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Levenberg A, Shafiei G, Lujan MA, Giannacopoulos S, Picorel R, Zazubovich V. Probing Energy Landscapes of Cytochrome b 6f with Spectral Hole Burning: Effects of Deuterated Solvent and Detergent. J Phys Chem B 2017; 121:9848-9858. [PMID: 28956922 DOI: 10.1021/acs.jpcb.7b07686] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In non-photochemical spectral hole burning (NPHB) and spectral hole recovery experiments, cytochrome b6f protein exhibits behavior that is almost independent of the deuteration of the buffer/glycerol glassy matrix containing the protein, apart from some differences in heat dissipation. On the other hand, strong dependence of the hole burning properties on sample preparation procedures was observed and attributed to a large increase of the electron-phonon coupling and shortening of the excited-state lifetime occurring when n-dodecyl β-d-maltoside (DM) is used as a detergent instead of n-octyl β-d-glucopyranoside (OGP). The data was analyzed assuming that the tunneling parameter distribution or barrier distribution probed by NPHB and encoded into the spectral holes contains contributions from two nonidentical components with accidentally degenerate excited state λ-distributions. Both components likely reflect protein dynamics, although with some small probability one of them (with larger md2) may still represent the dynamics involving specifically the -OH groups of the water/glycerol solvent. Single proton tunneling in the water/glycerol solvent environment or in the protein can be safely excluded as the origin of observed NPHB and hole recovery dynamics. The intensity dependence of the hole growth kinetics in deuterated samples likely reflects differences in heat dissipation between protonated and deuterated samples. These differences are most probably due to the higher interface thermal resistivity between (still protonated) protein and deuterated water/glycerol outside environment.
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Affiliation(s)
- Alexander Levenberg
- Department of Physics, Concordia University , 7141 Sherbrooke Street West, Montreal, Quebec H4B 1R6, Canada
| | - Golia Shafiei
- Department of Physics, Concordia University , 7141 Sherbrooke Street West, Montreal, Quebec H4B 1R6, Canada
| | - Maria A Lujan
- Estacion Experimental de Aula Dei (CSIC) , Avda. Montañana 1005, 50059 Zaragoza, Spain
| | - Steven Giannacopoulos
- Department of Physics, Concordia University , 7141 Sherbrooke Street West, Montreal, Quebec H4B 1R6, Canada
| | - Rafael Picorel
- Estacion Experimental de Aula Dei (CSIC) , Avda. Montañana 1005, 50059 Zaragoza, Spain
| | - Valter Zazubovich
- Department of Physics, Concordia University , 7141 Sherbrooke Street West, Montreal, Quebec H4B 1R6, Canada
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Duffy CD, Ruban AV. Dissipative pathways in the photosystem-II antenna in plants. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2015; 152:215-26. [DOI: 10.1016/j.jphotobiol.2015.09.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 09/07/2015] [Accepted: 09/11/2015] [Indexed: 10/23/2022]
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Mokvist F, Sjöholm J, Mamedov F, Styring S. The Photochemistry in Photosystem II at 5 K Is Different in Visible and Far-Red Light. Biochemistry 2014; 53:4228-38. [DOI: 10.1021/bi5006392] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Fredrik Mokvist
- Molecular Biomimetics, Department
of Chemistry-Ångström, Uppsala University, Ångström Laboratory, P.O. Box 523, S-751 20 Uppsala, Sweden
| | - Johannes Sjöholm
- Molecular Biomimetics, Department
of Chemistry-Ångström, Uppsala University, Ångström Laboratory, P.O. Box 523, S-751 20 Uppsala, Sweden
| | - Fikret Mamedov
- Molecular Biomimetics, Department
of Chemistry-Ångström, Uppsala University, Ångström Laboratory, P.O. Box 523, S-751 20 Uppsala, Sweden
| | - Stenbjörn Styring
- Molecular Biomimetics, Department
of Chemistry-Ångström, Uppsala University, Ångström Laboratory, P.O. Box 523, S-751 20 Uppsala, Sweden
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Determination of the PS I content of PS II core preparations using selective emission: A new emission of PS II at 780nm. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1837:167-77. [DOI: 10.1016/j.bbabio.2013.09.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Revised: 09/06/2013] [Accepted: 09/11/2013] [Indexed: 11/20/2022]
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Belgio E, Johnson M, Jurić S, Ruban A. Higher plant photosystem II light-harvesting antenna, not the reaction center, determines the excited-state lifetime-both the maximum and the nonphotochemically quenched. Biophys J 2012; 102:2761-71. [PMID: 22735526 PMCID: PMC3379028 DOI: 10.1016/j.bpj.2012.05.004] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 05/02/2012] [Accepted: 05/07/2012] [Indexed: 11/28/2022] Open
Abstract
The maximum chlorophyll fluorescence lifetime in isolated photosystem II (PSII) light-harvesting complex (LHCII) antenna is 4 ns; however, it is quenched to 2 ns in intact thylakoid membranes when PSII reaction centers (RCIIs) are closed (Fm). It has been proposed that the closed state of RCIIs is responsible for the quenching. We investigated this proposal using a new, to our knowledge, model system in which the concentration of RCIIs was highly reduced within the thylakoid membrane. The system was developed in Arabidopsis thaliana plants under long-term treatment with lincomycin, a chloroplast protein synthesis inhibitor. The treatment led to 1), a decreased concentration of RCIIs to 10% of the control level and, interestingly, an increased antenna component; 2), an average reduction in the yield of photochemistry to 0.2; and 3), an increased nonphotochemical chlorophyll fluorescence quenching (NPQ). Despite these changes, the average fluorescence lifetimes measured in Fm and Fm' (with NPQ) states were nearly identical to those obtained from the control. A 77 K fluorescence spectrum analysis of treated PSII membranes showed the typical features of preaggregation of LHCII, indicating that the state of LHCII antenna in the dark-adapted photosynthetic membrane is sufficient to determine the 2 ns Fm lifetime. Therefore, we conclude that the closed RCs do not cause quenching of excitation in the PSII antenna, and play no role in the formation of NPQ.
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Affiliation(s)
- Erica Belgio
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Matthew P. Johnson
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom
| | - Snježana Jurić
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Alexander V. Ruban
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
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Jankowiak R, Reppert M, Zazubovich V, Pieper J, Reinot T. Site Selective and Single Complex Laser-Based Spectroscopies: A Window on Excited State Electronic Structure, Excitation Energy Transfer, and Electron–Phonon Coupling of Selected Photosynthetic Complexes. Chem Rev 2011; 111:4546-98. [DOI: 10.1021/cr100234j] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ryszard Jankowiak
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
| | - Mike Reppert
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
| | - Valter Zazubovich
- Department of Physics, Concordia University, Montreal H4B1R6 Quebec, Canada
| | - Jörg Pieper
- Max-Volmer-Laboratories for Biophysical Chemistry, Technical University of Berlin, Germany
- Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia
| | - Tonu Reinot
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
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Andreeva A, Apostolova I, Velitchkova M. Temperature dependence of resonance Raman spectra of carotenoids. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2011; 78:1261-1265. [PMID: 21269874 DOI: 10.1016/j.saa.2010.12.071] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2010] [Revised: 12/15/2010] [Accepted: 12/20/2010] [Indexed: 05/30/2023]
Abstract
To understand the mechanism of the photoprotective and antioxidative functions of carotenoids, it is essential to have a profound knowledge of their excited electronic and vibronic states. In the present study we investigate the most powerful antioxidants: β-carotene and lutein by means of resonance Raman spectroscopy. The aim was to study in detail their Raman spectra in solution at room temperature and their changes as a function of temperature. To measure the spectra in their natural environment pyridine has been used as a solvent. It has been chosen because of its polarizability (n=1.5092) which is close to that of membrane lipids and proteins. The temperature dependence of the most intensive ν(1) band in the range from 77 K to 295 K at 514.5 nm excitation has been obtained. It was found that in pyridine the CC stretching frequency, its intensity, line shape, and line width are very sensitive to the temperature (the sensitivity being different for the two studied carotenoids). The observed linear temperature dependence of the CC stretching frequency is explained by a mechanism involving changes of the vibronic coupling and the extent of π-electron delocalization. The different behavior of the temperature-induced broadening of the ν(1) band and its intensity for the two studied carotenoids can be associated with the different nature of their solid matrices: glassy for β-carotene and crystalline-like for lutein, owing to their different chemical structures.
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Affiliation(s)
- A Andreeva
- Sofia University, Faculty of Physics, Department of Condensed Matter Physics, Sofia, Bulgaria.
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Neupane B, Dang NC, Acharya K, Reppert M, Zazubovich V, Picorel R, Seibert M, Jankowiak R. Insight into the electronic structure of the CP47 antenna protein complex of photosystem II: hole burning and fluorescence study. J Am Chem Soc 2010; 132:4214-29. [PMID: 20218564 DOI: 10.1021/ja908510w] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report low temperature (T) optical spectra of the isolated CP47 antenna complex from Photosystem II (PSII) with a low-T fluorescence emission maximum near 695 nm and not, as previously reported, at 690-693 nm. The latter emission is suggested to result from three distinct bands: a lowest-state emission band near 695 nm (labeled F1) originating from the lowest-energy excitonic state A1 of intact complexes (located near 693 nm and characterized by very weak oscillator strength) as well as emission peaks near 691 nm (FT1) and 685 nm (FT2) originating from subpopulations of partly destabilized complexes. The observation of the F1 emission is in excellent agreement with the 695 nm emission observed in intact PSII cores and thylakoid membranes. We argue that the band near 684 nm previously observed in singlet-minus-triplet spectra originates from a subpopulation of partially destabilized complexes with lowest-energy traps located near 684 nm in absorption (referred to as AT2) giving rise to FT2 emission. It is demonstrated that varying contributions from the F1, FT1, and FT2 emission bands led to different maxima of fluorescence spectra reported in the literature. The fluorescence spectra are consistent with the zero-phonon hole action spectra obtained in absorption mode, the profiles of the nonresonantly burned holes as a function of fluence, as well as the fluorescence line-narrowed spectra obtained for the Q(y) band. The lowest Q(y) state in absorption band (A1) is characterized by an electron-phonon coupling with the Huang-Rhys factor S of approximately 1 and an inhomogeneous width of approximately 180 cm(-1). The mean phonon frequency of the A1 band is 20 cm(-1). In contrast to previous observations, intact isolated CP47 reveals negligible contribution from the triplet-bottleneck hole, i.e., the AT2 trap. It has been shown that Chls in intact CP47 are connected via efficient excitation energy transfer to the A1 trap near 693 nm and that the position of the fluorescence maximum depends on the burn fluence. That is, the 695 nm fluorescence maximum shifts blue with increasing fluence, in agreement with nonresonant hole burned spectra. The above findings provide important constraints and parameters for future excitonic calculations, which in turn should offer new insight into the excitonic structure and composition of low-energy absorption traps.
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Affiliation(s)
- Bhanu Neupane
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, USA
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D1 protein variants in Photosystem II from Thermosynechococcus elongatus studied by low temperature optical spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1797:11-9. [DOI: 10.1016/j.bbabio.2009.07.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2009] [Revised: 07/17/2009] [Accepted: 07/20/2009] [Indexed: 11/24/2022]
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Purchase R, Völker S. Spectral hole burning: examples from photosynthesis. PHOTOSYNTHESIS RESEARCH 2009; 101:245-66. [PMID: 19714478 PMCID: PMC2744831 DOI: 10.1007/s11120-009-9484-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2009] [Accepted: 07/31/2009] [Indexed: 05/14/2023]
Abstract
The optical spectra of photosynthetic pigment-protein complexes usually show broad absorption bands, often consisting of a number of overlapping, "hidden" bands belonging to different species. Spectral hole burning is an ideal technique to unravel the optical and dynamic properties of such hidden species. Here, the principles of spectral hole burning (HB) and the experimental set-up used in its continuous wave (CW) and time-resolved versions are described. Examples from photosynthesis studied with hole burning, obtained in our laboratory, are then presented. These examples have been classified into three groups according to the parameters that were measured: (1) hole widths as a function of temperature, (2) hole widths as a function of delay time and (3) hole depths as a function of wavelength. Two examples from light-harvesting (LH) 2 complexes of purple bacteria are given within the first group: (a) the determination of energy-transfer times from the chromophores in the B800 ring to the B850 ring, and (b) optical dephasing in the B850 absorption band. One example from photosystem II (PSII) sub-core complexes of higher plants is given within the second group: it shows that the size of the complex determines the amount of spectral diffusion measured. Within the third group, two examples from (green) plants and purple bacteria have been chosen for: (a) the identification of "traps" for energy transfer in PSII sub-core complexes of green plants, and (b) the uncovering of the lowest k = 0 exciton-state distribution within the B850 band of LH2 complexes of purple bacteria. The results prove the potential of spectral hole burning measurements for getting quantitative insight into dynamic processes in photosynthetic systems at low temperature, in particular, when individual bands are hidden within broad absorption bands. Because of its high-resolution wavelength selectivity, HB is a technique that is complementary to ultrafast pump-probe methods. In this review, we have provided an extensive bibliography for the benefit of scientists who plan to make use of this valuable technique in their future research.
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Affiliation(s)
- Robin Purchase
- Huygens and Gorlaeus Laboratories, Leiden University, 2300 RA Leiden, The Netherlands
| | - Silvia Völker
- Huygens and Gorlaeus Laboratories, Leiden University, 2300 RA Leiden, The Netherlands
- Department of Biophysics, Faculty of Exact Sciences, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
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Renger G, Renger T. Photosystem II: The machinery of photosynthetic water splitting. PHOTOSYNTHESIS RESEARCH 2008; 98:53-80. [PMID: 18830685 DOI: 10.1007/s11120-008-9345-7] [Citation(s) in RCA: 192] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Accepted: 07/29/2008] [Indexed: 05/26/2023]
Abstract
This review summarizes our current state of knowledge on the structural organization and functional pattern of photosynthetic water splitting in the multimeric Photosystem II (PS II) complex, which acts as a light-driven water: plastoquinone-oxidoreductase. The overall process comprises three types of reaction sequences: (1) photon absorption and excited singlet state trapping by charge separation leading to the ion radical pair [Formula: see text] formation, (2) oxidative water splitting into four protons and molecular dioxygen at the water oxidizing complex (WOC) with P680+* as driving force and tyrosine Y(Z) as intermediary redox carrier, and (3) reduction of plastoquinone to plastoquinol at the special Q(B) binding site with Q(A)-* acting as reductant. Based on recent progress in structure analysis and using new theoretical approaches the mechanism of reaction sequence (1) is discussed with special emphasis on the excited energy transfer pathways and the sequence of charge transfer steps: [Formula: see text] where (1)(RC-PC)* denotes the excited singlet state (1)P680* of the reaction centre pigment complex. The structure of the catalytic Mn(4)O(X)Ca cluster of the WOC and the four step reaction sequence leading to oxidative water splitting are described and problems arising for the electronic configuration, in particular for the nature of redox state S(3), are discussed. The unravelling of the mode of O-O bond formation is of key relevance for understanding the mechanism of the process. This problem is not yet solved. A multistate model is proposed for S(3) and the functional role of proton shifts and hydrogen bond network(s) is emphasized. Analogously, the structure of the Q(B) site for PQ reduction to PQH(2) and the energetic and kinetics of the two step redox reaction sequence are described. Furthermore, the relevance of the protein dynamics and the role of water molecules for its flexibility are briefly outlined. We end this review by presenting future perspectives on the water oxidation process.
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Affiliation(s)
- Gernot Renger
- Max Volmer Laboratory for Biophysical Chemistry, Berlin Institute of Technology, Berlin, Germany.
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Vassiliev S, Bruce D. Toward understanding molecular mechanisms of light harvesting and charge separation in photosystem II. PHOTOSYNTHESIS RESEARCH 2008; 97:75-89. [PMID: 18443918 DOI: 10.1007/s11120-008-9303-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2007] [Accepted: 03/31/2008] [Indexed: 05/26/2023]
Abstract
Conversion of light energy in photosynthesis is extremely fast and efficient, and understanding the nature of this complex photophysical process is challenging. This review describes current progress in understanding molecular mechanisms of light harvesting and charge separation in photosystem II (PSII). Breakthroughs in X-ray crystallography have allowed the development and testing of more detailed kinetic models than have previously been possible. However, due to the complexity of the light conversion processes, satisfactory descriptions remain elusive. Recent advances point out the importance of variations in the photochemical properties of PSII in situ in different thylakoid membrane regions as well as the advantages of combining sophisticated time-resolved spectroscopic experiments with atomic level computational modeling which includes the effects of molecular dynamics.
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Affiliation(s)
- Serguei Vassiliev
- Department of Biology, Brock University, St. Catharines, ON, Canada L2S 3A1.
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Santabarbara S, Agostini G, Casazza AP, Syme CD, Heathcote P, Böhles F, Evans MC, Jennings RC, Carbonera D. Chlorophyll triplet states associated with Photosystem I and Photosystem II in thylakoids of the green alga Chlamydomonas reinhardtii. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:88-105. [DOI: 10.1016/j.bbabio.2006.10.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2006] [Revised: 10/16/2006] [Accepted: 10/17/2006] [Indexed: 12/01/2022]
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Hughes JL, Picorel R, Seibert M, Krausz E. Photophysical Behavior and Assignment of the Low-Energy Chlorophyll States in the CP43 Proximal Antenna Protein of Higher Plant Photosystem II. Biochemistry 2006; 45:12345-57. [PMID: 17014087 DOI: 10.1021/bi0614683] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have employed absorption, circular dichroism (CD), and persistent spectral hole-burning measurements at 1.7 K to study the photoconversion properties and exciton coupling of low-energy chlorophylls (Chls) in the CP43 proximal antenna light-harvesting subunit of photosystem II (PSII) isolated from spinach. These approximately 683 nm states act as traps for excitation energy in isolated CP43. They "bleach" at 683 nm upon illumination and photoconvert to a form absorbing in the range approximately 660-680 nm. We present new data that show the changes in the CD spectrum due to the photoconversion process. These changes occur in parallel with those in absorption, providing evidence that the feature undergoing the apparent bleach is a component of a weakly exciton-coupled system. From our photoconversion difference spectra, we assign four states in the Chl long-wavelength region of CP43, two of which are the known trap states and are both highly localized on single Chls. The other two states are associated with weak exciton coupling (maximally approximately 50 cm(-)(1)) to one of these traps. We propose a mechanism for photoconversion that involves Chl-protein hydrogen bonding. New hole-burning data are presented that indicate this mechanism is distinct to that for narrow-band spectral hole burning in CP43. We discuss the photophysical behavior of the Chl trap states in isolated CP43 compared to their behavior in intact PSII preparations. The latter represent a more intact, physiological complex, and we find no clear evidence that they exhibit the photoconversion process reported here.
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Affiliation(s)
- Joseph L Hughes
- Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia.
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Hughes JL, Smith P, Pace R, Krausz E. Charge separation in photosystem II core complexes induced by 690-730 nm excitation at 1.7 K. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:841-51. [PMID: 16859635 DOI: 10.1016/j.bbabio.2006.05.035] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2006] [Revised: 05/01/2006] [Accepted: 05/22/2006] [Indexed: 11/24/2022]
Abstract
The illumination of oxygen-evolving PSII core complexes at very low temperatures in spectral regions not expected to excite P680 leads to charge separation in a majority of centers. The fraction of centers photoconverted as a function of the number of absorbed photons per PSII core is determined by quantification of electrochromic shifts on Pheo(D1). These shifts arise from the formation of metastable plastoquinone anion (Q(A)(-)) configurations. Spectra of concentrated samples identify absorption in the 700-730 nm range. This is well beyond absorption attributable to CP47. Spectra in the 690-730 nm region can be described by the 'trap' CP47 absorption at 689 nm, with dipole strength of approximately 1 chlorophyll a (chl a), partially overlapping a broader feature near 705 nm with a dipole strength of approximately 0.15 chl a. This absorption strength in the 700-730 nm region falls by 40% in the photoconverted configuration. Quantum efficiencies of photoconversion following illumination in the 690-700 nm region are similar to those obtained with green illumination but fall significantly in the 700-730 nm range. Two possible assignments of the long-wavelength absorption are considered. Firstly, as a low intensity component of strongly exciton-coupled reaction center chlorin excitations and secondly as a nominally 'dark' charge-transfer excitation of the 'special pair' P(D1)-P(D2). The opportunities offered by these observations towards the understanding of the nature of P680 and PSII fluorescence are discussed.
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Affiliation(s)
- Joseph L Hughes
- Research School of Chemistry, Australian National University, Canberra
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