pH Dependence of the speciation and optical properties of 4-benzoylbenzoic acid
pH Dependence of the speciation and optical properties of 4-benzoylbenzoic acid
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4-苯甲酰基苯甲酸的形态和光学性质的 pH 依赖性
DOI：
10.1039/d3cp01520c
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发表时间：
2023
影响因子：
3.3
通讯作者：
Navea, Juan G.
中科院分区：
文献类型：
--
作者：
Karimova, Natalia;Alija, Onita;Mora García, Stephanie L.;Grassian, Vicki H.;Gerber, R. Benny;Navea, Juan G.
有机发色团引发环境中大部分白天水相化学反应。因此，研究常用有机光敏剂的吸收光谱对于充分了解它们在环境过程中的相关性至关重要。在这项工作中，我们结合了紫外-可见光谱、1H-核磁共振光谱、量子化学计算和分子动力学模拟来研究 4-苯甲酰基苯甲酸 (4BBA) 的吸收光谱，4-苯甲酰基苯甲酸 (4BBA) 是一种广泛使用的光敏剂，也是环境相关发色团的常见替代物。不同 pH 值下的 4BBA 溶液表明，质子化和去质子化物质对其吸收光谱有影响。对水簇中这些物质的理论计算提供了对光谱的物理和化学见解。我们进行了量子化学计算，以分析使用不同簇尺寸（例如 C6H5COC6H4COOH·(H2O)n）的 4BBA 物种的紫外-可见吸收光谱，其中对于相对较小的簇，n = 8，对于较大的簇，n = 30。虽然相对较小的簇已成功用于较小的发色团，但我们的结果表明，4BBA 质子化物质的模拟需要 n = 30 的相对较大的簇。实验与理论结果之间的比较表明，水合簇模型与实验数据之间的 pH 依赖性光谱偏移具有良好的一致性。总体而言，理论和实验结果表明，水相4BBA的实验光谱可以用酮形式的酸碱平衡来表示，光谱测得的pKa为3.41±0.04。这里总结的结果有助于通过仅限于簇模型的计算对溶剂化有机分子进行分子水平的理解，从而更广泛地了解环境相关的发色团。
Organic chromophores initiate much of daytime aqueous phase chemistry in the environment. Thus, studying the absorption spectra of commonly used organic photosensitizers is paramount to fully understand their relevance in environmental processes. In this work, we combined UV-Vis spectroscopy, 1H-NMR spectroscopy, quantum chemical calculations, and molecular dynamics simulations to investigate the absorption spectra of 4-benzoyl benzoic acid (4BBA), a widely used photosensitizer and a common proxy of environmentally relevant chromophores. Solutions of 4BBA at different pH values show that protonated and deprotonated species have an effect on its absorbance spectra. Theoretical calculations of these species in water clusters provide physical and chemical insights into the spectra. Quantum chemical calculations were conducted to analyze the UV-Vis absorbance spectra of 4BBA species using various cluster sizes, such as C6H5COC6H4COOH·(H2O)n, where n = 8 for relatively small clusters and n = 30 for larger clusters. While relatively small clusters have been successfully used for smaller chromophores, our results indicate that simulations of protonated species of 4BBA require relatively larger clusters of n = 30. A comparison between the experimental and theoretical results shows good agreement in the pH-dependent spectral shift between the hydrated cluster model and the experimental data. Overall, the theoretical and empirical results indicate that the experimental optical spectra of aqueous phase 4BBA can be represented by the acid–base equilibrium of the keto-forms, with a spectroscopically measured pKa of 3.41 ± 0.04. The results summarized here contribute to a molecular-level understanding of solvated organic molecules through calculations restricted to cluster models, and thereby, broader insight into environmentally relevant chromophores.