Elementary reconstitution of the water splitting light reaction in photosynthesis. 1. Time-resolved fluorescence and electron spin resonance studies of chlorophyll a dihydrate photoreaction with water in nonpolar solutions

Fong, Francis K.; Kusunoki, Masami; Galloway, L.; Matthews, T.G.; Lytle, Fred E.; Hoff, A. J.; Brinkman, F. A.

doi:10.1021/ja00374a012

Cited by 30 publications

(5 citation statements)

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“…These results agree with the experimental findings that, in nonrigorously dried nonpolar solvents, Chl a can easily form a five-coordinated complex, ,,, as well as with the fact that, in the presence of small amounts of water, there is formation of mono- and dihydrated Chl a species, as well as their corresponding dimers. ,, Not surprisingly, upon further addition of water to a solution inducing Chl a aggregation, the equilibrium mixture is greatly shifted in favor of the dihydrated polymeric Chl a form (Chl a −2H 2 O) n . ,,, Note that the structure of this aggregate has been the subject of extensive debate in the literature. Both a cylindrical micelle and a planar sheetlike structure have been proposed. ,,, Evidence for the presence of neutral structural water molecules forming a hydrogen-bonded network in an arrangement similar to that of crystals of the ethyl chlorophyllide has been reported. ,,, Other experimental studies have suggested the possibility that polymeric (Chl a −2H 2 O) aggregates are stabilized in hexameric units …”

Section: Discussionmentioning

confidence: 99%

“…36,37,60,61 Other experimental studies have suggested the possibility that polymeric (Chla-2H 2 O) aggregates are stabilized in hexameric units. 25 In sharp contrast to nonpolar media, in coordinating solvents of type II such as THF or pyridine, Chla is essentially in the form of the unhydrated diaxial solvate. In principle, a significant concentration of Chla hydrates could not be reached, except perhaps at large water concentrations.…”

Section: Discussionmentioning

confidence: 99%

“…Since these pioneering works, the role of water in Chl a aggregation has been the subject of many publications. Most of these works have regarded the aggregation mechanisms of Chl a (or other chlorophylls) in aqueous organic solvents as a function of water concentration. ,– The nature of the solvent has been shown to be decisive. A seminal study using IR spectroscopy was carried out by Ballschmiter and Katz in the 1960s.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical Study of Chlorophyll a Hydrates Formation in Aqueous Organic Solvents

Fredj¹,

Ruiz‐López²

2009

J. Phys. Chem. B

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A theoretical analysis of chlorophyll a (Chla) hydration processes in aqueous organic solvents has been carried out by means of quantum chemistry calculations. A detailed knowledge of the thermodynamics of these processes is fundamental in order to better understand the organization of chlorophyll molecules in vivo, specifically the structure of chlorophyll pairs in photosystems I and II. In the present work, we assumed a Chla model in which the phytyl chain is replaced by a methyl group. Calculations were performed at the B3LYP/6-31G(d) level corrected for basis set superposition errors and dispersion interaction energy. This computational scheme was previously shown to provide data close to MP2/6-311++(2d,2p) results. Solvents effects were taken into account using either continuum (for nonpolar solvents) or discrete-continuum (for polar coordinating solvents) methods. In the latter case, we first examined the structure of Chla in rigorously dry solutions. Two types of solvents were characterized according to Mg-atom coordination: In type I solvents (acetone, acetonitrile, DMSO), Mg exhibits five-coordination, whereas in type II solvents (THF, pyridine), Mg exhibits six-coordination. Hydration processes are quite dependent on solvent nature. In nonpolar or low-polarity solvents such as cyclohexane or chloroform, hydration is always exothermic and exergonic, despite a large entropy term that strongly opposes hydration. In polar solvents of type II, hydration is quite unfavorable, and essentially no hydrates are expected in these media, except perhaps at very large water concentrations (although, in such a case, the medium cannot be simply described as an organic solvent). In polar solvents of type I, the situation is intermediate, and dihydration is favorable in some cases (acetone, acetonitrile) and unfavorable in others (DMSO). It is interesting to note that first hydration processes in coordinating solvents (of either type I or type II), where a water molecule must displace a solvent molecule coordinated to Mg, exhibit values of DeltaH > 0 and DeltaS > 0, in sharp contrast to first hydration processes in nonpolar media. The present results represent the first theoretical attempt to rationalize the large amount of experimental data on hydration and aggregation of Chla in aqueous organic media that have been accumulated over the past four decades. The data stress, in particular, the key role of Chla dihydrates, a point that has been the object of intense debate in the literature. Clearly, dihydrates are found to be more stable than monohydrates owing to a particular structure in which cooperative interactions occur between the water molecules and Chla. The calculations also explain the irregular behavior observed for Chla in aqueous THF or pyridine: In these media, Chla remains basically unhydrated because the Chla-solvent adducts are stabilized by strong dispersion interactions.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Theoretical Study of Chlorophyll a Hydrates Formation in Aqueous Organic Solvents

Fredj¹,

Ruiz‐López²

2009

J. Phys. Chem. B

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“…The application of tunable pulsed lasers to the study of chlorophyll a (Chi a) in vitro is a recent innovation in the history of chlorophyll research.1-4 Over the last three decades, the coordination properties and aggregation behavior of Chi a in solution have been established by a number of techniques including vapor-phase osmometry,5 nuclear magnetic resonance,6 infrared absorption,6 Raman scattering,7 and visible absorption6,8-11 and fluorescence studies.2,11-13 Investigation of the spectroscopic properties of dimeric, oligomeric, and aggregated Chi a in vitro is now directed toward an understanding of the nature of the interaction of two or more Chi a molecules and the effects of aggregation on the electronic states of Chi a in relation to the characteristics of Chi a in vitro. 8,12 There have been a number of recent investigations of laserinduced fluorescence from monomeric Chi a4,14-16 and aggregated species of Chi a involving water12 or another nucleophilic species.2…”

Section: Introductionmentioning

confidence: 99%

Analysis of the pulsed-laser-induced fluorescence spectrum of the chlorophyll a dimer in solution

Wilton¹,

Haley²,

Koningstein³

1984

J. Phys. Chem.

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“…Great attention is given to the investigation of chlorophyll-water complexes in recent years (Brace et al, 1978;Fong e t a / . , 1982;Alfano and Fong, 1982;Showell and Fong, 1982;Fong, 1985).…”

Section: Introductionmentioning

confidence: 99%

PICOSECOND ABSORPTION SPECTROSCOPY OF CHLOROPHYLL A DIHYDRATE

Malý

Danielius²,

Gadonas³

1987

Photochem & Photobiology

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The solution of chlorophyll a in hexane with more than 70% of chlorophyll molecules in the form of the dihydrate (CHl-a.2H20)n is investigated at room temperature by picosecond absorption technique. The transient difference spectra and the kinetic dependences of the absorption changes are measured for several excitation and probe wavelengths. Creation of a new state with blue-shifted absorption band is observed in the system after excitation. A model of the behaviour of the system after excitation is proposed and checked by comparison of the computer-simulated spectral and time dependences with the experimental data. According to the model, about 30% of excited molecules are in the state with the 0.046 eV shift of the absorption band in comparison with the ground state absorption. The lifetime of this state has 170-ps component. The rest of the excited molecules are in the first excited state with the decay time component of 37 ps.

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Elementary reconstitution of the water splitting light reaction in photosynthesis. 1. Time-resolved fluorescence and electron spin resonance studies of chlorophyll a dihydrate photoreaction with water in nonpolar solutions

Cited by 30 publications

References 7 publications

Theoretical Study of Chlorophyll a Hydrates Formation in Aqueous Organic Solvents

Theoretical Study of Chlorophyll a Hydrates Formation in Aqueous Organic Solvents

Analysis of the pulsed-laser-induced fluorescence spectrum of the chlorophyll a dimer in solution

PICOSECOND ABSORPTION SPECTROSCOPY OF CHLOROPHYLL A DIHYDRATE

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