Solvent Effects on the Resonance Raman and Electronic Absorption Spectra of Bacteriochlorophyll <i>a</i> Cation Radical

Misono, Yasuhito; Limantara, Leenawaty; Koyama, Yasushi; Itoh, Koichi

doi:10.1021/jp952295m

Cited by 11 publications

(7 citation statements)

References 24 publications

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“…Observed charge redistributions suggest noncovalent binding of acetone with the Mg atom. Such noncovalent bonding mechanisms for Chls and Bchls in solution and in protein have been suggested in several structural and spectroscopic studies. ,,,,,,,,,− …”

Section: Resultsmentioning

confidence: 93%

“…The result is in accordance with the experimental interpretation that in acetone solution the Mg atom of Chls and Bchls is five coordinated. [100][101][102][103][104][105][106][107] Calculations show that there is a small energy difference between the two binding sites of the 1:1 complexes. The energetically more favorable (about 2 kcal/mol) binding site is the one where acetone is on the same side with the R 17 group.…”

Section: Resultsmentioning

confidence: 99%

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Structural and Spectroscopic Properties of Mg−Bacteriochlorin and Methyl Bacteriochlorophyllidesa,b,g, andhStudied by Semiempirical, ab Initio, and Density Functional Molecular Orbital Methods

Linnanto

Korppi-Tommola

2004

J. Phys. Chem. A

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Ab initio HF/6-31G* and density functional B3LYP/6-31G* methods have been used to calculate fully optimized structures of methyl bacteriochlorophyllides a, b, g, and h and magnesium-bacteriochlorin. Semiempirical ZINDO/S CIS and ab initio CIS/6-31G* and CIS/6-311G** configuration interaction methods and time dependent HF/6-31G*, HF/6-311G**, B3LYP/6-31G*, and B3LYP/6-311G** methods were used to estimate corresponding spectroscopic transition energies of the chromophores. The effects of solvent coordination were also studied by optimizing structures of 1:1 complexes of the methyl bacteriochlorophyllides and acetone. The self-consistent reaction field model was used to estimate bulk solvent effects. Differences in B3LYP and HF bond lengths of the bacteriochlorin had a strong influence on the calculated transition energies. Large variations of calculated transition energies were also observed when coordinates from different X-ray structure determinations were used for the same pigment. In the five coordinated solvent complex, the Mg atom is shifted from the bacteriochlorin plane, inducing red shifts of the Q x and Soret transitions. Linear correlations of the calculated and experimental solution transition energies were obtained with characteristic slopes and intercepts for each method used, reflecting inadequacy of the methods to describe transition energies in bacteriochlorins. Such correlations were shown to be useful in prediction of site transition energies for a pigment (pigment group) in solution or in protein under a given computational approach. Best correlations and the best calculated transition energies were obtained by using the ZINDO/S CIS method with B3LYP/6-31G* optimized structures. Calculations suggested the existence of a number of dark electronic states of bacteriochlorophylls below the main Soret transition. The density of these states was dependent on pigment surroundings. Dark states may have an important role in carotenoid to chlorophyll or to bacteriochlorophyll energy transfer in photosynthetic light harvesting complexes. It was also shown that conformation of an acetyl group of methyl bacteriochlorophyll a has an effect on calculated transition energies.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Structural and Spectroscopic Properties of Mg−Bacteriochlorin and Methyl Bacteriochlorophyllidesa,b,g, andhStudied by Semiempirical, ab Initio, and Density Functional Molecular Orbital Methods

Linnanto

Korppi-Tommola

2004

J. Phys. Chem. A

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“…On the basis of experimental spectroscopic shifts (UV-Vis, NMR and FTIR), it has been proposed that chlorophylls and bacteriochlorophylls are five-coordinated in acetone solution. 44,[112][113][114][115] At B3LYP level, stable minimum energy structures for the 1 : 2 MeBchl-acetone complexes were obtained (Fig. 3, bottom).…”

Section: Optimised Structuresmentioning

confidence: 99%

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

Linnanto

Korppi-Tommola

2006

Phys. Chem. Chem. Phys.

143

164

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The present review describes the use of quantum chemical methods in estimation of structures and electronic transition energies of photosynthetic pigments in vacuum, in solution and imbedded in proteins. Monomeric Mg-porphyrins, chlorophylls and bacteriochlorophylls and their solvent 1:1 and 1:2 complexes were studied. Calculations were performed for Mg-porphyrin, Mg-chlorin, Mg-bacteriochlorin, mesochlorophyll a, chlorophylls a, b, c(1), c(2), c(3), d and bacteriochlorophylls a, b, c, d, e, f, g, h, plus several homologues. Geometries were optimised with PM3, PM3/CISD, PM5, ab initio HF (6-31G*/6-311G**) and density functional B3LYP (6-31G*/6-311G**) methods. Spectroscopic transition energies were calculated with ZINDO/S CIS, PM3 CIS, PM3 CISD, ab initio CIS, time-dependent HF and time-dependent B3LYP methods. Estimates for experimental transition energies were obtained from linear correlations of the calculated transition energies of 1:1 solvent complexes against experimentally recorded solution energies (scaling). According to the calculations in five-coordinated solvent complexes the magnesium atom lies out of the porphyrin plane, while in six-coordinated complexes the porphyrin is nearly planar. Charge densities on magnesium and nitrogen atoms were strongly dependent on the computational method deployed. Several dark states of low oscillator strength below the main Soret band were predicted for solvent complexes and chlorophylls and bacteriochlorophylls in protein environment. Such states, though not yet identified experimentally, might serve as intermediate states for excitation energy transfer in photosynthetic complexes. Q(y), Q(x) and Soret transition energies were found to depend on the orientation of the acetyl group and external pressure. A method to estimate site energies and dimeric interaction energies and to simulate absorption and CD spectra of photosynthetic complexes is described. Simulations for the light harvesting complexes Rhodospirillum molischianum, chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, and LHC-II of Spinacia oleracea are presented as examples.

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“…LHCs can be determined by picosecond and nanosecond transient Raman spectroscopy: As in the S 0 state, the frequency of the ring-breathing Raman line, which appears with the highest intensity when in resonance with the Soret absorption, can be used as a coordination marker in the triplet (T 1 ) and the cation-radical (D 0 ) states as well (13,14,40,43). (Hereafter, the ring-breathing modes in the S 1 , T 1 , and D 0 states will be denoted ν r ′, ν r ′′, and ν r + , respectively.)…”

Section: Generation Of Triplet-state and Cation-radical Bchl A Upon P...mentioning

confidence: 99%

Generation of Triplet and Cation-Radical Bacteriochlorophyll a in Carotenoidless LH1 and LH2 Antenna Complexes from Rhodobacter sphaeroides

et al. 1998

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The LH1 antenna complex and a native form of the LH2 complex were isolated from the carotenoidless R26 and R26.1 mutants of Rhodobacter sphaeroides by the use of a new detergent, sucrose monocholate. One-color, pump-and-probe transient Raman spectroscopy of these complexes using 351 nm, approximately 50 ps pulses showed the generation of the triplet state of bacteriochlorophyll a (BChl a), whereas measurements using 355 nm, approximately 12 ns pulses showed the generation of BChl a cation radical. Subpicosecond to nanosecond time-resolved absorption spectroscopy using 388 nm, 200 fs pulses for excitation showed rapid (<1 ps) generation of the triplet state and fast decay (<10 ps) of the singlet state of BChl a. Microsecond absorption spectroscopy confirmed the generation of BChl a cation radical. EPR spectroscopy using 532 nm, approximately 5 ns pulses for excitation established the generation of BChl a cation radical. The EPR line width suggested that the unpaired electron is shared by two BChl a molecules. In LH1, the yield of BChl a cation radical per complex was estimated to be about 80% of that in the reaction center, and in LH2 about 50%. Thus, rapid generation of the triplet state, and its subsequent transformation into the cation-radical state of BChl a have been shown to be intrinsic properties of B870 and B850 BChl a assembly in the carotenoidless LH1 and LH2 antenna complexes. In the case of the carotenoid-containing LH2 complex, the triplet states of BChl a and carotenoid (spheroidene) were generated immediately after excitation, but the triplet-state BChl a was quenched efficiently by the carotenoid so that no BChl a cation radical was generated. Thus, the photoprotective function of the carotenoid in this antenna complex is shown.

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Solvent Effects on the Resonance Raman and Electronic Absorption Spectra of Bacteriochlorophyll a Cation Radical

Cited by 11 publications

References 24 publications

Structural and Spectroscopic Properties of Mg−Bacteriochlorin and Methyl Bacteriochlorophyllidesa,b,g, andhStudied by Semiempirical, ab Initio, and Density Functional Molecular Orbital Methods

Structural and Spectroscopic Properties of Mg−Bacteriochlorin and Methyl Bacteriochlorophyllidesa,b,g, andhStudied by Semiempirical, ab Initio, and Density Functional Molecular Orbital Methods

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

Generation of Triplet and Cation-Radical Bacteriochlorophyll a in Carotenoidless LH1 and LH2 Antenna Complexes from Rhodobacter sphaeroides

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