Estudo das propriedades de recobrimento em ligações de hidrogênio envolvendo dímeros e heterodímeros formados com água

Abstract

The dissertation investigates hydrogen bonds, important for several chemical and biological functions, such as the structure of DNA. Different analysis methodologies, such as Quantum Theory of Atoms in Molecules – QTAIM and Local Vibrational Mode – LVM, are common to study these connections. This work focuses on the approach of the overlap properties, as an alternative analysis of chemical bonds, which includes the overlap polarizability (αOP), intra-overlap repulsions (JOP 𝑖𝑛𝑡𝑟𝑎) and overlap electron density (ρOP) as bond descriptors chemicals. Thirteen systems were analyzed, including a water dimer and heterodimers with water as a proton donor, divided into four groups: (R,R’)−O⋯H2O; (R,R’)C=O⋯H2O; (R,R’,R’’)−N⋯H2O; (R’’’)C≡N⋯H2O, where R, R’ and R’’ = H, CH3, and R’’’ = H, CH3. CH2CH3. Thus, the gradual replacement of hydrogens by methyl groups, with an electron-donating effect, was considered. Using the density functional theory at the ωB97X-D/Def2-TZVP level and the ChemBOS software, developed by Computational Chemistry Research Group at the Federal University of Paraíba (GPQTC – UFPB), the calculations were compared with the QTAIM. Analysis of the properties revealed behavioral trends and highlighted the potential of the emerging chemical bond analysis method. It was observed that the density of overlap of the proton-donor O-H bond increases with each substitution in the heterodimers, reflecting the Push-pull effect on the Brönsted acid of each system. This leads to shortening of the passive O-H bond as the donated hydrogen becomes more positive. This work explores the computational analysis of hydrogen bonds, using the overlap model and comparing the results with QTAIM. The findings show trends and the push-pull effect in each heterodimer system analyzed. This contributes to the understanding of chemical bonds and the validation of a promising approach for future studies.