Radiation and Photochemistry Division , Bhabha Atomic Research Centre , Mumbai 400085 , India.
Homi Bhabha National Institute , Training School Complex , Anushaktinagar, Mumbai 400094 , India.
J Phys Chem B. 2018 Sep 27;122(38):8900-8907. doi: 10.1021/acs.jpcb.8b04691. Epub 2018 Sep 12.
The solvated electron being the simplest form of an extremely reactive intermediate is of great fundamental interest in chemistry, physics, and biology since its discovery. Recently, deep eutectic solvents (DESs) have been in focus as biodegradable and cost-effective alternative to ionic liquids (ILs) for different applications. These include areas where electron transport and transfer processes are involved. Herein, we present the first report on the existence, yield, and properties of solvated electrons in three deep eutectic solvents, reline, ethaline, and glyceline, composed of choline chloride as a hydrogen bond acceptor and urea, ethylene glycol, and glycerol (Gly) as hydrogen bond donors, respectively, at a molar ratio of 1:2. The varied transient absorption spectra of solvated electrons in these DESs have been explained on the basis of polarity, hydrogen-bonding effect, and the moieties responsible for creating the environment for solvation. The yield and average lifetime follow the trends in viscosity as well as the reactivity of electrons with the components. The C value, a measure of the efficiency of scavenging presolvated electrons, is the highest in ethaline in the case of nitrate ions, which indicates the slowest solvation process in this DES. The presolvated electron capture by a DNA base, an aspect considered to be important in cancer radiotherapy, could be monitored conveniently in these liquids at a much longer time scale compared to that reported in aqueous solutions. Bimolecular rate constants for the reaction of solvated electrons with nitrate and the DNA base have been calculated and compared in the three DESs. Unlike in ILs, these experimentally obtained values are comparable to the diffusion-controlled rate constants in DESs.
溶剂化电子作为一种极具反应活性的中间体的最简单形式，自发现以来，在化学、物理和生物学中都具有重要的基础研究意义。最近，深共晶溶剂（DESs）作为一种可生物降解且具有成本效益的替代物，受到了人们的关注，可用于离子液体（ILs）的不同应用，包括涉及电子输运和转移过程的领域。在此，我们首次报道了三种深共晶溶剂（reline、ethaline 和 glyceline）中溶剂化电子的存在、产率和性质，这三种溶剂由氯化胆碱作为氢键受体，尿素、乙二醇和甘油（Gly）分别作为氢键供体，摩尔比为 1:2。根据极性、氢键效应以及形成溶剂化环境的部分，解释了这些 DES 中溶剂化电子的瞬态吸收光谱的变化。产率和平均寿命遵循粘度和电子与组分反应性的趋势。C 值是衡量捕获预溶剂化电子效率的指标，在硝酸盐的情况下，ethaline 中的 C 值最高，这表明在这种 DES 中溶剂化过程最慢。与在水溶液中相比，在这些液体中可以方便地监测 presolvated 电子与 DNA 碱基的捕获，这在癌症放射治疗中被认为是重要的方面。在三种 DES 中计算并比较了溶剂化电子与硝酸盐和 DNA 碱基反应的双分子速率常数。与在 ILs 中不同，这些实验获得的值与 DES 中的扩散控制速率常数相当。
