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Mohamed A, Edington SC, Secor M, Breton JR, Hammes-Schiffer S, Johnson MA. Spectroscopic Characterization of the Divalent Metal Docking Motif to Isolated Cyanobenzoate: Direct Observation of Tridentate Binding to ortho-Cyanobenzoate and Implications for the CN Response. J Phys Chem A 2023; 127:1413-1421. [PMID: 36748882 DOI: 10.1021/acs.jpca.2c07658] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Cryogenic ion vibrational spectra of D2-tagged cyanobenzoate (CBA) derivatives are obtained and analyzed to characterize the intrinsic spectroscopic responses of the -CO2- headgroup to its location on the ring in both the isolated anions and the cationic complexes with divalent metal ions, M2+ (M = Mg, Ca, Sr). The benzonitrile functionality establishes the different ring isomers (para, meta, ortho) according to the location of the carboxylate and provides an additional reporter on the molecular response to the proximal charge center. The aromatic carboxylates display shifts slightly smaller than those observed for a related aliphatic system upon metal ion complexation. Although the CBA anions display very similar band patterns for all three ring positions, upon complexation with metal ions, the ortho isomer yields dramatically different spectral responses in both the -CO2- moiety and the CN group. This behavior is traced to the emergence of a tridentate binding motif unique to the ortho isomer in which the metal ions bind to both the oxygen atoms of the carboxylate group and the N atom of the cyano group. In that configuration, the -CO2- moiety is oriented perpendicular to the phenyl ring, and the CN stretching fundamental is both strong and red-shifted relative to its behavior in the isolated neutral. The behaviors of the metal-bound ortho complexes occur in contrast to the usual blue shifts associated with "Lewis" type binding of metal ions end-on to -CN. The origins of these spectroscopic features are analyzed with the aid of electronic structure calculations, which also explore differences expected for complexation of monovalent cations to the ortho carboxylate. The resulting insights have implications for understanding the balance between electrostatic and steric interactions at metal binding sites in chemical and biological systems.
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Affiliation(s)
- Ahmed Mohamed
- Sterling Chemistry Laboratory Department of Chemistry, Yale University, New Haven, Connecticut 06512, United States
| | - Sean C Edington
- Sterling Chemistry Laboratory Department of Chemistry, Yale University, New Haven, Connecticut 06512, United States
| | - Maxim Secor
- Sterling Chemistry Laboratory Department of Chemistry, Yale University, New Haven, Connecticut 06512, United States
| | - James R Breton
- Sterling Chemistry Laboratory Department of Chemistry, Yale University, New Haven, Connecticut 06512, United States
| | - Sharon Hammes-Schiffer
- Sterling Chemistry Laboratory Department of Chemistry, Yale University, New Haven, Connecticut 06512, United States
| | - Mark A Johnson
- Sterling Chemistry Laboratory Department of Chemistry, Yale University, New Haven, Connecticut 06512, United States
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Abstract
The utilization of artificial neural networks (ANNs) provides strategies for accelerating molecular simulations. Herein, ANNs are implemented as propagators of the time-dependent Schrödinger equation to simulate the quantum dynamics of systems with time-dependent potentials. These ANN propagators are trained to map nonstationary wavepackets from a given time to a future time within the discrete variable representation. Each propagator is trained for a specified time step, and iterative application of the propagator enables the propagation of wavepackets over long time scales. Such ANN propagators are developed and applied to one- and two-dimensional proton transfer systems, which exhibit nuclear quantum effects such as hydrogen tunneling. These ANN propagators are trained for either a specific time-independent potential or general potentials that can be time-dependent. Hierarchical, multiple time step algorithms enable parallelization, and the extension to higher dimensions is straightforward. This strategy is applicable to quantum dynamical simulations of diverse chemical and biological processes.
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Affiliation(s)
- Maxim Secor
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Alexander V Soudackov
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Secor M, Soudackov AV, Hammes-Schiffer S. Artificial Neural Networks as Mappings between Proton Potentials, Wave Functions, Densities, and Energy Levels. J Phys Chem Lett 2021; 12:2206-2212. [PMID: 33630595 PMCID: PMC8021271 DOI: 10.1021/acs.jpclett.1c00229] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Artificial neural networks (ANNs) have become important in quantum chemistry. Herein, applications to nuclear quantum effects, such as zero-point energy, vibrationally excited states, and hydrogen tunneling, are explored. ANNs are used to solve the time-independent Schrödinger equation for single- and double-well potentials representing hydrogen-bonded molecular systems capable of proton transfer. ANN mappings are trained to predict the lowest five proton vibrational energies, wave functions, and densities from the proton potentials and to predict the excited state proton vibrational energies and densities from the proton ground state density. For the inverse problem, ANN mappings are trained to predict the proton potential from the proton vibrational energy levels or the proton ground state density. This latter mapping is theoretically justified by the first Hohenberg-Kohn theorem establishing a one-to-one correspondence between the external potential and the ground state density. ANNs for two- and three-dimensional systems are also presented to illustrate the straightforward extension to higher dimensions.
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Affiliation(s)
- Maxim Secor
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520
| | - Alexander V. Soudackov
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520
| | - Sharon Hammes-Schiffer
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520
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Guerra WD, Odella E, Secor M, Goings JJ, Urrutia MN, Wadsworth BL, Gervaldo M, Sereno LE, Moore TA, Moore GF, Hammes-Schiffer S, Moore AL. Role of Intact Hydrogen-Bond Networks in Multiproton-Coupled Electron Transfer. J Am Chem Soc 2020; 142:21842-21851. [DOI: 10.1021/jacs.0c10474] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Walter D. Guerra
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, United States
| | - 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
| | - Joshua J. Goings
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - María N. Urrutia
- 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
| | - 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
| | - 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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Goldsmith Z, Secor M, Hammes-Schiffer S. Inhomogeneity of Interfacial Electric Fields at Vibrational Probes on Electrode Surfaces. ACS Cent Sci 2020; 6:304-311. [PMID: 32123749 PMCID: PMC7047426 DOI: 10.1021/acscentsci.9b01297] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Indexed: 05/06/2023]
Abstract
Electric fields control chemical reactivity in a wide range of systems, including enzymes and electrochemical interfaces. Characterizing the electric fields at electrode-solution interfaces is critical for understanding heterogeneous catalysis and associated energy conversion processes. To address this challenge, recent experiments have probed the response of the nitrile stretching frequency of 4-mercaptobenzonitrile (4-MBN) attached to a gold electrode to changes in the solvent and applied electrode potential. Herein, this system is modeled with periodic density functional theory using a multilayer dielectric continuum treatment of the solvent and at constant applied potentials. The impact of the solvent dielectric constant and the applied electrode potential on the nitrile stretching frequency computed with a grid-based method is in qualitative agreement with the experimental data. In addition, the interfacial electrostatic potentials and electric fields as a function of applied potential were calculated directly with density functional theory. Substantial spatial inhomogeneity of the interfacial electric fields was observed, including oscillations in the region of the molecular probe attached to the electrode. These simulations highlight the microscopic inhomogeneity of the electric fields and the role of molecular polarizability at electrode-solution interfaces, thereby demonstrating the limitations of mean-field models and providing insights relevant to the interpretation of vibrational Stark effect experiments.
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Małolepsza E, Secor M, Keyes T. Isobaric Molecular Dynamics Version of the Generalized Replica Exchange Method (gREM): Liquid–Vapor Equilibrium. J Phys Chem B 2015; 119:13379-84. [DOI: 10.1021/acs.jpcb.5b07614] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Edyta Małolepsza
- Department of Chemistry, Boston University, Boston, Massachusetts 02215-2521, United States
| | - Maxim Secor
- Department of Chemistry, Boston University, Boston, Massachusetts 02215-2521, United States
| | - Tom Keyes
- Department of Chemistry, Boston University, Boston, Massachusetts 02215-2521, United States
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Secor M. Mimi Secor: nurse practitioner entrepreneur. Interview by Karna Bramble. Nurse Pract Forum 1991; 2:142-3. [PMID: 1840961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Connolly J, Secor M. Cortisone treatment of pathologic fracture through a bone cyst. Nebr Med J 1982; 67:286-7. [PMID: 7144974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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