去质子化<i>对-</i>香豆酸中的光引发分子内质子转移,The Journal of Physical Chemistry A

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去质子化对-香豆酸中的光引发分子内质子转移
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2019-04-09 00:00:00 , DOI: 10.1021/acs.jpca.9b02023
James N. Bull _{1,

2} , Gabriel da Silva ₃ , Michael S. Scholz ₁ , Eduardo Carrascosa ₁ , Evan J. Bieske ₁

Affiliation

通常认为去质子化对香豆酸是光敏黄色蛋白中发色团的模型，该蛋白在吸收蓝光后经历E → Z异构化。在此，串联离子迁移质谱与激光激发相结合，研究了去质子化的对香豆酸的光化学性质，表明苯氧化物和羧酸盐形式的E异构体在430和360 nm的作用光谱中具有明显的光化学响应，最大值，分别。酚盐阴离子的E异构体在其最低的ππ*跃迁激发后会发生有效的自分离。对于E羧酸盐去质子的异构体，一种单向光引发的质子转移，通过一种机制来产生酚盐去质子，该机制被认为涉及激发态的烯醇-酮互变异构，随后发生一系列的基态重排，包括第二次质子转移。通过制备相关中间体酮异构体并进行光谱探测的实验，以及可能的基态异构化过程的主方程模型，为该机理提供了支持。羧酸盐去质子体的Z异构体显示出弱的Z → E光异构化反应，该反应在与光解构竞争（可能是电子脱离）的竞争中发生，表明E和Z异构体在其激发态下经历不同的过程。这项研究强调了异构体选择性光谱法在表征具有多个去质子化位点的分离阴离子的光化学特性方面的实用性。

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Photoinitiated Intramolecular Proton Transfer in Deprotonated para-Coumaric Acid

Deprotonated para-coumaric acid is commonly considered as a model for the chromophore in photoactive yellow protein, which undergoes E → Z isomerization following absorption of blue light. Here, tandem ion mobility mass spectrometry is coupled with laser excitation to study the photochemistry of deprotonated para-coumaric acid, to show that the E isomers of the phenoxide and carboxylate forms have distinct photochemical responses with maxima in their action spectra at 430 and 360 nm, respectively. The E isomer of the phenoxide anion undergoes efficient autodetachment upon excitation of its lowest ππ* transition. For the E isomer of the carboxylate deprotomer, a one-way photoinitiated proton transfer generates the phenoxide deprotomer through a mechanism postulated to involve an excited-state enol–keto tautomerism followed by a series of ground-state rearrangements including a second proton transfer. This mechanism is supported by experiments in which the relevant intermediate keto isomer is prepared and spectroscopically probed and through master equation modeling of possible ground-state isomerization processes. The Z isomer of the carboxylate deprotomer shows a weak Z → E photoisomerization response that occurs in competition with photodestruction (presumably electron detachment), demonstrating that the E and Z isomers undergo different processes in their excited states. The study highlights the utility of isomer-selective spectroscopy for characterizing the photochemistry of isolated anions possessing multiple deprotonation sites.

更新日期：2019-04-09

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