Brandariz-de-Pedro Guillem, Heyes Derren J, Hardman Samantha J O, Shanmugam Muralidharan, Jones Alex R, Weber Stefan, Nohr Daniel, Scrutton Nigel S, Fielding Alistair J
School of Chemistry and the Photon Science Institute, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.
Manchester Institute of Biotechnology, University of Manchester , 131 Princess Street, Manchester M1 7DN, United Kingdom.
J Phys Chem Lett. 2017 Mar 16;8(6):1219-1223. doi: 10.1021/acs.jpclett.7b00200. Epub 2017 Mar 2.
The chlorophyll precursor protochlorophyllide (Pchlide), which is the substrate for the light-driven enzyme protochlorophyllide oxidoreductase, has unique excited-state properties that facilitate photocatalysis. Previous time-resolved spectroscopy measurements have implied that a long-lived triplet state is formed during the excited-state relaxation of Pchlide, although direct evidence of its existence is still lacking. Here we use time-resolved electron paramagnetic resonance (EPR) in combination with time-resolved absorption measurements at a range of temperatures (10-290 K), solvents, and oxygen concentrations to provide a detailed characterization of the triplet state of Pchlide. The triplet decays in a biphasic, oxygen-dependent manner, while the first reported EPR signature of a Pchlide triplet displays both emissive and absorptive features and an antisymmetric spectrum similar to other porphyrin triplet states. This work demonstrates that the Pchlide triplet is accessible to various cryogenic spectroscopic probes over a range of time scales and paves the way for understanding its potential role in catalysis.
叶绿素前体原叶绿素酸酯（Pchlide）是光驱动酶原叶绿素酸酯氧化还原酶的底物，具有独特的激发态性质，有助于光催化作用。先前的时间分辨光谱测量表明，在Pchlide的激发态弛豫过程中会形成长寿命的三重态，尽管其存在的直接证据仍然缺乏。在这里，我们结合时间分辨电子顺磁共振（EPR）以及在一系列温度（10 - 290 K）、溶剂和氧气浓度下的时间分辨吸收测量，对Pchlide的三重态进行详细表征。三重态以双相、氧依赖的方式衰减，而首次报道的Pchlide三重态的EPR信号显示出发射和吸收特征以及与其他卟啉三重态相似的反对称光谱。这项工作表明，在一系列时间尺度上，各种低温光谱探针都可以检测到Pchlide三重态，为理解其在催化中的潜在作用铺平了道路。
