Excited singlet-state lifetimes of hydrated chlorophyll aggregates

Alfano, Angelo J.; Lytle, Fred E.; Showell, Michael S.; Fong, Francis K.

doi:10.1063/1.448500

Cited by 31 publications

(9 citation statements)

References 37 publications

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“…One such factor might be oligomer size. Experimentally determined excited singlet-state lifetimes of a hydrated chlorophyll a aggregate absorbing at 740 nm are in the 40-60-ps range (Alfano et al, 1985;Maly et al, 1987), and Alfano et al (1985) have argued that fluorescence lifetimes in oligomers decrease in proportion to the number of molecules in the oligomer. The large size of BChl c oligomers in hexane is indicated by their tendency to precipitate and by the fact that they can be filtered from solution with a 0.2-µ filter.…”

Section: Discussionmentioning

confidence: 99%

Antenna organization in green photosynthetic bacteria. 1. Oligomeric bacteriochlorophyll c as a model for the 740 nm absorbing bacteriochlorophyll c in Chloroflexus aurantiacus chlorosomes

Brune¹,

Nozawa²,

Blankenship³

1987

Biochemistry

168

117

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Bacteriochlorophyll (BChl) c was extracted from Chloroflexus aurantiacus and purified by reverse-phase high-pressure liquid chromatography. This pigment consists of a complex mixture of homologues, the major component of which is 4-ethyl-5-methylbacteriochlorophyll c stearyl ester. Unlike previously characterized BChls c, the pigment from C. aurantiacus is a racemic mixture of diastereoisomers with different configurations at the 2a chiral center. Diluting a concentrated methylene chloride solution of BChl c with hexane produces an oligomer with absorption maxima at 740-742 and at 460-462 nm. Both the absorption spectrum and the fluorescence emission spectrum (maximum at 750 nm) of this oligomer closely match those of BChl c in chlorosomes. Further support for this model comes from the ability of alcohols, which disrupt BChl c oligomers by ligating the central Mg atom, to convert BChl c in chlorosomes to a monomeric form when added in low concentrations. The lifetime of fluorescence from the 740 nm absorbing BChl c oligomer is about 80 ps. Although exciton quenching might be unusually fast in the in vitro BChl c oligomer because of its large size and/or the presence of minor impurities, this result suggests that energy transfer from the BChl c antenna in chlorosomes must be very fast if it is to be efficient.

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Section: Discussionmentioning

confidence: 99%

Antenna organization in green photosynthetic bacteria. 1. Oligomeric bacteriochlorophyll c as a model for the 740 nm absorbing bacteriochlorophyll c in Chloroflexus aurantiacus chlorosomes

Brune¹,

Nozawa²,

Blankenship³

1987

Biochemistry

168

117

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“…Thus, the main conclusion from this comparison is that in the group I solvents, the water molecules succeed to replace the initial solvent molecules from the first solvation shell of Chl a giving rise to the polymeric aggregates of the type (Chl a·2H 2 O) n , while in group II (PYR and THF) water is not able to do this. Alfano et al (43) have shown that the fluorescence lifetime of such aggregates can be used for estimation of their aggregation number. It is equal to the f of the monomer divided by the f of the aggregate.…”

Section: Spectral Characteristics Of Chl a Solubility And Aggregationmentioning

confidence: 99%

Chlorophyll a Self-assembly in Polar Solvent–Water Mixtures†

Vladkova

2000

Photochem Photobiol

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“…Thus, a comparison to modelcompound spectra is essential for the interpretation of the difference bands. IR spectroscopy has established the role of the C=O groups in the intermolecular interaction of aggregated forms of chlorophylls (Chls) (9,12). These model studies of Chl have covered only the neutral species.…”

mentioning

confidence: 99%

Infrared spectroelectrochemistry of bacteriochlorophylls and bacteriopheophytins: Implications for the binding of the pigments in the reaction center from photosynthetic bacteria

Mäntele

Wollenweber

Nabedryk³

et al. 1988

Proc. Natl. Acad. Sci. U.S.A.

131

140

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The IR spectra of the bacteriochlorophyll a and b cations and the bacteriopheophytin a and b anions were obtained by using an ER and optically transparent electrochemical cell. Prominent effects of radical formation on the vibrational spectra were found for bands assigned to the ester, keto, and acetyl C=O groups and for vibrations from macrocycle bonds. The (radical-minus-neutral) difference spectra are compared to the light-induced difference spectra ofthe primary donor photooxidation and the intermediary acceptor photoreduction in the reaction center of photosynthetic bacteria. Light-induced absorbance changes from bacteriochlorophyll a-containing reaction centers bear striking similarities to the electrochemically induced absorbance changes observed upon formation ofbacteriochlorophyll a' in vitro. Comparison ofthe radical formation in vitro in a hydrogen-bonding or a nonhydrogen-bonding solvent suggests an ester C=O group hydrogen bonded in the neutral state but free in the cation state. For the keto C=O group, the same comparison indicates one free carbonyl group. The (anion-minus-neutral) difference spectra of bacteriopheophytin a and b exhibit a single band in the ester C=O frequency range. In contrast, two bands are observed in the difference spectra of the intermediary acceptor reduction in the reaction center of Rhodopseudomonas viridis.The higher frequency band exhibits a sensitivity to 'H-2H exchange, which suggests a contribution from a protonated carboxyl group of an amino acid side chain.In the primary events in photosynthesis, absorption of light leads to charge separation between electron donor and acceptor molecules. In the bacterial reaction center (RC), the primary electron donor (P) is a bacteriochlorophyll (BChl)-a or -b dimer, the intermediary electron acceptor (H) is a bacteriopheophytin (BPheo)-a or -b monomer, and the primary acceptor is a quinone. Spectroscopic data on these components have been reported (1-3), and, together with the high-resolution structure analysis (4-7), electron transport pathways can be visualized. Specific interactions of the pigment molecules with their polypeptide environment, in addition to pigment-pigment interactions, account for the spectral and redox properties of BChls in vivo. Among these interactions are external liganding to the Mg atom ofthe BChl (8) as well as hydrogen-bonding from pigment groups to polypeptide side chains (7,8). Although such interactions have been studied by resonance Raman (RR) and IR spectroscopy in model systems (8,9), details about the interactions in vivo both in the neutral and charge-separated state still have to be collected.In previous studies, we have used IR difference spectroscopy to investigate the molecular changes in bacterial RC and chromatophores concomitant with P photooxidation (10) as well as with H reduction (11). By using Fourier transform infrared (FTIR) difference spectroscopy, sensitivity can be high enough to detect single bonds. The light-induced FTIR difference spectra consist of a number ofcha...

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Excited singlet-state lifetimes of hydrated chlorophyll aggregates

Cited by 31 publications

References 37 publications

Antenna organization in green photosynthetic bacteria. 1. Oligomeric bacteriochlorophyll c as a model for the 740 nm absorbing bacteriochlorophyll c in Chloroflexus aurantiacus chlorosomes

Antenna organization in green photosynthetic bacteria. 1. Oligomeric bacteriochlorophyll c as a model for the 740 nm absorbing bacteriochlorophyll c in Chloroflexus aurantiacus chlorosomes

Chlorophyll a Self-assembly in Polar Solvent–Water Mixtures†

Infrared spectroelectrochemistry of bacteriochlorophylls and bacteriopheophytins: Implications for the binding of the pigments in the reaction center from photosynthetic bacteria

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