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
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
复制标题
3位不同取代基叶绿素锌衍生物脱金属动力学的系统分析：外围取代基吸电子和给电子强度的影响
DOI：
10.1021/ic3016782
复制
发表时间：
2013
影响因子：
4.6
通讯作者：
定岡香菜
中科院分区：
文献类型：
--
作者：
佐賀佳央;小走裕太;定岡香菜
从叶绿素 (Chl) 分子中去除中心金属对于光系统 II 光合反应中心初级电子受体的产生和 Chl 降解的早期阶段具有重要的生物学意义。叶绿素色素脱金属的物理化学性质有助于理解光合生物中的此类反应机制。在此，我们分析了一系列二氢卟酚大环3位吸电子和供电子取代基发生系统变化的Zn-Chl衍生物在酸性条件下的脱金属动力学，以彻底阐明取代对叶绿素色素脱金属性能的影响。 3位脂肪族基团(CH2CH3→CHCH2→CCH)的脱氢减缓了中心锌从二氢卟酚大环中的脱除。三种锌二氢卟酚的脱金属速率常数的逐渐降低源于与二氢卟酚π大环直接连接的乙基、乙烯基和乙炔基的吸电子强度的差异。 31-羰基的还原显着增加了脱金属速率常数，并且具有羰基的锌二氢卟酚与具有相应羟基的锌二氢卟酚的脱金属速率常数的相对比率在3-甲酰基-和3-乙酰基-二氢卟酚的情况下是类似的。七种具有不同吸电子基团和给电子基团的Zn-Chl衍生物的脱金属速率常数与3位取代基的Hammett σ参数表现出良好的相关性。
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→ CHCH2→ CCH) 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-withdrawing strength of the ethyl, vinyl, and ethynyl groups directly linked to the chlorin π macrocycle. Reduction of the 31-carbonyl groups significantly increased the demetalation rate constants, and the relative ratios of the demetalation rate constants of the zinc chlorins possessing a carbonyl group to those possessing the corresponding hydroxy group were analogous in the cases of 3-formyl- and 3-acetyl-zinc chlorins. The demetalation rate constants of the seven Zn-Chl derivatives possessing various electron-withdrawing and -donating groups exhibited good correlation with the Hammett σ parameters of the 3-position substituents.