Plasmonically Generated Tryptophan Radical Anion on Gold Nanoparticles Investigated by Combined Surface-Enhanced Raman Scattering and Density Functional Theory Calculations
Plasmonically Generated Tryptophan Radical Anion on Gold Nanoparticles Investigated by Combined Surface-Enhanced Raman Scattering and Density Functional Theory Calculations
复制标题
DOI：
10.1021/acs.jpcc.1c07840
复制
发表时间：
2021-12
期刊：
影响因子：
--
通讯作者：
Chelsea M. Zoltowski;Remy F Lalisse;C. Hadad;Zachary D. Schultz
中科院分区：
文献类型：
--
作者：
Chelsea M. Zoltowski;Remy F Lalisse;C. Hadad;Zachary D. Schultz
表面增强拉曼散射(SERS)提供了与来自与等离子体纳米粒子相互作用的分子的拉曼信号相关的化学灵敏度的增加，以及用于各种应用。这种信号增强是金属纳米结构表面产生的增强电磁场和被检测分子特有的可能的化学增强相结合的结果。这些化学效应可以改变分析物的化学特性，表现为SERS光谱相对于自发拉曼光谱的不同。在这项工作中，我们研究了由于先前假设的氨基酸色氨酸在金(Au)纳米颗粒上形成自由基阴离子而导致的振动光谱的变化。用密度泛函理论计算了色氨酸阴离子振动频率的变化，并与实验观察到的色氨酸在金纳米颗粒表面的表面增强拉曼散射光谱中的振动模式进行了关联。计算的振动频率与实验数据吻合较好。N-乙酰色胺(NATA)的振动趋势与实验结果基本一致，说明俘获的电子主要集中在吲哚环结构中。SERS光谱随pH的变化很容易被计算解释，进一步表明在这些实验中观察到的信号来自基态自由基阴离子。色氨酸捕获热电子的证据以及由此引起的振动光谱的变化对于SERS检测到的蛋白质和其他分子的分子理解是重要的。
Surface-enhanced Raman scattering (SERS) offers increases in chemical sensitivity associated with the Raman signal from molecules interacting with plasmonic nanoparticles and with use for diverse applications. This signal enhancement is the result of a combination of the enhanced electromagnetic field generated at the surface of the metal nanostructures and possible chemical enhancements specific to the molecule being detected. These chemical effects can alter the chemical identity of the analyte and manifest as differences in the SERS spectrum relative to the spontaneous Raman spectrum. In this work, we examine changes in the vibrational spectrum resulting from the previously hypothesized formation of a radical anion of the amino acid tryptophan on gold (Au) nanoparticles. Density functional theory calculations are used to model changes in the vibrational frequencies attendant to the tryptophan radical anion and correlated with the experimentally observed vibrational modes in the SERS spectrum of tryptophan (Trp) on Au nanoparticles. The calculated vibrational frequencies are in close agreement with the experimental data.N-Acetyltryptophanamide (NATA) is shown to have the same trends in the calculated and experimental vibrations, indicating that the captured electron is localized to the indole ring structure. Changes in the SERS spectrum with pH are readily explained by the calculations, further indicating that the observed signal originates from the ground-state radical anion in these experiments. This evidence for the capture of a hot electron by tryptophan and the resulting changes in the vibrational spectrum are important for molecular understanding of proteins and other molecules as detected by SERS.