Detecção de compostos via SERS em superfícies metálicas modificadas: estudo de reatividade e dinâmica molecular para acefato, diuron e levodopa
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2023-04-27
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Universidade Estadual Paulista (Unesp)
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A dificuldade de detecção de compostos de interesse em baixas concentrações requer técnicas de monitoramento mais sensíveis, destacando-se a técnica de espalhamento Raman amplificado por superfície (SERS) com o uso de nanopartículas (NP). Contudo, apesar da potencialidade desta técnica, a detecção de espécies químicas negativamente carregadas é ainda um desafio, dada a baixa afinidade destes compostos com as superfícies das NP empregadas. Visando contornar tal problema, diferentes recobrimentos têm sido testados, contudo, detalhes acerca das interações envolvidas ainda não são bem compreendidos. Neste contexto, no presente trabalho, técnicas de modelagem molecular foram empregadas no estudo de substratos de ouro recobertos com brometo de hexadeciltrimetilamônio (CTAB) interagindo com diferentes analitos de difícil detecção: diuron, acefato e levodopa. Cálculos de estrutura eletrônica e simulações de dinâmica molecular (MD) foram empregados para melhor entendimento acerca dos mecanismos relevantes de interação, visando uma melhor compreensão do efeito (SERS) e a identificação de variáveis relevantes. Tais estudos foram estendidos para outras estruturas dos analitos, em especial isômeros, subprodutos de degradação e diferentes formas redox. Os resultados obtidos permitem identificar sítios preferenciais de adsorção dos compostos os quais são mais propensos à interação com agentes externos eletrofílicos, nucleofílicos e radicais livres. Em especial, para o acefato nota-se a dominância do átomo de S para interação com agentes externos eletrofílicos. O composto diuron apresenta um átomo de Cl e o N como regiões mais propensas à interação com a superfície de ouro. Por fim, a L-dopa verificou a relevância dos átomos de O na reatividade dos sistemas, o que depende do seu grau de oxidação. A análise dos dados de atividade Raman sugere que os compostos diuron e L-dopa podem apresentar aumento significativo em bandas específicas devido à ancoragem na superfície metálica. Dados de dinâmica molecular permitiram avaliar uma maior tendência de interação do acefato com cadeias alquílicas do CTAB, enquanto diuron e L-dopa tendem a interagir mais efetivamente com os grupos polares catiônicos desta molécula. A análise das simulações de MD indicam a relevância de uma densidade apropriada de moléculas de CTAB para uma interação efetiva dos analitos com a superfície metálica.
The difficulty in detecting compounds of interest at low concentrations requires more sensitive monitoring techniques, especially the surface-amplified Raman scattering technique (SERS) using nanoparticles (NP). Nonetheless, despite the potential of this technique, the detection of negatively charged chemical species is still a challenge, given the low affinity of these compounds with the surfaces of the NP employed. Aiming to overcome this problem, different coatings have been tested, however, details about the interactions involved are still not well understood. In this context, in the present work, molecular modeling techniques were employed in the study of gold substrates coated with hexadecyltrimethylammonium bromide (CTAB) interacting with different difficult-to-detect analytes: diuron, acephate, and levodopa. Electronic structure calculations and molecular dynamics (MD) simulations were used to better understand the relevant interaction mechanisms, aiming at a better understanding of the effect (SERS) and the identification of relevant variables. Such studies were extended to other analyte structures, especially isomers, degradation by-products, and different redox forms. The results obtained allow the identification of preferential sites of adsorption of compounds that are more prone to interact with external electrophilic and nucleophilic agents and free radicals. In particular, for acephate, the dominance of the S atom for interaction with external electrophilic agents is noted. The diuron compound presents the Cl and N atom as regions more prone to interaction with the gold surface. Finally, L-dopa verified the relevance of O atoms in the reactivity of the systems, which depends on their degree of oxidation. The analysis of the Raman activity data suggests that the diuron and L-dopa compounds may present a significant increase in specific bands due to the anchoring on the metal surface. Molecular dynamics data allowed the evaluation of a greater tendency for acephate to interact with CTAB alkyl chains, while diuron and L-dopa tend to interact more effectively with the cationic polar groups of this molecule. The analysis of the MD simulations indicates the relevance of an appropriate density of CTAB molecules for the effective interaction of the analytes with the metallic surface.
The difficulty in detecting compounds of interest at low concentrations requires more sensitive monitoring techniques, especially the surface-amplified Raman scattering technique (SERS) using nanoparticles (NP). Nonetheless, despite the potential of this technique, the detection of negatively charged chemical species is still a challenge, given the low affinity of these compounds with the surfaces of the NP employed. Aiming to overcome this problem, different coatings have been tested, however, details about the interactions involved are still not well understood. In this context, in the present work, molecular modeling techniques were employed in the study of gold substrates coated with hexadecyltrimethylammonium bromide (CTAB) interacting with different difficult-to-detect analytes: diuron, acephate, and levodopa. Electronic structure calculations and molecular dynamics (MD) simulations were used to better understand the relevant interaction mechanisms, aiming at a better understanding of the effect (SERS) and the identification of relevant variables. Such studies were extended to other analyte structures, especially isomers, degradation by-products, and different redox forms. The results obtained allow the identification of preferential sites of adsorption of compounds that are more prone to interact with external electrophilic and nucleophilic agents and free radicals. In particular, for acephate, the dominance of the S atom for interaction with external electrophilic agents is noted. The diuron compound presents the Cl and N atom as regions more prone to interaction with the gold surface. Finally, L-dopa verified the relevance of O atoms in the reactivity of the systems, which depends on their degree of oxidation. The analysis of the Raman activity data suggests that the diuron and L-dopa compounds may present a significant increase in specific bands due to the anchoring on the metal surface. Molecular dynamics data allowed the evaluation of a greater tendency for acephate to interact with CTAB alkyl chains, while diuron and L-dopa tend to interact more effectively with the cationic polar groups of this molecule. The analysis of the MD simulations indicates the relevance of an appropriate density of CTAB molecules for the effective interaction of the analytes with the metallic surface.
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Índices de Reatividade, SERS, Diuron, Acefato, Levodopa, Dinâmica Molecular, Nanorods de Ouro Recobertos, Reactivity Indices, Acephate, Molecular Dynamics, Recovered Gold Nanorods