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Expanded polystyrene (EPS) and polyurethane foams (PUFs) are widely produced and used due to their properties and, recently, it has been described that polystyrene present π–π interactions. Therefore, this work proposes to use recycled EPS to modify the surface of PUFs for the retention of 12 polycyclic aromatic hydrocarbons (PAHs) in air samples. PUF cylinders were modified with recycled polystyrene and characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and affinity experiments. The proposed material is suitable for the retention-elution of PAHs from air samples, and can be incorporated to liquid chromatography generating a quantitative methodology. This methodology is efficient, fast and use lower volumes of organic solvents compared with other methodologies. Eighteen urban air samples were collected and analyzed weekly, using principal component analysis (PCA), and a relation between meteorological parameters and concentration of PAHs was observed. [ABSTRACT FROM AUTHOR]

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 (A/cm) vs. inhibition efficiency ( η%) and (ii) Δ G° 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 (Fe, Fe, Fe, and Fe) 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 Δ G of −10.2 kcal/mol, with an energy difference of 5.3 kcal/mol between the two possible protonated conformers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

DFT studies of both the Fe cluster and the Fe(110) surface interaction with pyrrole, furan, thiophene, and selenophene showed that selenophene forms a stabler adsorbate iron complex than the other heterocyclic molecules; this is consistent with the binding energy data that were calculated between the Fe cluster and the Fe(110) surface with the heterocycles. Furthermore, when the adsorption of the compounds with the iron cluster was analyzed by molecular orbital studies, the orbitals of selenophene overlapped more strongly with the Fe atom than that of the other molecules. In TD-DFT, the π → π* peak observed for the molecules disappeared when they formed complexes, and there appeared a charge transfer band (ligand to metal), thus confirming the coordination of these molecules with the cluster. The data suggest that the chemisorption is an exothermic process. [ABSTRACT FROM AUTHOR]

The interactions of L-aminoglucosidic stereoisomers such as rhodostreptomycins A (Rho A) and B (Rho B) with cations (Mg, Ca, and H) were studied by a quantum mechanical method that utilized DFT with B3LYP/6-311G**. Docking studies were also carried out in order to explore the surface recognition properties of L-aminoglucoside with respect to Mg and Ca ions under solvated and nonsolvated conditions. Although both of the stereoisomers possess similar physicochemical/antibiotic properties against Helicobacter pylori, the thermochemical values for these complexes showed that its high affinity for Mg cations caused the hydration of Rho B. According to the results of the calculations, for Rho A-Ca(HO), Δ H = −72.21 kcal mol; for Rho B-Ca(HO), Δ H = −72.53 kcal mol; for Rho A-Mg(HO), Δ H = −72.99 kcal mol and for Rho B-Mg(HO), Δ H = −95.00 kcal mol, confirming that Rho B binds most strongly with hydrated Mg, considering the energy associated with this binding process. This result suggests that Rho B forms a more stable complex than its isomer does with magnesium ion. Docking results show that both of these rhodostreptomycin molecules bind to solvated Ca or Mg through hydrogen bonding. Finally, Rho B is more stable than Rho A when protonation occurs. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

• Interaction between α-zein and Ca2+ in nixtamalization was analyzed and described. • The calcium-binding constant of α-zein from nixtamalized flour was 1.45/mM. • α-Zein from nixtamalized flour presented a higher affinity for Ca2+. • Calcium bridges occurs mainly through carboxylate from C-ter of zein. The possible interactions between α-zein and Ca2+ in nixtamalization process were analyzed from a multidisciplinary approach, considering the effect of these interactions on the thermal properties of the nixtamalized flour. SDS-PAGE under reducing and non-reducing conditions did not reveal differences between patterns of zeins from nixtamalized and control samples. However, analysis from affinity capillary electrophoresis indicated an increment in protein volume when calcium is added to zein extracted from nixtamalized flour. In addition, the binding constant for the zein-calcium interaction was calculated indicating a higher affinity for calcium by zein from nixtamalized samples. Molecular dynamics simulations indicated that the interaction α-zein-Ca2+ through C-ter was more favorable than Glu48. However, in excess of Ca2+ ions, each site could bind one calcium atom at the same time, confirming that aggregation of α-zein through calcium bridges is possible, expanding the technological applications of this protein. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]