Pshenichnyuk Stanislav A, Asfandiarov Nail L, Markova Angelina V, Komolov Alexei S, Timoshnikov Viktor A, Polyakov Nikolay E
Institute of Molecule and Crystal Physics, Ufa Federal Research Centre, Russian Academy of Sciences, Prospekt Oktyabrya 151, 450075 Ufa, Russia.
St. Petersburg State University, Universitetskaya nab. 7/9, 199034 St. Petersburg, Russia.
J Chem Phys. 2023 Dec 7;159(21). doi: 10.1063/5.0180053.
Electron-driven processes in isolated curcumin (CUR) molecules are studied by means of dissociative electron attachment (DEA) spectroscopy under gas-phase conditions. Elementary photostimulated reactions initiated in CUR molecules under UV irradiation are studied using the chemically induced dynamic nuclear polarization method in an acetonitrile solvent. Density functional theory is applied to elucidate the energetics of fragmentation of CUR by low-energy (0-15 eV) resonance electron attachment and to characterize various CUR radical forms. The adiabatic electron affinity of CUR molecule is experimentally estimated to be about 1 eV. An extra electron attachment to the π1* LUMO and π2* molecular orbitals is responsible for the most intense DEA signals observed at thermal electron energy. The most abundant long-lived (hundreds of micro- to milliseconds) molecular negative ions CUR- are detected not only at the thermal energy of incident electrons but also at 0.6 eV, which is due to the formation of the π3* and π4* temporary negative ion states predicted to lie around 1 eV. Proton-assisted electron transfer between CUR molecules is registered under UV irradiation. The formation of both radical-anions and radical-cations of CUR is found to be more favorable in its enol form. The present findings shed some light on the elementary processes triggered in CUR by electrons and photons and, therefore, can be useful to understand the molecular mechanisms responsible for a variety of biological effects produced by CUR.
在气相条件下，通过解离电子附着（DEA）光谱研究了孤立姜黄素（CUR）分子中的电子驱动过程。利用化学诱导动态核极化方法，在乙腈溶剂中研究了紫外线照射下CUR分子引发的基本光刺激反应。应用密度泛函理论来阐明低能（0 - 15 eV）共振电子附着导致的CUR碎片化的能量学，并表征各种CUR自由基形式。实验估计CUR分子的绝热电子亲和能约为1 eV。对π1最低未占分子轨道和π2分子轨道的额外电子附着是在热电子能量下观察到的最强DEA信号的原因。不仅在入射电子的热能下，而且在0.6 eV时都检测到了最丰富的长寿命（数百微秒到毫秒）分子负离子CUR-，这是由于预测位于1 eV左右的π3和π4临时负离子态的形成。在紫外线照射下记录到了CUR分子之间的质子辅助电子转移。发现CUR的自由基阴离子和自由基阳离子在其烯醇形式下的形成更有利。本研究结果揭示了电子和光子在CUR中引发的基本过程，因此有助于理解导致CUR产生多种生物学效应的分子机制。
