SPECTROSCOPIC STUDIES OF CHLOROPHYLL <i>a</i> AGGREGATES FORMED BY AQUEOUS DIMETHYL SULFOXIDE

Uehara, Kaku; Mimuro, Mamoru; Tanaka, Makoto

doi:10.1111/j.1751-1097.1991.tb03643.x

Cited by 19 publications

(17 citation statements)

References 29 publications

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“…In contrast to this, it is noted that a general spectral feature for the presented Chl a' aggregate is well interpreted by assuming a single dominant species in which Chl a' molecules are strongly exciton coupled. This is supported by the observation that emission bands of the heterogeneous Chl a aggregates are to be observed unambiguously and resolved into individual components for a multicomponent system (39). Possible by-products have probably made a contribution minor enough to be neglected in the first approximation, even if they would exist.…”

Section: Simplicity Of the Aggregation Of Chl A'mentioning

confidence: 69%

“…The peak at 1655-1660 cm-I originates in the C13' keto carbonyl stretching. This was downshifted from that of monomeric Chl a in methanol (1668 cm-I) (38) and is far from the Chl a aggregates in aqueous dimethyl sulfoxide (39,40) and aqueous tetrahydrofuran (1 690-1 698 cm-') (41) where the keto carbonyls are supposed to be out of the molecular linkage. These are in line with a general view that the C13I keto carbonyl moieties are involved in the molecular linkage.…”

Section: Resonance Raman Spectra Of Chl A' Aggregatementioning

confidence: 81%

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Aggregation of Chlorophyll a′ in Aqueous Methanol

Oba

Watanabe

Mimuro

et al. 1996

Photochem & Photobiology

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An aggregate of chlorophyll a′ (Chi a′, C132‐epimer of ChI a) formed in a methanovwater (40160, vol/vol) mixed solvent was examined by visible absorption, circular dichro‐ism (CD), fluorescence and resonance Raman spectrosco‐pies in relation to its possible involvement in the core of photosystem I reaction center. The Chl a′ aggregate exhibited a sharp, double‐peaked absorption spectrum (690 and 715 nm) accompanied by an intense, conservative CD signal. The fluorescence excitation polarization spectrum showed that the doublet results from the exciton splitting in a single aggregate species. Time‐dependent changes in the spectroscopic properties clearly point to a simple transformation process from one molecular species to another, though a minor component appears to coexist. This conclusion was supported also by the principal multicom‐ponent spectral estimation analysis of the transients of absorption spectra. The species formed at the initial stage is most probably a T‐shaped dimer or oligomer, which is then gradually converted into the final major product, presumably a stacked dimer. In both of these states, the Chl molecules are linked together via direct coordination of the C13’keto carbonyl oxygen onto the Mg atom of neighboring molecules, as suggested by almost identical resonance Raman spectra in ordinary and deuterated methanovwater mixed solvents. The stacked dimers probably further associate to form a colloidal state in this solvent system. Based on these results, a model for the Chl a′ aggregation is proposed.

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Section: Simplicity Of the Aggregation Of Chl A'mentioning

confidence: 69%

Section: Resonance Raman Spectra Of Chl A' Aggregatementioning

confidence: 81%

Aggregation of Chlorophyll a′ in Aqueous Methanol

Oba

Watanabe

Mimuro

et al. 1996

Photochem & Photobiology

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“…DMSO has a molecular structure somewhat similar to that of methionine sulfoxide, which can be formed by photooxidation of methionine residues in polypeptides. Uehara et al have proposed a structure for the chlorophyll a aggregate formed in the DMSO-water mixtures (36). Figure 8a,b shows the absorption spectra of R-and S-epimers of [P,E] BChl c F aggregates formed in a mixture DMSO 50% and water 50%.…”

Section: Difference In the Aggregates Formed By R-and Sepimersmentioning

confidence: 99%

The Effects of Epimerization at the 31-position of Bacteriochlorophylls c on their Aggregation in Chlorosomes of Green Sulfur Bacteria. Control of the Ratio of 31 Epimers by Light Intensity ‡

Ishii

Kimura

Yamamoto

et al. 2007

Photochemistry and Photobiology

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R‐ and S‐epimerization at the 31 position of bacteriochlorophyll (BChl) c and the formation of rod‐like aggregates in chlorosomes of green sulfur bacteria were markedly affected in Chlorobium (Cb.) tepidum and Cb.limicola by cultivation under various light intensities (photon fluence rate). The stronger the light, the higher the ratio of the S‐epimer to the R‐epimer for each homolog of BChl c in the bacteria. S[P,E] BChl cF and S[I,E] BChl cF were found to be the major S‐epimers in Cb. tepidum and Cb. limicola, respectively. R[P,E] BChl cF decreased markedly compared to R[E,E] BChl cF in Cb. tepidum, whereas no observable change in the ratio of R[P,E]/R[E,E] was detected for Cb. limicola. With increase in light intensity the Qy absorption maximum of the bacteria shifted to shorter wavelengths. In vitro spectroscopic studies of the aggregates showed a marked difference in the formation of aggregates from R‐ and S‐epimers of BChl c; the S‐epimers formed aggregates much more slowly than did the R‐epimers. These results suggest that the ratio of the epimers of BChl c might significantly affect the aggregation of BChl in the chlorosome. We propose different roles for the R‐ and S‐epimers in chlorosomes of Cb. limicola and Cb. tepidum.

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“…That such knowledge is of importance is evident by the same effects that medium composition has on both the chlorosomes (3) and Bchl c and d aggregates in aqueous media (4) or on chloroplast fragments (5) and Chl a aggregates in aqueous solvents (6). While the formation of Chl aggregates in various organic solvent-water mixtures is well documented (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18), little is known about the contribution of the structure and properties of the medium for the assembly and stabilization of different Chl aggregate organizations in aqueous media. A study on the relationship between the Chl aggregation and solvent structure and properties can lead to an elucidation of the mechanism for Chl assembly and dissolution in aqueous media and consequently in the photosynthetic antenna complexes.…”

Section: Introductionmentioning

confidence: 99%