José G. Alvarado-Rodríguez

Density Functional Theory and Electrochemical Studies: Structure–Efficiency Relationship on Corrosion Inhibition

The relationship between structure and corrosion inhibition of a series of 30 imidazol, benzimidazol, and pyridine derivatives has been established through the investigation of quantum descriptors calculated with PBE/6-311++G**. A quantitative structure-property relationship model was obtained by examination of these descriptors using a genetic functional approximation method based on a multiple linear regression analysis. Our results indicate that the efficiency of corrosion inhibitors is strongly associated with aromaticity, electron donor ability, and molecular volume descriptors. In order to calibrate and validate the proposed model, we performed electrochemical impedance spectroscopy (EIS) studies on imidazole, 2-methylimidazole, benzimidazole, 2-chloromethylbenzimidazole, pyridine, and 2-aminopyridine compounds. The experimental values for efficiency of corrosion inhibition are in good agreement with the estimated values obtained by our model, thus confirming that our approach represents a promising and suitable tool to predict the inhibition of corrosion attributes of nitrogen containing heterocyclic compounds. The adsorption behavior of imidazole or benzimidazole heterocyclic molecules on the Fe(110) surface was also studied to elucidate the inhibition mechanism; the aromaticity played an important role in the adsorbate-surface complex.

Synthesis and structural characterization of mono- and dinuclear NiII and PdII complexes derived from tetradentate 1,7-bis-(pyridin-2-yl)-2,6-diaza-1,6-heptadiene

The reaction of Schiff base 1,7-bis-(pyridin-2-yl)-2,6-diaza-1,6-heptadiene (L) with either NiCl2·6H2O or [PdIICl2(CH3CN)2]/Na[BF4] in 1 : 1 stoichiometry yielded mononuclear ionic complexes, trans-[NiII(L)(H2O)2]Cl2·3H2O (1·3H2O) and [PdII(L)][BF4]2 (2), respectively; the reaction of L with [PdIICl2(CH3CN)2] in 1 : 2 ratio yielded dinuclear cis-[PdII 2(μ-L)Cl4] (3). Complexes 1–3 were characterized by vibrational spectroscopy and X-ray diffraction; diamagnetic 2 and 3 were also characterized by NMR in solution. The molecular structures of 1 and 2 displayed tetradentate coordination of L with formation of two five-membered and one six-membered chelate rings for both complexes. In 3, L showed bidentate coordination mode for each pyridylimine toward PdII. Complex 1 has distorted octahedral geometry around NiII and an extended hydrogen-bond network; distorted square planar geometry around PdII in 2 and 3 was observed.

Selective Liquid-Liquid Extraction of Mercury(II) from Aqueous Solution by N-Alkyldithiophosphate Compounds CH3(CH2)nS2P(OC6H4)2 (n = 0 to 4)

The extraction of mercury(II) from nitric acid solutions by the dithiophosphate compounds CH3(CH2)nS2P(OC6H4)2 (n = 0 to 4) has been examined. The best extracting properties were displayed by the liquid compound containing the longest alkyl chain CH3(CH2)4S2P(OC6H4)2 (Pen-DTP) in acidic media. The results indicate the stability of Pen-DTPA in nitric and sulphuric media. Pen-DTP selectively extracted Hg(II) in the presence of some interfering ions such as Cd(II), Pb(II) and Bi(III). The Hg(II) recovery from back-extraction experiments with chloridric acid is higher than 70%. Mostly, this extractant shows a remarkable selectivity in the extraction of mercury (76.6%) in the presence of Ag(I) (9.2%) without using a masking agent.

Activation of aldehydes by exocyclic iridium(I)-η4:π2-diene complexes derived from 1,3-oxazolidin-2-ones

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.

Reduced density gradient as a novel approach for estimating QSAR descriptors, and its application to 1, 4-dihydropyridine derivatives with potential antihypertensive effects

AbstractThe relationship between the chemical structure and biological activity (log IC50) of 40 derivatives of 1,4-dihydropyridines (DHPs) was studied using density functional theory (DFT) and multiple linear regression analysis methods. With the aim of improving the quantitative structure-activity relationship (QSAR) model, the reduced density gradient s(r) of the optimized equilibrium geometries was used as a descriptor to include weak non-covalent interactions. The QSAR model highlights the correlation between the log IC50 with highest molecular orbital energy (EHOMO), molecular volume (V), partition coefficient (log P), non-covalent interactions NCI(H4-G) and the dual descriptor [Δf(r)]. The model yielded values of R2=79.57 and Q2=69.67 that were validated with the next four internal analytical validations DK=0.076, DQ=−0.006, RP=0.056, and RN=0.000, and the external validation Q2boot=64.26. The QSAR model found can be used to estimate biological activity with high reliability in new compounds based on a DHP series. Graphical abstractThe good correlation between the log IC50 with the NCI (H4-G) estimated by the reduced density gradient approach of the DHP derivatives

Pentacoordination at antimony via endocyclic and exocyclic intramolecular interactions in dibenzostibocine diorganodithiophosphates [{D(C6H4S)2}Sb{S2P(OR)2}] (D=O, S)

Abstract Treatment of [{D(C6H4S)2}SbCl] (D=O, 1; D=S, 2) with MS2P(OR)2 afforded the stable dibenzostibocine dithiophosphate compounds [{D(C6H4S)2}Sb{S2P(OR)2}] with D=O, R=1,2-C6H4 (3); for D=S, R=1,2-C6H4 (4), Et (5), nPr (6), iPr (7), and Ph (8). The compounds were characterized by IR and 1H, 13C{1H}, and 31P{1H} NMR spectroscopy in solution. The 31P{1H} NMR data are consistent with an anisobidentate coordination mode of the dithiophosphate ligand to the Sb atom. Single crystal X-ray diffraction analyses of compounds 3, 4, 7, and 8 revealed that the antimony atom acts as an acceptor atom exhibiting endocyclic and exocyclic intramolecular interactions with the donor D atom and with both sulfur atoms of the dithiophosphate ligand, expanding its coordination sphere from four in the starting materials to five and displaying a skew-trapezoidal pyramidal local geometry.

A new computational model for the prediction of toxicity of phosphonate derivatives using QSPR

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 [

Removal and confinement of Hg(II) by polyurethane foam functionalized with potassium O-ethyldithiocarbonate

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