叶绿素Chlorophyll

四个吡咯环通过次甲基桥连成大环共轭体系，Mg²⁺ 与四个氮配位，第五个环（环戊酮环）和 C17 上的叶绿醇酯是叶绿素的特征。叶绿素 a 在乙醚中的吸收峰约 430 nm 和 662 nm，叶绿素 b 在 C7 位为醛基（而非甲基），吸收峰约 453 nm 和 642 nm，起辅助捕光作用。共轭大环的 π→π* 跃迁（Q 带与 Soret 带）产生这些吸收。

Four pyrrole rings joined by methine bridges form a large conjugated macrocycle with Mg²⁺ bound to the four nitrogens; a fifth, cyclopentanone ring and a phytyl ester at C17 are characteristic. Chlorophyll a absorbs at about 430 and 662 nm in ether; chlorophyll b, with an aldehyde instead of a methyl at C7, absorbs at about 453 and 642 nm and acts as an accessory light-harvester. The absorptions are π→π* transitions of the macrocycle (the Q and Soret bands).

1817 年佩尔蒂埃和卡旺图从叶子中提取出绿色物质并命名为 chlorophylle（希腊语“绿叶”）。1906 年茨维特用碳酸钙柱分离出叶绿素 a、b 和类胡萝卜素，并由此发明了色谱法。1915 年维尔施泰特因叶绿素研究获诺贝尔化学奖，证明其中含镁。1940 年费歇尔确定其结构（他 1930 年因血红素研究获奖），1960 年伍德沃德完成叶绿素 a 的全合成。

In 1817 Pelletier and Caventou extracted the green substance from leaves and named it chlorophylle, from the Greek for green leaf. In 1906 Tsvet separated chlorophylls a and b and carotenoids on a calcium carbonate column, inventing chromatography. Willstätter received the 1915 Nobel Prize in Chemistry for chlorophyll research and showed it contains magnesium. Hans Fischer worked out its structure by 1940 (he had won the 1930 prize for haem), and Woodward completed the total synthesis of chlorophyll a in 1960.

大多数叶绿素分子在捕光复合体中吸收光能并以共振能量转移方式传递给反应中心的特殊叶绿素对（P680、P700），在那里发生电荷分离。秋天叶绿素降解，类胡萝卜素的黄、橙色显现出来。叶绿素铜钠盐用作食品着色剂；用 Cu²⁺ 替代 Mg²⁺ 后颜色更稳定。

Most chlorophyll molecules sit in light-harvesting complexes, absorbing light and passing the energy by resonance transfer to special chlorophyll pairs in the reaction centres (P680 and P700), where charge separation occurs. In autumn chlorophyll breaks down and the yellow and orange of carotenoids show through. Sodium copper chlorophyllin is a food colourant; replacing Mg²⁺ with Cu²⁺ makes the colour more stable.