Photoinitiated Intramolecular Proton Transfer in Deprotonated para-Coumaric Acid.

08:00 EDT 9th April 2019 | BioPortfolio

Summary of "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 where it 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 phenoxide and carboxylate forms have distinct photochemical responses with maxima in their action spectra at 430nm and 360nm, respectively. A one-way photoinitiated proton transfer was found to convert the E isomer of the carboxylate deprotomer to the phenoxide deprotomer through a mechanism postulated to involve an excited-state enol-keto tautomerism followed by a series of ground state rearrange- ments including a second proton transfer. This mechanism is supported by experiments in which the intermediate keto isomer was prepared and spectroscopically probed, and through master equation modelling of possible ground state isomerization processes. The Z isomer of the carboxylate deprotomer shows weak Z→E photoisomerization response that occurs in competition with photodestruction (presumably electron de- tachment), 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.


Journal Details

This article was published in the following journal.

Name: The journal of physical chemistry. A
ISSN: 1520-5215


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