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Odella E, Secor M, Reyes Cruz EA, Guerra WD, Urrutia MN, Liddell PA, Moore TA, Moore GF, Hammes-Schiffer S, Moore AL. Managing the Redox Potential of PCET in Grotthuss-Type Proton Wires. J Am Chem Soc 2022; 144:15672-15679. [PMID: 35993888 DOI: 10.1021/jacs.2c05820] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Expanding proton-coupled electron transfer to multiproton translocations (MPCET) provides a bioinspired mechanism to transport protons away from the redox site. This expansion has been accomplished by separating the initial phenolic proton donor from the pyridine-based terminal proton acceptor by a Grotthuss-type proton wire made up of concatenated benzimidazoles that form a hydrogen-bonded network. However, it was found that the midpoint potential of the phenol oxidation that launched the Grotthuss-type proton translocations is a function of the number of benzimidazoles in the hydrogen-bonded network; it becomes less positive (i.e., a weaker oxidant) as the number of bridging benzimidazoles increases. Herein, we report a strategy to maintain the high redox potential necessary for oxidative processes relevant to artificial photosynthesis, e.g., water oxidation and long-range MPCET processes for managing protons. The integrated structural and functional roles of the benzimidazole-based bridge provide sites for substitution of the benzimidazoles with electron-withdrawing groups (e.g., trifluoromethyl groups). Such substitution increases the midpoint potential of the phenoxyl radical/phenol couple so that proton translocations over ∼11 Å become thermodynamically comparable to that of an unsubstituted system where one proton is transferred over ∼2.5 Å. The extended, substituted system maintains the hydrogen-bonded network; infrared spectroelectrochemistry confirms reversible proton translocations from the phenol to the pyridyl terminal proton acceptor upon oxidation and reduction. Theory supports the change in driving force with added electron-withdrawing groups and provides insight into the role of electron density and electrostatic potential in MPCET processes associated with these Grotthuss-type proton translocations.
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Affiliation(s)
- Emmanuel Odella
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Maxim Secor
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Edgar A Reyes Cruz
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Walter D Guerra
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - María N Urrutia
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - Paul A Liddell
- 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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Stathi P, Fotou E, Moussis V, Tsikaris V, Louloudi M, Deligiannakis Y. Control of Tyrosyl Radical Stabilization by {SiO 2@Oligopeptide} Hybrid Biomimetic Materials. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:9799-9809. [PMID: 35915965 DOI: 10.1021/acs.langmuir.2c00710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Tyrosine radicals are notoriously short-lived/unstable in solution, while they present an impressive degree of stability and versatility in bioenzymes. Herein, we have developed a library of hybrid biomimetic materials (HBMs), which consists of tyrosine-containing oligopeptides covalently grafted on SiO2 nanoparticles, and studied the formation, lifetime, and redox properties of tyrosyl radicals. Using electron paramagnetic resonance spectroscopy, we have studied the radical-spin distribution as a probe of the local microenvironment of the tyrosyl radicals in the HBMs. We find that the lifetime of the tyrosyl radical can be enhanced by up to 6 times, by adjusting three factors, namely, a proximal histidine, the length of the oligopeptide, and the interface with the SiO2 nanomatrix. This is shown to be correlated to a significant lowering of E1/2 from +736 mV, in free tyrosine, to +548 mV in the {12-peptide}@SiO2 material. Moreover, we show that grafting on SiO2 lowers the E1/2 of tyrosine radicals by ∼50 mV in all oligopeptides. Analysis of the spin-distribution by EPR reveals that the positioning of a histidine at a H-bonding distance from the tyrosine further favors tyrosine radical stabilization.
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Affiliation(s)
- Panagiota Stathi
- Department of Chemistry, Laboratory of Biomimetic Catalysis & Hybrid Materials, University of Ioannina, Ioannina 4550, Greece
| | - Evgenia Fotou
- Department of Chemistry, Laboratory of Protein and Peptide Chemistry, University of Ioannina, Ioannina 4550, Greece
| | - Vassilios Moussis
- Department of Chemistry, Laboratory of Protein and Peptide Chemistry, University of Ioannina, Ioannina 4550, Greece
| | - Vassilios Tsikaris
- Department of Chemistry, Laboratory of Protein and Peptide Chemistry, University of Ioannina, Ioannina 4550, Greece
| | - Maria Louloudi
- Department of Chemistry, Laboratory of Biomimetic Catalysis & Hybrid Materials, University of Ioannina, Ioannina 4550, Greece
| | - Yiannis Deligiannakis
- Department of Physics, Laboratory of Physical Chemistry of Materials & Environment, University of Ioannina, Ioannina 4550, Greece
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Odella E, Secor M, Elliott M, Groy TL, Moore TA, Hammes-Schiffer S, Moore AL. Multi PCET in symmetrically substituted benzimidazoles. Chem Sci 2021; 12:12667-12675. [PMID: 34703552 PMCID: PMC8494046 DOI: 10.1039/d1sc03782j] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Accepted: 08/21/2021] [Indexed: 12/02/2022] Open
Abstract
Proton-coupled electron transfer (PCET) reactions depend on the hydrogen-bond connectivity between sites of proton donors and acceptors. The 2-(2′-hydroxyphenyl) benzimidazole (BIP) based systems, which mimic the natural TyrZ-His190 pair of Photosystem II, have been useful for understanding the associated PCET process triggered by one-electron oxidation of the phenol. Substitution of the benzimidazole by an appropriate terminal proton acceptor (TPA) group allows for two-proton translocations. However, the prototropic properties of substituted benzimidazole rings and rotation around the bond linking the phenol and the benzimidazole can lead to isomers that interrupt the intramolecular hydrogen-bonded network and thereby prevent a second proton translocation. Herein, a strategic symmetrization of a benzimidazole based system with two identical TPAs yields an uninterrupted network of intramolecular hydrogen bonds regardless of the isomeric form. NMR data confirms the presence of a single isomeric form in the disubstituted system but not in the monosubstituted system in certain solvents. Infrared spectroelectrochemistry demonstrates a two-proton transfer process associated with the oxidation of the phenol occurring at a lower redox potential in the disubstituted system relative to its monosubstituted analogue. Computational studies support these findings and show that the disubstituted system stabilizes the oxidized two-proton transfer product through the formation of a bifurcated hydrogen bond. Considering the prototropic properties of the benzimidazole heterocycle in the context of multiple PCET will improve the next generation of novel, bioinspired constructs built by concatenated units of benzimidazoles, thus allowing proton translocations at nanoscale length. Proton-coupled electron transfer (PCET) reactions depend on the hydrogen-bond connectivity between sites of proton donors and acceptors.![]()
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Affiliation(s)
- Emmanuel Odella
- School of Molecular Sciences, Arizona State University Tempe Arizona 85287-1604 USA
| | - Maxim Secor
- Department of Chemistry, Yale University New Haven Connecticut 06520-8107 USA
| | - Mackenna Elliott
- School of Molecular Sciences, Arizona State University Tempe Arizona 85287-1604 USA
| | - Thomas L Groy
- School of Molecular Sciences, Arizona State University Tempe Arizona 85287-1604 USA
| | - Thomas A Moore
- School of Molecular Sciences, Arizona State University Tempe Arizona 85287-1604 USA
| | | | - Ana L Moore
- School of Molecular Sciences, Arizona State University Tempe Arizona 85287-1604 USA
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Morozova OB, Stass DV, Yurkovskaya AV. Kinetic evidence for the transiently shifted acidity constant of histidine linked to paramagnetic tyrosine probed by intramolecular electron transfer in oxidized peptides. Phys Chem Chem Phys 2021; 23:16698-16706. [PMID: 34338250 DOI: 10.1039/d1cp02408f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The kinetics of electron transfer (ET) from tyrosine (Tyr) to short-lived histidine (His) radicals in peptides of different structures was monitored using time-resolved chemically induced dynamic nuclear polarization (CIDNP) to follow the reduction of the His radicals using NMR detection of the diamagnetic hyperpolarized reaction products. In aqueous solution over a wide pH range, His radicals were generated in situ in the photo-induced reaction with the photosensitizer, 3,3',4,4'-tetracarboxy benzophenone. Model simulations of the CIDNP kinetics provided pH-dependent rate constants of intra- and intermolecular ET, and the pH dependencies of the reaction under study were interpreted in terms of protonation states of the reactants and the product, His with either protonated or neutral imidazole. In some cases, an increase of pKa of imidazole in the presence of the short-lived radical center at a nearby Tyr residue was revealed. Interpretation of the obtained pH dependencies made is possible to quantify the degree of paramagnetic shift of the acidity constant of the imidazole of the His residue in the peptides with a Tyr residue in its paramagnetic state, and to correlate this degree with the intramolecular ET rate constant - a higher intramolecular ET rate constant corresponded to a greater acidity constant shift.
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Affiliation(s)
- Olga B Morozova
- International Tomography Center, Institutskaya 3a, 630090 Novosibirsk, Russia.
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