Demetalation kinetics of natural chlorophylls purified from oxygenic photosynthetic organisms: effect of the formyl groups conjugated directly to the chlorin π-macrocycle

Hirai, Yoshito; Tamiaki, Hitoshi; Kashimura, Shigenori; Saga, Yoshitaka

doi:10.1039/b9pp00018f

Cited by 26 publications

(40 citation statements)

References 46 publications

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“…The substitution effect of weakly electron‐withdrawing 8‐vinyl group on demetalation properties of Chls is much smaller than the strongly electron‐withdrawing 7‐formyl effects based on the comparison of the present k′ ‐value of DV‐Chl a with the reported one of Chl b under the identical acidic conditions . Such a difference between the 8‐vinyl and 7‐formyl groups would allow DV‐Phe a to function as the primary electron acceptor in PS II by in vivo demetalation of DV‐Chl a in oxygenic photosynthetic organisms.…”

Section: Resultsmentioning

confidence: 68%

“…It has been reported that electron‐withdrawing groups such as formyl and acetyl groups directly conjugated with the π‐system of cyclic tetrapyrroles slow down removal of the central metal . Such peripheral electron‐withdrawing groups would decrease the electron densities of the core nitrogen atoms, preventing electrophilic attack of protons to pyrrole nitrogen atoms.…”

Section: Resultsmentioning

confidence: 99%

“…Physicochemical studies of demetalation properties of chlorophyllous pigments will provide useful information to unravel biologically important reactions in photosynthetic organisms described above, and in vitro demetalation of natural Chls and their model compounds have been examined . Mackinney and Joslyn first reported difference in demetalation kinetics between Chls a and b in the early 1940s .…”

Section: Introductionmentioning

confidence: 99%

“…analyzed demetalation of zinc bacteriochlorophyll (BChl) a , which was discovered in a purple photosynthetic bacterium, Acidiphilium rubrum . Recently, we examined demetalation properties of other naturally occurring (B)Chls and synthetic zinc complexes , which were model compounds of natural Chls. These studies indicate that peripheral substituents on the chlorin macrocycle are responsible for physicochemical properties on demetalation of chlorophyllous pigments.…”

Section: Introductionmentioning

confidence: 99%

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Structure‐Dependent Demetalation Kinetics of Chlorophyll a Analogs under Acidic Conditions

Saga

Hirai

Sadaoka

et al. 2012

Photochem & Photobiology

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Demetalation of chlorophyll (Chl) a and its analogs is an important reaction in oxygenic photosynthetic organisms, which produces the primary electron acceptors in photosystem II reaction centers and is crucial in the Chl degradation. From these viewpoints, demetalation reactions of four Chl a analogs, 3,8‐divinyl‐Chl a (DV‐Chl a), 3‐devinyl‐3‐ethyl‐Chl a (mesoChl a), 132‐demethoxycarbonyl‐Chl a (pyroChl a) and protochlorophyll a (PChl a), were kinetically analyzed under weakly acidic conditions, and were compared with that of Chl a. DV‐Chl a exhibited slower demetalation kinetics than did Chl a, whereas demetalation of mesoChl a was faster than that of Chl a. The difference in demetalation kinetics of the three chlorophyllous pigments originates from the electron‐withdrawing ability of the vinyl group as the peripheral substituent compared with the ethyl group. Removal of the electron‐withdrawing and homoconjugating 132‐methoxycarbonyl group in Chl a (Chl a → pyroChl a) accelerated demetalation kinetics by two‐fold. PChl a possessing the porphyrin‐type skeleton exhibited slower demetalation kinetics than Chl a. The structure‐dependent demetalation properties of Chl a analogs will be useful for understanding in vivo Chl demetalation reactions in oxygenic photosynthetic organisms.

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Section: Resultsmentioning

confidence: 68%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Structure‐Dependent Demetalation Kinetics of Chlorophyll a Analogs under Acidic Conditions

Saga

Hirai

Sadaoka

et al. 2012

Photochem & Photobiology

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“…Although the central magnesium was removed from natural (B)Chl molecules even by action of weak acid (Hirai et al 2009), the 3-and 7-formyl groups of Chl-d(d 0 ) and BChl-e were efficiently 18 O-labeled to give the corresponding magnesium complexes with a high 18 O-labeling degree (ca. 90%).…”

Section: Resultsmentioning

confidence: 99%

Synthesis of 18O-labeled photosynthetically active chlorophylls at the 3- or 7-carbonyl group with high regioselectivity

2010

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The 3- and 7-formyl groups of chlorophyll-d (Chl-d) and bacteriochlorophyll-e (BChl-e), respectively, were regioselectively labeled with an isotopically stable oxygen-18 (¹⁸O) atom to give 3¹-¹⁸O-labeled Chl-d and 7¹-¹⁸O-labeled BChl-e (ca. 90% ¹⁸O) by exchanging the carbonyl oxygen atoms in the presence of acidic H₂ ¹⁸O (ca. 95% ¹⁸O). Another photosynthetically active chlorophyll, BChl-a possessing the 3-acetyl group was treated under similar acidic conditions to afford a trace amount of 3¹-¹⁸O-labeled BChl-a and further demetallated compound, the corresponding 3¹-¹⁸O-labeled bacteriopheophytin-a as the major product with 55% ¹⁸O-degree. The FT-IR spectra of ¹⁸O-(un)labeled chlorophylls in the solution and the solid states showed that the 3- and 7-carbonyl stretching vibration modes moved to about a 30-cm⁻¹ lower wavenumber by ¹⁸O-labeling at the 3¹- and 7¹-oxo moieties. In artificial chlorosome-like self-aggregates of BChl-e, the ¹⁸O-labeled 7-carbonyl stretching mode was completely resolved from the specially hydrogen-bonded 13-C=O stretching mode, evidently indicating no interaction of the 7-CHO with other functional groups in the supramolecules.

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Demetalation of Chlorophyll Pigments

Saga

Tamiaki

2012

Chemistry & Biodiversity

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Natural chlorophylls (Chls) and bacteriochlorophyll (BChls), which are major pigments in photosynthesis, possess a central Mg (or Zn) in their cyclic tetrapyrrole macrocycles. Removal of the central metal atom from chlorophyllous pigments, called pheophytinization, is a biologically important reaction in that it allows production of the primary electron acceptors in photosystem II(-type) reaction centers and is one of the crucial steps in the Chl degradation pathway. Pheophytinization in processed and postharvest foods derived from vegetables and fruits has attracted considerable attention in agricultural and food chemistry from the viewpoints of maintenance of their color level and evaluation by consumers. In this review, we focus on in vivo demetalation reactions and demetalated products of chlorophyllous pigments. In addition, we summarize kinetic studies on in vitro demetalation of natural (B)Chl molecules and their synthetic analogs under acidic conditions.

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Demetalation kinetics of natural chlorophylls purified from oxygenic photosynthetic organisms: effect of the formyl groups conjugated directly to the chlorin π-macrocycle

Cited by 26 publications

References 46 publications

Structure‐Dependent Demetalation Kinetics of Chlorophyll a Analogs under Acidic Conditions

Structure‐Dependent Demetalation Kinetics of Chlorophyll a Analogs under Acidic Conditions

Synthesis of 18O-labeled photosynthetically active chlorophylls at the 3- or 7-carbonyl group with high regioselectivity

Demetalation of Chlorophyll Pigments

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