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Yoshitaka Saga - One of the best experts on this subject based on the ideXlab platform.
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Demetalation kinetics of the zinc chlorophyll derivative possessing two formyl groups: effects of formyl groups conjugated to the chlorin macrocycle on physicochemical properties of photosynthetic pigments
Journal of Porphyrins and Phthalocyanines, 2013Co-Authors: Kana Sadaoka, Hitoshi Tamiaki, Shigenori Kashimura, Toru Oba, Yoshitaka SagaAbstract:Demetalation kinetics of zinc chlorophyll derivative 1 possessing two formyl groups directly linked to the A- and B-rings of the chlorin macrocycle, which was synthesized from chlorophyll b, was examined under acidic conditions and compared with those of Zn chlorins 2 and 3 possessing a single formyl group in the A- and B-ring, respectively, as well as Zn chlorin 4 lacking any formyl group to unravel the substitution effects on Demetalation properties of chlorophyllous pigments. Demetalation kinetics of diformylated Zn chlorin 1 was slower than those of monoformylated Zn chlorins 2 and 3, indicating that the effect of the electron-withdrawing formyl group on Demetalation kinetics was amplified by introduction of two formyl groups to the chlorin macrocycle. High correlations were observed between Demetalation rate constants of Zn chlorins 1–4 and the sum of Hammett σ parameters of the 3- and 7-substituents on the chlorin macrocycle, indicating that the combination of electron-withdrawing abilities of the substituents linked directly to the cyclic tetrapyrrole was responsible for Demetalation properties of zinc chlorophyll derivatives.
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effects of the 13 keto group in the e ring of zinc chlorophyll derivatives on Demetalation kinetics under acidic conditions
Chemistry Letters, 2013Co-Authors: Yoshitaka Saga, Kana Sadaoka, Akane Maruko, Naoya TakahashiAbstract:Zinc methyl 131-deoxopyropheophorbide a, which lacked the 131-oxo group in the exo five-membered E-ring, exhibited faster Demetalation kinetics than zinc methyl pyropheophorbide a under acidic cond...
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systematic analysis of the Demetalation kinetics of zinc chlorophyll derivatives possessing different substituents at the 3 position effects of the electron withdrawing and electron donating strength of peripheral substituents
Inorganic Chemistry, 2013Co-Authors: Yoshitaka Saga, Yuta Kobashiri, Kana SadaokaAbstract:Removal of the central metal from chlorophyll (Chl) molecules is biologically important in terms of production of the primary electron acceptors in photosystem-II photosynthetic reaction centers and the early stage in Chl degradation. The physicochemical properties on Demetalation of chlorophyllous pigments are useful in the understanding of such reaction mechanisms in photosynthetic organisms. Here we analyzed the Demetalation kinetics of a series of Zn-Chl derivatives with a systematic variation in the electron-withdrawing and -donating substituents at the 3-position of the chlorin macrocycle under acidic conditions to elucidate thoroughly the substitution effects on the Demetalation properties of chlorophyllous pigments. Dehydrogenation of the aliphatic group (CH2CH3 → CH═CH2 → C≡CH) at the 3-position slowed the removal of the central zinc from the chlorin macrocycle. The gradual decrease in the Demetalation rate constants of the three zinc chlorins originates from differences in the electron-withdrawi...
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structure dependent Demetalation kinetics of chlorophyll a analogs under acidic conditions
Photochemistry and Photobiology, 2013Co-Authors: Yoshitaka Saga, Yuki Hirai, Kana Sadaoka, Megumi Isaji, Hitoshi TamiakiAbstract: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), 13(2)-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 13(2) -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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Demetalation of Chlorophyll Pigments
Chemistry & Biodiversity, 2012Co-Authors: Yoshitaka Saga, Hitoshi TamiakiAbstract: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.
Yuki Hirai - One of the best experts on this subject based on the ideXlab platform.
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structure dependent Demetalation kinetics of chlorophyll a analogs under acidic conditions
Photochemistry and Photobiology, 2013Co-Authors: Yoshitaka Saga, Yuki Hirai, Kana Sadaoka, Megumi Isaji, Hitoshi TamiakiAbstract: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), 13(2)-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 13(2) -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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Kinetic analysis of Demetalation of synthetic zinc cyclic tetrapyrroles possessing an acetyl group at the 3-position: effects of tetrapyrrole structures and peripheral substitution.
The Journal of Physical Chemistry B, 2011Co-Authors: Yoshitaka Saga, Kana Sadaoka, Ryosuke Miura, Yuki HiraiAbstract:Demetalation of three synthetic zinc cyclic tetrapyrroles that possess identical peripheral substituents, zinc methyl bacteriopyropheophorbide a (zinc bacteriochlorin 1), zinc methyl 3-devinyl-3-acetyl-pyropheophorbide a (zinc chlorin 2), and zinc methyl 3-devinyl-3-acetyl-protopyropheophorbide a (zinc porphyrin 3), was kinetically analyzed under acidic conditions to examine the effects of macrocyclic structures on Demetalation without peripheral substitution effects. Zinc bacteriochlorin 1 exhibited much slower Demetalation kinetics than zinc chlorin 2 and zinc porphyrin 3. These results indicate that the bacteriochlorin skeleton provides significant resistance to the removal of the central metal from the tetrapyrrole ligand. Comparison of Demetalation kinetics of 3-acetyl zinc complexes 2 and 3 with that of 3-vinyl zinc complexes under the same reaction condition demonstrated that the relative ratio (5.0 × 10(-2)) of the Demetalation rate constant of the 3-acetyl zinc chlorin 2 to that of the corresponding 3-vinyl zinc chlorin 4 resembled the case of the 3-acetyl zinc porphyrin 3 to the 3-vinyl zinc porphyrin 5 (the relative ratio was 6.8 × 10(-2)). These suggest that the electron-withdrawing 3-acetyl group slows down the Demetalation from the tetrapyrrole ligands more than the 3-vinyl group and that the 3-acetyl effect is analogous in both chlorin and porphyrin π-systems.
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Demetalation kinetics of chlorophyll derivatives possessing different substituents at the 7 position under acidic conditions
Photochemistry and Photobiology, 2011Co-Authors: Yuki Hirai, Shigenori Kashimura, Yoshitaka SagaAbstract:Conversion of the formyl group at the 7-position in chlorophyll (Chl) b to the methyl group via the hydroxymethyl group is biologically important in Chl b degradation. To clarify the effects of the 7-substituents on Demetalation properties of chlorophyllous pigments in the early process of Chl b degradation, we report Demetalation kinetics of the zinc Chl derivative possessing a 7-hydroxymethyl group, which is a good model compound of the intermediate molecule in the early process of Chl b degradation, under acidic conditions, and compare its properties with those of zinc Chl derivatives possessing a methyl and a formyl group, which are model compounds of Chls a and b, respectively. Demetalation rate constants of 7-hydroxymethyl zinc chlorin were much larger than those of 7-formyl zinc chlorin, but were slightly smaller than those of 7-methyl zinc chlorin. The activation energy for Demetalation reaction of 7-formyl zinc chlorin was larger than those of other derivatives. Demetalation rate constants of 7-deformyl-7-hydroxymethyl Chl b were also larger than those of Chl b, and were similar to those of Chl a. These indicate that the 7-hydroxymethyl group in the chlorin macrocycle has a smaller effect on Demetalation compared with the 7-formyl group.
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Substitution effects in the A- and B-rings of the chlorin macrocycle on Demetalation properties of zinc chlorophyll derivatives.
Journal of Physical Chemistry B, 2011Co-Authors: Yuki Hirai, Shigenori Kashimura, Shin-ichi Sasaki, Yoshitaka SagaAbstract:Effects of peripheral substituents in the A- and B-rings of the chlorin macrocycle on Demetalation of zinc chlorophyll derivatives were examined. The Demetalation rate constants of zinc 8-formyl-chlorin (1) were comparable to those of zinc 3-formyl-chlorin (2). Both 1 and 2 exhibited significantly slower Demetalation kinetics than the corresponding zinc chlorin 3, which had no formyl group. Comparison of Demetalation kinetics between zinc 3-ethyl-chlorin (3) and zinc 3-vinyl-chlorin (4) indicated that the substitution at the 3-position of the chlorin macrocycle from a vinyl to an ethyl group accelerated removal of the central zinc. Activation energies of Demetalation of zinc chlorins 1, 2, and 5 possessing a formyl group in the A- or B-ring of the chlorin macrocycle were larger than those of zinc chlorins 3 and 4 lacking a formyl group. These results indicate that the formyl groups in the A- or B-ring provide tolerance to Demetalation of chlorin molecules due to their electron-withdrawing effects.
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Comparison of Demetalation properties between zinc chlorin and zinc porphyrin derivatives: Effect of macrocyclic structures
Bioorganic & Medicinal Chemistry, 2010Co-Authors: Yoshitaka Saga, Sayaka Hojo, Yuki HiraiAbstract:Abstract Metalloporphyrins and metallochlorins are important biological molecules in nature. To examine the effect of macrocyclic structures on removal of central metals from these cyclic tetrapyrrole molecules without peripheral substitution effects, Demetalation of zinc methyl pyropheophorbide a (zinc chlorin 1 ) and zinc methyl protopyropheophorbide a (zinc porphyrin 2 ) was kinetically analyzed under acidic conditions. Both 1 and 2 exhibited gradual spectral changes from zinc complexes to free-base forms with several isosbectic points in acetone/water (10:1) at the proton concentration of 6.1 × 10 −3 M. Demetalation of zinc porphyrin 2 was slower than that of zinc chlorin 1 in the temperature range between 15 and 35 °C. This indicates that the porphyrin macrocycle provides tolerance to removal of the central metal from cyclic tetrapyrrole ligands compared with the chlorin macrocycle.
Hitoshi Tamiaki - One of the best experts on this subject based on the ideXlab platform.
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Demetalation kinetics of the zinc chlorophyll derivative possessing two formyl groups: effects of formyl groups conjugated to the chlorin macrocycle on physicochemical properties of photosynthetic pigments
Journal of Porphyrins and Phthalocyanines, 2013Co-Authors: Kana Sadaoka, Hitoshi Tamiaki, Shigenori Kashimura, Toru Oba, Yoshitaka SagaAbstract:Demetalation kinetics of zinc chlorophyll derivative 1 possessing two formyl groups directly linked to the A- and B-rings of the chlorin macrocycle, which was synthesized from chlorophyll b, was examined under acidic conditions and compared with those of Zn chlorins 2 and 3 possessing a single formyl group in the A- and B-ring, respectively, as well as Zn chlorin 4 lacking any formyl group to unravel the substitution effects on Demetalation properties of chlorophyllous pigments. Demetalation kinetics of diformylated Zn chlorin 1 was slower than those of monoformylated Zn chlorins 2 and 3, indicating that the effect of the electron-withdrawing formyl group on Demetalation kinetics was amplified by introduction of two formyl groups to the chlorin macrocycle. High correlations were observed between Demetalation rate constants of Zn chlorins 1–4 and the sum of Hammett σ parameters of the 3- and 7-substituents on the chlorin macrocycle, indicating that the combination of electron-withdrawing abilities of the substituents linked directly to the cyclic tetrapyrrole was responsible for Demetalation properties of zinc chlorophyll derivatives.
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Cyclopropane-ring formation in the acyl groups of chlorosome glycolipids is crucial for acid resistance of green bacterial antenna systems.
Bioorganic & medicinal chemistry, 2013Co-Authors: Tadashi Mizoguchi, Yusuke Tsukatani, Jiro Harada, Shin Takasaki, Taichi Yoshitomi, Hitoshi TamiakiAbstract:Abstract Green photosynthetic bacteria have unique light-harvesting antenna systems called chlorosomes. Chlorobaculum tepidum , a model organism of the bacteria, biosynthesized monogalactosyl- and rhamnosylgalactosyldiacylglycerides possessing a methylene-bridged palmitoleyl group characterized by a cis -substituted cyclopropane ring as the dominant glycolipids of its chlorosome surface. The formation of the cyclopropane ring was chemically inhibited by supplementation of sinefungin, an analog of S -adenosyl- l -methionine, into the bacterial cultivation. The presence of the cyclopropane ring reinforced acid resistance of the light-harvesting chlorosomes and suppressed acidic Demetalation (pheophytinization) of bacteriochlorophyll- c pigments constructing the core part of chlorosomes. The ring-formation would represent direct and post-synthetic modifications of chlorosome membrane properties and was tolerant of acidic environments.
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structure dependent Demetalation kinetics of chlorophyll a analogs under acidic conditions
Photochemistry and Photobiology, 2013Co-Authors: Yoshitaka Saga, Yuki Hirai, Kana Sadaoka, Megumi Isaji, Hitoshi TamiakiAbstract: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), 13(2)-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 13(2) -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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Demetalation of Chlorophyll Pigments
Chemistry & Biodiversity, 2012Co-Authors: Yoshitaka Saga, Hitoshi TamiakiAbstract: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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physicochemical studies of Demetalation of light harvesting bacteriochlorophyll isomers purified from green sulfur photosynthetic bacteria
Photochemistry and Photobiology, 2009Co-Authors: Yuki Hirai, Hitoshi Tamiaki, Shigenori Kashimura, Yoshitaka SagaAbstract:Demetalation kinetics of bacteriochlorophylls (BChls) c, d and e from green sulfur photosynthetic bacteria were studied under weakly acidic conditions. Demetalation rate constants of BChl e possessing a formyl group at the 7-position were significantly smaller than those of BChls c and d, which had a methyl group at this position. The activation energy of Demetalation of 3 1 R-8,12-diethyl([E,E])-BChl e was 1.5-times larger than that of 3 1 R-[E,E]-BChl c. 15 N-labeled 3 1 R-[E,E]-BChls c and e were purified from cells of green sulfur bacteria grown in a medium containing 15 NH 4 Cl, and their 15 N NMR spectra were measured. The chemical shifts of N 21 , N 22 and N 23 atoms of 3 1 R-[E,E]-BChl e were lower-field shifted than those of 3 1 R-[E,E]-BChl c, respectively, and especially the difference in chemical shifts of N 22 was significantly large. These results suggest that the electron-withdrawing formyl group at the 7-position of BChl e affected an electronic state of the chlorin macrocycle and caused BChl e to be more tolerant for removal of the central magnesium compared with BChls c and d.
Lanny S Liebeskind - One of the best experts on this subject based on the ideXlab platform.
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organometallic enantiomeric scaffolding a strategy for the enantiocontrolled construction of regio and stereodivergent trisubstituted piperidines from a common precursor
Journal of the American Chemical Society, 2011Co-Authors: Heilam Wong, Ethel C Garnieramblard, Lanny S LiebeskindAbstract:Reported herein is a general and efficient method to construct 2,3,6-trisubstituted piperidines in a substituent-independent fashion. From the high enantiopurity organometallic scaffold (-)-Tp(CO)(2)[(η-2,3,4)-(1S,2S)-1-benzyloxycarbonyl-5-oxo-5,6-dihydro-2H-pyridin-2-yl)molybdenum (Tp = hydridotrispyrazolylborato), a variety of TpMo(CO)(2)-based 2,3,6-trifunctionalized complexes of the (η-3,4,5-dihydropyridinyl) ligand were easily obtained in 5 steps through a sequence of highly regio- and stereospecific metal-influenced transformations (15 examples). From the 2,3,6-trifunctionalized molybdenum complexes, either 2,6-cis-3-trans or 2,3,6-cis systems were selectively obtained through the choice of an appropriate stereodivergent Demetalation protocol. The potential of this strategy in synthetic chemistry was demonstrated by the short total synthesis of four natural and one non-natural alkaloids: indolizidines (±)-209I and (±)-8-epi-219F in the racemic series, and enantiocontrolled syntheses of (-)-indolizidine 251N, (-)-quinolizidine 251AA, and (-)-dehydroindolizidine 233E.
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organometallic enantiomeric scaffolding general access to 2 substituted oxa and azabicyclo 3 2 1 octenes via a bronsted acid catalyzed 5 2 cycloaddition reaction
Journal of the American Chemical Society, 2008Co-Authors: Ethel C Garnier, Lanny S LiebeskindAbstract:6-Substituted TpMo(CO)2(η-2,3,4-pyranyl)- and TpMo(CO)2(η-2,3,4-pyridinyl) scaffolds (Tp = hydridotrispyrazolylborato) function as reaction partners in an efficient regio- and stereocontrolled synthesis of functionalized oxa- and azabicyclo[3.2.1]octenes through a novel Bronsted acid catalyzed [5 + 2] cycloaddition reaction. Excellent exo-selectivities are obtained, and the reaction gives products with complete retention of enantiomeric purity when carried out with chiral, nonracemic scaffolds. The substituent at C-6 of the η3-coordinated heterocyclic scaffold not only influences [5 + 2] reactivity but also plays a critical role in the Demetalation step directing the reaction to only one of two possible products.
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new oxidative Demetalation protocol for molybdenum π complexes enantiocontrolled synthesis of unsaturated ketones and lactones
Journal of Organic Chemistry, 2002Co-Authors: Ana Alcudia, Ramon Gomez Arrayas, Lanny S LiebeskindAbstract:An efficient and general oxidative Demetalation of (η3-allyl)molybdenum complexes using pyridinium dichromate allows the introduction of a carbonyl group at an allylic terminus of the π-system. The...
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enantiocontrolled synthesis of highly functionalized tropanes via 5 2 cycloaddition to η3 pyridinylmolybdenum π complexes
Organic Letters, 2000Co-Authors: Helena C Malinakova, Lanny S LiebeskindAbstract:A chiral, nonracemic η3-pyridinyl scaffold participates in [5 + 2] cycloaddition with electron-deficient alkenes, an allene, and an alkyne to give η3-allylmolybdenum bicyclic adducts. The adducts can be demetalated, providing a convergent route to highly functionalized tropanes. High enantiocontrol can be achieved throughout the cycloaddition and Demetalation sequence.
Shigenori Kashimura - One of the best experts on this subject based on the ideXlab platform.
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Demetalation kinetics of the zinc chlorophyll derivative possessing two formyl groups: effects of formyl groups conjugated to the chlorin macrocycle on physicochemical properties of photosynthetic pigments
Journal of Porphyrins and Phthalocyanines, 2013Co-Authors: Kana Sadaoka, Hitoshi Tamiaki, Shigenori Kashimura, Toru Oba, Yoshitaka SagaAbstract:Demetalation kinetics of zinc chlorophyll derivative 1 possessing two formyl groups directly linked to the A- and B-rings of the chlorin macrocycle, which was synthesized from chlorophyll b, was examined under acidic conditions and compared with those of Zn chlorins 2 and 3 possessing a single formyl group in the A- and B-ring, respectively, as well as Zn chlorin 4 lacking any formyl group to unravel the substitution effects on Demetalation properties of chlorophyllous pigments. Demetalation kinetics of diformylated Zn chlorin 1 was slower than those of monoformylated Zn chlorins 2 and 3, indicating that the effect of the electron-withdrawing formyl group on Demetalation kinetics was amplified by introduction of two formyl groups to the chlorin macrocycle. High correlations were observed between Demetalation rate constants of Zn chlorins 1–4 and the sum of Hammett σ parameters of the 3- and 7-substituents on the chlorin macrocycle, indicating that the combination of electron-withdrawing abilities of the substituents linked directly to the cyclic tetrapyrrole was responsible for Demetalation properties of zinc chlorophyll derivatives.
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Demetalation kinetics of chlorophyll derivatives possessing different substituents at the 7 position under acidic conditions
Photochemistry and Photobiology, 2011Co-Authors: Yuki Hirai, Shigenori Kashimura, Yoshitaka SagaAbstract:Conversion of the formyl group at the 7-position in chlorophyll (Chl) b to the methyl group via the hydroxymethyl group is biologically important in Chl b degradation. To clarify the effects of the 7-substituents on Demetalation properties of chlorophyllous pigments in the early process of Chl b degradation, we report Demetalation kinetics of the zinc Chl derivative possessing a 7-hydroxymethyl group, which is a good model compound of the intermediate molecule in the early process of Chl b degradation, under acidic conditions, and compare its properties with those of zinc Chl derivatives possessing a methyl and a formyl group, which are model compounds of Chls a and b, respectively. Demetalation rate constants of 7-hydroxymethyl zinc chlorin were much larger than those of 7-formyl zinc chlorin, but were slightly smaller than those of 7-methyl zinc chlorin. The activation energy for Demetalation reaction of 7-formyl zinc chlorin was larger than those of other derivatives. Demetalation rate constants of 7-deformyl-7-hydroxymethyl Chl b were also larger than those of Chl b, and were similar to those of Chl a. These indicate that the 7-hydroxymethyl group in the chlorin macrocycle has a smaller effect on Demetalation compared with the 7-formyl group.
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Substitution effects in the A- and B-rings of the chlorin macrocycle on Demetalation properties of zinc chlorophyll derivatives.
Journal of Physical Chemistry B, 2011Co-Authors: Yuki Hirai, Shigenori Kashimura, Shin-ichi Sasaki, Yoshitaka SagaAbstract:Effects of peripheral substituents in the A- and B-rings of the chlorin macrocycle on Demetalation of zinc chlorophyll derivatives were examined. The Demetalation rate constants of zinc 8-formyl-chlorin (1) were comparable to those of zinc 3-formyl-chlorin (2). Both 1 and 2 exhibited significantly slower Demetalation kinetics than the corresponding zinc chlorin 3, which had no formyl group. Comparison of Demetalation kinetics between zinc 3-ethyl-chlorin (3) and zinc 3-vinyl-chlorin (4) indicated that the substitution at the 3-position of the chlorin macrocycle from a vinyl to an ethyl group accelerated removal of the central zinc. Activation energies of Demetalation of zinc chlorins 1, 2, and 5 possessing a formyl group in the A- or B-ring of the chlorin macrocycle were larger than those of zinc chlorins 3 and 4 lacking a formyl group. These results indicate that the formyl groups in the A- or B-ring provide tolerance to Demetalation of chlorin molecules due to their electron-withdrawing effects.
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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
Photochemical and Photobiological Sciences, 2009Co-Authors: Yuki Hirai, Shigenori Kashimura, Yoshitaka SagaAbstract:Demetalation kinetics of natural chlorophyll (Chl) d purified from Acaryochloris marina was first studied and compared with those of Chls a and b. The Demetalation rate constant of Chl d, which possessed a formyl group at the 3-position, was five-fold smaller than that of Chl a possessing a vinyl group at the same position in aqueous acetone at the proton concentration of 1.2 × 10−3 M at 25 °C. In contrast, the Demetalation rate constant of Chl b possessing a formyl group at the 7-position was 26 times smaller than that of Chl a. The activation energy of Demetalation reaction of Chl d was larger than that of Chl a, but smaller than that of Chl b. These indicate that the substitution effect of 3-formyl group on the acidic removal of central magnesium in Chls was smaller than that of 7-formyl group.
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physicochemical studies of Demetalation of light harvesting bacteriochlorophyll isomers purified from green sulfur photosynthetic bacteria
Photochemistry and Photobiology, 2009Co-Authors: Yuki Hirai, Hitoshi Tamiaki, Shigenori Kashimura, Yoshitaka SagaAbstract:Demetalation kinetics of bacteriochlorophylls (BChls) c, d and e from green sulfur photosynthetic bacteria were studied under weakly acidic conditions. Demetalation rate constants of BChl e possessing a formyl group at the 7-position were significantly smaller than those of BChls c and d, which had a methyl group at this position. The activation energy of Demetalation of 3 1 R-8,12-diethyl([E,E])-BChl e was 1.5-times larger than that of 3 1 R-[E,E]-BChl c. 15 N-labeled 3 1 R-[E,E]-BChls c and e were purified from cells of green sulfur bacteria grown in a medium containing 15 NH 4 Cl, and their 15 N NMR spectra were measured. The chemical shifts of N 21 , N 22 and N 23 atoms of 3 1 R-[E,E]-BChl e were lower-field shifted than those of 3 1 R-[E,E]-BChl c, respectively, and especially the difference in chemical shifts of N 22 was significantly large. These results suggest that the electron-withdrawing formyl group at the 7-position of BChl e affected an electronic state of the chlorin macrocycle and caused BChl e to be more tolerant for removal of the central magnesium compared with BChls c and d.