Banca de DEFESA: ANTONIO MORAIS NETO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : ANTONIO MORAIS NETO
DATA : 23/01/2024
HORA: 14:30
LOCAL: https://conferenciaweb.rnp.br/sala/paula-38
TÍTULO:

NATURE OF THE INTERACTION OF ADENINE-5-HALOURACIL PAIRS WITH SILVER NANOPARTICLES: A THEORETICAL-EXPERIMENTAL APPROACH

PÁGINAS: 67
RESUMO:

In recent years, the halogenated 5-substituted uracil derivatives (5-fluor-, 5-chloro, and 5-
bromouracil) have drawn attention due to their pharmacological properties and their importance
as biomarkers and, recently, also as 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. Raman
technique and its special effect, Surface Enhanced Raman Scattering (SERS), is a very suitable
approach for detecting and quantifying this kind of compound, mainly because most DNA and
RNA derivatives are good light scatterers, yielding rich-information spectra. In practice,
enhancing the Raman signal requires a nanostructured noble metal surface with the species of
interest attached to it, and 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 reinforced by theoretical approaches, such as the Density Functional Theory (DFT)
calculations. In the first part of this work, the 5-halouracils attached to silver nanoparticles
(AgNPs) were studied experimentally and theoretically. From the results, those moieties
showing higher band enhancement were identified. Also, the observed patterns in the
spectroscopic behavior showed a trend related to the electronegativity at the halogenated bonds,
suggesting their direct influence in enhancing C=C and C=O stretching modes. The 5-
bromouracil showed a higher affinity for the silver surface, suggesting a stronger effect of
electronegativity and halogen atom size. In the following stages, their ability to form base pairs
with adenine through hydrogen bonding will be studied as a strategy to improve the detectability
through SERS. This is based on the well-known high affinity of adenine towards metal
nanoparticles, which would favor the orientation of the 5-halouracils to lower the limit of
detection. To accomplish this, an optimization based on the Design of Experiments
methodology is being developed to improve the reproducibility of SERS spectra. Here, a
fractional factorial design was first run, and the more significant variables identified were the
volume of 5-halouracil and sodium chloride (aggregating agent). Then, through a central
composite rotatable design (DCCR), the optimal ranges for validation were the lowest volumes
for 5-FU (3.43 μL), 5-ClU (20 μL), and the higher volume value for 5-BrU (200 μL). NaCl's
optimized volume was 60, 20, and 100 μL for 5-FU, 5-ClU, and 5-BrU, respectively. In this
study, a principal component analysis (PCA) was also performed to understand the behavior of
pairs and which vibrational modes are responsible for the signal intensification. Finally, DFT was applied as a tool for observation between theoretical and experimental data, revealing how base pairs behave theoretically in the presence of Ag and revealing more intense vibrational modes in the presence of adenine, such as the formation of hydrogen bonding (N-H----N).

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1544394 - PAULA HOMEM DE MELLO
Membro Titular - Examinador(a) Interno ao Programa - 1544403 - MAURICIO DOMINGUES COUTINHO NETO
Membro Titular - Examinador(a) Externo à Instituição - MICHELE LEMOS DE SOUZA - UNIVIC
Membro Suplente - Examinador(a) Interno ao Programa - 3008569 - BRUNO GUZZO DA SILVA
Membro Suplente - Examinador(a) Externo à Instituição - RAFAELLA FERNANDES - UFSCAR