HN2(2A') electronic manifold. II. Ab initio based double-sheeted DMBE potential energy surface via a global diabatization angle

A double-sheeted double many-body expansion potential energy surface is reported for the coupled 12A'/22A' states of HN2 by fitting about 6000 ab initio energies. All crossing seams are described to their full extent on the basis of converged results. The lowest adiabatic sheet is fitted with a rmsd of 0.8 kcal mol-1 with respect to the calculated energies up to 100 kcal mol-1 above the absolute minimum, and the topology of the first excited-state investigated with the aid of the upper adiabatic sheet. A new scheme that overcomes obstacles in previous diabatization methods for modeling global double-sheeted potential energy surfaces is also reported. The novel approach uses a global diabatization angle which allows the diabats to mimic both the crossing seams and atom-diatom dissociation limits.     

Different origins of green-light photoluminescence emission in structurally ordered and disordered powders of calcium molybdate

A strong greenish-light photoluminescence (PL) emission was measured at room temperature for disordered and ordered powders of CaMoO4 prepared by the polymeric precursor method. The structural evolution from disordered to ordered powders was accompanied by XRD, Raman spectroscopy, and TEM imagery. High-level quantum mechanical calculations in the density functional framework were used to interpret the formation of the structural defects of disorder powders in terms of band diagram and density of states. Complex cluster vacancies [MoO3 x V(O(z))] and [CaO7 x V(O(z))] (where V(O(z)) = V(O(X)), V(O(*)), V(O(**))) were suggested to be responsible to the appearance of new states shallow and deeply inserted in the band gap. These defects give rise to the PL in disordered powders. The natural PL emission of ordered CaMoO4 was attributed to an intrinsic slight distortion of the [MoO4] tetrahedral in the short range.     

Preliminary evaluation of new polymer matrix for solid-phase extraction of nonylphenol from water samples

Molecularly imprinted (MIP) and blank polymers with affinity for nonylphenol were designed using computational modelling. Chromatographic tests demonstrated higher affinity of imprinted polymers towards the template nonylphenol as compared with blank polymers. The performance of both polymers in solid-phase extraction was however very similar. Both blank and imprinted polymers appeared to be suitable for the removal and pre-concentration of nonylphenol from contaminated water samples with 99% efficiency of the recovery. The commercial resins PH(EC) (Biotage) and C18 (Varian) tested in the same conditions used for comparative purposes had recovery rate <84%. The polymer capacity for nonylphenol was 231 mg g⁻¹ for blank and 228 mg g⁻¹ for MIP. The synthesised materials can have significance for sample pre-concentration and environmental analysis of this class of compounds.     

New proline analogues for organocatalysis

This paper describes an anomalous behaviour of the Sharpless dihydroxylation of a terminal olefin. The synthesis of a new chiral pyrrolidine and its application as an organocatalyst in the Michael addition of cyclohexanone into nitrostyrenes are described.     

The quaternisation reaction of phosphines and amines in aliphatic alcohols. A similarity analysis using the isokinetic, isosolvent and isoselective relationships

Accurate second-order rate constants were measured at 5 K intervals in the temperature range 298.15-328.15 K for the quaternisation reaction of triethylphosphine with iodoethane in methanol, ethanol, propan-1-ol and butan-1-ol. These data are complemented previously reported rate constants for the quaternisation reaction of triethylamine with iodoethane in the same solvents and at similar temperatures. Each of these two reaction series is analysed in terms of the isokinetic relationship (IKR) with respect to solvent variation and of the isosolvent relationship (ISoR) with respect to temperature variation, using in the latter case five different empirical solvent scales. Statistically validated IKR and ISoR have been found for both reaction series. The resulting isokinetic temperatures of 347 K (phosphine series) and of 730 K (amine series) are discussed in terms of Linert's theory of the isokinetic relationship. The best ISoR correlation is obtained using the Dimroth-Reichardt E(T)(N) solvent scale for the phosphine series and the Kamlet-Taft alpha(KT) solvent scale for the amine series. It is demonstrated that no real solvent can be envisaged as having the characteristics of an isokinetic solvent. The selectivity of the nucleophiles triethylphosphine and triethylamine in the attack on iodoethane is examined by treating together both reaction series in terms of the isoselective relationship (ISeR). The isoselective temperature with respect to solvent is found to be 289 K, which is close to the value of 302 K predicted by Exner and Giese's formula on the basis of the individual isokinetic temperatures. A novel ISeR analysis with respect to temperature is performed. It reveals that the alpha(KT) scale is the most appropriate solvent scale for describing this selectivity series, and that it is feasible to find an isoselective solvent. A new equation is developed for predicting the isoselective solvent parameter from individual isosolvent parameters and is shown to yield realistic values. The present similarity analysis shows that there are significant differences between the courses of these quaternisation reactions. On the basis of the experimentally determined isoparameter values, in liquid alcohols as solvent it is proposed that the reaction between triethylphosphine and iodoethane follows a classic bimolecular nucleophilic substitution pathway, whereas the desolvation of triethylamine molecules has to be taken into account to describe the mechanism of the original Menshutkin reaction.     

On the photostability of some benzanthrone dye derivatives and their copolymers with methylmethacrylate

The photostability of five benzanthrone dye derivatives containing unsaturated allylic group(s) was investigated and the structure-photostability relationship was found. Their copolymers with methylmethacrylate had an intense colour, and were stable to solvents and fluorescence, due to the chemical bonding of the dye in the polymer chain. Photostability of the dyes thus included in the polymer molecule increased and their influence on the photostability of the polymers was determined.     

Cu,Fe, or Ni doped molybdenum oxide supported on Al2O3 for the oxidative dehydrogenation of ethylbenzene

Molybdenum-based catalysts supported on Al2O3 doped with Ni, Cu, or Fe oxide were synthesized and used in ethylbenzene dehydrogenation to produce styrene. The molybdenum oxide was sup-ported using an u...     

Immobilization of Thermomyces lanuginosus Lipase by Different Techniques on Immobead 150 Support: Characterization and Applications

Thermomyces lanuginosus lipase (TLL) was immobilized on native and modified Immobead 150, with epoxy groups removed by hydrolysis and oxidized to add aldehyde on its surface. Immobilizations on both supports were performed by adsorption, adsorption and cross-linking, covalent attachment, multipoint covalent attachment, and, for the modified support, multipoint covalent attachment using ethylenediamine. Biocatalysts were evaluated for thermal and solvent stabilities, and the best biocatalyst was also tested after incubation in ionic liquids and used in the synthesis of butyl butyrate and isoamyl butyrate. Multipoint covalent immobilized TLL on the native Immobead 150 (Emulti) showed a half-life of 5.32 h at 70 °C, being approximately 30 times more stable than its soluble form; it showed high stability in acetone, hexane, and isooctane. Its enzymatic activity was up to 40 % when incubated in ionic liquids. Ester synthesis produced yields of esterification above 60 % in 24 h. Of all immobilization protocols, the Emulti performed best concerning the thermal, solvent, and ionic liquids stabilities. Emulti was successfully applied to the synthesis of butyl butyrate and isoamyl butyrate, which are very important products for the food and beverage industries.     

Benzene,toluene and o-xylene (BTX) removal from aqueous solutions through adsorptive processes

In this study, the monocomponent adsorption of benzene, toluene and o-xylene (BTX) compounds, as model contaminants present in the petrochemical wastewaters, was investigated using three types of adsorbents: activated carbon (Carbon CD 500), a polymeric resin (MN-202) and a modified clay (Claytone-40). Langmuir and Freundlich models were able to fit well the equilibrium experimental data. The BTX adsorption capacity increased in the following order: Claytone-40 < CD 500 < MN-202. The maximum uptake capacity of MN-202, given by the Langmuir fitting parameter, for benzene, toluene and o-xylene was 0.8 ± 0.1, 0.70 ± 0.08 and 0.63 ± 0.06 mmol/g at 26 °C. Desorption kinetics for polymeric resin with 50 % methanol solution were fast being able to reuse the resin in consecutive adsorption/desorption cycles without loss of sorption capacity. The adsorptive behaviour at batch system was modelled using a mass transfer kinetic model, considering that the sorption rate is controlled by a linear driving force model, which successfully predicts benzene, toluene and o-xylene concentration profiles, with homogeneous diffusivity coefficients, D _h , between 3.8 × 10^?10 and 3.6 × 10^?9 cm²/s. In general, benzene diffuses faster than toluene and o-xylene, which is in agreement with molecular diffusivity in water.     

Nonadiabatic effects in the H+D2 reaction

The state-to-state dynamics of the H+D2 reaction is studied by the reactant-product decoupling method using the double many-body expansion potential energy surface. Two approaches are compared: one uses only the lowest adiabatic sheet while the other employs both coupled diabatic sheets. Rotational distributions for the reaction H+D2 (upsilon = 0, j = 0)-->HD(upsilon' = 3, j')+D are obtained at eight different collision energies between 1.49 and 1.85 eV; no significant difference are found between the two approaches. Initial state-selected total reaction probabilities and integral cross sections are also given for energies ranging from 0.25 up to 2.0 eV with extremely small differences being observed between the two sets of results, thus showing that the nonadiabatic effects in the title reaction are negligible at least for small energies below 2.0 eV.