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Gibbard JA, Castracane E, Krylov AI, Continetti RE. Photoelectron photofragment coincidence spectroscopy of aromatic carboxylates: benzoate and p-coumarate. Phys Chem Chem Phys 2021; 23:18414-18424. [PMID: 34612382 DOI: 10.1039/d1cp02972j] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Photoelectron-photofragment coincidence spectroscopy was used to study the dissociation dynamics of the conjugate bases of benzoic acid and p-coumaric acid. Upon photodetachment at 266 nm (4.66 eV) both aromatic carboxylates undergo decarboxylation, as well as the formation of stable carboxyl radicals. The key energetics are computed using high-level electronic structure methods. The dissociation dynamics of benzoate were dominated by a two-body DPD channel resulting in CO2 + C6H5 + e-, with a very small amount of stable C6H5CO2 showing that the radical ground state is stable and the excited states are dissociative. For p-coumarate (p-CA-) the dominant channel is photodetachment resulting in a stable radical and a photoelectron with electron kinetic energy (eKE) <2 eV. We also observed a minor two-body dissociative photodetachment (DPD) channel resulting in CO2 + HOC6H4CHCH + e-, characterized by eKE <0.8 eV. Evidence was also found for a three-body ionic photodissociation channel producing HOC6H5 + HCC- + CO2. The ion beam contained both the phenolate and carboxylate isomers of p-CA-, but DPD only occurred from the carboxylate form. For both species DPD is seen from the first and second excited states of the radical, where vibrational excitation is required for decarboxylation from the first excited radical state.
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Affiliation(s)
- J A Gibbard
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0340, USA.
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Langeland J, Persen NW, Gruber E, Kiefer HV, Kabylda AM, Bochenkova AV, Andersen LH. Controlling Light-Induced Proton Transfer from the GFP Chromophore. Chemphyschem 2021; 22:833-841. [PMID: 33591586 DOI: 10.1002/cphc.202100068] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 02/16/2021] [Indexed: 01/01/2023]
Abstract
Green Fluorescent Protein (GFP) is known to undergo excited-state proton transfer (ESPT). Formation of a short H-bond favors ultrafast ESPT in GFP-like proteins, such as the GFP S65T/H148D mutant, but the detailed mechanism and its quantum nature remain to be resolved. Here we study in vacuo, light-induced proton transfer from the GFP chromophore in hydrogen-bonded complexes with two anionic proton acceptors, I- and deprotonated trichloroacetic acid (TCA- ). We address the role of the strong H-bond and the quantum mechanical proton-density distribution in the excited state, which determines the proton-transfer probability. Our study shows that chemical modifications to the molecular network drastically change the proton-transfer probability and it can become strongly wavelength dependent. The proton-transfer branching ratio is found to be 60 % for the TCA complex and 10 % for the iodide complex, being highly dependent on the photon energy in the latter case. Using high-level ab initio calculations, we show that light-induced proton transfer takes place in S1 , revealing intrinsic photoacid properties of the isolated GFP chromophore in strongly bound H-bonded complexes. ESPT is found to be very sensitive to the topography of the highly anharmonic potential in S1 , depending on the quantum-density distribution upon vibrational excitation. We also show that the S1 potential-energy surface, and hence excited-state proton transfer, can be controlled by altering the chromophore microenvironment.
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Affiliation(s)
- Jeppe Langeland
- Department of Physics and Astronomy, Aarhus University, DK-8000, Aarhus C, Denmark
| | - Natascha W Persen
- Department of Physics and Astronomy, Aarhus University, DK-8000, Aarhus C, Denmark
| | - Elisabeth Gruber
- Department of Physics and Astronomy, Aarhus University, DK-8000, Aarhus C, Denmark
| | - Hjalte V Kiefer
- Department of Physics and Astronomy, Aarhus University, DK-8000, Aarhus C, Denmark
| | - Adil M Kabylda
- Department of Chemistry, Lomonosov Moscow State University, 119991, Moscow, Russia
| | | | - Lars H Andersen
- Department of Physics and Astronomy, Aarhus University, DK-8000, Aarhus C, Denmark
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3
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Gibbard JA, Continetti RE. Photoelectron photofragment coincidence spectroscopy of carboxylates. RSC Adv 2021; 11:34250-34261. [PMID: 35497305 PMCID: PMC9042398 DOI: 10.1039/d1ra06340e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2021] [Accepted: 10/06/2021] [Indexed: 12/23/2022] Open
Abstract
Photoelectron–photofragment coincidence (PPC) spectroscopy is a powerful technique for studying the decarboxylation dynamics of carboxyl radicals. Measurement of photoelectron and photofragment kinetic energies in coincidence provides a kinematically complete measure of the dissociative photodetachment (DPD) dynamics of carboxylate anions. PPC spectroscopy studies of methanoate, ethanoate, propanoate, 2-butenoate, benzoate, p-coumarate and the oxalate monoanion are reviewed. All of the systems studied undergo decarboxylation via a two-body DPD channel i.e., driven by the thermodynamic stability of CO2. Additionally, decarboxylation is observed via a three-body ionic photodissociation channel for p-coumarate. In some cases photodetachment also results in a stable carboxyl radical (RCO2). The branching ratio for DPD, the threshold detachment energy and the peak of the kinetic energy release spectrum are compared for different carboxylates, as a probe of the character of the potential energy landscape in the Franck–Condon region. Photoelectron photofragment coincidence spectroscopy studies of a range of carboxylate anions are reviewed, revealing details of the decarboxylation dynamics of carboxyl radicals.![]()
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Affiliation(s)
- J. A. Gibbard
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr, La Jolla, Ca, 92093-0340, USA
| | - R. E. Continetti
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr, La Jolla, Ca, 92093-0340, USA
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Bull JN, Anstöter CS, Verlet JRR. Ultrafast valence to non-valence excited state dynamics in a common anionic chromophore. Nat Commun 2019; 10:5820. [PMID: 31862884 PMCID: PMC6925192 DOI: 10.1038/s41467-019-13819-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Accepted: 11/27/2019] [Indexed: 12/19/2022] Open
Abstract
Non-valence states in neutral molecules (Rydberg states) have well-established roles and importance in photochemistry, however, considerably less is known about the role of non-valence states in photo-induced processes in anions. Here, femtosecond time-resolved photoelectron imaging is used to show that photoexcitation of the S1(ππ*) state of the methyl ester of deprotonated para-coumaric acid – a model chromophore for photoactive yellow protein (PYP) – leads to a bifurcation of the excited state wavepacket. One part remains on the S1(ππ*) state forming a twisted intermediate, whilst a second part leads to the formation of a non-valence (dipole-bound) state. Both populations eventually decay independently by vibrational autodetachment. Valence-to-non-valence internal conversion has hitherto not been observed in the intramolecular photophysics of an isolated anion, raising questions into how common such processes might be, given that many anionic chromophores have bright valence states near the detachment threshold. Photoactive biomolecules rely on chromophores whose photochemistry depends on the environment. Here, the excited state dynamics of a model for the anionic biochromophore in photoactive yellow protein is investigated by time-resolved photoelectron spectroscopy showing involvement of a non-valence state, and lack of E-Z isomerisation in the gas phase.
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Affiliation(s)
- James N Bull
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich, NR4 7TJ, UK
| | - Cate S Anstöter
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK
| | - Jan R R Verlet
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK.
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Bull JN, Silva GD, Scholz MS, Carrascosa E, Bieske EJ. Photoinitiated Intramolecular Proton Transfer in Deprotonated para-Coumaric Acid. J Phys Chem A 2019; 123:4419-4430. [DOI: 10.1021/acs.jpca.9b02023] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- James N. Bull
- School of Chemistry, University of Melbourne, Parkville, VIC 3010, Australia
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, United Kingdom
| | - Gabriel da Silva
- Department of Chemical Engineering, University of Melbourne, Parkville, VIC 3010, Australia
| | - Michael S. Scholz
- School of Chemistry, University of Melbourne, Parkville, VIC 3010, Australia
| | - Eduardo Carrascosa
- School of Chemistry, University of Melbourne, Parkville, VIC 3010, Australia
| | - Evan J. Bieske
- School of Chemistry, University of Melbourne, Parkville, VIC 3010, Australia
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Safko TM, Jiang S, Zhang L, Zhang Q, Weiss RG. Proton-coupled charge-transfer reactions and photoacidity of N,N-dimethyl-3-arylpropan-1-ammonium chloride salts. Photochem Photobiol Sci 2017; 16:972-984. [DOI: 10.1039/c7pp00044h] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Excited-state, intermolecular proton-transfers of aromatics tethered to ammonium groups are solvent mediated and coupled to either the formation of an exciplex or a solvent-separated ion pair.
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Affiliation(s)
| | - Shenlong Jiang
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- Synergetic Innovation Center of Quantum Information and Quantum Physics
- University of Science and Technology of China
- Hefei
| | - Lei Zhang
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- Synergetic Innovation Center of Quantum Information and Quantum Physics
- University of Science and Technology of China
- Hefei
| | - Qun Zhang
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- Synergetic Innovation Center of Quantum Information and Quantum Physics
- University of Science and Technology of China
- Hefei
| | - Richard G. Weiss
- Department of Chemistry
- Georgetown University
- Washington
- USA
- Institute for Soft Matter Synthesis and Metrology
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Anstöter CS, Dean CR, Verlet JRR. Chromophores of chromophores: a bottom-up Hückel picture of the excited states of photoactive proteins. Phys Chem Chem Phys 2017; 19:29772-29779. [DOI: 10.1039/c7cp05766k] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Many photoactive proteins contain chromophores based on para-substituted phenolate anions which are an essential component of their electronic structure.
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