Comparative Study of the Removal Efficiency of Nalidixic Acid by Poly[(4-vinylbenzyl)trimethylammonium Chloride] and N-Alkylated Chitosan through the Ultrafiltration Technique and Its Approximation through Theoretical Calculations

Emerging antibiotic contaminants in water is a global problem because bacterial strains resistant to these antibiotics arise, risking human health. This study describes the use of poly[(4-vinylbenzyl) trimethylammonium chloride] and N-alkylated chitosan, two cationic polymers with different natures and structures to remove nalidixic acid. Both contain ammonium salt as a functional group. One of them is a synthetic polymer, and the other is a modified artificial polymer. The removal of the antibiotic was investigated under various experimental conditions (pH, ionic strength, and antibiotic concentration) using the technique of liquid-phase polymer-based retention (LPR). In addition, a stochastic algorithm provided by Fukui's functions is used. It was shown that alkylated N-chitosan presents 65.0% removal at pH 7, while poly[(4-vinylbenzyl)trimethylammonium chloride] removes 75.0% at pH 9. The interaction mechanisms that predominate the removal processes are electrostatic interactions, π-π interactions, and hydrogen bonding. The polymers reached maximum retention capacities of 1605 mg g-1 for poly[(4-vinylbenzyl) trimethylammonium chloride] and 561 mg g-1 of antibiotic per gram for alkylated poly(N-chitosan). In conclusion, the presence of aromatic groups improves the capacity and polymer-antibiotic interactions.

Kick-Fukui: A Fukui Function-Guided Method for Molecular Structure Prediction

Here, we introduce a hybrid method, named Kick-Fukui, to explore the potential energy surface (PES) of clusters and molecules using the Coulombic integral between the Fukui functions in the first screening of the best individuals. In the process, small stable molecules or clusters whose combination has the stoichiometry of the explored species are used as assembly units. First, a small set of candidates has been selected from a large and stochastically generated (Kick) population according to the maximum value of the Coulombic integral between the Fukui functions of both fragments. Subsequently, these few candidates are optimized using a gradient method and density functional theory (DFT) calculations. The performance of the program has been evaluated to explore the PES of various systems, including atomic and molecular clusters. In most cases studied, the global minimum (GM) has been identified with a low computational cost. The strategy does not allow to identify the GM of some silicon clusters; however, it predicts local minima very close in energy to the GM that could be used as the initial population of evolutionary algorithms.

Exploring the Potential Energy Surface of Trimetallic Deltahedral Zintl Ions: Lowest-Energy [Sn6Ge2Bi]3- and [(Sn6Ge2Bi)2]4- Structures

The synthesis and structural characterization of the dimer [(Sn₆Ge₂Bi)₂]^4- raise the possibility of obtaining a broad variety of analogous compounds with different Sn/Ge/Bi proportions. Several combinations of nine atoms have been detected by electrospray mass spectrometry as potential assembly units. However, [(Sn₆Ge₂Bi)₂]^4- remains as the unique experimentally characterized species in this series. This fact has motivated us to explore its potential energy surface, as well as its monomers' [Sn₆Ge₂Bi]^3-/2-, in an effort to gain insight into the factors that might be privileging the experimental viability of this species. Our results show that the lowest-energy [Sn₆Ge₂Bi]^3- structure remains in its oxidized product [Sn₆Ge₂Bi]^2-, which corresponds to that identified in the dimer [(Sn₆Ge₂Bi)₂]^4-. Additionally, local minima, very close in energy to the lowest-energy monomer, are chiral mixtures that dimerize into diverse structures with a probable energetic cost, making them noncompetitive isomers. Finally, the global minimum of the dimer [(Sn₆Ge₂Bi)₂]^4- presents the most stable monomers as assembly units. These results show the importance of considering the simultaneity of all of these conditions for the viability of these types of compounds.

Carbon rings decorated with group 14 elements: new aromatic clusters containing planar tetracoordinate carbon

A simple and chemically intuitive approach is used to design ptC-containing E–C clusters (E = Si–Pb).

Electrochemical behaviors and relativistic DFT calculations to understand the terminal ligand influence on the [Re6(μ3-Q)8X6]4− clusters

A Born–Haber thermodynamic cycle was used to determine the redox potential in a series of rhenium(iii) clusters theoretical analysis at DFT level was considered to estimate the free energy of the reversible process ReIII6/ReIII5Re^IV.

Exploring the potential energy surface of small lead clusters using the gradient embedded genetic algorithm and an adequate treatment of relativistic effects

Theoretical inclusion of relativistic effects (scalar and spin–orbit) play a crucial role to assure an adequate structural assignment on lead clusters.

Insights into bonding interactions and excitation energies of 3d-4f mixed lanthanide transition metal macrocyclic complexes

In this contribution, a computational study of equatorial bound tetranuclear macrocycle (butylene linked) [LnZn(HOM^Bu)]³⁺ (Ln = La³⁺, Ce³⁺) complexes was carried out. Here, the electronic structure, bonding interaction and excitation energies were studied within the relativistic density functional theory framework. From the electronic structure analysis, the frontier molecular orbitals (FMOs) were strongly localized in the d-orbitals of the Zn centers and the f-orbitals of the lanthanide ions. Besides, the inner MOs were found to exhibit a π-character from the organic part of the macrocyclic chain. EDA-NOCV was used as a tool for evaluating the bonding interaction, taking the trinuclear metallomacrocycle (ZnHOM^Bu) and the lanthanide center as fragments. This analysis showed that the interaction between these fragments was slightly covalent; with this covalency being the result of a charge transfer from the metallomacrocyclic ring to the lanthanide. This phenomenon was observed in the deformation density channels obtained from the EDA-NOCV study; in which π- and σ-charge transfer was observed. Finally, the TD-DFT study of the excitation energies evidenced three sets of bands: the first set with the highest intensity represented the ligand to metal charge transfer bands; the second set could be attributed to the 3d-4f electronic transitions between the metal centers; and the third set represented the f-f bands found for the open-shell cerium complex. This class of complexes accomplishes the "antenna effect" principle, which states that highly absorptive transition-metal (TM) complexes can be used to enhance the luminescence of poorly emissive systems, and are introduced in this study as self-sensitizer bimetallic d-f systems with potential applications in near infra-red (NIR) technologies.

New Insights into Re3(μ-Cl)3Cl6 Aromaticity. Evidence of σ- and π-Diatropicity

We have theoretically evaluated the behavior of the Re3(μ-Cl)3Cl6 cluster under magnetic perturbation, and it clearly shows that the magnetic response within the Re3(μ-Cl)3 plane is highly diatropic in nature. An analysis of both the magnetically induced current density (MICD) and induced magnetic field (B(ind)) allows us to classify this cluster as doubly σ- and also π-aromatic on the magnetic criterion. These findings contradict the classical Re-Re double bond representation and favor a chemical bonding pattern that involves delocalized bonds.

Exploring the nature of the excitation energies in [Re6(μ3-Q8)X6]4− clusters: a relativistic approach

This contribution is focused on the characterization of the electronic transitions of the [Re₆(μ₃-Q₈)X₆]⁴⁻ clusters, with the aim of understanding the substitution effect of the terminal and chalcogenide ligands, and the significance of the spin–orbit coupling over the description of excitation energies.

Understanding the influence of terminal ligands on the electronic structure and bonding nature in [Re6(μ3-Q8)](2+) clusters

Since the synthesis of the first molecular cluster [Re6(μ3-Q8)X6](4-), the substitutional lability of the terminal ligands prompted new developments in their chemistry, making these molecular clusters a reasonable point of departure for building new materials. The development of novel inorganic materials of technological interest certainly requires an understanding of the electronic structure, bonding, spectroscopy, photophysical and structural properties of these clusters. Taking into account the potential applications in material sciences and the lack of systematization in the study of these kinds of clusters, the proposal of the present work is to perform a detailed theoretical study of the [Re6(μ3-Q8)X6](4-) (Q = S(2-), Se(2-), Te(2-); X = F(-), Cl(-), Br(-), I(-), CN(-), NC(-), SCN(-), NCS(-), OCN(-), NCO(-)) clusters based on the detailed description of the electronic structure of these complexes and the bonding nature between the [Re6(μ3-Q8)](2+) core and several donor-acceptor peripheral ligands. All this work was developed on the framework of the relativistic density functional theory, in which relativistic effects were incorporated by means of a two-component Hamiltonian with the zeroth-order regular approximation. To describe the relative stability of these complexes, we employed the global descriptors of chemical hardness and softness introduced by Pearson. Moreover, an analysis of bonding energetics was performed by combining a fragment approach to the molecular structure with the decomposition of the total bonding energy according to the Morokuma-Ziegler energy partitioning scheme. After an analysis of these results, we found in all cases an extensive ionic character in the bonding between the core and each peripheral ligand. The interaction between the halide ligand and the core gives about 75% ionic character, whereas the other ligands show a more covalent interaction due to effective synergic mechanisms. We conclude that the most stable clusters are those that present the stronger σ-donor terminal ligands, whereas the cluster stability starts to decrease when the π-acceptor effect will be stronger; this fact is directly related to the terminal ligand lability and the strong electrophilic character of the [Re6(μ3-Q8)](2+) core.

Covalent lanthanide(iii) macrocyclic complexes: the bonding nature and optical properties of a promising single antenna molecule

The present work is focused on the elucidation of the electronic structure, bonding and optical properties of a series of coordination compounds of type [Ln^IIIHAM]³⁺, where “Ln^III” are the trivalent lanthanide ions: La³⁺, Ce³⁺, Eu³⁺ and Lu³⁺, while “HAM” is the neutral six-nitrogen macrocyclic ligand [C₂₂N₆H₂₆].