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Direct Evidence of an Excited-State Triplet Species upon Photoactivation of the Chlorophyll Precursor Protochlorophyllide
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2017-03-02 00:00:00 , DOI: 10.1021/acs.jpclett.7b00200 Guillem Brandariz-de-Pedro 1, 2 , Derren J. Heyes 2 , Samantha J. O. Hardman 2 , Muralidharan Shanmugam 2 , Alex R. Jones 1, 2 , Stefan Weber 3 , Daniel Nohr 3 , Nigel S. Scrutton 2 , Alistair J. Fielding 1
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2017-03-02 00:00:00 , DOI: 10.1021/acs.jpclett.7b00200 Guillem Brandariz-de-Pedro 1, 2 , Derren J. Heyes 2 , Samantha J. O. Hardman 2 , Muralidharan Shanmugam 2 , Alex R. Jones 1, 2 , Stefan Weber 3 , Daniel Nohr 3 , Nigel S. Scrutton 2 , Alistair J. Fielding 1
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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.
中文翻译：
叶绿素前体原叶绿素内酯光活化后的激发态三重态物种的直接证据。
叶绿素前体原叶绿素（Pchlide）是光驱动酶原叶绿素氧化还原酶的底物，具有促进光催化的独特激发态特性。先前的时间分辨光谱测量结果暗示，在Pchlide的激发态弛豫期间会形成长寿命的三重态，尽管仍然缺乏其存在的直接证据。在这里，我们将时间分辨电子顺磁共振（EPR）与时间分辨吸收测量值结合起来，在一系列温度（10–290 K），溶剂和氧气浓度下提供了Pchlide三重态的详细表征。三重态以双相依赖于氧气的方式衰减，而首次报告的Pchlide三重态的EPR签名显示了发射和吸收特征，并具有类似于其他卟啉三重态的反对称光谱。这项工作表明，在各种时间范围内，各种低温光谱探针都可以使用Pchlide三重态，并为理解其在催化中的潜在作用铺平了道路。
更新日期：2017-03-02
中文翻译：
叶绿素前体原叶绿素内酯光活化后的激发态三重态物种的直接证据。
叶绿素前体原叶绿素（Pchlide）是光驱动酶原叶绿素氧化还原酶的底物，具有促进光催化的独特激发态特性。先前的时间分辨光谱测量结果暗示，在Pchlide的激发态弛豫期间会形成长寿命的三重态，尽管仍然缺乏其存在的直接证据。在这里，我们将时间分辨电子顺磁共振（EPR）与时间分辨吸收测量值结合起来，在一系列温度（10–290 K），溶剂和氧气浓度下提供了Pchlide三重态的详细表征。三重态以双相依赖于氧气的方式衰减，而首次报告的Pchlide三重态的EPR签名显示了发射和吸收特征，并具有类似于其他卟啉三重态的反对称光谱。这项工作表明，在各种时间范围内，各种低温光谱探针都可以使用Pchlide三重态，并为理解其在催化中的潜在作用铺平了道路。
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