Four molecules that have been proven to act as corrosion inhibitors of mild steel in acidic media are studied. The inhibitive efficiency of these molecules is explained by means of electronic structure calculations of the protonated species that seem to represent better the actual situation of the experimental conditions. By assuming that the interaction between the inhibitor and the metallic surface occurs through donation and back-donation, it is shown, with a simple charge transfer model, that the interaction energy is favored when hardness increases, in agreement with the experimentally observed inhibition efficiencies. A local analysis with Hirshfeld condensed Fukui functions, and local Fukui functions, provides further support to the donation and back-donation mechanism.

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Electrocyclic transformation between cis-butadiene and cyclobutene has been studied at the HF and DFT levels with 6-311G** basis sets. The disrotatory stationary point with two imaginary vibrational frequencies is associated with higher energy and polarizability values and a smaller hardness value in comparison to those of the symmetry-allowed conrotatory transition state for the thermolysis of cyclobutene. For cis-butadiene, the actual minimum energy structure is of C 2 symmetry. cis-Butadiene and cyclobutene have energy and polarizability values lower than those of both stationary points, and the respective hardness values are higher than the stationary point hardness values.

In the present work, the molecular interactions of four amino acid compounds were simulated through the density functional theory (DFT) indexes to study their inhibitive properties. The prototype inhibitors previously synthesized 2-amino-N-decylacetamide (G), 2-amino-N-decylpropionamide (A), 2-amino-N-decyl-3-methylbutyramide (V), and 2-amino-N-decyl-3-(4-hydroxyphenyl)propionamide (T) were used to test the accuracy of this calculation. The generalized gradient approximation (GGA) was the ab initio approach used to optimize the ground state of the molecules. The simulation of molecular dynamics with force field (AMBER) was calculated to obtain the interaction energy between the metallic surface and the inhibitor molecules. A strong correlation of the global and local indexes with the inhibiting capacity was observed. The inhibitive properties of compounds on mild steel in an aqueous hydrochloric acid solution agreed well with those derived from the reactivity and selectivity indexes in gaseous phase.

SUMMARY:The aim of this study was to assess the morphology of the mesial root canal system of maxillary molars and the frequency of MB2 canals using cone-beam computed tomography (CBCT). A total of 1374 teeth, first maxillary (1MS, n= 802) and second maxillary molars (2SM, n= 572) of 508 Chilean patients between 8 to 77 years were evaluated through CBCT. The mesiobuccal root was evaluated in all three thirds. Root canal morphology was classified according to Vertucci's method. Data were analyzed by Pearson's Chi-square and Cuzick trend tests. MB2 canal frequency in 1MS was 73.44% and in 2MS 42.48%. The most frequent morphology in 1MS and 2MS were Vertucci type II and I, respectively. No statistically significant association was found between frequencies and side or according to gender (P>0.05). A positive association was found as the age increased in both 1MS and 2MS (P<0.001 and P= 0.023, respectively). Given the anatomical complexity of the mesiobuccal root and the frequent presence of the MB2 canal, the clinician must assume the existence of two canals in this root. CBCT scanning is a good way to initially identify this canal in the different root thirds.

A thorough quantitative analysis of the HSAB principle is performed. Complex formation reactions of a typical soft acid, Ag + , and typical hard acid, HF, with the bases XH 3 (X ) N, P, As) are studied using the DFT/B3LYP method with the 6-311G** basis set. For the molecules containing Ag + and As, corresponding pseudopotentials are used. Results of the calculations pertaining to the interactions of the hard acid, HF, are robust in comparison to those of Ag + . Correlation and nuclear relaxation effects are important in the case of the interactions of Ag + . Basis set superposition error changes the trend, and the results vary drastically with the quality of the basis set. Pseudopotentials do not introduce any error, and the zero-point energy represents at most 5% of the binding energy. The presence of the solvent, modeled as in Onsager's dipole method and in PCM, does not significantly change the trend. In the exchange reactions, both HSAB and maximum hardness principles are shown to be valid.

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The (7,7) and (10,5) carbon nanotubes were studied in the context of the Density Functional Theory (DFT) within a generalized gradient approximation (GGA). The Becke's exchange functional along with the correlation functional of Lee, Yang, and Parr (BLYP) were used with the DZVP basis set aided via auxiliary functions for the electron density. In both materials, the global indexes were calculated from the optimized structure with Kopmanns' theorem. The energy values calculated for the physisorption and chemisorption processes suggested that the physisorption process is more likely to occur for the (7,7) than for the (10,5) carbon nanotube, as well as for the achiral than chiral structure for both nanotubes and for both surface phenomena. This effect may be ascribed to the more homogeneous distribution of molecular orbital for the achiral carbon nanotube, which seems to be supported by the DOS calculations.