Difference between Chlorophylls <i>a</i> and <i>a</i>′ in the Intermolecular Association Behavior. Visible Absorption and Circular Dichroism Spectral Features in Aqueous Methanol

Watanabe, Tadashi; Kobayashi, Masami; Hongu, Akinori; Oba, Toru

doi:10.1246/cl.1992.1847

Cited by 10 publications

(11 citation statements)

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“…The mass spectrum of #2 was the same as that of #1 ( m / z 683.3 for [ M +H] + ), so #2 should be the isomer of #1. The visible and circular dichroism spectra of bands #1 and #2 (Figure S1) unambiguously indicated that band #2 was that of the C13 2 ‐epimer, Zn‐ 1 c′ , of Zn‐ 1 c (#1), upon comparison with reported data . Additionally, the fact that the 13 2 R forms of Chl a and its analogues moved faster than that of the corresponding 13 2 S form in RP‐HPLC analysis supports the assignment of #2 as prime form Zn‐ 1 c′ .…”

Section: Resultssupporting

confidence: 68%

BciC‐Catalyzed C13²‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters

et al. 2020

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Bacteriochlorophyll c molecules self‐aggregate to form large oligomers in the core part of chlorosomes, which are the main light‐harvesting antenna systems of green photosynthetic bacteria. In the biosynthetic pathway of bacteriochlorophyll c, a BciC enzyme catalyzes the removal of the C132‐methoxycarbonyl group of chlorophyllide a, which possesses a free propionate residue at the C17‐position and a magnesium ion as the central metal. The in vitro C132‐demethoxycarbonylations of chlorophyll a derivatives with various alkyl propionate residues and central metals were examined by using the BciC enzyme derived from one green sulfur bacteria species, Chlorobaculum tepidum. The BciC enzymatic reactions of zinc pheophorbide a alkyl esters were gradually suppressed with an increase of the alkyl chain length in the C17‐propionate residue (from methyl to pentyl esters) and finally the hexyl ester became inactive for the BciC reaction. Although not only the zinc but also nickel and copper complexes were demethoxycarbonylated by the BciC enzyme, the reactions were largely dependent on the coordination ability of the central metals: Zn>Ni>Cu. The above substrate specificity indicates that the BciC enzyme would not bind directly to the carboxy group of chlorophyllide a, but would bind to its central magnesium to form the stereospecific complex of BciC with chlorophyllide a, giving pyrochlorophyllide a, which lacks the (132R)‐methoxycarbonyl group.

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Section: Resultssupporting

confidence: 68%

BciC‐Catalyzed C13²‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters

et al. 2020

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“…The peak heights in both regions were reduced by roughly 40% compared with those of Chl a' monomer in methanol. There was almost no absorption tailing into the near IR region, in contrast with a Chl a' aggregate at M 60% (17). The most characteristic feature in Fig.…”

Section: Methodsmentioning

confidence: 87%

“…3). The conservative components are very intense: their amplitudes for a 4.95 k*.M solution (monomer base concentration) were +288 mdeg (694 nm) and -275 mdeg (715 nm), which was roughly 100-fold larger than the Q, signal of monomeric Chl a' in methanol (17). The band widths (FWHM) were 260 cm-' (694 nm) and 245 cm-I (715 nm).…”

Section: Absorption and CD Spectra Of Chl A' Aggregate At Stationary mentioning

confidence: 92%

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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“…This has a historical reason as Oba was involved in the first demonstration that in PS I the Chl a¢ epimer (i.e. with reverse orientation of the 13 2 -carbomethoxy group) is present and has extensively studied the spectral differences between the two Chl a epimers (Watanabe et al 1992). In some BChls, as in pyrochlorophyllides, the 13 2 -carbomethoxy group is absent.…”

Section: Introduction and A Note On Nomenclaturementioning

confidence: 99%

Relevance of the Diastereotopic Ligation of Magnesium Atoms of Chlorophylls in the Major Light-harvesting Complex II (LHC II) of Green Plants

Balaban¹

2005

Photosynth Res

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The recent high-resolution crystal structure of LHC II [Liu et al. (2004) Nature 428: 287-292] makes possible an unprecedented insight into the stereochemical features of how chlorophylls (Chl)s are bound. The diastereotopic ligation generates four structurally different pigment types, two Chl a and two Chl b, which are distinguished not only by the groups in the 7-position (methyl in Chl a and formyl in Chl b) but also by the face of the tetrapyrrole to which the fifth magnesium ligand is bound. Within a LHC II monomer, out of the eight Chl a six have a 'normal' alpha-coordination and two are beta-coordinated while out of the six Chl b only one has the 'special' beta-coordination. In Photosystem I where a more meaningful statistical analysis could be made, out of 96 Chl a only 14 are beta-coordinated, again indicating a preference for the 'normal' alpha-coordination [Balaban et al. (2002) Biochim Biophys Acta Bioenerget 1556: 197-207; Oba and Tamiaki (2002a) Photosynth Res 74: 1-10]. Astonishingly, all the special beta-Chls are part of the stromal ring of Chls within the LHC II trimers and occupy key positions for the excitation energy transfer. Sequential energy traps are engineered with one hetero- and three homo-dimers. A careful pairing of carotenoids with the special beta-Chls, which could quench their triplet states efficiently, implies a functional relevance of this diastereotopic ligation.

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Difference between Chlorophylls a and a′ in the Intermolecular Association Behavior. Visible Absorption and Circular Dichroism Spectral Features in Aqueous Methanol

Abstract: Visible absorption and circular dichroism (CD) spectroscopies on a series of chlorophyll (Chl) a/a′ epimeric mixtures in aqueous methanol have unraveled a striking influence of the stereochemistry at carbon 132 on the mode of intermolecular association of these pigments.

Cited by 10 publications

References 7 publications

BciC‐Catalyzed C13²‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters

BciC‐Catalyzed C13²‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters

Aggregation of Chlorophyll a′ in Aqueous Methanol

Relevance of the Diastereotopic Ligation of Magnesium Atoms of Chlorophylls in the Major Light-harvesting Complex II (LHC II) of Green Plants

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Difference between Chlorophylls a and a′ in the Intermolecular Association Behavior. Visible Absorption and Circular Dichroism Spectral Features in Aqueous Methanol

Abstract: Visible absorption and circular dichroism (CD) spectroscopies on a series of chlorophyll (Chl) a/a′ epimeric mixtures in aqueous methanol have unraveled a striking influence of the stereochemistry at carbon 132 on the mode of intermolecular association of these pigments.

Cited by 10 publications

References 7 publications

BciC‐Catalyzed C132‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters

BciC‐Catalyzed C132‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters

Aggregation of Chlorophyll a′ in Aqueous Methanol

Relevance of the Diastereotopic Ligation of Magnesium Atoms of Chlorophylls in the Major Light-harvesting Complex II (LHC II) of Green Plants

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BciC‐Catalyzed C13²‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters

BciC‐Catalyzed C13²‐Demethoxycarbonylation of Metal Pheophorbide a Alkyl Esters