乌洛托品表面增强拉曼光谱的密度泛函理论研究

Density Functional Theory Study on Surface-Enhanced Raman Spectroscopy of HMTA

摘要: 乌洛托品(C₆H₁₂N₄)在生产和生活中发挥重要作用，但是有不法分子利用其漂白性对食品进行二次处理，其残留物对人体有致癌作用。本文采用拉曼光谱、表面增强拉曼光谱(SERS)和密度泛函理论(DFT)模拟方法，对C₆H₁₂N₄分子及其与纳米金颗粒的复合物进行了理论研究。利用纳米金颗粒与分析物的选择性结合，研究了C₆H₁₂N₄分子静电势(MEP)、吸附能、前线分子轨道(FMO)和拉曼活性谱，以及配合物的拉曼活性谱。在MEP中发现了C₆H₁₂N₄的吸附位点，并推测这些位点可能是该分子在纳米金的吸附位点。计算了N7位点上的吸附能，C₆H₁₂N₄-Au、Au2、Au3、Au4、Au5和Au6的吸附能分别为−24.92、−34.92、−39.39、−58.68、−44.6和−34.58 Kcal/mol，这结果表明C₆H₁₂N₄与Au4为最佳的结合形式。C₆H₁₂N₄的FMO能隙为0.30258 eV，在加入4个纳米金颗粒后，FMO能隙为0.10947 eV。结果表明，在加入Au的C₆H₁₂N₄更容易发生化学增强，并且在加入Au4时，其模拟的SERS谱图与实验SERS谱图最为接近，其特征峰分别在710、756、1047 cm⁻¹相对应。

Abstract: HMTA (C₆H₁₂N₄) plays a significant role in production and daily life. However, some unscrupulous individuals take advantage of its bleaching properties to conduct secondary processing on food, and its residues are carcinogenic to the human body. In this paper, Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), and density functional theory (DFT) simulation methods were adopted to conduct theoretical research on the C₆H₁₂N₄ molecule and its complexes with nano-gold particles. The electrostatic potential (MEP), adsorption energy, frontier molecular orbitals (FMO) and Raman activity spectra of C₆H₁₂N₄ molecules, as well as the Raman activity spectra of complexes, were investigated by taking advantage of the selective binding of nano-gold particles to the analyte. Adsorption sites of C₆H₁₂N₄ were found in MEP, and it was speculated that these sites might be the adsorption sites of this molecule in nano-gold. The adsorption energy at the N7 site was calculated. The adsorption energies of C₆H₁₂N₄-Au, Au2, Au3, Au4, Au5 and Au6 were −24.92, −34.92, −39.39, −58.68, −44.6 and −34.58Kcal/mol, respectively. This result indicates that C₆H₁₂N₄ and Au4 are the optimal combination forms. The FMO band gap of C₆H₁₂N₄ is 0.30258 eV. After adding 4 nano-gold particles, the FMO band gap is 0.10947 eV. The results show that C₆H₁₂N₄ with Au added is more likely to undergo chemical enhancement. Moreover, when Au4 is added, the simulated SERS spectrum is the closest to the experimental SERS spectrum, and its characteristic peaks correspond to 710, 756, and 1047 cm⁻¹, respectively.