Molecular Science, Department of Chemistry, Ångström Laboratory, Uppsala University, Box 532, SE-751 20 Uppsala, Sweden
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23
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Warren JJ, Winkler JR, Gray HB. Redox properties of tyrosine and related molecules. FEBS Lett 2012; 586:596-602. [PMID: 22210190 PMCID: PMC3298607 DOI: 10.1016/j.febslet.2011.12.014] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Revised: 12/04/2011] [Accepted: 12/12/2011] [Indexed: 11/25/2022]
Abstract
Redox reactions of tyrosine play key roles in many biological processes, including water oxidation and DNA synthesis. We first review the redox properties of tyrosine (and other phenols) in small molecules and related polypeptides, then report work on (H20)/(Y48)-modified Pseudomonas aeruginosa azurin. The crystal structure of this protein (1.18Å resolution) shows that H20 is strongly hydrogen bonded to Y48 (2.7-2.8Å tyrosine-O to histidine-N distance). A firm conclusion is that proper tuning of the tyrosine potential by a proton-accepting base is critical for biological redox functions.
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Affiliation(s)
- Jeffrey J. Warren
- Beckman Institute, California Institute of Technology, Pasadena, CA 91125
| | - Jay R. Winkler
- Beckman Institute, California Institute of Technology, Pasadena, CA 91125
| | - Harry B. Gray
- Beckman Institute, California Institute of Technology, Pasadena, CA 91125
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24
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Costentin C, Robert M, Savéant JM. Update 1 of: Electrochemical Approach to the Mechanistic Study of Proton-Coupled Electron Transfer. Chem Rev 2010; 110:PR1-40. [DOI: 10.1021/cr100038y] [Citation(s) in RCA: 142] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Cyrille Costentin
- Laboratoire d’Electrochimie Moléculaire, Unité Mixte de Recherche Université, CNRS No. 7591, Université Paris Diderot, 15 rue Jean de Baïf, 75013 Paris, France
- This is a Chemical Reviews Perennial Review. The root paper of this title was published in Chem. Rev. 2008, 108 (7), 2145−2179, DOI: 10.1021/cr068065t; Published (Web) July 11, 2008. Updates to the text appear in red type
| | - Marc Robert
- Laboratoire d’Electrochimie Moléculaire, Unité Mixte de Recherche Université, CNRS No. 7591, Université Paris Diderot, 15 rue Jean de Baïf, 75013 Paris, France
- This is a Chemical Reviews Perennial Review. The root paper of this title was published in Chem. Rev. 2008, 108 (7), 2145−2179, DOI: 10.1021/cr068065t; Published (Web) July 11, 2008. Updates to the text appear in red type
| | - Jean-Michel Savéant
- Laboratoire d’Electrochimie Moléculaire, Unité Mixte de Recherche Université, CNRS No. 7591, Université Paris Diderot, 15 rue Jean de Baïf, 75013 Paris, France
- This is a Chemical Reviews Perennial Review. The root paper of this title was published in Chem. Rev. 2008, 108 (7), 2145−2179, DOI: 10.1021/cr068065t; Published (Web) July 11, 2008. Updates to the text appear in red type
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25
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Affiliation(s)
- Jillian L. Dempsey
- Beckman Institute, California Institute of Technology, Pasadena, CA 91125
| | - Jay R. Winkler
- Beckman Institute, California Institute of Technology, Pasadena, CA 91125
| | - Harry B. Gray
- Beckman Institute, California Institute of Technology, Pasadena, CA 91125
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26
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Snir O, Wang Y, Tuckerman ME, Geletii YV, Weinstock IA. Concerted Proton−Electron Transfer to Dioxygen in Water. J Am Chem Soc 2010; 132:11678-91. [DOI: 10.1021/ja104392k] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Ophir Snir
- Department of Chemistry, Ben Gurion University of the Negev, Beer Sheva 84105, Israel, Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, New York, New York 10003
| | - Yifeng Wang
- Department of Chemistry, Ben Gurion University of the Negev, Beer Sheva 84105, Israel, Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, New York, New York 10003
| | - Mark E. Tuckerman
- Department of Chemistry, Ben Gurion University of the Negev, Beer Sheva 84105, Israel, Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, New York, New York 10003
| | - Yurii V. Geletii
- Department of Chemistry, Ben Gurion University of the Negev, Beer Sheva 84105, Israel, Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, New York, New York 10003
| | - Ira A. Weinstock
- Department of Chemistry, Ben Gurion University of the Negev, Beer Sheva 84105, Israel, Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry and Courant Institute of Mathematical Sciences, New York University, New York, New York 10003
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27
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Costentin C, Robert M, Savéant JM. Concerted proton-electron transfers: electrochemical and related approaches. Acc Chem Res 2010; 43:1019-29. [PMID: 20232879 DOI: 10.1021/ar9002812] [Citation(s) in RCA: 190] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Proton-coupled electron transfers (PCETs) are omnipresent in natural and artificial chemical processes. Given the contemporary challenges associated with energy conversion, pollution abatement, and the development of high-performance sensors, a greater understanding of the mechanisms that underlie the practical efficiency of PCETs is a timely research topic. In contrast to hydrogen-atom transfers, proton and electron transfers involve different centers in PCET reactions. The reaction may go through an electron- or proton-transfer intermediate, giving rise to the electron-proton transfer (EPT) and the proton-electron transfer (PET) pathways. When the proton and electron transfers are concerted (the CPET pathway), the high-energy intermediates of the stepwise pathways are bypassed, although this thermodynamic benefit may have a kinetic cost. The primary task of kinetics-based mechanism analysis is therefore to distinguish the three pathways, quantifying the factors that govern the competition between them, which requires modeling of CPET reactivity. CPET models of varying sophistication have appeared, but the large number of parameters involved and the uncertainty of the quantum chemical calculations they may have to resort to make experimental confrontation and inspiration a necessary component of model testing and refinement. Electrochemical PCETs are worthy of particular attention, if only because most applications in which PCET mechanisms are operative involve collection or injection of electricity through electrodes. More fundamentally, changing the electrode potential is an easy and continuous means of varying the driving force of the reaction, whereas the current flowing through the electrode is a straightforward measure of its rate. Consequently, the current-potential response in nondestructive techniques (such as cyclic voltammetry) can be read as an activation-driving force relationship, provided the contribution of diffusion has been taken into account. Intrinsic properties (properties at zero driving force) are consequently a natural outcome of the electrochemical approach. In this Account, we begin by examining the modeling of CPET reactions and then describe illustrating experimental examples inspired by two biological systems, photosystem II and superoxide dismutase. One series of studies examined the oxidation of phenols with, as proton acceptor, either an attached nitrogen base or water (in water as solvent). Another addressed interconversion of aquo-hydroxo-oxo couples of transition metal complexes, using osmium complexes as prototypes. Finally, the reduction of superoxide ion, which is closely related to its dismutation, allowed the observation and rationalization of the remarkable properties of water as a proton donor. Water is also an exceptional proton acceptor in the oxidation of phenols, requiring very small reorganization energies, both in the electrochemical and homogeneous cases. These varied examples reveal general features of PCET reactions that may serve as guidelines for future studies, suggesting that research emphasis might be profitably directed toward new biological systems on the one hand and on the role of hydrogen bonding and hydrogen-bonded environments (such as water or proteins) on the other.
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Affiliation(s)
- Cyrille Costentin
- Laboratoire d’Electrochimie Moléculaire, Unité Mixte de Recherche Université - CNRS No 7591, Université Paris Diderot, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
| | - Marc Robert
- Laboratoire d’Electrochimie Moléculaire, Unité Mixte de Recherche Université - CNRS No 7591, Université Paris Diderot, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
| | - Jean-Michel Savéant
- Laboratoire d’Electrochimie Moléculaire, Unité Mixte de Recherche Université - CNRS No 7591, Université Paris Diderot, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
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Costentin C, Robert M, Savéant JM. Concerted proton-electron transfers in the oxidation of phenols. Phys Chem Chem Phys 2010; 12:11179-90. [PMID: 20625575 DOI: 10.1039/c0cp00063a] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The oxidation of phenols is an emblematic example where the mechanisms of proton-coupled electron transfers could be investigated in depth thanks to non-destructive electrochemical techniques such as cyclic voltammetry. A concerted proton-electron transfer could then be shown to be the prevailing pathway in the oxidation of amino-phenols mimicking the tyrosine-histidine couple in Photosystem II. The theoretical model developed on this occasion leads to the introduction of two main parameters characterizing reorganization of heavy atoms in the reactant and in the solvent on the one hand and proton tunneling on the other. When water used as the solvent is at the same time the proton acceptor, the concerted pathway also predominates. It is characterized by a remarkably large standard rate constant both in electrochemistry and in the oxidation by homogenous reactants. Another aspect of the importance of H-bonding in concerted proton-electron transfer is provided by H-bond relays that efficiently mediate the electron transfer-triggered transport of protons between two sites over large distances thanks to the displacement of two protons concerted with electron transfer. Intermediary protonation of the relay is avoided by fine tuning of its H-bond acceptor and donor properties.
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Affiliation(s)
- Cyrille Costentin
- Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université-CNRS No 7591, Université Paris Diderot, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France
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Intrinsic reactivity and driving force dependence in concerted proton-electron transfers to water illustrated by phenol oxidation. Proc Natl Acad Sci U S A 2010; 107:3367-72. [PMID: 20139306 DOI: 10.1073/pnas.0914693107] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Three experimental techniques, laser flash photolysis, redox catalysis, and stopped-flow, were used to investigate the variation of the oxidation rate constant of phenol in neat water with the driving force offered by a series of electron acceptors. Taking into account a result previously obtained with a low-driving force electron acceptor thus allowed scanning more than half an electron-volt driving force range. Variation of the rate constant with pH showed the transition between a direct phenol oxidation reaction at low pH, where the rate constant does not vary with pH, and a stepwise reaction involving the prior deprotonation of phenol by OH(-), characterized by a unity-slope variation. Analyses of the direct oxidation kinetics, based on its variation with the driving force and on the determination of H/D isotope effects, ruled out a stepwise mechanism in which electron transfer is followed by the deprotonation of the initial cation radical at the benefit of a pathway in which proton and electron are transferred concertedly. Derivation of the characteristics of counterdiffusion in termolecular reactions allowed showing that the concerted process is under activation control. It is characterized by a remarkably small reorganization energy, in line with the electrochemical counterpart of the reaction, underpinning the very peculiar behavior of water as proton acceptor when it is used as the solvent.
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Hammes-Schiffer S. Theory of proton-coupled electron transfer in energy conversion processes. Acc Chem Res 2009; 42:1881-9. [PMID: 19807148 DOI: 10.1021/ar9001284] [Citation(s) in RCA: 261] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Proton-coupled electron transfer (PCET) reactions play an essential role in a broad range of energy conversion processes, including photosynthesis and respiration. These reactions also form the basis of many types of solar fuel cells and electrochemical devices. Recent advances in the theory of PCET enable the prediction of the impact of system properties on the reaction rates. These predictions may guide the design of more efficient catalysts for energy production, including those based on artificial photosynthesis and solar energy conversion. This Account summarizes the theoretically predicted dependence of PCET rates on system properties and illustrates potential approaches for tuning the reaction rates in chemical systems. A general theoretical formulation for PCET reactions has been developed over the past decade. In this theory, PCET reactions are described in terms of nonadiabatic transitions between the reactant and product electron-proton vibronic states. A series of nonadiabatic rate constant expressions for both homogeneous and electrochemical PCET reactions have been derived in various well-defined limits. Recently this theory has been extended to include the effects of solvent dynamics and to describe ultrafast interfacial PCET. Analysis of the rate constant expressions provides insight into the underlying physical principles of PCET and enables the prediction of the dependence of the rates on the physical properties of the system. Moreover, the kinetic isotope effect, which is the ratio of the rates for hydrogen and deuterium, provides a useful mechanistic probe. Typically the PCET rate will increase as the electronic coupling and temperature increase and as the total reorganization energy and equilibrium proton donor-acceptor distance decrease. The rate constant is predicted to increase as the driving force becomes more negative, rather than exhibit turnover behavior in the inverted region, because excited vibronic product states associated with low free energy barriers and relatively large vibronic couplings become accessible. The physical basis for the experimentally observed pH dependence of PCET reactions has been debated in the literature. When the proton acceptor is a buffer species, the pH dependence may arise from the protonation equilibrium of the buffer. It could also arise from kinetic complexity of competing concerted and sequential PCET reaction pathways. In electrochemical PCET, the heterogeneous rate constants and current densities depend strongly on the overpotential. The change in equilibrium proton donor-acceptor distance upon electron transfer may lead to asymmetries in the Tafel plots and deviations of the transfer coefficient from the standard value of one-half at zero overpotential. Applications of this theory to experimentally studied systems illustrate approaches that can be utilized to tune the PCET rate. For example, the rate can be tuned by changing the pH or using different buffer species as proton acceptors. The rate can also be tuned with site-specific mutagenesis in biological systems or chemical modifications that vary the substituents on the redox species in chemical systems. Understanding the impact of these changes on the PCET rate may assist experimental efforts to enhance energy conversion processes.
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Affiliation(s)
- Sharon Hammes-Schiffer
- Department of Chemistry, 104 Chemistry Building, Pennsylvania State University, University Park, Pennsylvania 16802
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Costentin C, Robert M, Savéant JM, Teillout AL. Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+). Chemphyschem 2009; 10:191-8. [PMID: 18816536 DOI: 10.1002/cphc.200800361] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.
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Affiliation(s)
- Cyrille Costentin
- Laboratoire d'Electrochimie Moléculaire, UMR 7591 CNRS, Université Paris Diderot, 2 place Jussieu 75251 Paris Cedex 05, France
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Hammes-Schiffer S, Soudackov AV. Proton-coupled electron transfer in solution, proteins, and electrochemistry. J Phys Chem B 2008; 112:14108-23. [PMID: 18842015 PMCID: PMC2720037 DOI: 10.1021/jp805876e] [Citation(s) in RCA: 286] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recent advances in the theoretical treatment of proton-coupled electron transfer (PCET) reactions are reviewed. These reactions play an important role in a wide range of biological processes, as well as in fuel cells, solar cells, chemical sensors, and electrochemical devices. A unified theoretical framework has been developed to describe both sequential and concerted PCET, as well as hydrogen atom transfer (HAT). A quantitative diagnostic has been proposed to differentiate between HAT and PCET in terms of the degree of electronic nonadiabaticity, where HAT corresponds to electronically adiabatic proton transfer and PCET corresponds to electronically nonadiabatic proton transfer. In both cases, the overall reaction is typically vibronically nonadiabatic. A series of rate constant expressions have been derived in various limits by describing the PCET reactions in terms of nonadiabatic transitions between electron-proton vibronic states. These expressions account for the solvent response to both electron and proton transfer and the effects of the proton donor-acceptor vibrational motion. The solvent and protein environment can be represented by a dielectric continuum or described with explicit molecular dynamics. These theoretical treatments have been applied to numerous PCET reactions in solution and proteins. Expressions for heterogeneous rate constants and current densities for electrochemical PCET have also been derived and applied to model systems.
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Affiliation(s)
- Sharon Hammes-Schiffer
- Department of Chemistry, 104 Chemistry Building, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
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Costentin C. Electrochemical Approach to the Mechanistic Study of Proton-Coupled Electron Transfer. Chem Rev 2008; 108:2145-79. [DOI: 10.1021/cr068065t] [Citation(s) in RCA: 328] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Hammarström L, Styring S. Coupled electron transfers in artificial photosynthesis. Philos Trans R Soc Lond B Biol Sci 2008; 363:1283-91; discussion 1291. [PMID: 17954432 DOI: 10.1098/rstb.2007.2225] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Light-induced charge separation in molecular assemblies has been widely investigated in the context of artificial photosynthesis. Important progress has been made in the fundamental understanding of electron and energy transfer and in stabilizing charge separation by multi-step electron transfer. In the Swedish Consortium for Artificial Photosynthesis, we build on principles from the natural enzyme photosystem II and Fe-hydrogenases. An important theme in this biomimetic effort is that of coupled electron-transfer reactions, which have so far received only little attention. (i) Each absorbed photon leads to charge separation on a single-electron level only, while catalytic water splitting and hydrogen production are multi-electron processes; thus there is the need for controlling accumulative electron transfer on molecular components. (ii) Water splitting and proton reduction at the potential catalysts necessarily require the management of proton release and/or uptake. Far from being just a stoichiometric requirement, this controls the electron transfer processes by proton-coupled electron transfer (PCET). (iii) Redox-active links between the photosensitizers and the catalysts are required to rectify the accumulative electron-transfer reactions, and will often be the starting points of PCET.
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Affiliation(s)
- Leif Hammarström
- Department of Photochemistry and Molecular Science, Uppsala University, PO Box 523, 751 20 Uppsala, Sweden.
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Irebo T, Reece SY, Sjödin M, Nocera DG, Hammarström L. Proton-Coupled Electron Transfer of Tyrosine Oxidation: Buffer Dependence and Parallel Mechanisms. J Am Chem Soc 2007; 129:15462-4. [DOI: 10.1021/ja073012u] [Citation(s) in RCA: 175] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Affiliation(s)
- My Hang V Huynh
- DE-1: High Explosive Science and Technology Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Meyer TJ, Huynh MHV, Thorp HH. The Possible Role of Proton-Coupled Electron Transfer (PCET) in Water Oxidation by Photosystem II. Angew Chem Int Ed Engl 2007; 46:5284-304. [PMID: 17604381 DOI: 10.1002/anie.200600917] [Citation(s) in RCA: 410] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
All higher life forms use oxygen and respiration as their primary energy source. The oxygen comes from water by solar-energy conversion in photosynthetic membranes. In green plants, light absorption in photosystem II (PSII) drives electron-transfer activation of the oxygen-evolving complex (OEC). The mechanism of water oxidation by the OEC has long been a subject of great interest to biologists and chemists. With the availability of new molecular-level protein structures from X-ray crystallography and EXAFS, as well as the accumulated results from numerous experiments and theoretical studies, it is possible to suggest how water may be oxidized at the OEC. An integrated sequence of light-driven reactions that exploit coupled electron-proton transfer (EPT) could be the key to water oxidation. When these reactions are combined with long-range proton transfer (by sequential local proton transfers), it may be possible to view the OEC as an intricate structure that is "wired for protons".
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Affiliation(s)
- Thomas J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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Meyer T, Huynh M, Thorp H. Zur möglichen Rolle des protonengekoppelten Elektronentransfers (PCET) bei der Oxidation von Wasser durch das Photosystem II. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200600917] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Costentin C, Robert M, Savéant JM. Concerted Proton−Electron Transfer Reactions in Water. Are the Driving Force and Rate Constant Depending on pH When Water Acts as Proton Donor or Acceptor? J Am Chem Soc 2007; 129:5870-9. [PMID: 17428051 DOI: 10.1021/ja067950q] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The competition between stepwise and concerted (CPET) pathways in proton-coupled electron-transfer reactions in water is discussed on thermodynamic and kinetic bases. In the case where water is the proton acceptor, the CPET pathway may compete favorably with the stepwise pathway. The main parameter of the competition is pK of the oxidized form of the substrate being smaller or larger than 0. The driving force of the forward reaction is however independent of pH, despite the equilibrium redox potential of the proton-electron system being a function of pH. At high pH values, CPET reactions involving OH- as proton acceptor may likewise compete favorably with stepwise pathways. The overall reaction rate constant is an increasing function of pH, not because the driving force depends on pH but because OH- is a reactant. In buffered media, association of the substrate with the basic components of the buffer offers an alternative CPET route; the driving force comes closer to that offered by the pH-dependent equilibrium redox potential.
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Affiliation(s)
- Cyrille Costentin
- Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université, CNRS No 7591, Université de Paris 7-Denis Diderot, 2 place Jussieu, 75251 Paris Cedex 05, France
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Kiang NY, Segura A, Tinetti G, Blankenship RE, Cohen M, Siefert J, Crisp D, Meadows VS. Spectral signatures of photosynthesis. II. Coevolution with other stars and the atmosphere on extrasolar worlds. ASTROBIOLOGY 2007; 7:252-74. [PMID: 17407410 DOI: 10.1089/ast.2006.0108] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
As photosynthesis on Earth produces the primary signatures of life that can be detected astronomically at the global scale, a strong focus of the search for extrasolar life will be photosynthesis, particularly photosynthesis that has evolved with a different parent star. We take previously simulated planetary atmospheric compositions for Earth-like planets around observed F2V and K2V, modeled M1V and M5V stars, and around the active M4.5V star AD Leo; our scenarios use Earth's atmospheric composition as well as very low O2 content in case anoxygenic photosynthesis dominates. With a line-by-line radiative transfer model, we calculate the incident spectral photon flux densities at the surface of the planet and under water. We identify bands of available photosynthetically relevant radiation and find that photosynthetic pigments on planets around F2V stars may peak in absorbance in the blue, K2V in the red-orange, and M stars in the near-infrared, in bands at 0.93-1.1 microm, 1.1-1.4 microm, 1.5-1.8 microm, and 1.8-2.5 microm. However, underwater organisms will be restricted to wavelengths shorter than 1.4 microm and more likely below 1.1 microm. M star planets without oxygenic photosynthesis will have photon fluxes above 1.6 microm curtailed by methane. Longer-wavelength, multi-photo-system series would reduce the quantum yield but could allow for oxygenic photosystems at longer wavelengths. A wavelength of 1.1 microm is a possible upper cutoff for electronic transitions versus only vibrational energy; however, this cutoff is not strict, since such energetics depend on molecular configuration. M star planets could be a half to a tenth as productive as Earth in the visible, but exceed Earth if useful photons extend to 1.1 microm for anoxygenic photosynthesis. Under water, organisms would still be able to survive ultraviolet flares from young M stars and acquire adequate light for growth.
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Affiliation(s)
- Nancy Y Kiang
- NASA Goddard Institute for Space Studies, New York, New York 10025, USA.
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Mulkidjanian AY. Ubiquinol oxidation in the cytochrome bc1 complex: Reaction mechanism and prevention of short-circuiting. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1709:5-34. [PMID: 16005845 DOI: 10.1016/j.bbabio.2005.03.009] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2004] [Revised: 12/01/2004] [Accepted: 03/22/2005] [Indexed: 11/26/2022]
Abstract
This review is focused on the mechanism of ubiquinol oxidation by the cytochrome bc1 complex (bc1). This integral membrane complex serves as a "hub" in the vast majority of electron transfer chains. The bc1 oxidizes a ubiquinol molecule to ubiquinone by a unique "bifurcated" reaction where the two released electrons go to different acceptors: one is accepted by the mobile redox active domain of the [2Fe-2S] iron-sulfur Rieske protein (FeS protein) and the other goes to cytochrome b. The nature of intermediates in this reaction remains unclear. It is also debatable how the enzyme prevents short-circuiting that could happen if both electrons escape to the FeS protein. Here, I consider a reaction mechanism that (i) agrees with the available experimental data, (ii) entails three traits preventing the short-circuiting in bc1, and (iii) exploits the evident structural similarity of the ubiquinone binding sites in the bc1 and the bacterial photosynthetic reaction center (RC). Based on the latter congruence, it is suggested that the reaction route of ubiquinol oxidation by bc1 is a reversal of that leading to the ubiquinol formation in the RC. The rate-limiting step of ubiquinol oxidation is then the re-location of a ubiquinol molecule from its stand-by site within cytochrome b into a catalytic site, which is formed only transiently, after docking of the mobile redox domain of the FeS protein to cytochrome b. In the catalytic site, the quinone ring is stabilized by Glu-272 of cytochrome b and His-161 of the FeS protein. The short circuiting is prevented as long as: (i) the formed semiquinone anion remains bound to the reduced FeS domain and impedes its undocking, so that the second electron is forced to go to cytochrome b; (ii) even after ubiquinol is fully oxidized, the reduced FeS domain remains docked to cytochrome b until electron(s) pass through cytochrome b; (iii) if cytochrome b becomes (over)reduced, the binding and oxidation of further ubiquinol molecules is hampered; the reason is that the Glu-272 residue is turned towards the reduced hemes of cytochrome b and is protonated to stabilize the surplus negative charge; in this state, this residue cannot participate in the binding/stabilization of a ubiquinol molecule.
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Affiliation(s)
- Armen Y Mulkidjanian
- Max Planck Institute of Biophysics, Department of Biophysical Chemistry, Max-von-Laue-Str. 3, D-60438 Frankfurt-am-Main, Germany.
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Sjödin M, Styring S, Wolpher H, Xu Y, Sun L, Hammarström L. Switching the Redox Mechanism: Models for Proton-Coupled Electron Transfer from Tyrosine and Tryptophan. J Am Chem Soc 2005; 127:3855-63. [PMID: 15771521 DOI: 10.1021/ja044395o] [Citation(s) in RCA: 209] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The coupling of electron and proton transfer is an important controlling factor in radical proteins, such as photosystem II, ribinucleotide reductase, cytochrome oxidases, and DNA photolyase. This was investigated in model complexes in which a tyrosine or tryptophan residue was oxidized by a laser-flash generated trisbipyridine-Ru(III) moiety in an intramolecular, proton-coupled electron transfer (PCET) reaction. The PCET was found to proceed in a competition between a stepwise reaction, in which electron transfer is followed by deprotonation of the amino acid radical (ETPT), and a concerted reaction, in which both the electron and proton are transferred in a single reaction step (CEP). Moreover, we found that we could analyze the kinetic data for PCET by Marcus' theory for electron transfer. By altering the solution pH, the strength of the Ru(III) oxidant, or the identity of the amino acid, we could induce a switch between the two mechanisms and obtain quantitative data for the parameters that control which one will dominate. The characteristic pH-dependence of the CEP rate (M. Sjodin et al. J. Am. Chem. Soc. 2000, 122, 3932) reflects the pH-dependence of the driving force caused by proton release to the bulk. For the pH-independent ETPT on the other hand, the driving force of the rate-determining ET step is pH-independent and smaller. On the other hand, temperature-dependent data showed that the reorganization energy was higher for CEP, while the pre-exponential factors showed no significant difference between the mechanisms. Thus, the opposing effect of the differences in driving force and reorganization energy determines which of the mechanisms will dominate. Our results show that a concerted mechanism is in general quite likely and provides a low-barrier reaction pathway for weakly exoergonic reactions. In addition, the kinetic isotope effect was much higher for CEP (kH/kD > 10) than for ETPT (kH/kD = 2), consistent with significant changes along the proton reaction coordinate in the rate-determining step of CEP.
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Affiliation(s)
- Martin Sjödin
- Department of Physical Chemistry, BMC, Uppsala University, PO Box 579, SE-751 23 Uppsala, Sweden
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