Neto Antonio M, Valeriano Maycom C, Temperini Marcia L A, Homem-de-Mello Paula, Mamián-López Mónica B
Laboratório de Espectroscopia Molecular e Atômica, Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo, Brazil.
Laboratório de Espectroscopia Molecular, Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil.
Spectrochim Acta A Mol Biomol Spectrosc. 2025 Sep 5;337:126091. doi: 10.1016/j.saa.2025.126091. Epub 2025 Mar 22.
The halogenated C5-substituted uracil derivatives (5-fluor-, 5-chloro, and 5-bromouracil) have drawn attention recently due to their pharmacological uses, properties, and importance as biomarkers and water pollutants. From an analytical point of view, these species are expected to be at very low levels in biological and environmental samples, and the development of methodologies for their determination is a central goal in research. The Raman technique and one of its special effects, Surface-Enhanced Raman Scattering (SERS), is a very suitable approach for detecting and quantifying these compounds. In practice, enhancing Raman scattering requires a nanostructured noble metal surface with the species of interest attached to it. Still, to maximize the effect, a deeper comprehension of the nature of the analyte-metal surface interaction is desirable. The structural information SERS spectra provide can be complemented by theoretical approaches, such as the Density Functional Theory (DFT) calculations. This work studied three 5-halouracils attached to silver nanoparticles (AgNPs) from experimental and theoretical perspectives. The observed patterns in the spectroscopic behavior showed a trend related to the electronegativity at the halogenated moieties, suggesting their direct influence in enhancing CC and CO stretching modes. Then, the formation of base pairs with adenine through hydrogen bonding was studied as a strategy to improve the detectability through SERS, supported by the well-known high affinity of adenine towards metal nanoparticles. We show that adenine favors the orientation of the 5-halouracils, reaching an additional signal enhancement that is very useful for analytical purposes, as demonstrated for 5-FU, reaching a limit of detection (LOD) of 2.36 nmol L. Wavenumber shifts and intensification of NH modes observed in the SERS spectra, along with DFT calculations, strongly suggest that forming hydrogen bonding (NH----N) upon the interaction of the base pairs with an Ag cluster is key for improving the halouracils LOD through SERS.
卤代C5取代尿嘧啶衍生物（5-氟、5-氯和5-溴尿嘧啶）由于其药理用途、性质以及作为生物标志物和水污染物的重要性，最近受到了关注。从分析的角度来看，这些物质在生物和环境样品中的含量预计非常低，因此开发测定它们的方法是研究的核心目标。拉曼技术及其特殊效应之一，表面增强拉曼散射（SERS），是检测和定量这些化合物的非常合适的方法。在实际应用中，增强拉曼散射需要一个附着有待测物质的纳米结构贵金属表面。然而，为了最大化这种效应，需要更深入地理解分析物与金属表面相互作用的本质。SERS光谱提供的结构信息可以通过理论方法进行补充，例如密度泛函理论（DFT）计算。这项工作从实验和理论角度研究了三种附着在银纳米颗粒（AgNP）上的5-卤代尿嘧啶。光谱行为中观察到的模式显示出与卤代部分电负性相关的趋势，表明它们对增强C-C和C-O伸缩模式有直接影响。然后，研究了通过氢键与腺嘌呤形成碱基对作为一种通过SERS提高可检测性的策略，这得到了腺嘌呤对金属纳米颗粒具有众所周知的高亲和力的支持。我们表明，腺嘌呤有利于5-卤代尿嘧啶的取向，实现了额外的信号增强，这对于分析目的非常有用，如对5-氟尿嘧啶的检测，检测限（LOD）达到2.36 nmol/L。在SERS光谱中观察到的NH模式的波数位移和增强，以及DFT计算，强烈表明碱基对与银簇相互作用时形成氢键（NH----N）是通过SERS提高卤代尿嘧啶LOD的关键。
