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Odella E, Wadsworth BL, Mora SJ, Goings JJ, Huynh MT, Gust D, Moore TA, Moore GF, Hammes-Schiffer S, Moore AL. Proton-Coupled Electron Transfer Drives Long-Range Proton Translocation in Bioinspired Systems. J Am Chem Soc 2019; 141:14057-14061. [DOI: 10.1021/jacs.9b06978] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Emmanuel Odella
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Brian L. Wadsworth
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - S. Jimena Mora
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Joshua J. Goings
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Mioy T. Huynh
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Devens Gust
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Thomas A. Moore
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Gary F. Moore
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Ana L. Moore
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
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2
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Odella E, Mora SJ, Wadsworth BL, Huynh MT, Goings JJ, Liddell PA, Groy TL, Gervaldo M, Sereno LE, Gust D, Moore TA, Moore GF, Hammes-Schiffer S, Moore AL. Controlling Proton-Coupled Electron Transfer in Bioinspired Artificial Photosynthetic Relays. J Am Chem Soc 2018; 140:15450-15460. [DOI: 10.1021/jacs.8b09724] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Emmanuel Odella
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - S. Jimena Mora
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Brian L. Wadsworth
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Mioy T. Huynh
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Joshua J. Goings
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Paul A. Liddell
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Thomas L. Groy
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Miguel Gervaldo
- Departamento de Química, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Agencia Postal No. 3, 5800 Río Cuarto, Córdoba, Argentina
| | - Leónides E. Sereno
- Departamento de Química, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Agencia Postal No. 3, 5800 Río Cuarto, Córdoba, Argentina
| | - Devens Gust
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Thomas A. Moore
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Gary F. Moore
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Ana L. Moore
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
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Huynh MT, Mora SJ, Villalba M, Tejeda-Ferrari ME, Liddell PA, Cherry BR, Teillout AL, Machan CW, Kubiak CP, Gust D, Moore TA, Hammes-Schiffer S, Moore AL. Concerted One-Electron Two-Proton Transfer Processes in Models Inspired by the Tyr-His Couple of Photosystem II. ACS Cent Sci 2017; 3:372-380. [PMID: 28573198 PMCID: PMC5445534 DOI: 10.1021/acscentsci.7b00125] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Indexed: 05/28/2023]
Abstract
Nature employs a TyrZ-His pair as a redox relay that couples proton transfer to the redox process between P680 and the water oxidizing catalyst in photosystem II. Artificial redox relays composed of different benzimidazole-phenol dyads (benzimidazole models His and phenol models Tyr) with substituents designed to simulate the hydrogen bond network surrounding the TyrZ-His pair have been prepared. When the benzimidazole substituents are strong proton acceptors such as primary or tertiary amines, theory predicts that a concerted two proton transfer process associated with the electrochemical oxidation of the phenol will take place. Also, theory predicts a decrease in the redox potential of the phenol by ∼300 mV and a small kinetic isotope effect (KIE). Indeed, electrochemical, spectroelectrochemical, and KIE experimental data are consistent with these predictions. Notably, these results were obtained by using theory to guide the rational design of artificial systems and have implications for managing proton activity to optimize efficiency at energy conversion sites involving water oxidation and reduction.
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Affiliation(s)
- Mioy T. Huynh
- Department
of Chemistry, University of Illinois at
Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United
States
| | - S. Jimena Mora
- School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | - Matias Villalba
- School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | | | - Paul A. Liddell
- School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | - Brian R. Cherry
- School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | - Anne-Lucie Teillout
- Laboratoire
de Chimie Physique, Groupe d’Electrochimie et de Photoélectrochimie,
UMR 8000 CNRS, Université Paris-Sud, Batiment 350, 91405 Orsay Cedex, France
| | - Charles W. Machan
- Department
of Chemistry, University of Virginia, McCormick Road,
PO 400319, Charlottesville, Virginia 22904, United States
| | - Clifford P. Kubiak
- Department
of Chemistry and Biochemistry, University
of California, San Diego, 9500 Gilman Drive, MC 0358, La Jolla, California 92093, United States
| | - Devens Gust
- School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | - Thomas A. Moore
- School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | - Sharon Hammes-Schiffer
- Department
of Chemistry, University of Illinois at
Urbana−Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United
States
| | - Ana L. Moore
- School
of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
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Yu X, Tung CH, Wang W, Huynh MT, Gray DL, Hammes-Schiffer S, Rauchfuss TB. Interplay between Terminal and Bridging Diiron Hydrides in Neutral and Oxidized States. Organometallics 2017; 36:2245-2253. [PMID: 28781408 DOI: 10.1021/acs.organomet.7b00297] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
This study describes the structural, spectroscopic, and electrochemical properties of electronically unsymmetrical diiron hydrides. The terminal hydride Cp*Fe(pdt)Fe(dppe)(CO)H ([1(t-H)]0, Cp*- = Me5C5-, pdt2- = CH2(CH2S-)2, dppe = Ph2PC2H4PPh2) was prepared by hydride reduction of [Cp*Fe(pdt)Fe(dppe)(CO)(NCMe)]+. As established by X-ray crystallography, [1(t-H)]0 features a terminal hydride ligand. Unlike previous examples of terminal diiron hydrides, [1(t-H)]0 does not isomerize to the bridging hydride [1(μ-H)]0. Oxidation of [1(t-H)]0 gives [1(t-H)]+, which was also characterized crystallographically as its BF4- salt. Density functional theory (DFT) calculations indicate that [1(t-H)]+ is best described as containing an Cp*FeIII center. In solution, [1(t-H)]+ isomerizes to [1(μ-H)]+, as anticipated by DFT. Reduction of [1(μ-H)]+ by Cp2Co afforded the diferrous bridging hydride [1(μ-H)]0. Electrochemical measurements and DFT calculations indicate that the couples [1(t-H)]+/0 and [1(μ-H)]+/0 differ by 210 mV. Qualitative measurements indicate that [1(t-H)]0 and [1(μ-H)]0 are close in free energy. Protonation of [1(t-H)]0 in MeCN solution affords H2 even with weak acids via hydride transfer. In contrast, protonation of [1(μ-H)]0 yields 0.5 equiv of H2 by a proposed protonation-induced electron transfer process. Isotopic labeling indicates that μ-H/D ligands are inert.
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Affiliation(s)
- Xin Yu
- School of Chemistry and Chemical Engineering, Shandong University, 27 South Shanda Road, Jinan, Shandong 250100, People's Republic of China
| | - Chen-Ho Tung
- School of Chemistry and Chemical Engineering, Shandong University, 27 South Shanda Road, Jinan, Shandong 250100, People's Republic of China
| | - Wenguang Wang
- School of Chemistry and Chemical Engineering, Shandong University, 27 South Shanda Road, Jinan, Shandong 250100, People's Republic of China
| | - Mioy T Huynh
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Goodwin Avenue, Urbana, Illinois 61801, United States
| | - Danielle L Gray
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Goodwin Avenue, Urbana, Illinois 61801, United States
| | - Sharon Hammes-Schiffer
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Goodwin Avenue, Urbana, Illinois 61801, United States
| | - Thomas B Rauchfuss
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Goodwin Avenue, Urbana, Illinois 61801, United States
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Huynh MT, Anson CW, Cavell AC, Stahl SS, Hammes-Schiffer S. Quinone 1 e - and 2 e -/2 H + Reduction Potentials: Identification and Analysis of Deviations from Systematic Scaling Relationships. J Am Chem Soc 2016; 138:15903-15910. [PMID: 27960306 PMCID: PMC6206872 DOI: 10.1021/jacs.6b05797] [Citation(s) in RCA: 148] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Quinones participate in diverse electron transfer and proton-coupled electron transfer processes in chemistry and biology. To understand the relationship between these redox processes, an experimental study was carried out to probe the 1 e- and 2 e-/2 H+ reduction potentials of a number of common quinones. The results reveal a non-linear correlation between the 1 e- and 2 e-/2 H+ reduction potentials. This unexpected observation prompted a computational study of 134 different quinones, probing their 1 e- reduction potentials, pKa values, and 2 e-/2 H+ reduction potentials. The density functional theory calculations reveal an approximately linear correlation between these three properties and an effective Hammett constant associated with the quinone substituent(s). However, deviations from this linear scaling relationship are evident for quinones that feature intramolecular hydrogen bonding, halogen substituents, charged substituents, and/or sterically bulky substituents. These results, particularly the different substituent effects on the 1 e- versus 2 e-/2 H+ reduction potentials, have important implications for designing quinones with tailored redox properties.
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Affiliation(s)
- Mioy T. Huynh
- Department of Chemistry, University of Illinois at
Urbana–Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United
States
| | - Colin W. Anson
- Department of Chemistry, University of
Wisconsin–Madison, 1101 University Avenue, Madison, Wisconsin 53706, United
States
| | - Andrew C. Cavell
- Department of Chemistry, University of
Wisconsin–Madison, 1101 University Avenue, Madison, Wisconsin 53706, United
States
| | - Shannon S. Stahl
- Department of Chemistry, University of
Wisconsin–Madison, 1101 University Avenue, Madison, Wisconsin 53706, United
States
| | - Sharon Hammes-Schiffer
- Department of Chemistry, University of Illinois at
Urbana–Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United
States
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Abstract
Hydrogenase enzymes efficiently process H2 and protons at organometallic FeFe, NiFe, or Fe active sites. Synthetic modeling of the many H2ase states has provided insight into H2ase structure and mechanism, as well as afforded catalysts for the H2 energy vector. Particularly important are hydride-bearing states, with synthetic hydride analogues now known for each hydrogenase class. These hydrides are typically prepared by protonation of low-valent cores. Examples of FeFe and NiFe hydrides derived from H2 have also been prepared. Such chemistry is more developed than mimicry of the redox-inactive monoFe enzyme, although functional models of the latter are now emerging. Advances in physical and theoretical characterization of H2ase enzymes and synthetic models have proven key to the study of hydrides in particular, and will guide modeling efforts toward more robust and active species optimized for practical applications.
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Affiliation(s)
- David Schilter
- Center for Multidimensional Carbon Materials, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea
| | - James M. Camara
- Department of Chemistry, Yeshiva University, 500 West 185th Street, New York, New York 10033, United States
| | - Mioy T. Huynh
- Department of Chemistry, University of Illinois at Urbana–Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry, University of Illinois at Urbana–Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Thomas B. Rauchfuss
- Department of Chemistry, University of Illinois at Urbana–Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
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Ulloa OA, Huynh MT, Richers CP, Bertke JA, Nilges MJ, Hammes-Schiffer S, Rauchfuss TB. Mechanism of H2 Production by Models for the [NiFe]-Hydrogenases: Role of Reduced Hydrides. J Am Chem Soc 2016; 138:9234-45. [PMID: 27328053 DOI: 10.1021/jacs.6b04579] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The intermediacy of a reduced nickel-iron hydride in hydrogen evolution catalyzed by Ni-Fe complexes was verified experimentally and computationally. In addition to catalyzing hydrogen evolution, the highly basic and bulky (dppv)Ni(μ-pdt)Fe(CO)(dppv) ([1](0); dppv = cis-C2H2(PPh2)2) and its hydride derivatives have yielded to detailed characterization in terms of spectroscopy, bonding, and reactivity. The protonation of [1](0) initially produces unsym-[H1](+), which converts by a first-order pathway to sym-[H1](+). These species have C1 (unsym) and Cs (sym) symmetries, respectively, depending on the stereochemistry of the octahedral Fe site. Both experimental and computational studies show that [H1](+) protonates at sulfur. The S = 1/2 hydride [H1](0) was generated by reduction of [H1](+) with Cp*2Co. Density functional theory (DFT) calculations indicate that [H1](0) is best described as a Ni(I)-Fe(II) derivative with significant spin density on Ni and some delocalization on S and Fe. EPR spectroscopy reveals both kinetic and thermodynamic isomers of [H1](0). Whereas [H1](+) does not evolve H2 upon protonation, treatment of [H1](0) with acids gives H2. The redox state of the "remote" metal (Ni) modulates the hydridic character of the Fe(II)-H center. As supported by DFT calculations, H2 evolution proceeds either directly from [H1](0) and external acid or from protonation of the Fe-H bond in [H1](0) to give a labile dihydrogen complex. Stoichiometric tests indicate that protonation-induced hydrogen evolution from [H1](0) initially produces [1](+), which is reduced by [H1](0). Our results reconcile the required reductive activation of a metal hydride and the resistance of metal hydrides toward reduction. This dichotomy is resolved by reduction of the remote (non-hydride) metal of the bimetallic unit.
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Affiliation(s)
- Olbelina A Ulloa
- Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Mioy T Huynh
- Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Casseday P Richers
- Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Jeffery A Bertke
- Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Mark J Nilges
- Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Thomas B Rauchfuss
- Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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Chambers GM, Huynh MT, Li Y, Hammes-Schiffer S, Rauchfuss TB, Reijerse E, Lubitz W. Models of the Ni-L and Ni-SIa States of the [NiFe]-Hydrogenase Active Site. Inorg Chem 2015; 55:419-31. [PMID: 26421729 DOI: 10.1021/acs.inorgchem.5b01662] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A new class of synthetic models for the active site of [NiFe]-hydrogenases are described. The Ni(I/II)(SCys)2 and Fe(II)(CN)2CO sites are represented with (RC5H4)Ni(I/II) and Fe(II)(diphos)(CO) modules, where diphos = 1,2-C2H4(PPh2)2(dppe) or cis-1,2-C2H2(PPh2)2(dppv). The two bridging thiolate ligands are represented by CH2(CH2S)2(2-) (pdt(2-)), Me2C(CH2S)2(2-) (Me2pdt(2-)), and (C6H5S)2(2-). The reaction of Fe(pdt)(CO)2(dppe) and [(C5H5)3Ni2]BF4 affords [(C5H5)Ni(pdt)Fe(dppe)(CO)]BF4 ([1a]BF4). Monocarbonyl [1a]BF4 features an S = 0 Ni(II)Fe(II) center with five-coordinated iron, as proposed for the Ni-SIa state of the enzyme. One-electron reduction of [1a](+) affords the S = 1/2 derivative [1a](0), which, according to density functional theory (DFT) calculations and electron paramagnetic resonance and Mössbauer spectroscopies, is best described as a Ni(I)Fe(II) compound. The Ni(I)Fe(II) assignment matches that for the Ni-L state in [NiFe]-hydrogenase, unlike recently reported Ni(II)Fe(I)-based models. Compound [1a](0) reacts with strong acids to liberate 0.5 equiv of H2 and regenerate [1a](+), indicating that H2 evolution is catalyzed by [1a](0). DFT calculations were used to investigate the pathway for H2 evolution and revealed that the mechanism can proceed through two isomers of [1a](0) that differ in the stereochemistry of the Fe(dppe)CO center. Calculations suggest that protonation of [1a](0) (both isomers) affords Ni(III)-H-Fe(II) intermediates, which represent mimics of the Ni-C state of the enzyme.
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Affiliation(s)
- Geoffrey M Chambers
- School of Chemical Sciences, University of Illinois , Urbana, Illinois 61801, United States.,International Center of Carbon-Neutral Energy Research, Kyushu University , 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan
| | - Mioy T Huynh
- School of Chemical Sciences, University of Illinois , Urbana, Illinois 61801, United States
| | - Yulong Li
- School of Chemical Sciences, University of Illinois , Urbana, Illinois 61801, United States
| | - Sharon Hammes-Schiffer
- School of Chemical Sciences, University of Illinois , Urbana, Illinois 61801, United States
| | - Thomas B Rauchfuss
- School of Chemical Sciences, University of Illinois , Urbana, Illinois 61801, United States.,International Center of Carbon-Neutral Energy Research, Kyushu University , 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan
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Huynh MT, Wang W, Rauchfuss TB, Hammes-Schiffer S. Computational investigation of [FeFe]-hydrogenase models: characterization of singly and doubly protonated intermediates and mechanistic insights. Inorg Chem 2014; 53:10301-11. [PMID: 25207842 PMCID: PMC4186672 DOI: 10.1021/ic5013523] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
![]()
The [FeFe]-hydrogenase enzymes catalyze
hydrogen oxidation and production efficiently with binuclear Fe metal
centers. Recently the bioinspired H2-producing model system
Fe2(adt)(CO)2(dppv)2 (adt=azadithiolate
and dppv=diphosphine) was synthesized and studied experimentally.
In this system, the azadithiolate bridge facilitates the formation
of a doubly protonated ammonium-hydride species through a proton relay.
Herein computational methods are utilized to examine this system in
the various oxidation states and protonation states along proposed
mechanistic pathways for H2 production. The calculated
results agree well with the experimental data for the geometries,
CO vibrational stretching frequencies, and reduction potentials. The
calculations illustrate that the NH···HFe dihydrogen
bonding distance in the doubly protonated species is highly sensitive
to the effects of ion-pairing between the ammonium and BF4– counterions, which are present in the crystal
structure, in that the inclusion of BF4– counterions leads to a significantly longer dihydrogen bond. The
non-hydride Fe center was found to be the site of reduction for terminal
hydride species and unsymmetric bridging hydride species, whereas
the reduced symmetric bridging hydride species exhibited spin delocalization
between the Fe centers. According to both experimental measurements
and theoretical calculations of the relative pKa values, the Fed center of the neutral species
is more basic than the amine, and the bridging hydride species is
more thermodynamically stable than the terminal hydride species. The
calculations implicate a possible pathway for H2 evolution
that involves an intermediate with H2 weakly bonded to
one Fe, a short H2 distance similar to the molecular bond
length, the spin density delocalized over the two Fe centers, and
a nearly symmetrically bridged CO ligand. Overall, this study illustrates
the mechanistic roles of the ammonium-hydride interaction, flexibility
of the bridging CO ligand, and intramolecular electron transfer between
the Fe centers in the catalytic cycle. Such insights will assist in
the design of more effective bioinspired catalysts for H2 production. Theoretical calculations
in conjunction with supporting experimental data are used to analyze
the mechanistic pathway for hydrogen evolution catalyzed by the bioinspired
model Fe2(adt)(CO)2(dppv)2. This
study elucidates the site of reduction and the pKa values associated with formation of the singly and doubly
protonated species, as well as the roles of the ammonium-hydride interaction,
flexibility of the bridging CO ligand, and intramolecular electron
transfer between the Fe centers in the catalytic cycle for H2 production.
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Affiliation(s)
- Mioy T Huynh
- Department of Chemistry, 600 South Mathews Avenue, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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10
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Abstract
![]()
Theory
and experiment indicate that the protonation of reduced
NiFe dithiolates proceeds via a previously undetected isomer with
enhanced basicity. In particular, it is proposed that protonation
of (OC)3Fe(pdt)Ni(dppe) (1; pdt2– = –S(CH2)3S–; dppe = Ph2P(CH2)2PPh2) occurs at the Fe site of the two-electron mixed-valence Fe(0)Ni(II)
species, not the Fe(I)-Ni(I) bond for the homovalence isomer of 1. The new pathway, which may have implications for protonation
of other complexes and clusters, was uncovered through studies on
the homologous series L(OC)2Fe(pdt)M(dppe), where M = Ni,
Pd (2), and Pt (3) and L = CO, PCy3. Similar to 1, complexes 2 and 3 undergo both protonation and 1e– oxidation to
afford well-characterized hydrides ([2H]+ and
[3H]+) and mixed-valence derivatives ([2]+ and [3]+), respectively.
Whereas the Pd site is tetrahedral in 2, the Pt site
is square-planar in 3, indicating that this complex is
best described as Fe(0)Pt(II). In view of the results on 2 and 3, the potential energy surface of 1 was reinvestigated with density functional theory. These calculations
revealed the existence of an energetically accessible and more basic
Fe(0)Ni(II) isomer with a square-planar Ni site.
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Affiliation(s)
- Mioy T Huynh
- Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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11
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Alexandrova AN, Nayhouse MJ, Huynh MT, Kuo JL, Melkonian AV, Chavez G, Hernando NM, Kowal MD, Liu CP. Selected AB4(2-/-) (A = C, Si, Ge; B = Al, Ga, In) ions: a battle between covalency and aromaticity, and prediction of square planar Si in SiIn4(2-/-). Phys Chem Chem Phys 2012; 14:14815-21. [PMID: 22868353 PMCID: PMC3478443 DOI: 10.1039/c2cp41821e] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
CAl(4)(2-/-) (D(4h), (1)A(1g)) is a cluster ion that has been established to be planar, aromatic, and contain a tetracoordinate planar C atom. Valence isoelectronic substitution of C with Si and Ge in this cluster leads to a radical change of structure toward distorted pentagonal species. We find that this structural change goes together with the cluster acquiring partial covalency of bonding between Si/Ge and Al(4), facilitated by hybridization of the atomic orbitals (AOs). Counter intuitively, for the AAl(4)(2-/-) (A = C, Si, Ge) clusters, hybridization in the dopant atom is strengthened from C, to Si, and to Ge, even though typically AOs are more likely to hybridize if they are closer in energy (i.e. in earlier elements in the Periodic Table). The trend is explained by the better overlap of the hybrids of the heavier dopants with the orbitals of Al(4). From the thus understood trend, it is inferred that covalency in such clusters can be switched off, by varying the relative sizes of the AOs of the main element and the dopant. Using this mechanism, we then successfully killed covalency in Si, and predicted a new aromatic cluster ion containing a tetracoordinate square planar Si, SiIn(4)(2-/-).
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Affiliation(s)
- Anastassia N Alexandrova
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, USA.
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Huynh MT, Pollack RA, Cunningham RA. Universal newborn hearing screening: feasibility in a community hospital. J Fam Pract 1996; 42:487-490. [PMID: 8642366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
BACKGROUND The National Institutes of Health and the Joint Committee on Infant Hearing have recommended universal newborn hearing screening. The feasibility of universal newborn hearing screening in a community hospital, however, has not been demonstrated. We initiated a universal newborn hearing screening program using transient evoked otoacoustic emissions (TEOAE) at a community hospital to assess the feasibility of universal hearing screening in this setting. METHODS A screening team composed of a family practice physician, family medicine resident, audiologist, and four technicians was developed. The study compared testing time between the technicians and the audiologist and assessed whether the technicians were able to perform hearing testing accurately and reliably. RESULTS A total of 627 infants were screened. Of those, 11 (1.8%) failed TEOAE screening and were referred to a tertiary care center for further evaluation. Six of the 11 referrals were found to have a hearing impairment. Trained technicians were found to be capable of performing the screening accurately and reliably. CONCLUSIONS Universal newborn hearing screening using transient evoked otoacoustic emissions is feasible in a community hospital.
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Affiliation(s)
- M T Huynh
- Department of Family Practice, Malcolm Grow Medical Center, Andrews Air Force Base, Maryland, USA
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