Metal-sensitive bands in the Raman and infrared spectra of intact and metal-substituted chlorophyll a

Fujiwara, Mai; Tasumi, Mitsuo

doi:10.1021/j100280a033

Cited by 88 publications

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“…Rate constants for the reactions were determined from the slope of the plot of equation (3) against time over fixed temperatures of 313, 322.8 and 332.9 K. Rate constants at these temperatures are presented in Table 1. The kinetic stability of the cobalt ion in the centre of the chlorophyll macrocycle is comparable to results obtained by other workers [19][20][21] in this field, which show that transition metals coordinated to the chlorophyll macrocycle provide an increase in the stability 22 of the chlorophyll macrocycle. This stability is reflected in the activation energy of the electron transfer reaction obtained.…”

Section: Resultssupporting

confidence: 87%

Synthesis and Oxidation ofCobalt(II) Pheophytin‐α Complex

Dikio

Isabirye²

2011

Journal of Chemistry

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Abstract:The mechanism of oxidation of natural pheophytin-a incorporated with cobalt as the central metal ion has been investigated. Natural pheophytin-a extracted from spinach was metallated with cobalt(II) to form the complex, cobalt(II) pheophytin-a [Cophe]. The complex was characterized by Ultraviolet and Visible, Fourier Transform Infrared and Electrospray ion Mass Spectroscopy. The synthesis of cobalt(II) pheophytin-a was carried out and the effect of the substitution on the chlorophyll macrocycle was studied by the reaction of hexaaquachromium(III) cation. The presence of cobalt as the central metal ion increases the energies of the chlorophyll main absorption transitions. The oxidation of the cobalt(II) pheophytin-a, [Cophe] by hexaaquachromium(III) cation in dilute hydrochloric acid has been studied and found to follow first-order kinetics. Rate constants for the oxidation reaction at 313, 322.8 and 332.9 K were found to be 5.4x10 -5 , 1.8x10 -4 and 5.9x10 -4 /s respectively. An outer-sphere mechanism has been proposed for the oxidation of cobalt(II) pheophytin-a.

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Section: Resultssupporting

confidence: 87%

Synthesis and Oxidation ofCobalt(II) Pheophytin‐α Complex

Dikio

Isabirye²

2011

Journal of Chemistry

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“…These modes often arise from vibrations delocalized on the Chl a macrocycle, some in the low frequency range (around 300 cm Ϫ1 ), which involve the central magnesium atom, and others in the mid-frequency range (800 -1500 cm Ϫ1 ) sensitive to the Chl a macrocycle conformation (26). However, none of these modes in the low to mid frequencies undergo shifts large enough so that they can be used for conclusive analysis of pigment protein complexes containing as many chlorophylls as LHCs.…”

Section: Resultsmentioning

confidence: 99%

“…, are sensitive to the macrocycle core size and have been widely used to assess the number of axial ligands bound to the central magnesium of these molecules (26,28). This methine bridge mode is observed at about 1600 cm Ϫ1 when the central magnesium is six-coordinated, and is up-shifted to 1610 -1615 cm Ϫ1 for five-coordinated magnesium.…”

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confidence: 99%

Twisting a β-Carotene, an Adaptive Trick from Nature for Dissipating Energy during Photoprotection

Llansola-Portolés

Sobotka

Kish

et al. 2017

Journal of Biological Chemistry

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Edited by James N. SiedowCyanobacteria possess a family of one-helix high light-inducible proteins (Hlips) that are homologous to light-harvesting antenna of plants and algae. An Hlip protein, high light-inducible protein D (HliD) purified as a small complex with the Ycf39 protein is evaluated using resonance Raman spectroscopy. We show that the HliD binds two different ␤-carotenes, each present in two non-equivalent binding pockets with different conformations, having their (0,0) absorption maxima at 489 and 522 nm, respectively. Both populations of ␤-carotene molecules were in all-trans configuration and the absorption position of the farthest blue-shifted ␤-carotene was attributed entirely to the polarizability of the environment in its binding pocket. In contrast, the absorption maximum of the red-shifted ␤-carotene was attributed to two different factors: the polarizability of the environment in its binding pocket and, more importantly, to the conformation of its ␤-rings. This second ␤-carotene has highly twisted ␤-rings adopting a flat conformation, which implies that the effective conjugation length N is extended up to 10.5 modifying the energetic levels. This increase in N will also result in a lower S 1 energy state, which may provide a permanent energy dissipation channel. Analysis of the carbonyl stretching region for chlorophyll a excitations indicates that the HliD binds six chlorophyll a molecules in five non-equivalent binding sites, with at least one chlorophyll a presenting a slight distortion to its macrocycle. The binding modes and conformations of HliD-bound pigments are discussed with respect to the known structures of LHCII and CP29.In nature, photosynthetic organisms obtain their energy by collecting solar photons, using complex arrays of pigments known as antennas. Subsequently, the energy harvested by the antennas is transferred to reaction centers to be transduced into electrochemical potential. Finally after a cascade of molecular steps, this energy is stored as potential chemical energy that is easy to store and transport (1). To accomplish this process, these organisms have developed a large number of different protein antenna assemblies, a notable subgroup of which are the light-harvesting complexes (LHCs) 3 of green plants and algae. LHCs constitute a large family of proteins, which can exist as monomers, dimers, or trimers in the membrane, and have related amino acid sequences. It is hypothesized that in the evolution of photosynthesis there was, and continues to be, a selective advantage for the organism to make optimum use of low light conditions to drive the relatively slow downstream metabolic reactions of legacy biochemistry (2). Plants, algae, and cyanobacteria are oxygenic photosynthetic organisms that are exposed to random fluctuations in light intensity. In the case of low light requiring large antennas, during high light exposure, most of the energy absorbed is in excess of that required to drive downstream metabolism. If excess light energy is not dealt with properly, i...

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“…For excitation conditions within the Soret electronic transition, it has been shown that resonance Raman spectra of chlorophyll a contain a number of bands that may be used for determining accurately the conformation of these molecules in vitro, as well as in their protein binding pocket (21,22). As the molecular conformation of chl depends in particular on the number of axial ligands on the central magnesium atom, the coordination number of this atom may be deduced from the frequency of some of these bands (8).…”

Section: Resultsmentioning

confidence: 99%

Pigment Binding Site Properties of Two Photosystem II Antenna Proteins

Pascal¹,

Wacker²,

Irrgang³

et al. 2000

Journal of Biological Chemistry

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Two light-harvesting proteins associated with photosystem II of higher plants, namely the major antenna complex LHCIIb and the minor Lhcb4 protein (CP29), have been investigated by resonance Raman spectroscopy. One of the two chlorophylls b and up to five of the six chlorophylls a present in Lhcb4 are shown to adopt similar binding conformations to the (presumably) corresponding molecules in LHCIIb, whereas at least two chlorophylls in the former protein assume unique conformations relative to the bulk complex. The overall conformation of bound xanthophyll molecules is identical in the two antenna proteins, although some small differences are apparent. The pigment binding properties of these two LHCs are discussed, with particular reference to possible structural motifs within this extended family of proteins.

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Metal-sensitive bands in the Raman and infrared spectra of intact and metal-substituted chlorophyll a

Cited by 88 publications

References 0 publications

Synthesis and Oxidation ofCobalt(II) Pheophytin‐α Complex

Synthesis and Oxidation ofCobalt(II) Pheophytin‐α Complex

Twisting a β-Carotene, an Adaptive Trick from Nature for Dissipating Energy during Photoprotection

Pigment Binding Site Properties of Two Photosystem II Antenna Proteins

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