A Density Functional Theory Study of Optical Rotation in Some Aziridine and Oxirane Derivatives

We present time-dependent density functional theory (TDDFT) calculations of the electronic optical rotation (ORP) for seven oxirane and two aziridine derivatives in the gas phase and in solution and compare the results with the available experimental values. For seven of the studied molecules it is the first time that their optical rotation was studied theoretically and we have therefore investigated the influence of several settings in the TDDFT calculations on the results. This includes the choice of the one-electron basis set, the exchange-correlation functional or the particular polarizable continuum model (PCM). We can confirm that polarized quadruple zeta basis sets augmented with diffuse functions are necessary for converged results and find that the aug-pc-3 basis set is a viable alternative to the frequently employed aug-cc-pVQZ basis set. Based on our study, we cannot recommend the generalized gradient functional KT3 for calculations of the ORP in these compounds, whereas the hybrid functional PBE0 gives results quite similar to the long-range correct CAM−B3LYP functional. Finally, we observe large differences in the solvent effects predicted by the integral equation formalism of PCM and the SMD variant of PCM. For the majority of solute/solvent combinations in this study, we find that the SMD model in combination with the PBE0 functional and the aug-pc-3 basis set gives the best agreement with the experimental values.     

Lavandin (Lavandula × intermedia Emeric ex Loiseleur) essential oil from Spain: determination of aromatic profile by gas chromatography–mass spectrometry,antioxidant and lipoxygenase inhibitory bioactivities

Lavandin (Lavandula × intermedia Emeric ex Loiseleur) essential oils (EOs), from Abrial, Super and Grosso cultivars, cultivated and extracted in the South East of Spain, were analysed by using GC/MS to determine their composition, in both relative (peak area) and absolute (using standard curves) concentrations. Linalool (34–47%), linalyl acetate (17–34%), camphor (4–9%) and eucalyptol (3–7%) were determined as the main molecules. This characterisation was completed with the enantioselective gas chromatography, where ( ? )-linalool, (+)-camphor and ( ? )-linalyl acetate were determined as the main components. Antioxidant activity was evaluated positively by several methods: activity against free radicals, chelating and reducing power, probably due to linalool and linalyl acetate. Mild inhibitory activity on lipoxygenase was observed supporting potential anti-inflammatory activity, mainly due to linalool and camphor. These properties support the potential use of L. × intermedia essential oils as natural cosmetic and natural pharmaceutical ingredient to fight several skin diseases.     

Magnetic resonance study of a vanadium pentoxide gel

In this work we report results from continuous-wave (CW) and pulsed electron paramagnetic resonance (EPR) and proton nuclear magnetic resonance (NMR) studies of the vanadium pentoxide xerogel V₂O₅:nH₂O (n ≈ 1.6). The low temperature CW-EPR spectrum shows hyperfine structure due to coupling of unpaired V⁴⁺ electron with the vanadium nucleus. The analysis of the spin Hamiltonian parameters suggests that the V⁴⁺ ions are located in tetragonally distorted octahedral sites. The transition temperature from the rigid-lattice low-temperature regime to the high temperature liquid-like regime was determined from the analysis of the temperature dependence of the hyperfine splitting and the V⁴⁺ motional correlation time. The Electron Spin Echo Envelope Modulation (ESEEM) data shows the signals resulting from the interaction of ¹H nuclei with V⁴⁺ ions. The modulation effect was observed only for field values in the center of the EPR absorption spectrum corresponding to the single crystals orientated perpendicular to the magnetic field direction. At least three protons are identified in the xerogel by our magnetic resonance experiments: (I) the OH groups in the equatorial plane, (ii) the bound water molecules in the axial V=O bond and (iii) the free mobile water molecules between the oxide layers. Proton NMR lineshapes and spin-lattice relaxation times were measured in the temperature range between 150 K and 323 K. Our analysis indicates that only a fraction of the xerogel protons contribute to the measured conductivity.     

Synthesis of an epoxy functionalized spiroorthocarbonate used as low shrinkage additive in cationic UV curing of an epoxy resin

The synthesis of an epoxy functionalized spiroorthocarbonate (SOC) is reported. The obtained monomer has been used a slow shrinkable additive in cationic UV curing of a commercially available dicycloepoxy resin. A polymer network flexibilization was evidenced by increasing the SOC content in the photocurable formulation. It has been demonstrated that SOC acts as shrinkage reduction additive reaching expansion on volume after polymerization in the presence of 10 wt% of the functionalized spiroorthocarbonate.     

Density, excess volume, and excess coefficient of thermal expansion of the binary systems of dimethyl carbonate with butyl methacrylate, allyl methacrylate, styrene, and vinyl acetate at T = (293.15, 303.15, and 313.15) K

Densities of the binary systems of dimethyl carbonate with butyl methacrylate, allyl methacrylate, styrene, and vinyl acetate have been measured as a function of the composition at (293.15, 303.15, and 313.15) K at atmospheric pressure, using an Anton Paar DMA 5000 oscillating U-tube densimeter. The excess molar volumes are negative for the (dimethyl carbonate + vinyl acetate) system and positive for the three other binaries, and become more so as the temperature increases from (293.15 to 313.15) K. The apparent volumes were used to calculate the values of the partial excess molar volumes at infinite dilution. The excess coefficient of thermal expansion is positive for the four binary systems. The calculated excess molar volumes were correlated with the Redlich-Kister equation and with a series of Legendre polynomials. An explanation of the results is offered based on the FT-IR (ATR) spectra of several mixtures of the different systems.     

Kinetics analysis of precipitation in a quasi-binary Cu-1 at.% CoTi alloy

The precipitation process for a concentration of CoTi of super-saturated solutions of Cu-0.50 at.% Co-0.45 at.% Ti (Cu-1 at.% CoTi) was studied through differential scanning calorimetry (DSC) and microhardness measurements. The analysis of the calorimetric curves between the environmental temperature and 900 K shows the presence of only one exothermic reaction attributed to the formation of CoTi particles in the matrix of copper. The energy of activation estimated by using the modified Kissinger method came out much lower than the corresponding to the diffusion of the cobalt and titanium in copper. We may attribute this fact to the strong contribution of the vacancies introduced by quenching. We used the formalism of Johnson-Mehl-Avrami (JMA) to assess the kinetic parameters. The energetic and kinetic evaluations and the molar heats of precipitation obtained from the isochor of van’t Hoff allow us to infer that the reaction corresponds to the formation of CoTi precipitates. The isothermal kinetics of precipitation reaction could be represented satisfactory by an overall kinetic function based in a macroscopic parameter (Vickers hardness). The kinetic parameters obtained from microhardness model are in agreements with those obtained from DSC traces.     

Evolution of class C β-lactamases: factors influencing their hydrolysis and recognition mechanisms

The most common bacterial resistance mechanism to β-lactam antibiotics is the production of β-lactamases. So far, β-lactamases have been classified into four different classes, three of them (A, C and D) have a serine in the active site as the nucleophilic group, which attacks to lactam antibiotic. Despite the large number of kinetic and theoretical studies and many native and complexed β-lactamases crystal structures, the mechanism by which they act is not well understood. The aim of this review is to show the different hypotheses which have been proposed to explain the hydrolysis mechanisms for class A and C lactamases and to cast light onto the interactions between the antibiotic and the Enterobacter cloacae P99 (a class C β-lactamase) in the Henry-Michaelis complex formed previous to the serine attack. Knowledge of these crucial points is essential for obtaining new β-lactam antibiotics not vulnerable to β-lactamases in order to minimize bacterial resistance.     

Synthesis and characterization of rhenium(I) complexes with the polypyridinic quinone functionalized electron acceptor ligand [3,2-a:2′,3′-c]-benzo[3,4]-phenazine-11,16-quinone, Nqphen

In this work, the synthesis and characterization of fac-[Re(CO)₃(Nqphen)(L)]PF₆ complexes is reported. Nqphen is the quinone substituted acceptor ligand [3,2-a:2′,3′-c]-benzo[3,4]-phenazine-11,16-quinone, and L represents the donor monodentate pyridine substituted ligands 4-tert-butylpyridine (t-Bupy), 4-methoxypyridine (MeO-py) or 10-(4-picolyl)phenothiazine (py-PTZ). The complexes were synthesized by refluxing in methanol the metal precursor fac-Re(CO)₃(Nqphen)TfO (TfO = trifluoromethanesulphonate anion) with the corresponding L ligand. The UV-Vis spectra of the complexes are dominated by intense intraligand (IL) bands, and less intense metal ligand charge transfer (MLCT) bands with maxima in the 380-400 nm region. The IR shows the typical pattern for tricarbonyl Re complexes with facial (fac) geometry. An additional v(CO) stretching band, attributed to the quinone fragment of Nqphen, is observed.Electrochemical data indicate that the acceptor capacity of Nqphen is increased in the complexes with regard to the free ligand. This effect is sensitive to the nature of the L ligand, following the order: MeO-py < t-Bupy < py-PTZ, indicating therefore that the donor capacity of L affects the rest of the molecule. The results obtained for the fac-[Re (CO)₃(Nqphen)(pyPTZ)]PF₆ complex here reported were compared with those observed for the homologous complex fac-[Re(CO)₃(Aqphen)(L)]^0/+, with Aqphen = 12,17-dihydronaphtho[2,3-h]dipyrido[3,2-a:2′,3′-c]-phenazine-12,17-dione, and L = Cl⁻, TfO⁻, py-PTZ.     

Theoretical study of the interaction between Pt(0) and MPH3 + fragments in complexes of the [Pt3 (��-CO)3(PH3)3]�CMPH3 + (M?=?Cu+, Au+, Ag+) type

Ab initio calculations suggest that a series of complexes of the [Pt₃(??-CO)₃(PH₃)₃]?CMPH₃ ⁺ type (M?=?Cu, Au, Ag) are stable. We have studied these complexes at the HF, MP2, B3LYP, and PBE levels of theory. The magnitude of the interaction energies and Pt₃?CM distances indicate a substantial covalent character of the bond, the latter being confirmed by orbital diagrams. The chemical bond is sensitive to electron correlation effects. In addition, the Fukui index of nucleophilic attack and electrophilicity index on the metal were used to explore possible sites where chemical reactivity may play a role.