Epimerization of chlorophyll derivatives. V: Effects of the central magnesium and ring substituents on the epimerization of chlorophyll derivatives
Epimerization of chlorophyll derivatives. V: Effects of the central magnesium and ring substituents on the epimerization of chlorophyll derivatives
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叶绿素衍生物的差向异构化。
DOI：
10.1246/bcsj.65.3080
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发表时间：
1992
影响因子：
4
通讯作者：
H. Scheer
中科院分区：
文献类型：
--
作者：
H. Mazaki;Tadashi Watanabe;Terumi Takahashi;A. Struck;H. Scheer
叶绿素（Chl）a/a′、Chl B/B′、脱镁叶绿素（Pheo）a/a ′、Pheo B/B ′、C20-氯代Chl（Cl-Chl）a/a′和Cl-Pheo a/a′在碱催化下的差向异构化反应动力学和平衡特征（三乙胺、吡咯烷和哌啶）和刘易斯酸（乙酰丙酮镁和氯化镁），已经在乙醚和甲醇中进行了研究。差向异构化速率和平衡差向异构体组成的显着差异之间的色素系统。速率常数的差异是合理的，在C132-质子脱离的容易程度方面，受环π-电子密度的影响，这反过来又取决于电子捐赠或撤回的中心金属和/或环取代基。对于刘易斯酸催化，一个主导因素似乎是通过与外来Mg 2+形成松散络合物来稳定C131-烯醇阴离子。研究了碱（三乙胺）和刘易斯酸（Mg 2...
Kinetic and equilibrium features of the epimerization in six C132-epimer pairs of chlorophyllous pigments, namely chlorophyll (Chl) a/a′, Chl b/b′, pheophytin (Pheo) a/a′, Pheo b/b′, C20-chlorinated Chl (Cl–Chl) a/a′, and Cl–Pheo a/a′, catalyzed by bases (triethylamine, pyrrolidine, and piperidine) and by Lewis acids (magnesium acetylacetonate and magnesium chloride), have been studied in diethyl ether and methanol. A significant difference was noted in the epimerization rate and equilibrium epimeric composition among the pigment systems. The difference in the rate constants was rationalized in terms of the ease in C132-proton detachment, affected by the ring π-electron density which in turn depends on the electron donation or withdrawal by the central metal and/or ring substituents. For Lewis acid-catalysis, a dominant factor appears to be the stabilization of the C131-enolate anion via formation of a loose complex with extraneous Mg2+. A synergistic action of a base (triethylamine) and a Lewis acid (Mg2...