Leonardo Moreira da Costa

Interaction between alkaline earth cations and oxo-ligands. DFT study of the affinity of the Ca2+ cation for carbonyl ligands

AbstractThe affinity of the Ca2+ ion for a set of substituted carbonyl ligands was analyzed with both the DFT (B3LYP/6-31+G(d)) and semi-empirical (PM6) methods. Two types of ligands were studied: a set of monosubstituted [O=CH(R)] and a set of disubstituted ligands [O=C(R)2] (R=H, F, Cl, Br, OH, OCH3, CH3, CN, NH2 and NO2), with R either directly bound to the carbonyl carbon atom or to the para position of a phenyl ring. The interaction energy was calculated to quantify the affinity of the Ca2+ cation for the ligands. Geometric and electronic parameters were correlated with the intensity of the metal-ligand interaction. The electronic nature of the substituent is the main parameter that determines the interaction energy. Donor groups make the interaction energy more negative (stabilizing the complex formed), while acceptor groups make the interaction energy less negative (destabilizing the complex formed). FigureThe affinity of Ca2+ for carbonyl ligands is determined by the electronic nature of the substituent. Electron donor substituents bind more strongly than electron acceptor substituents.

Interactions between alkaline earth cations and oxo ligands. DFT study of the affinity of the Mg2+ cation for phosphoryl ligands

DFT (B3LYP/6-31+G(d)) calculations of Mg2+ affinities for a set of phosphoryl ligands were performed. Two types of ligands were studied: a set of trivalent [O = P(R)] and a set of pentavalent phosphoryl ligands [O = P(R)3] (R = H, F, Cl, Br, OH, OCH3, CH3, CN, NH2 and NO2), with R either bound directly to the phosphorus atom or to the para position of a phenyl ring. The affinity of the Mg2+ cation for the ligands was quantified by means of the enthalpy for the substitution of one water molecule in the [Mg(H2O)6]2+ complex for a ligand. The enthalpy of substitution was correlated with electronic and geometric parameters. Electron-donor groups increase the interaction between the cation and the ligand, while electron-acceptor groups decrease the interaction enthalpy.

DFT studies of imino and thiocarbonyl ligands with the pentaaqua Mg2+ cation: affinity and associated parameters

AbstractThe affinity of the pentaaqua Mg2+ cation for a set of para-substituted imino [HN = CHC6H4(R)] and thiocarbonyl [S = CHC6H4(R)] ligands (R = H, F, Cl, Br, OH, OCH3, CH3, CN, NH2 and NO2) was analyzed with DFT (B3LYP/6-31+G(d)) and semi-empirical (PM6-DH2) methods. The interaction enthalpy was calculated to quantify the affinity of the Mg2+ cation for the ligands. Additionally, geometric and electronic parameters were correlated with the intensity of the metal-ligand interaction. The imino ligands have stronger interaction with the pentaaqua Mg2+ cation than the thiocarbonyl derivatives. The electronic nature of the substituent is the main parameter that determines the interaction enthalpy. Ligands with electron donor substituents have more exothermic interaction enthalpies than those with electron withdrawing groups. The HSBA analysis showed that the interaction between the Mg2+ cation and hard bases (imino ligands) is stronger than with soft bases (thiocarbonyl derivatives). The EDA analysis showed that the electrostatic, covalent and repulsion components of the interaction are the most affected by the substituent, whereas the dispersion and exchange components are almost constant. The affinity of the Mg2+ cation for a set of para-substituted imino and thiocarbonyl ligands was evaluated in terms of interaction enthalpy, Gibbs free energy, geometric and electronic parameters, showing that the nature of the substituent directly modulates the electrostatic, covalent and repulsion components of the interaction.

Interaction between alkaline earth cations and oxo ligands: a DFT study of the affinity of Mg2+ for carbonyl ligands

The affinities of Mg2+ for various substituted carbonyl ligands were determined at the DFT (B3LYP/6-31+G(d)) and semi-empirical (PM6) levels of theory. Two sets of carbonyl ligands were studied: monosubstituted [aldehydes R–CHO and RPh–CHO] and homodisubstituted [ketones R2C=O and (RPh)2C=O], where R = NH2, OCH3, OH, CH3, H, F, Cl, Br, CN, or NO2). In the (RPh)2CO case, the R group was bonded to the para position of a phenyl ring. The enthalpies of interaction between the ligands and a pentaaquomagnesium(II) complex were calculated to determine the affinity of each ligand for the Mg2+ cation and to correlate with geometrical and electronic parameters. These parameters exhibited the same trends for all of the ligands studied, showing that the affinity of Mg2+ for electron-donating ligands is higher than its affinity for electron-withdrawing ligands. In the complexes, electron-donating groups increase both the electrostatic and the covalent components of the Mg–ligand interaction. This behavior correlates with the Mg–O(carbonyl) distance and the ligand electron-donor strength.

Cianogenese em esporofitos de pteridofitas avaliada pelo teste do acido picrico

Cyanogenesis in sporophytes of pteridophytes evidenced by the picric acid test). Cyanogenic glycosides are defense substances found in some plants that are able to produce cyanhydric acid on hydrolysis. The present work aimed to study the occ urrence of cyanogenesis in pteridophytes of rocky areas of Pedra de Itacoatiara, State Park of Serra da Tiririca, Rio de Janeiro State. Nineteen species, distributed in 13 genera and nine families have been analyzed monthly, during one year. In each species, the analysis was carried out on fertile leaves, sterile ones, young leaves (croziers) and stems. Cyanogenesis was evidenced using filter paper embedded with picric acid. Among studied species, 14 were analysed here for the first time, and 14 gave a positive picric test. Our results showed v ariation along time in the production of cyanhydric acid in the vegetal species and parts. The species, Microgramma vacciniifolia (Langsd. & Fisch.) Copel. (Polypodiaceae) and Pteridium aquilinum (L.) Kuhn var. arachnoideum (Kaulf.) Brade (Dennstaedtiaceae) were cyanogenic all along the studied period.

A density functional theory investigation of the interaction of the tetraaqua calcium cation with bidentate carbonyl ligands

AbstractCalcium complexes with bidentate carbonyl ligands are important in biological systems, medicine and industry, where the concentration of Ca2+ is controlled using chelating ligands. The exchange of two water molecules of [Ca(H2O)6]2+ for one bidentate monosubstituted and homo disubstituted dicarbonyl ligand was investigated using the B3LYP/6-311++G(d,p) method. The ligand substituents NH2, OCH3, OH, CH3, H, F, Cl, CN and NO2 are functional groups with distinct electron-donating and -withdrawing effects that bond directly to the sp2 C atom of the carbonyl group. The geometry, charge and energy characteristics of the complexes were analyzed to help understand the effects of substituents, spacer length and chelation. Coordination strength was quantified in terms of the enthalpy and free energy of the exchange reaction. The most negative enthalpies were calculated for the coordination of bidentate ligands containing three to five methylene group spacers between carbonyls. The chelate effect contribution was analyzed based on the thermochemistry. The electronic character of the substituent modulates the strength of binding to the metal cation, as ligands containing electron-donor substituents coordinate stronger than those with electron-acceptor substituents. This is reflected in the geometric (bond length and chelating angle), electronic (atomic charges) and energetic (components of the total interacting energy) characteristics of the complexes. Energy decomposition analysis (EDA)—an approach for partitioning of the energy into its chemical origins—shows that the electrostatic component of the coordination is predominant, and yields relevant contribution of the covalent term, especially for the electron-withdrawing substituted ligands. The chelate effect of the bidentate ligands was noticeable when compared with substitution by two monodentate ligands. Graphical abstractThe affinity of 18 bidentate carbonyl ligands toward the [Ca(H2O)4]2+ cation is evaluated in terms of energetic, geometric and electronic parameters of the isolated ligands and the substituted aqua complexes. The electronic effects—inductive and mesomeric—intrinsic to the molecular structure of each ligand are found to modulate the strength of the metal-ligand interaction. The effects of polysubstitution, chelation and the length of the alkyl spacers between the anchor points of the ligand are also analyzed.

Theoretical Study of the Interaction of 1,2-Dithiolene Ligands with the Mg2+ and Ca2+ Aquacations: Electronic, Geometric and Energetic Analysis

The B3LYP/6-311++G(d,p) method is employed to carry out calculations of the interaction strength of bidentate dithiolene ligands with the [M(H2O)6] and [M(H2O)4] (M = Mg or Ca) aquacations. Two series of ligands are studied: one with a phenyl ring directly bonded to the S interacting atoms and the other with a substituted ethylene (>C=C<) bonded to the two sulfide groups. These ligands present substituents with distinct induction and resonance electronic donor/acceptor effects. Fundamental characteristics, such as geometry, charges and energy of the complexed aquacations and isolated ligands, are analyzed and rationalized to correlate with the substituents effects and the metal-ligand affinity. The thermodynamic results, energy decomposition analysis (EDA) and natural bond order (NBO) show the chelate effect has an important contribution to complex stabilization and leading to an enhanced knowledge of the metal-dithiolene interaction and coordination affinity between the alkaline earth metals and sulfured ligands.