1
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Woodhouse JL, Henley A, Lewin R, Ward JM, Hailes HC, Bochenkova AV, Fielding HH. A photoelectron imaging study of the deprotonated GFP chromophore anion and RNA fluorescent tags. Phys Chem Chem Phys 2021; 23:19911-19922. [PMID: 34474467 DOI: 10.1039/d1cp01901e] [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
Green fluorescent protein (GFP), together with its family of variants, is the most widely used fluorescent protein for in vivo imaging. Numerous spectroscopic studies of the isolated GFP chromophore have been aimed at understanding the electronic properties of GFP. Here, we build on earlier work [A. V. Bochenkova, C. Mooney, M. A. Parkes, J. Woodhouse, L. Zhang, R. Lewin, J. M. Ward, H. Hailes, L. H. Andersen and H. H. Fielding, Chem. Sci., 2017, 8, 3154] investigating the impact of fluorine and methoxy substituents that have been employed to tune the electronic structure of the GFP chromophore for use as fluorescent RNA tags. We present photoelectron spectra following photoexcitation over a broad range of wavelengths (364-230 nm) together with photoelectron angular distributions following photoexcitation at 364 nm, which are interpreted with the aid of quantum chemistry calculations. The results support the earlier high-level quantum chemistry calculations that predicted how fluorine and methoxy substituents tune the electronic structure and we find evidence to suggest that the methoxy substituents enhance internal conversion, most likely from the 2ππ* state which has predominantly Feshbach resonance character, to the 1ππ* state.
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Affiliation(s)
- Joanne L Woodhouse
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - Alice Henley
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - Ross Lewin
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - John M Ward
- The Advanced Centre for Biochemical Engineering, Department of Biochemical Engineering, University College London, Gower Street, London WC1E 6BT, UK
| | - Helen C Hailes
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | | | - Helen H Fielding
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
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2
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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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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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4
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Zhang TS, Fang YG, Song XF, Fang WH, Cui G. Hydrogen-Bonding Interaction Regulates Photoisomerization of a Single-Bond-Rotation Locked Photoactive Yellow Protein Chromophore in Protein. J Phys Chem Lett 2020; 11:2470-2476. [PMID: 32150415 DOI: 10.1021/acs.jpclett.0c00294] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We have employed the QM(CASPT2//CASSCF)/MM method to explore the excited-state isomerization and decay mechanism of a single-bond-rotation locked photoactive yellow protein (PYP) chromophore in wild-type and mutant proteins. The S1 state is a spectroscopically bright state in the Franck-Condon region. In this state, there exist two excited-state isomerization pathways separately related to the clockwise and anticlockwise rotations of the C=C bond. The clockwise path is favorable because of a small barrier of 2 kcal/mol and uses a novel bicycle-pedal unidirectional photoisomerization mechanism in which the involved two dihedral angles rotate asynchronously because of the reinforced hydrogen-bonding interaction between the chromophore and Cys69. Near the twisted S1 minimum, the chromophore hops to the S0 state via the S1/S0 conical intersection. Finally, the R52A mutation has small effects on the excited-state properties and photoisomerization of the locked PYP chromophore. The present work provides new insights for understanding the photochemistry of PYP chromophores in protein surroundings.
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Affiliation(s)
- Teng-Shuo Zhang
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, Chemistry College, Beijing Normal University, Beijing 100875, P.R. China
| | - Ye-Guang Fang
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, Chemistry College, Beijing Normal University, Beijing 100875, P.R. China
| | - Xiu-Fang Song
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, Chemistry College, Beijing Normal University, Beijing 100875, P.R. China
| | - Wei-Hai Fang
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, Chemistry College, Beijing Normal University, Beijing 100875, P.R. China
| | - Ganglong Cui
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, Chemistry College, Beijing Normal University, Beijing 100875, P.R. China
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5
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Bull JN, Anstöter CS, Verlet JRR. Fingerprinting the Excited-State Dynamics in Methyl Ester and Methyl Ether Anions of Deprotonated para-Coumaric Acid. J Phys Chem A 2020; 124:2140-2151. [PMID: 32105474 DOI: 10.1021/acs.jpca.9b11993] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Chromophores based on the para-hydroxycinnamate moiety are widespread in the natural world, including as the photoswitching unit in photoactive yellow protein and as a sunscreen in the leaves of plants. Here, photodetachment action spectroscopy combined with frequency- and angle-resolved photoelectron imaging is used to fingerprint the excited-state dynamics over the first three bright action-absorption bands in the methyl ester anions (pCEs-) of deprotonated para-coumaric acid at a temperature of ∼300 K. The excited states associated with the action-absorption bands are classified as resonances because they are situated in the detachment continuum and are open to autodetachment. The frequency-resolved photoelectron spectrum for pCEs- indicates that all photon energies over the S1(ππ*) band lead to similar vibrational autodetachment dynamics. The S2(nπ*) band is Herzberg-Teller active and has comparable brightness to the higher lying 21(ππ*) band. The frequency-resolved photoelectron spectrum over the S2(nπ*) band indicates more efficient internal conversion to the S1(ππ*) state for photon energies resonant with the Franck-Condon modes (∼80%) compared with the Herzberg-Teller modes (∼60%). The third action-absorption band, which corresponds to excitation of the 21(ππ*) state, shows complex and photon energy-dependent dynamics, with 20-40% of photoexcited population internally converting to the S1(ππ*) state. There is also evidence for a mode-specific competition between prompt autodetachment and internal conversion on the red edge of the 21(ππ*) band. There is no evidence for recovery of the ground electronic state and statistical electron ejection (thermionic emission) following photoexcitation over any of the three action-absorption bands. The photoelectron spectra for the deprotonated methyl ether derivative (pCEt-) at photon energies over the S1(ππ*) and S2(nπ*) bands indicate diametrically opposed dynamics compared with pCEs-, namely, intense thermionic emission due to efficient recovery of the ground electronic state.
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Affiliation(s)
- James N Bull
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, U.K
| | - Cate S Anstöter
- Department of Chemistry, Durham University, Durham DH1 3LE, U.K
| | - Jan R R Verlet
- Department of Chemistry, Durham University, Durham DH1 3LE, U.K
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6
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Muramatsu S, Nakayama S, Kinoshita SN, Onitsuka Y, Kohguchi H, Inokuchi Y, Zhu C, Ebata T. Electronic State and Photophysics of 2-Ethylhexyl-4-methoxycinnamate as UV-B Sunscreen under Jet-Cooled Condition. J Phys Chem A 2020; 124:1272-1278. [PMID: 31992045 DOI: 10.1021/acs.jpca.9b11893] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The title compound, 2-ethylhexyl-4-methoxycinnamate (2EH4MC), is known as a typical ingredient of sunscreen cosmetics that effectively converts the absorbed UV-B light to thermal energy. This energy conversion process includes the nonradiative decay (NRD): trans-cis isomerization and finally going back to the original structure with a release of thermal energy. In this study, we performed UV spectroscopy for jet-cooled 2EH4MC to investigate the electronic/geometrical structures as well as the NRD mechanism. Laser-induced-fluorescence (LIF) spectroscopy gave the well-resolved vibronic structure of the S1-S0 transition; UV-UV hole-burning (HB) spectroscopy and density functional theory (DFT) calculations revealed the presence of syn and anti isomers, where the methoxy (-OCH3) groups orient in opposite directions to each other. Picosecond UV-UV pump-probe spectroscopy revealed the NRD process from the excited singlet (S1 (1ππ*)) state occurs at a rate constant of ∼1010-1011 s-1, attributed to internal conversion (IC) to the 1nπ* state. Nanosecond UV-deep UV (DUV) pump-probe spectroscopy identified a transient triplet (T1 (3ππ*)) state, whose energy (from S0) and lifetime are 18 400 cm-1 and 20 ns, respectively. These results demonstrate that the photoisomerization of 2EH4MC includes multistep internal conversions and intersystem crossings, described as "S1 (trans, 1ππ*) → 1nπ* → T1 (3ππ*) → S0 (cis)".
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Affiliation(s)
- Satoru Muramatsu
- Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan
| | - Shingo Nakayama
- Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan
| | - Shin-Nosuke Kinoshita
- Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan
| | - Yuuki Onitsuka
- Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan
| | - Hiroshi Kohguchi
- Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan
| | - Yoshiya Inokuchi
- Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan
| | - Chaoyuan Zhu
- Department of Applied Chemistry and Institute for Molecular Science , National Chiao Tung University , Hsinchu 30010 , Taiwan.,Center for Emergent Functional Matter Science , National Chiao Tung University , Hsinchu 30010 , Taiwan
| | - Takayuki Ebata
- Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan.,Department of Applied Chemistry and Institute for Molecular Science , National Chiao Tung University , Hsinchu 30010 , Taiwan
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7
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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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8
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Parkes MA, Bennett A, Fielding HH. A photoelectron imaging and quantum chemistry study of the deprotonated cyan fluorescent protein chromophore anion. Mol Phys 2019. [DOI: 10.1080/00268976.2019.1603410] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
| | - Anabel Bennett
- Department of Chemistry, University College London, London, UK
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9
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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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10
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Woodhouse JL, Henley A, Parkes MA, Fielding HH. Photoelectron Imaging and Quantum Chemistry Study of Phenolate, Difluorophenolate, and Dimethoxyphenolate Anions. J Phys Chem A 2019; 123:2709-2718. [PMID: 30848907 DOI: 10.1021/acs.jpca.8b11121] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Joanne L. Woodhouse
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AH, U.K
| | - Alice Henley
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AH, U.K
| | - Michael A. Parkes
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AH, U.K
| | - Helen H. Fielding
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AH, U.K
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11
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Affiliation(s)
- Alice Henley
- Department of Chemistry, University College London, London, UK
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12
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Henley A, Patel AM, Parkes MA, Anderson JC, Fielding HH. Role of Photoisomerization on the Photodetachment of the Photoactive Yellow Protein Chromophore. J Phys Chem A 2018; 122:8222-8228. [PMID: 30234981 DOI: 10.1021/acs.jpca.8b07770] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photocycle of photoactive yellow protein (PYP) is initiated by a photoinduced trans-cis isomerization around a C═C bond in the chromophore that lies at the heart of the protein; however, in addition to the desired photochemical pathway, the chromophore can undergo competing electronic relaxation processes. Here we combine gas-phase anion photoelectron spectroscopy and quantum chemistry calculations to investigate how locking the C═C bond in the chromophore controls the competition between these electronic relaxation processes following photoexcitation in the range 400-310 nm. We find evidence to suggest that preventing trans-cis isomerization effectively turns off internal conversion to the ground electronic state and enhances electron emission from the first electronically excited state.
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Affiliation(s)
- Alice Henley
- Department of Chemistry , University College London , London WC1H 0AJ , United Kingdom
| | - Anand M Patel
- Department of Chemistry , University College London , London WC1H 0AJ , United Kingdom
| | - Michael A Parkes
- Department of Chemistry , University College London , London WC1H 0AJ , United Kingdom
| | - James C Anderson
- Department of Chemistry , University College London , London WC1H 0AJ , United Kingdom
| | - Helen H Fielding
- Department of Chemistry , University College London , London WC1H 0AJ , United Kingdom
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13
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Díaz-Tinoco M, Corzo HH, Ortiz JV. Electron Propagator Methods for Vertical Electron Detachment Energies of Anions: Benchmarks and Case Studies. J Chem Theory Comput 2018; 14:5881-5895. [DOI: 10.1021/acs.jctc.8b00736] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Manuel Díaz-Tinoco
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States
| | - H. H. Corzo
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States
| | - J. V. Ortiz
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States
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14
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Parkes MA, Crellin J, Henley A, Fielding HH. A photoelectron imaging and quantum chemistry study of the deprotonated indole anion. Phys Chem Chem Phys 2018; 20:15543-15549. [PMID: 29808860 DOI: 10.1039/c8cp01902a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Indole is an important molecular motif in many biological molecules and exists in its deprotonated anionic form in the cyan fluorescent protein, an analogue of green fluorescent protein. However, the electronic structure of the deprotonated indole anion has been relatively unexplored. Here, we use a combination of anion photoelectron velocity-map imaging measurements and quantum chemistry calculations to probe the electronic structure of the deprotonated indole anion. We report vertical detachment energies (VDEs) of 2.45 ± 0.05 eV and 3.20 ± 0.05 eV, respectively. The value for D0 is in agreement with recent high-resolution measurements whereas the value for D1 is a new measurement. We find that the first electronically excited singlet state of the anion, S1(ππ*), lies above the VDE and has shape resonance character with respect to the D0 detachment continuum and Feshbach resonance character with respect to the D1 continuum.
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Affiliation(s)
- Michael A Parkes
- Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.
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15
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Henley A, Diveky ME, Patel AM, Parkes MA, Anderson JC, Fielding HH. Electronic structure and dynamics of torsion-locked photoactive yellow protein chromophores. Phys Chem Chem Phys 2017; 19:31572-31580. [PMID: 29165495 DOI: 10.1039/c7cp06950b] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The photocycle of photoactive yellow protein (PYP) begins with small-scale torsional motions of the chromophore leading to large-scale movements of the protein scaffold triggering a biological response. The role of single-bond torsional molecular motions of the chromophore in the initial steps of the PYP photocycle are not fully understood. Here, we employ anion photoelectron spectroscopy measurements and quantum chemistry calculations to investigate the electronic relaxation dynamics following photoexcitation of four model chromophores, para-coumaric acid, its methyl ester, and two analogues with aliphatic bridges hindering torsional motions around the single bonds adjacent to the alkene group. Following direct photoexcitation of S1 at 400 nm, we find that both single bond rotations play a role in steering the PYP chromophore through the S1/S0 conical intersection but that rotation around the single bond between the alkene moiety and the phenoxide group is particularly important. Following photoexcitation of higher lying electronic states in the range 346-310 nm, we find that rotation around the single bond between the alkene and phenoxide groups also plays a key role in the electronic relaxation from higher lying states to the S1 state. These results have potential applications in tuning the photoresponse of photoactive proteins and materials with chromophores based on PYP.
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Affiliation(s)
- Alice Henley
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - Matus E Diveky
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - Anand M Patel
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - Michael A Parkes
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - James C Anderson
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - Helen H Fielding
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
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16
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Pimenta FM, Chiappetta G, Le Saux T, Vinh J, Jullien L, Gautier A. Chromophore Renewal and Fluorogen-Binding Tags: A Match Made to Last. Sci Rep 2017; 7:12316. [PMID: 28951577 PMCID: PMC5615068 DOI: 10.1038/s41598-017-12400-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 09/08/2017] [Indexed: 01/20/2023] Open
Abstract
Fluorogen-binding tags, which activate the fluorescence of a specific chromophore (so-called fluorogen) upon reversible binding, have recently been proposed as a way of reducing photobleaching via fluorogen renewal. However, no generic methodology has been proposed to systematically analyze the photodamage of the fluorogen and the protein tag. Using Y-FAST (Yellow Fluorescence-activating and Absorption-Shifting Tag) as a case study we propose here a generic experimental and theoretical approach to assess how fluorogen renewal reduces the apparent photobleaching rate of a fluorogen-binding tag. Y-FAST has its apparent photobleaching rate greatly reduced by fluorogen renewal and its photostability is mainly limited by oxidation of specific residues in the protein scaffold by reactive oxygen species generated by the bound fluorogen. This study sets the groundwork for the optimization of fluorogenic systems, helping guide rational improvements to their photostability.
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Affiliation(s)
- Frederico M Pimenta
- École Normale Supérieure, PSL Research University, UPMC Univ Paris 06, CNRS, Département de Chimie, PASTEUR, 24 rue Lhomond, 75005, Paris, France.,Sorbonne Universités, UPMC Univ Paris 06, ENS, CNRS, PASTEUR, 75005, Paris, France
| | - Giovanni Chiappetta
- ESPCI Biological Mass Spectrometry and Proteomics USR 3149 CNRS/ESPCI-PSL, Paris, France
| | - Thomas Le Saux
- École Normale Supérieure, PSL Research University, UPMC Univ Paris 06, CNRS, Département de Chimie, PASTEUR, 24 rue Lhomond, 75005, Paris, France.,Sorbonne Universités, UPMC Univ Paris 06, ENS, CNRS, PASTEUR, 75005, Paris, France
| | - Joëlle Vinh
- ESPCI Biological Mass Spectrometry and Proteomics USR 3149 CNRS/ESPCI-PSL, Paris, France
| | - Ludovic Jullien
- École Normale Supérieure, PSL Research University, UPMC Univ Paris 06, CNRS, Département de Chimie, PASTEUR, 24 rue Lhomond, 75005, Paris, France. .,Sorbonne Universités, UPMC Univ Paris 06, ENS, CNRS, PASTEUR, 75005, Paris, France.
| | - Arnaud Gautier
- École Normale Supérieure, PSL Research University, UPMC Univ Paris 06, CNRS, Département de Chimie, PASTEUR, 24 rue Lhomond, 75005, Paris, France. .,Sorbonne Universités, UPMC Univ Paris 06, ENS, CNRS, PASTEUR, 75005, Paris, France.
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17
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Beekmeyer R, Parkes MA, Ridgwell L, Riley JW, Chen J, Feringa BL, Kerridge A, Fielding HH. Unravelling the electronic structure and dynamics of an isolated molecular rotary motor in the gas-phase. Chem Sci 2017; 8:6141-6148. [PMID: 28989644 PMCID: PMC5627543 DOI: 10.1039/c7sc01997a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 06/27/2017] [Indexed: 11/21/2022] Open
Abstract
Light-driven molecular motors derived from chiral overcrowded alkenes are an important class of compounds in which sequential photochemical and thermal rearrangements result in unidirectional rotation of one part of the molecule with respect to another. Here, we employ anion photoelectron spectroscopy to probe the electronic structure and dynamics of a unidirectional molecular rotary motor anion in the gas-phase and quantum chemistry calculations to guide the interpretation of our results. We find that following photoexcitation of the first electronically excited state, the molecule rotates around its axle and some population remains on the excited potential energy surface and some population undergoes internal conversion back to the electronic ground state. These observations are similar to those observed in time-resolved measurements of rotary molecular motors in solution. This work demonstrates the potential of anion photoelectron spectroscopy for studying the electronic structure and dynamics of molecular motors in the gas-phase, provides important benchmarks for theory and improves our fundamental understanding of light-activated molecular rotary motors, which can be used to inform the design of new photoactivated nanoscale devices.
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Affiliation(s)
- Reece Beekmeyer
- Department of Chemistry , University College London , 20 Gordon Street , London , WC1H 0AJ , UK .
| | - Michael A Parkes
- Department of Chemistry , University College London , 20 Gordon Street , London , WC1H 0AJ , UK .
| | - Luke Ridgwell
- Department of Chemistry , University College London , 20 Gordon Street , London , WC1H 0AJ , UK .
| | - Jamie W Riley
- Department of Chemistry , University College London , 20 Gordon Street , London , WC1H 0AJ , UK .
| | - Jiawen Chen
- Stratingh Institute for Chemistry , University of Groningen , Nijenborgh 4 , 9747 AG Groningen , The Netherlands
| | - Ben L Feringa
- Stratingh Institute for Chemistry , University of Groningen , Nijenborgh 4 , 9747 AG Groningen , The Netherlands
| | - Andrew Kerridge
- Department of Chemistry , Lancaster University , Lancaster , LA1 4YB , UK
| | - Helen H Fielding
- Department of Chemistry , University College London , 20 Gordon Street , London , WC1H 0AJ , UK .
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18
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Milanese JM, Provorse MR, Alameda E, Isborn CM. Convergence of Computed Aqueous Absorption Spectra with Explicit Quantum Mechanical Solvent. J Chem Theory Comput 2017; 13:2159-2171. [DOI: 10.1021/acs.jctc.7b00159] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Joel M. Milanese
- Chemistry and Chemical Biology, University of California at Merced, Merced, California 95343, United States
| | - Makenzie R. Provorse
- Chemistry and Chemical Biology, University of California at Merced, Merced, California 95343, United States
| | - Enrique Alameda
- Chemistry and Chemical Biology, University of California at Merced, Merced, California 95343, United States
| | - Christine M. Isborn
- Chemistry and Chemical Biology, University of California at Merced, Merced, California 95343, United States
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19
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Bochenkova AV, Mooney CRS, Parkes MA, Woodhouse JL, Zhang L, Lewin R, Ward JM, Hailes HC, Andersen LH, Fielding HH. Mechanism of resonant electron emission from the deprotonated GFP chromophore and its biomimetics. Chem Sci 2017; 8:3154-3163. [PMID: 28507691 PMCID: PMC5413970 DOI: 10.1039/c6sc05529j] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2016] [Accepted: 02/04/2017] [Indexed: 11/29/2022] Open
Abstract
The Green Fluorescent Protein (GFP), which is widely used in bioimaging, is known to undergo light-induced redox transformations. Electron transfer is thought to occur resonantly through excited states of its chromophore; however, a detailed understanding of the electron gateway states of the chromophore is still missing. Here, we use photoelectron spectroscopy and high-level quantum chemistry calculations to show that following UV excitation, the ultrafast electron dynamics in the chromophore anion proceeds via an excited shape resonance strongly coupled to the open continuum. The impact of this state is found across the entire 355-315 nm excitation range, from above the first bound-bound transition to below the opening of higher-lying continua. By disentangling the electron dynamics in the photodetachment channels, we provide an important reference for the adiabatic position of the electron gateway state, which is located at 348 nm, and discover the source of the curiously large widths of the photoelectron spectra that have been reported in the literature. By introducing chemical modifications to the GFP chromophore, we show that the detachment threshold and the position of the gateway state, and hence the underlying excited-state dynamics, can be changed systematically. This enables a fine tuning of the intrinsic electron emission properties of the GFP chromophore and has significant implications for its function, suggesting that the biomimetic GFP chromophores are more stable to photooxidation.
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Affiliation(s)
| | - Ciarán R S Mooney
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Michael A Parkes
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Joanne L Woodhouse
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Lijuan Zhang
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Ross Lewin
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - John M Ward
- Department of Biochemical Engineering , UCL , Bernard Katz Building, Gordon Street , London , WC1E 0AH , UK
| | - Helen C Hailes
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Lars H Andersen
- Department of Physics and Astronomy , Aarhus University , DK-8000 Aarhus C , Denmark
| | - Helen H Fielding
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
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20
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Tay J, Parkes MA, Addison K, Chan Y, Zhang L, Hailes HC, Bulman Page PC, Meech SR, Blancafort L, Fielding HH. The Effect of Conjugation on the Competition between Internal Conversion and Electron Detachment: A Comparison between Green Fluorescent and Red Kaede Protein Chromophores. J Phys Chem Lett 2017; 8:765-771. [PMID: 28124921 DOI: 10.1021/acs.jpclett.7b00174] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Kaede, an analogue of green fluorescent protein (GFP), is a green-to-red photoconvertible fluorescent protein used as an in vivo "optical highlighter" in bioimaging. The fluorescence quantum yield of the red Kaede protein is lower than that of GFP, suggesting that increasing the conjugation modifies the electronic relaxation pathway. Using a combination of anion photoelectron spectroscopy and electronic structure calculations, we find that the isolated red Kaede protein chromophore in the gas phase is deprotonated at the imidazole ring, unlike the GFP chromophore that is deprotonated at the phenol ring. We find evidence of an efficient electronic relaxation pathway from higher-lying electronically excited states to the S1 state of the red Kaede chromophore that is not accessible in the GFP chromophore. Rapid autodetachment from high-lying vibrational states of S1 is found to compete efficiently with internal conversion to the ground electronic state.
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Affiliation(s)
- Jamie Tay
- Department of Chemistry, University College London , 20 Gordon Street, London WC1H 0AJ, U.K
| | - Michael A Parkes
- Department of Chemistry, University College London , 20 Gordon Street, London WC1H 0AJ, U.K
| | - Kiri Addison
- School of Chemistry, University of East Anglia , Norwich NR4 7TJ, U.K
| | - Yohan Chan
- School of Chemistry, University of East Anglia , Norwich NR4 7TJ, U.K
| | - Lijuan Zhang
- Department of Chemistry, University College London , 20 Gordon Street, London WC1H 0AJ, U.K
| | - Helen C Hailes
- Department of Chemistry, University College London , 20 Gordon Street, London WC1H 0AJ, U.K
| | | | - Stephen R Meech
- School of Chemistry, University of East Anglia , Norwich NR4 7TJ, U.K
| | - Lluís Blancafort
- Institut de Química Computacional i Catàlisi and Departament de Química, Facultat de Ciències, Universitat de Girona , Campus de Montilivi, C/M. A. Campmany 69, 17003 Girona, Spain
| | - Helen H Fielding
- Department of Chemistry, University College London , 20 Gordon Street, London WC1H 0AJ, U.K
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21
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García-Prieto FF, Muñoz-Losa A, Fdez Galván I, Sánchez ML, Aguilar MA, Martín ME. QM/MM Study of Substituent and Solvent Effects on the Excited State Dynamics of the Photoactive Yellow Protein Chromophore. J Chem Theory Comput 2017; 13:737-748. [PMID: 28072537 DOI: 10.1021/acs.jctc.6b01069] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Substituent and solvent effects on the excited state dynamics of the Photoactive Yellow Protein chromophore are studied using the average solvent electrostatic potential from molecular dynamics (ASEP/MD) method. Four molecular models were considered: the ester and thioester derivatives of the p-coumaric acid anion and their methylated derivatives. We found that the solvent produces dramatic modifications on the free energy profile of the S1 state: 1) Two twisted structures that are minima in the gas phase could not be located in aqueous solution. 2) Conical intersections (CIs) associated with the rotation of the single bond adjacent to the phenyl group are found for the four derivatives in water solution but only for thio derivatives in the gas phase. 3) The relative stability of minima and CIs is reverted with respect to the gas phase values, affecting the prevalent de-excitation paths. As a consequence of these changes, three competitive de-excitation channels are open in aqueous solution: the fluorescence emission from a planar minimum on S1, the trans-cis photoisomerization through a CI that involves the rotation of the vinyl double bond, and the nonradiative, nonreactive, de-excitation through the CI associated with the rotation of the single bond adjacent to the phenyl group. In the gas phase, the minima are the structures with the lower energy, while in solution these are the conical intersections. In solution, the de-excitation prevalent path seems to be the photoisomerization for oxo compounds, while thio compounds return to the initial trans ground state without emission.
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Affiliation(s)
- Francisco F García-Prieto
- Área de Química Física, University of Extremadura , Avda. Elvas s/n, Edif. José Ma Viguera Lobo 3a planta, Badajoz, 06006 Spain
| | - Aurora Muñoz-Losa
- Área de Química Física, University of Extremadura , Avda. Elvas s/n, Edif. José Ma Viguera Lobo 3a planta, Badajoz, 06006 Spain
| | - Ignacio Fdez Galván
- Department of Chemistry-Ångström, The Theoretical Chemistry Programme, Uppsala University , Box 518, 751 20 Uppsala, Sweden
| | - M Luz Sánchez
- Área de Química Física, University of Extremadura , Avda. Elvas s/n, Edif. José Ma Viguera Lobo 3a planta, Badajoz, 06006 Spain
| | - Manuel A Aguilar
- Área de Química Física, University of Extremadura , Avda. Elvas s/n, Edif. José Ma Viguera Lobo 3a planta, Badajoz, 06006 Spain
| | - M Elena Martín
- Área de Química Física, University of Extremadura , Avda. Elvas s/n, Edif. José Ma Viguera Lobo 3a planta, Badajoz, 06006 Spain
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22
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McLaughlin C, Assmann M, Parkes MA, Woodhouse JL, Lewin R, Hailes HC, Worth GA, Fielding HH. ortho and para chromophores of green fluorescent protein: controlling electron emission and internal conversion. Chem Sci 2017; 8:1621-1630. [PMID: 29780449 PMCID: PMC5933426 DOI: 10.1039/c6sc03833f] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 11/05/2016] [Indexed: 12/22/2022] Open
Abstract
Green fluorescent protein (GFP) continues to play an important role in the biological and biochemical sciences as an efficient fluorescent probe and is also known to undergo light-induced redox transformations. Here, we employ photoelectron spectroscopy and quantum chemistry calculations to investigate how the phenoxide moiety controls the competition between electron emission and internal conversion in the isolated GFP chromophore anion, following photoexcitation with ultraviolet light in the range 400-230 nm. We find that moving the phenoxide group from the para position to the ortho position enhances internal conversion back to the ground electronic state but that adding an additional OH group to the para chromophore, at the ortho position, impedes internal conversion. Guided by quantum chemistry calculations, we interpret these observations in terms of torsions around the C-C-C bridge being enhanced by electrostatic repulsions or impeded by the formation of a hydrogen-bonded seven-membered ring. We also find that moving the phenoxide group from the para position to the ortho position reduces the energy required for detachment processes, whereas adding an additional OH group to the para chromophore at the ortho position increases the energy required for detachment processes. These results have potential applications in tuning light-induced redox processes of this biologically and technologically important fluorescent protein.
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Affiliation(s)
- Conor McLaughlin
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Mariana Assmann
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Michael A Parkes
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Joanne L Woodhouse
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Ross Lewin
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Helen C Hailes
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Graham A Worth
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
| | - Helen H Fielding
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , UK .
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23
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Woodhouse JL, Assmann M, Parkes MA, Grounds H, Pacman SJ, Anderson JC, Worth GA, Fielding HH. Photoelectron spectroscopy of isolated luciferin and infraluciferin anions in vacuo: competing photodetachment, photofragmentation and internal conversion. Phys Chem Chem Phys 2017; 19:22711-22720. [DOI: 10.1039/c7cp04815g] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The electronic structure and dynamics of luciferin and infraluciferin have been investigated using photoelectron spectroscopy and quantum chemistry calculations.
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Affiliation(s)
| | - Mariana Assmann
- Department of Chemistry
- University College London
- London WC1H 0AJ
- UK
| | | | - Helen Grounds
- Department of Chemistry
- University College London
- London WC1H 0AJ
- UK
| | - Steven J. Pacman
- Department of Chemistry
- University College London
- London WC1H 0AJ
- UK
| | | | - Graham A. Worth
- Department of Chemistry
- University College London
- London WC1H 0AJ
- UK
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24
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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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25
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Parkes MA, Phillips C, Porter MJ, Fielding HH. Controlling electron emission from the photoactive yellow protein chromophore by substitution at the coumaric acid group. Phys Chem Chem Phys 2016; 18:10329-36. [PMID: 27025529 DOI: 10.1039/c6cp00565a] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Understanding how the interactions between a chromophore and its surrounding protein control the function of a photoactive protein remains a challenge. Here, we present the results of photoelectron spectroscopy measurements and quantum chemistry calculations aimed at investigating how substitution at the coumaryl tail of the photoactive yellow protein chromophore controls competing relaxation pathways following photoexcitation of isolated chromophores in the gas phase with ultraviolet light in the range 350-315 nm. The photoelectron spectra are dominated by electrons resulting from direct detachment and fast detachment from the 2(1)ππ* state but also have a low electron kinetic energy component arising from autodetachment from lower lying electronically excited states or thermionic emission from the electronic ground state. We find that substituting the hydrogen atom of the carboxylic acid group with a methyl group lowers the threshold for electron detachment but has very little effect on the competition between the different relaxation pathways, whereas substituting with a thioester group raises the threshold for electron detachment and appears to 'turn off' the competing electron emission processes from lower lying electronically excited states. This has potential implications in terms of tuning the light-induced electron donor properties of photoactive yellow protein.
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Affiliation(s)
- Michael A Parkes
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
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26
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García-Prieto FF, Muñoz-Losa A, Luz Sánchez M, Elena Martín M, Aguilar MA. Solvent effects on de-excitation channels in the p-coumaric acid methyl ester anion, an analogue of the photoactive yellow protein (PYP) chromophore. Phys Chem Chem Phys 2016; 18:27476-27485. [DOI: 10.1039/c6cp03541h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Environmental effects on the deactivation channels of the PYP chromophore in the gas phase and water solution are compared at the CASPT2//CASSCF/cc-pVDZ level.
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Affiliation(s)
| | - Aurora Muñoz-Losa
- Institute of Theoretical Chemistry
- Faculty of Chemistry
- University of Vienna
- A-1090 Vienna
- Austria
| | - M. Luz Sánchez
- Área de Química Física
- University of Extremadura
- 06006 Badajoz
- Spain
| | - M. Elena Martín
- Área de Química Física
- University of Extremadura
- 06006 Badajoz
- Spain
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