Homo pair formations of thiobarbituric acid: DFT calculations and QTAIM analysis

Homo pair formations of thiobarbituric acid (TBA) were investigated in this work by performing density functional theory (DFT) calculations and the quantum theory of atoms in molecule (QTAIM) analysis. Different types of interactions including N–H . . . O, N–H . . . S, C–H . . . O, and C–H . . . S were involved in formations of five models of homo pair of TBA. In this regard, the results of energy strength and QTAIM features indicated that the model with two N–H . . . O interacting bond (D1) was placed at the highest stability and the model with one N–H . . . O and one C–H . . . S interacting bonds (D5) was placed at the lowest stability. Existence of hydrogen bond (HB) interactions in the models were confirmed based on the obtained results. As a consequence, self-interaction of TBA, as an initiator of pharmaceutical compounds production, was investigated in this work in addition to recognition of existence of different types of interactions.

Physical and Chemical Aspects of the interaction of Chitosan and Cellulose acetate with ions Ca2+ and K+ using DFT methods

Motivated by the use of chitosan (Ch), and cellulose acetate (AC) as organic matrices in several therapeutic drugs, a theoretical study has been elaborated through the density functional theory method (DFT) to investigate the interaction mechanism between two essential ions for the human body Ca2+, K+ and two organic matrices chitosan (Ch), and cellulose acetate (AC). Many physical and chemical aspects have been carried out after the achievement of structural optimization. This involves structural parameters, molecular electrostatic potential (MEPs), interaction energy, reactivity indexes, frontier molecular orbitals (FMOs), quantum theory atoms in molecules (QTAIM) analysis and non-covalent interaction (NCI) analysis. The results of FMOs, MEPs and reactivity index studies have revealed that the site of interaction can be predicted. The calculation of electron interaction energies shows that those ions interact with the matrix of AC and Ch. Concretely, the Ca2+ ion interacted efficiently with the AC matrix. The structural analysis results show that the interaction of Ch and ions appear spontaneously (ΔG < 0) while the interaction of AC and ions (ΔG > 0), requires more energy to occur. Finally, the QTAIM analysis data indicates that the interactions of AC -ions and Ch-ions are non-covalent presenting an electrostatic character.

Chemical interaction study between xanthate ligand and lead (II) using NBO, EDA and QTAIM analysis

As a useful flotation agent, the xanthate ligand, O-alkyldithiocarbonates, has been used by different countries by its easy and inexpensive synthesis. More recently papers explored many different applications using this ligand within a complex of several metals cation. In order to study the proprieties of the lead (II) complex with such ligand, the object of this work is to provide a better understanding of the Pb-S bond using different theoretical approaches as NBO, EDA and QTAIM analysis and the influence caused by the different alkyl groups of the ligand. By an optimized structure, the NBO showed that the Pb-S is mainly composed by p orbital of the lead and by the p lone pair of the sulfur atom. The calculation with different alkyl groups highlights that the presence of a larger hydrocarbon chain provides a higher contribution of the s orbital of the lead atom to the interaction. Through the EDA analysis, the interaction between ligand and metal has the predominance of an electrostatic character. The size of the alkyl group has an impact on the value of both covalent and electrostatic character, making the interaction more covalent, due to a higher presence of an electronic density on sulfur atom. This density can be evaluated by the topological study of the QTAIM analysis, which enhances the fact that the charge over the sulfur atom gets higher when using a larger alkyl group for the xanthate ligand.