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Diop M, El-Hayek M, Attard J, Muhieddine A, Veremeienko V, Soorkia S, Carbonnière P, de la Lande A, Soep B, Shafizadeh N. Chlorophyll and pheophytin protonated and deprotonated ions: Observation and theory. J Chem Phys 2023; 159:194308. [PMID: 37987519 DOI: 10.1063/5.0174351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Accepted: 10/30/2023] [Indexed: 11/22/2023] Open
Abstract
Pheophytin a and chlorophyll a have been investigated by electrospray mass spectrometry in the positive and negative modes, in view of the importance of the knowledge of their properties in photosynthesis. Pheophytin and chlorophyll are both observed intensely in the protonated mode, and their main fragmentation route is the loss of their phytyl chain. Pheophytin is observed intact in the negative mode, while under collisions, it is primarily cleaved beyond the phytyl chain and loses the attaching propionate group. Chlorophyll is not detected in normal conditions in the negative mode, but addition of methanol solvent molecule is detected. Fragmentation of this adduct primarily forms a product (-30 amu) that dissociates into dephytyllated deprotonated chlorophyll. Semi-empirical molecular dynamics calculations show that the phytyl chain is unfolded from the chlorin cycle in pheophytin a and folded in chlorophyll a. Density functional theory calculations have been conducted to locate the charges on protonated and deprotonated pheophytin a and chlorophyll a and have found the major location sites that are notably more stable in energy by more than 0.5 eV than the others. The deprotonation site is found identical for pheophytin a and the chlorophyll a-methanol adduct. This is in line with experiment and calculation locating the addition of methanol on a double bond of deprotonated chlorophyll a.
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Affiliation(s)
- M Diop
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d' Orsay, 91405 Orsay, France
| | - M El-Hayek
- Université Paris Saclay, CNRS, Institut de Chimie Physique, UMR 8000, 91405 Orsay, France
| | - J Attard
- Université Paris Saclay, CNRS, Institut de Chimie Physique, UMR 8000, 91405 Orsay, France
- Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux (IPREM), Pau, France
| | - A Muhieddine
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d' Orsay, 91405 Orsay, France
| | - V Veremeienko
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France
| | - S Soorkia
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d' Orsay, 91405 Orsay, France
| | - Ph Carbonnière
- Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux (IPREM), Pau, France
| | - A de la Lande
- Université Paris Saclay, CNRS, Institut de Chimie Physique, UMR 8000, 91405 Orsay, France
| | - B Soep
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d' Orsay, 91405 Orsay, France
| | - N Shafizadeh
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d' Orsay, 91405 Orsay, France
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2
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Gruber E, Teiwes R, Kjær C, Brøndsted Nielsen S, Andersen LH. Tuning fast excited-state decay by ligand attachment in isolated chlorophyll a. Phys Chem Chem Phys 2021; 24:149-155. [PMID: 34901981 DOI: 10.1039/d1cp04356k] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Excited-state dynamics plays a key role for light harvesting and energy transport in photosynthetic proteins but it is nontrivial to separate the intrinsic photophysics of the light-absorbers (chlorophylls) from interactions with the protein matrix. Here we study chlorophyll a (4-coordinate complex) and axially ligated chlorophyll a (5-coordinate complex) isolated in vacuo applying mass spectrometry to shed light on the intrinsic dynamics in the absence of nearby chlorophylls, carotenoids, amino acids, and water molecules. The 4-coordinate complexes are tagged by quaternary ammonium ions while the charge is provided by a formate ligand in the case of 5-coordinate complexes. Regardless of excitation to the Soret band or the Q band, a fast ps decay is observed, which is ascribed to the decay of the lowest excited singlet state either by intersystem crossing (ISC) to nearby triplet states or by excited-state relaxation on the excited-state potential-energy surface. The lifetime of the first excited state is 15 ps with Mg2+ at the chlorophyll center, but only 1.7 ps when formate is attached to Mg2+. When the Soret band is excited, an initial sup-ps relaxation is observed which is ascribed to fast internal conversion to the first excited state. With respect to ISC, two factors seem to play a role for the reduced lifetime of the formate-chlorophyll complex: (i) The Mg ion is pulled out of the porphyrin plane thus reducing the symmetry of the chromophore, and (ii) the first excited state (Q band) and T3 are tuned almost into resonance by the ligand, which increases the singlet-triplet mixing.
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Affiliation(s)
- Elisabeth Gruber
- Department of Physics and Astronomy, Aarhus University, Aarhus 8000C, Denmark.
| | - Ricky Teiwes
- Department of Physics and Astronomy, Aarhus University, Aarhus 8000C, Denmark.
| | - Christina Kjær
- Department of Physics and Astronomy, Aarhus University, Aarhus 8000C, Denmark.
| | | | - Lars H Andersen
- Department of Physics and Astronomy, Aarhus University, Aarhus 8000C, Denmark.
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3
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Giacomozzi L, Kjær C, Brøndsted Nielsen S, Ashworth EK, Bull JN, Stockett MH. Non-statistical fragmentation in photo-activated flavin mononucleotide anions. J Chem Phys 2021; 155:044305. [PMID: 34340366 DOI: 10.1063/5.0056415] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The spectroscopy and photo-induced dissociation of flavin mononucleotide anions in vacuo are investigated over the 300-500 nm wavelength range. Comparison of the dependence of fragment ion yields as a function of deposited photon energy with calculated dissociation energies and collision-induced dissociation measurements performed under single-collision conditions suggests that a substantial fraction of photo-activated ions decompose through non-statistical fragmentation pathways. Among these pathways is the dominant photo-induced fragmentation channel, the loss of a fragment identified as formylmethylflavin. The fragment ion specific action spectra reveal electronic transition energies close to those for flavins in solution and previously published gas-phase measurements, although the photo-fragment yield upon excitation of the S2 ← S0 transition appears to be suppressed.
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Affiliation(s)
| | - Christina Kjær
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | | | - Eleanor K Ashworth
- School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, United Kingdom
| | - James N Bull
- School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, United Kingdom
| | - Mark H Stockett
- Department of Physics, Stockholm University, Stockholm, Sweden
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4
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Sirohiwal A, Berraud-Pache R, Neese F, Izsák R, Pantazis DA. Accurate Computation of the Absorption Spectrum of Chlorophyll a with Pair Natural Orbital Coupled Cluster Methods. J Phys Chem B 2020; 124:8761-8771. [PMID: 32930590 PMCID: PMC7584356 DOI: 10.1021/acs.jpcb.0c05761] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
![]()
The
ability to accurately compute low-energy excited states of
chlorophylls is critically important for understanding the vital roles
they play in light harvesting, energy transfer, and photosynthetic
charge separation. The challenge for quantum chemical methods arises
both from the intrinsic complexity of the electronic structure problem
and, in the case of biological models, from the need to account for
protein–pigment interactions. In this work, we report electronic
structure calculations of unprecedented accuracy for the low-energy
excited states in the Q and B bands of chlorophyll a. This is achieved by using the newly developed domain-based local
pair natural orbital (DLPNO) implementation of the similarity transformed
equation of motion coupled cluster theory with single and double excitations
(STEOM-CCSD) in combination with sufficiently large and flexible basis
sets. The results of our DLPNO–STEOM-CCSD calculations are
compared with more approximate approaches. The results demonstrate
that, in contrast to time-dependent density functional theory, the
DLPNO–STEOM-CCSD method provides a balanced performance for
both absorption bands. In addition to vertical excitation energies,
we have calculated the vibronic spectrum for the Q and B bands through
a combination of DLPNO–STEOM-CCSD and ground-state density
functional theory frequency calculations. These results serve as a
basis for comparison with gas-phase experiments.
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Affiliation(s)
- Abhishek Sirohiwal
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.,Fakultät für Chemie und Biochemie, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - Romain Berraud-Pache
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Frank Neese
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Róbert Izsák
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Dimitrios A Pantazis
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
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5
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Kjær C, Gruber E, Nielsen SB, Andersen LH. Color tuning of chlorophyll a and b pigments revealed from gas-phase spectroscopy. Phys Chem Chem Phys 2020; 22:20331-20336. [PMID: 32895686 DOI: 10.1039/d0cp03210g] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Chlorophyll (Chl) pigments are responsible for vital mechanisms in photosynthetic proteins: light harvesting, energy transfer and charge separation. A complex interplay between the Chl molecule and its microenvironment determines its transition energy. Interactions such as excitonic coupling with one or more pigments (Chls or carotenoids), axial ligation to the magnesium center, or electrostatic interactions between Chl and nearby amino-acid residues all influence the photophysical properties. Here we use time-resolved photodissociation action spectroscopy to determine transition energies of Chla/b complexes in vacuo to directly compare the impact of a negatively charged axial ligand (formate) to that of exciton coupling between two Chls. Experiments carried out at the electrostatic ion storage ring ELISA allow dissociation to be sampled on hundreds of milliseconds time scale. Absorption-band maxima of Chla-formate complexes are found at 433 ± 4 nm/2.86 ± 0.03 eV (Soret band) and in the region 654-675 nm/1.84-1.90 eV (Q band) and those of Chla dimers tagged by a quaternary ammonium ion at 419 ± 5 nm/2.96 ± 0.04 eV (Soret band) and 647 nm/1.92 eV (Q band). The axial ligand strongly affects the Chla transition energies causing redshifts of 0.21 eV of the Soret band and 0.04-0.1 eV of the Q band compared to Chla tagged by a quaternary ammonium. Slightly smaller shifts were found in case of Chlb. The redshifts are approximately twice that induced by excitonic coupling between two Chlas, also tagged by a quaternary ammonium ion. Axial ligation brings the absorption by isolated Chls very close to that of photosynthetic proteins.
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Affiliation(s)
- Christina Kjær
- Department of Physics and Astronomy, Aarhus University, Denmark.
| | - Elisabeth Gruber
- Department of Physics and Astronomy, Aarhus University, Denmark.
| | | | - Lars H Andersen
- Department of Physics and Astronomy, Aarhus University, Denmark.
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6
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Gruber E, Kjaer C, Nielsen SB, Andersen LH. Intrinsic Photophysics of Light-harvesting Charge-tagged Chlorophyll a and b Pigments. Chemistry 2019; 25:9153-9158. [PMID: 31095797 DOI: 10.1002/chem.201901786] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2019] [Revised: 05/15/2019] [Indexed: 12/20/2022]
Abstract
Chlorophylls a and b (Chla/b) are responsible for light-harvesting by photosynthetic proteins in plants. They display broad absorption in the visible region with multiple bands, due to the asymmetry of the macrocycle and strong vibronic coupling. Their photophysics relies on the microenvironment, with regard to transition energies as well as quenching of triplet states. Here, we firmly establish the splitting of the Q and Soret bands into x- and y- polarized bands for the isolated molecules in vacuo, and resolve vibronic features. Storage-ring experiments reveal that dissociation of photoexcited charge-tagged complexes occurs over several milliseconds, but with two different time constants. A fast decay is ascribed to dissociation after internal conversion and a slow decay to the population of a triplet state that acts as a bottleneck. Support for the latter is provided by pump-probe experiments, where a second laser pulse probes the long-lived triplet state.
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Affiliation(s)
| | - Christina Kjaer
- Department of Physics and Astronomy, Aarhus University, Denmark
| | | | - Lars H Andersen
- Department of Physics and Astronomy, Aarhus University, Denmark
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7
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Bull JN, Carrascosa E, Giacomozzi L, Bieske EJ, Stockett MH. Ion mobility action spectroscopy of flavin dianions reveals deprotomer-dependent photochemistry. Phys Chem Chem Phys 2018; 20:19672-19681. [PMID: 30014081 PMCID: PMC6063075 DOI: 10.1039/c8cp03244k] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Photo-induced proton transfer, deprotomer-dependent photochemistry, and intramolecular charge transfer in flavin anions are investigated using action spectroscopy.
The intrinsic optical properties and photochemistry of flavin adenine dinucleotide (FAD) dianions are investigated using a combination of tandem ion mobility spectrometry and action spectroscopy. Two principal isomers are observed, the more stable form being deprotonated on the isoalloxazine group and a phosphate (N-3,PO4 deprotomer), and the other on the two phosphates (PO4,PO4 deprotomer). Ion mobility data and electronic action spectra suggest that photo-induced proton transfer occurs from the isoalloxazine group to a phosphate group, converting the PO4,PO4 deprotomer to the N-3,PO4 deprotomer. Comparisons of the isomer selective action spectra of FAD dianions and flavin monoanions with solution spectra and gas-phase photodissociation action spectra suggests that solvation shifts the electronic absorption of the deprotonated isoalloxazine group to higher energy. This is interpreted as evidence for significant charge transfer in the lowest optical transition of deprotonated isoalloxazine. Overall, this work demonstrates that the site of deprotonation of flavin anions strongly affects their electronic absorptions and photochemistry.
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Affiliation(s)
- James N Bull
- School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Eduardo Carrascosa
- School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia
| | | | - Evan J Bieske
- School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Mark H Stockett
- School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia and Department of Physics, Stockholm University, Stockholm, Sweden.
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8
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Giacomozzi L, Kjær C, Langeland Knudsen J, Andersen LH, Brøndsted Nielsen S, Stockett MH. Absorption and luminescence spectroscopy of mass-selected flavin adenine dinucleotide mono-anions. J Chem Phys 2018; 148:214309. [PMID: 29884035 DOI: 10.1063/1.5024028] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
We report the absorption profile of isolated Flavin Adenine Dinucleotide (FAD) mono-anions recorded using photo-induced dissociation action spectroscopy. In this charge state, one of the phosphoric acid groups is deprotonated and the chromophore itself is in its neutral oxidized state. These measurements cover the first four optical transitions of FAD with excitation energies from 2.3 to 6.0 eV (210-550 nm). The S0 → S2 transition is strongly blue shifted relative to aqueous solution, supporting the view that this transition has a significant charge-transfer character. The remaining bands are close to their solution-phase positions. This confirms that the large discrepancy between quantum chemical calculations of vertical transition energies and solution-phase band maxima cannot be explained by solvent effects. We also report the luminescence spectrum of FAD mono-anions in vacuo. The gas-phase Stokes shift for S1 is 3000 cm-1, which is considerably larger than any previously reported for other molecular ions and consistent with a significant displacement of the ground and excited state potential energy surfaces. Consideration of the vibronic structure is thus essential for simulating the absorption and luminescence spectra of flavins.
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Affiliation(s)
- L Giacomozzi
- Department of Physics, Stockholm University, Stockholm, Sweden
| | - C Kjær
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | | | - L H Andersen
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | | | - M H Stockett
- Department of Physics, Stockholm University, Stockholm, Sweden
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9
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Stockett MH. Photo-induced proton-coupled electron transfer and dissociation of isolated flavin adenine dinucleotide mono-anions. Phys Chem Chem Phys 2018; 19:25829-25833. [PMID: 28745349 DOI: 10.1039/c7cp04068g] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The intrinsic optical absorption spectrum and photo-dissociation pathways of flavin adenine dinucleotide (FAD) mono-anions isolated in vacuo are probed using photo-induced dissociation (PID) action spectroscopy. The main photo-products are lumichrome and formylmethylflavin. Evidence is presented that the dissociation pathway leading to these products is non-statistical i.e. occurs during the excited state lifetime. This suggests that the stacking of the adenine and alloxazine chromophores, which enables ultra-fast quenching of the flavin excited state by photo-induced electron transfer in aqueous solution, is inhibited in vacuo. These results provide firm experimental confirmation that lumichrome formation from flavins proceeds via photo-induced, intra-molecular proton-coupled electron transfer.
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Affiliation(s)
- Mark H Stockett
- Stockholm University Department of Physics, Stockholm, Sweden.
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10
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Anda A, De Vico L, Hansen T. Intermolecular Modes between LH2 Bacteriochlorophylls and Protein Residues: The Effect on the Excitation Energies. J Phys Chem B 2017; 121:5499-5508. [PMID: 28485594 DOI: 10.1021/acs.jpcb.7b02071] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Light-harvesting system 2 (LH2) executes the primary processes of photosynthesis in purple bacteria; photon absorption, and energy transportation to the reaction center. A detailed mechanistic insight into these operations is obscured by the complexity of the light-harvesting systems, particularly by the chromophore-environment interaction. In this work, we focus on the effects of the protein residues that are ligated to the bacteriochlorophylls (BChls) and construct potential energy surfaces of the ground and first optically excited state for the various BChl-residue systems where we in each case consider two degrees of freedom in the intermolecular region. We find that the excitation energies are only slightly affected by the considered modes. In addition, we see that axial ligands and hydrogen-bonded residues have opposite effects on both excitation energies and oscillator strengths by comparing to the isolated BChls. Our results indicate that only a small part of the chromophore-environment interaction can be associated with the intermolecular region between a BChl and an adjacent residue, but that it may be possible to selectively raise or lower the excitation energy at the axial and planar residue positions, respectively.
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Affiliation(s)
- André Anda
- Department of Chemistry, H. C. Ørsted Institute, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen, Denmark
| | - Luca De Vico
- Department of Chemistry, H. C. Ørsted Institute, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen, Denmark.,Department of Biotechnology, Chemistry and Pharmacy, University of Siena , via Aldo Moro 2, 53100 Siena, Italy
| | - Thorsten Hansen
- Department of Chemistry, H. C. Ørsted Institute, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen, Denmark
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