Julián Cruz-Borbolla

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.

Effects of Bentonite on p-Methoxybenzyl Acetate: A Theoretical Model for Oligomerization via an Electrophilic-Substitution Mechanism

Tonsil Actisil FF, a commercial bentonitic clay, promotes the formation of a series of electrophilic-aromatic-substitution products from para-methoxybenzyl acetate in carbon disulfide. The molecules obtained correspond to linear isomeric dimers, trimers, tetramers and a pentamer, according to their spectroscopic data. A clear indication of the title mechanistic pathway for the oligomerization growth was obtained from the analysis of a set of computational-chemistry calculations using the density-functional-theory level B3LYP/6-311++G(d,p). The corresponding conclusions were based on the computed dipole moments, the HOMO/LUMO distributions, and a natural-populations analysis of the studied molecules.

Theoretical and experimental studies of phenol oxidation by ruthenium complex with N,N,N- tris(benzimidazol - 2yl-methyl)amine

AbstractThe ruthenium complex with (N,N,N-tris(benzimidazol-2yl-methyl)amine, L1) was prepared, and characterized. Fukui data were used to localize the reactive sites on the ligand. The structural and electronic properties of the complex were analyzed by DFT in different oxidation states in order to evaluate its oxidant properties for phenol oxidation. The results show that the hard Ru(IV) cation bonds preferentially with a hard base (Namine = amine nitrogen, or axial chloride ion), and soft Ru(II) with a soft base (Nbzim = benzimidazole nitrogen or axial triphenyl phosphine). Furthermore, the Jahn-Teller effect causes an elongation of the axial bond in the octahedral structure. The bonding nature and the orbital contribution to the electronic transitions of the complex were studied. The experimental UV-visible bands were interpreted by using TD-DFT studies. The complex oxidizes phenol to benzoquinone in the presence of H2O2 and the intermediate was detected by HPLC and 13C NMR. A possible mechanism and rate law are proposed for the oxidation. The adduct formation of phenol with [Ru(O)L1]2+ or [Ru(OH)L1]+ is theoretically analyzed to show that [Ru(OH)L1-OPh]+ could produce the phenol radical. Graphical AbstractPhenol oxidation by ruthenium complex

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

Synthesis and Characterization of Amide Stationary Phases for the Determination of Sulfonamides by Sequential Injection Chromatography

ABSTRACT The synthesis of amide (butyl, cyclohexyl, and phenyl) modified silica and the use as stationary phases in sequential injection chromatography are described. The system was tested on the isocratic separation of seven sulfonamides (sulfachloropyridazine, sulfadimethoxine, sulfamethazine, sulfamethoxazole, sulfamethoxypyridazine, sulfaquinoxaline, and sulfathiazole) using each stationary phase with mobile phases composed of acetonitrile/water at a flow rate of 0.45 mL min−1. A mixed mode retention mechanism of sulfonamides in the stationary phases was obtained, including dipole-dipole, π-π, and hydrogen bonding interactions. The most appropriate phase for the separation of sulfonamides was phenylamide. The chromatographic behavior was confirmed using density functional theory of the interaction between sulfamethoxazole and the stationary phases.

Crystal Structure and Hirshfeld Surface Analysis of 1,2-Bis((2-(Bromomethyl)Phenyl)Thio)Ethane and Two Polymorphs of 1,2-Bis((2-((Pyridin-2-ylthio)Methyl)Phenyl)Thio)Ethane

1,2-Bis((2-(bromomethyl)phenyl)thio)ethane (1) and 1,2-bis((2-((pyridin-2-ylthio)methyl)phenyl)thio)ethane (2) were prepared and characterized by IR and NMR spectroscopy and single-crystal X-ray crystallography. X-ray diffraction studies shown that compound 1 crystallizes in a monoclinic space group P21/n with crystal parameters a=8.3970(3) A, b=12.4566(2) A, c=8.9251(3) A; β=117.911(3)°, V=824.96(5) A3 and z=2, and compound 2 exists in two monoclinic polymorphs (2a and 2b). Polymorph 2a crystals are in space group P21, with unit cell parameters a=5.3702(2) A, b=14.4235(6) A, c=15.4664(7) A, β=119.97(9)°, V=1197.97(9) A3 and z=2, while polymorph 2b crystals are in space group P21/c with unit cell parameters a=7.8312(3) A, b=9.6670(4) A, c=16.2962(5) A, β=121.219(3)°; V=1210.12(7) A3 and z=2. Variations in the crystal packing help to distinguish these two polymorphs via π-π and C−H•••π interactions. The 3D Hirshfeld surfaces and the associated 2D fingerprint plots have been performed to gain insight into the behavior of these interactions in compound 1 and polymorphs 2a and 2b.

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 [

Determination of antibiotics in feedstuff samples by microemulsion electrokinetic chromatography using fullerene as additive

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