Search

The present study examines bonding patterns between copper Cun clusters (n = 3–20) and aromatic compounds (benzene, phenol, and benzaldehyde) using a density-functional theory (DFT) approach. Hirshfeld population, natural bond orbital (NBO), molecular orbitals, and quantum theory of atoms in molecules (QTAIM) analyses suggested the formation of two types of interactions Cu–arene and C–H···Cu, in the complexation of copper clusters by an aromatic compound.

This work describes the reactions of [(μ-H)M3(CO)9(CCSiMe3)] (M = Ru, Os) with phosphines L (L = PMe3, PMe2Ph, PMePh2, and PPh3) which produce zwitterionic compounds [(μ-H)M3(CO)9(HCCPR3)] where cleavage of the C Si and formation of C P bonds occurs. In the case of the ruthenium derivatives, CO substitution also occurs. Spectroscopic and structural characterization of the products is described. A theoretical analysis was carried out in order to understand the transformation pathway in the formation of the zwitterionic compounds.

Monoaza-dithia- (1a – 3a) and diaza-tetrathia- (1b and 3b) macrocycles with a pendant 2-pyridylmethyl fragment have been prepared by the reaction between 2-(aminomethyl)pyridine with dibromide-dithioether derivatives. Four of the macrocycles have been characterized by X-ray crystallography, revealing the formation of two 14- and 15-membered monoaza-dithiaethers, and two 26- and 30-membered diaza-tetrathiaether macrocycles featuring one or two exo-2-pyridylmethyl fragments, respectively. The monoaza-dithiaethers macrorings adopt a twisted conformation while the diaza-tetrathiaethers macrorings display a rectangular conformation. Intramolecular interactions of macrorings 2a, 3a, 1b and 3b were studied by non-covalent interaction analysis. It was found that smaller macrorings are less stable than larger ones due to larger strain energies and that intramolecular dispersive interactions and hydrogen bonding play an important role in the macrocycle conformation adopted.

The structural and electronic properties were calculated for seventy organic compounds used as dye sensitizers in solar cells, applying the B3LYP exchange-correlation energy functional with the 6-311G∗∗ basis set. Moreover, the present study proposes two new quantitative structure-property relationship (QSPR) models that enable the prediction of the power conversion efficiency (PCE) and maximum absorption wavelength (λmax) of these systems, the two QSPR models were validated using the coefficient of determination (R2) of 0.62 for both models with the leave-one-out cross-validation correlation coefficient (Q2LOO) of 0.55 and 0.57, respectively. Furthermore, applicability domain analysis was conducted in order to identify the related compounds via the extrapolation of the model.

Two organotin compounds [{D(C6H4CH2)2}SnBr2] displaying intramolecular transannular Sn–D interactions (D = O, 3a; S, 3b) were synthesized by oxidation of elemental tin with the corresponding dibromo compounds D(C6H4CH2Br)2. Both organotin compounds were physicochemically characterized by EI-MS and NMR techniques and by single crystal X-ray crystallographic studies at room temperature. The spectroscopic and diffraction data agreed with the presence of a Sn–D intramolecular interaction. DFT calculations at the B3LYP/DGDZVP level were carried out. The topological analysis indicated that bond critical points are present along the Sn–D direction, and the electron localization function graphs showed the presence of electron lone pairs of the D donor atoms directed to the Sn acceptor atom.

The interaction of twenty anisole, thioanisole and derivatives with gold clusters was studied theoretically by DFT using different basis-sets. The Aun (n = 2–11) clusters were geometrically optimized and electronically characterized through their charges, molecular orbitals and bond energies. The studies of the most stable clusters Au10 and Au11 with the organic molecules displayed Cring Au, Au S, Au O, and Au---H C interactions; these last ones are significant because they play a crucial role in catalysis. The most stable systems were the Au11/sulfur derivatives, according to the HSAB model. These results were confirmed with the electron density topological analysis.

The structure of four type bis-1,4-dihydropyridine molecules was completely optimized employing semiempirical (PM3), ab initio (HF/3-21G(d), B3LYP/6-31G(d) and B3LYP/6-311++G(d,p) methods. The B3LYP/6-311++G(d,p) theory level provided a flat boat conformation. The observed ring distortions were not found to be influenced to a great extent by the position of the substituent present in the 4-phenyl ring, the second dihydropyridine ring. The HOMO, LUMO, chemical hardness, global softness, chemical electrophilicity and molecular electrostatic potential values were also appropriately calculated. The electronic parameters allowed to establish the reactivity of the four bis-1,4-dihydropyridine molecules. Moreover, the interactions between these compounds with two models of the voltage-gated calcium channel receptor were evaluated in connection to the reported vasodilator activity of these compounds.

The ring opening transformation of three substituted 2-(2-pyridyl)benzothiazolines of general formula [(C 6 H 4 NCS)(C 5 H 4 N)R] (R = C 5 H 4 N, 1 ; R = C 6 H 5 , 2 ; R = H, 3 ) was studied by their reaction with metal chlorides of Ni(II), Pd(II), and Pt(II). In these reactions, the anionic tridentate Schiff bases { L n } − coordinated to metal ions were identified. Seven metallic complexes of type [M( L n )Cl] [M = Pd, n = 1, R = C 5 H 4 N, ( 1a ); n = 2, R = C 6 H 5 , ( 2a ); n = 3, R = H, ( 3a ). M = Pt, n = 1, R = C 5 H 4 N, ( 1b ); n = 2, R = C 6 H 5 , ( 2b ); n = 3, R = H, ( 3b ), and M = Ni, R = C 6 H 5 , ( 2c )] were characterized in solution by NMR and vibrational spectroscopy in solid state. Crystal structures of benzothiazolines 1 and 2 and complexes 1a – 3a , 1b ·DMSO, and 2c were analyzed by X-ray diffraction studies. In all cases, mononuclear complexes with a distorted square planar geometry were obtained. For compounds 1 – 3 , the predominance of the benzothiazoline (ring form) over the Schiff base (open form) as well as the formation of the [Pd( L n )Cl] (n = 1–3) complexes were studied by DFT calculations at the PBEPBE/(Def2-TZVP,SDD) level in gas phase.

A convenient approach for the absolute configuration assignment of secondary alcohols in the (8R,1′R,2′S,5′R)-15,25, (8S,1′R,2′S,5′R)-15,25, (8R,1′R)-21–24, and (8S,1′R)-21–24 ester series, and of primary amines in the (8R,1′R)-32–37 and (8S,1′R)-32–37 amide series, by means of 1H NMR and VCD spectroscopy, using 2-cyano-2-indolylpropanoic acid as a chiral derivatizing agent is presented. DFT calculations were carried out to demonstrate the anisotropic effect of the indole skeleton on the chiral alcohol or the amine fragment. Vibrational circular dichroism (VCD) measurements of the above series indicated a VCD bisignated couplet resulting from the interaction of the ester carbonyl group and the CN group. The absolute configuration assignments were further tested by X-ray diffraction analysis.

The corrosion inhibition of N,N′-bis(benzimidazole-2-yl-methyl)amine (L1) and N, N′-bis(benzimidazole-2-yl-methyl)hydroxyethylamine (L2) was analyzed by electrochemical and theoretical methods. The data show that ligands form an adsorption layer over an iron surface, obeying the Langmuir isotherm ( Δ G a d s ° of −32.96 kJ mol−1); the value are higher than −20 kJ mol−1 but less than −40 kJ mol−1, belonging to a conversion stage of physical adsorption to chemical adsorption or a comprehensive adsorption. This is consistent with fractal dimension of the electrode surface, estimated by an impedance depression angle of a semicircle that the surface is homogeneously covered by the formation of an inhibitor film. Furthermore, the electronic parameters of the ligands were analyzed by DFT, showing that L1 and L2 possesses corrosion inhibition properties that give up its p orbital electron density through its HOMO orbital to the metal LUMO to form an adsorption layer, and this has been proved theoretically by the interaction of ligands with Fe30. In addition, we have collected corrosion inhibition data for around 70 organic compounds reported in the literature, and the inhibition data plotted against different inhibitors, showing that amine ligands are good corrosion inhibitors.

Two tin compounds [Sn(nBu)2(Ln)], where L1 {O(C6H4-2-N C(H)C6H4-2′-O)2}2 − and L2 {O(C6H4-2-C(H) NC6H4-2′-O)2}2 − enclosing five electron donors in an [ON2O2] core, were synthesized and structurally characterized by infrared and NMR spectroscopy and by single crystal X-ray crystallographic studies at room temperature. The hepta-coordinate geometry around the Sn centers is achieved through the bonding of two monodentate n-butyl groups and the coordination of the pentadentate Ln ligands, where the [ON2O2] core is forming a pentagonal base. The two types of oxygen atoms displayed different bonding situations around the Sn atom. DFT calculations with Gaussian 09 using PBEPBE/6-31G**/SDD level were carried out for both compounds. The topological analysis indicated that bond critical points are present along the Sn Oether direction.

The corrosion inhibition efficiency of carbon steel was evaluated using fifteen molecules derivated from imidazole and benzimidazole in 1.0 M HCl. The inhibition efficiency varies from 15.6 to 89.4%, depending on the chemical and the electronic structure of the compounds. The structural properties of the molecules under study were determined by density functional theory. Experimental and theoretical parameters were used to construct a model to predict the inhibition observed. The proposed model shows that inhibition efficiency is related to the molecule volume, charge, electronegativity, and aromaticity. The model is successfully used to predict the corrosion behavior of two additional molecules.

New derivatives of chrysin containing 2-mercaptopyridine (2a–2e) or 5-(trifluoromethyl)-2-mercaptopyridine (3a–3e) moieties were prepared from the reaction between bromides (1a–1e) and 2-mercaptopyridine or 5-(trifluoromethyl)-2-mercaptopyridine, respectively. Their structures were elucidated by NMR, IR and elemental analysis. The molecular structure of compounds 1a, 1c–1e, 2b–2e and 3a was determined by single-crystal X-ray diffraction studies. All rings in these structures are nearly coplanar and they showed an intramolecular hydrogen bond between the phenolic hydroxyl H atom and the carbonyl O atom that forms a six membered ring. The crystal packing also showed a wide variety of intermolecular contacts such as C–H⋯A, π–π, C–H⋯π and lone pair⋯π interactions which were supported by quantum theory of atoms in molecules (QTAIM), Hirshfeld surface, and fingerprint plot analyses. Biological activity of all compounds was tested in growth assays of the nematode Caenorhabiditis elegans. Compounds 2e, 3b and 3c inhibited larval development.

The Ir(I) complexes [TpMe2Ir(η4-1,4-diene)] 2b and 2c react thermally with a variety of aromatic aldehydes, 3a–e, to generate the metallabicyclic compounds 4e–k and the Fischer-type carbenes 5a–b in moderate yields. These reactions are proposed to take place with the initial formation of η1-aldehyde adducts as key intermediates. The formation of the metallabicyclic compounds 4e–k involves a formal decarboxylation process at the exo-2-oxazolidinone diene and an ortho metallation of the aromatic ring. The generation of the Fischer-type carbenes 5a–b is the result of a series of metal-based rearranged intermediates with no decarboxylation observed. Treatment of the η4-diene complex 2b with a variety of Lewis bases induces a change in the binding mode of the diene ligand from η4:π2 to η2:σ2 to form the Ir(III) derivatives 6b–d of composition TpMe2Ir-(η4:π2-1,4-diene)(L) (L = CO, MeCN, and C5H5N). A study of reactions of complex 2b with either mono- or poly-deuterated aldehydes was performed to understand the mechanisms of such processes. The results of these studies were used to determine plausible formation mechanisms of the metallabicyclic compounds 4e–4k and Fischer-type carbenes 5a–b compound series. These mechanisms were corroborated by density functional theory (DFT) calculations of the free energy profiles.

A systematic study was conducted on the production of hydrogen from formic acid with a Pd4 cluster using density functional theory (DFT) with the B3LYP and the 6-31G** orbital basis set for the C, H and O atoms, while a LANL2DZ effective core potential was used for palladium atoms. The thermodynamic results obtained show a favorable reaction mechanism for producing hydrogen with energy barriers lower than 30 kcal/mol. Moreover, the nature of the bonds involved in all system were analyzed using the theory of atoms in molecules (AIM) identifying the non-covalent interactions in this type of system.

The corrosion inhibition by cinnamic, p-coumaric and caffeic acid on carbon steel in 1.0 M HCl and its synergistic combination with KI was investigated using electrochemical and quantum chemical methods. A synergistic effect was observed when 2 mM potassium iodide was added to 0.1 mM inhibitor, where the corrosion inhibition efficiency (IE%) increased from 70% to 80%. In addition, the participation of iodide in the Fe surface was investigated during the adsorption of corrosion inhibitors such as cinnamic, p-coumaric and caffeic acids on Fe(1 1 0). The formation of an iodide monolayer on the Fe(1 1 0) surface was studied by density functional theory (DFT) periodic slab calculations. The DFT results revealed that cinnamic, p-coumaric and caffeic acids were adsorbed effectively on the metal surface through aromatic rings and carboxylic acid groups, as the bond distances with the Fe surface were 2.09 A for Fe C and 1.97 A for Fe O. Low adsorption energies were obtained; −52.90, −44.29 and −33.39 kcal/mol for cinnamic, p-coumaric and caffeic acids, respectively. Additionally, the magnetic moment of the Fe plane was changed significantly if the aromatic carboxylic acid adsorbed onto the metal surface had coating strengths as follows: cinnamic > p-coumaric > caffeic. The present study therefore provides a mechanistic understanding of the role of iodide in the corrosion inhibition process.

A microemulsion electrokinetic chromatography method was developed for the simultaneous detection and quantification of ciprofloxacin, norfloxacin, sulfamethoxazole, tetracycline, and oxytetracycline in feedstuff samples. The BGE composition was optimized by applying a Taguchi parameter design and consisted of phosphate 30 mmol/L, Tween-80 0.01 mmol/L, and fullerene 3 μmol/L, and adjusted to pH 8.0; the addition of surfactant and fullerene modifies the mobility of the analytes improving their resolution. Theoretical studies showed π-π and van der Waals interactions between antibiotic molecules and fullerene used as a pseudostationary phase. Under optimal conditions, limits of detection ranged from 0.7 to 1.5 μg/g; the analytes were separated in less than 6 min. The methodology proposed is useful for controlling and monitoring antibiotic residues in feedstuff samples.

The capacity of 2,6-bis[((2-pyridylmethyl)oxy)methyl)]pyridine (BPMMP) to inhibit the corrosion of mild carbon steel in HCl was analyzed. In a polarization study, both the cathodic and anodic currents were appreciably decreased in the presence of BPMMP, suggesting that this ligand is effective at inhibiting corrosion at the metal surface. This conclusion is consistent with the results of impedance analysis, where only one time constant corresponding to one depressed capacitive loop was detected, and the diameter of the impedance plot was directly related to the concentration of BPMMP. Furthermore, when recurrence analysis was performed, a decrease in regular noise was observed due to the change of Shannon entropy when the inhibitor was present in the corrosive medium, showing that a high degree of recurrence increases the entropy of the system. Electrochemical data on some pyridyl-based inhibitors were collected from the literature and used to plot (i) I corr (A/cm2) vs. inhibition efficiency (η%) and (ii) ΔG°ads vs. inhibition efficiency (ƞ%) in order to examine the general relationships between these parameters. Furthermore, the interactions of the ligand BPMMP with different iron clusters (Fe15, Fe30, Fe45, and Fe60) were analyzed theoretically using density functional theory (DFT). The structural and electronic properties of BPMMP and its protonated form BPMMPH+ were studied before and after the interactions of BPMMP with the iron clusters. The first protonation was found to occur at pyridine nitrogen atom N1, resulting in a Gibbs free energy ΔG of −10.2 kcal/mol, with an energy difference of 5.3 kcal/mol between the two possible protonated conformers.

Structural and electronic properties of a series of 25 phosphonate derivatives were analyzed applying density functional theory, with the exchange-correlation functional PBEPBE in combination with the 6-311++G** basis set for all atoms. The chemical reactivity of these derivatives has been interpreted using quantum descriptors such as frontier molecular orbitals (HOMO, LUMO), Hirshfeld charges, molecular electrostatic potential, and the dual descriptor [[Formula: see text]]. These descriptors are directly related to experimental median lethal dose ([Formula: see text], expressed as its decimal logarithm [[Formula: see text]([Formula: see text]] through a multiple linear regression equation. The proposed model predicts the toxicity of phosphonates in function of the volume (V), the load of the most electronegative atom of the molecule (q), and the eigenvalue of the molecular orbital HOMO ([Formula: see text]. The obtained values in the internal validation of the model are: [Formula: see text]%, [Formula: see text]%, [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]%. The toxicity of nine phosphonate derivatives used as test molecules was adequately predicted by the model. The theoretical results indicate that the oxygen atom of the O=P group plays an important role in the interaction mechanism between the phosphonate and the acetylcholinesterase enzyme, inhibiting the removal of the proton of the ser-200 residue by the his-440 residue.

Producción Científica, Deep eutectic solvents prepared by mixture of choline chloride with urea, thiourea and ethylene glycol (1:2 molar ratio) were used to study the electrochemical behavior Zn(II) at carbon steel 1018 electrode. Zn deposits were immersed in a corrosive media (NaCl 3%wt). Composition of the solvent employed causes a difference in electrodeposition and corrosion behaviors, being diffusion coefficient value a critical parameter associated to these processes.

The symmetric ligands [Ar-S-CH2-Ph-S-(CH2)-]2, L1 (Ar = o-FPh) and L2 (Ar = p-FPh), and their PdII complexes (1 and 2) were synthesized and structurally characterized. Molecular structures of complexes 1 and 2 display the L1 and L2 ligands coordinating palladium in a κ2-SS bidentate fashion. The metal center exhibits a square planar geometry involving the two sulfur atoms and two chloride atoms which are oriented in cis disposition. Interestingly, the two ortho-hydrogen atoms from the phenyl rings in both complexes are engaged in Pd⋯Hortho interactions with distances from 2.976 to 3.280 A. These distances can suffer an increase or decrease in their longitude due to the presence of intramolecular C–H⋯π interactions. Additionally, the presence of Pd⋯H interactions in palladium complexes (1 and 2) were identified by an NCI analysis. The complexes 1, 2 and a similar complex 3 that also displays Pd⋯Hortho interactions have been evaluated in the Suzuki-Miyaura cross-coupling reactions.