Effect of ethanol on micellization and on decarboxylation of 6-nitrobenzisoxazole-3-carboxylate in aqueous cationic micelles

The effects of ethanol on the critical micellar concentration (cmc) and the rates of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) have been investigated in aqueous cationic surfactants of the cetyltrialkylammonium family with bromide [CT(R)ABr], chloride [CT(R)ACl], and nitrate [CT(R)ANO3] counterions, and methyl (CTAX), n-propyl (CTPAX), and n-butyl (CTBAX) as the head group alkyl moieties. Effects upon cmc and reactivity are similar, featuring a break at the ethanol mole fraction, x(EtOH), of ca. 0.055; these effects have been related to changes in solvent structure, with formation of a clathrate at x(EtOH) = 0.055. Rate data in CTBABr were further investigated and fitting of raw kinetic data to the pseudophase model is possible up to x(EtOH) = 0.1, showing an unexpected decrease of rate constant values in the micellar pseudophase, kM', as ethanol content increases: a significant variation of micellar ionization degree could account for this kinetic effect.     

Nucleation of Pd dimers at defect sites of the MgO(100) surface

Point defects on oxide surfaces are presumed to be preferential nucleation sites for supported metal clusters. Under typical growth conditions, dimers constitute the first step in island nucleation. First-principles calculations on the formation of Pd dimers on regular and defect sites of the MgO(100) surface show that nucleation occurs with large dimer binding energies at divacancies and charged oxygen vacancies (F+ centers), while it is less favorable on steps and neutral F centers. The extensive database of defect trapping/attachment properties gives a firm basis to rationalize recent atomic-force microscopy findings and provides guidelines valid, in general, for ionic substrates.     

Paramagnetic defect centers at the MgO surface. An alternative model to oxygen vacancies

On the basis of embedded cluster calculations, we propose a new model for the structure of paramagnetic color centers at the MgO surface usually denoted as F(S)(H)(+) (an electron trapped near an adsorbed proton). These centers are produced by exposing the surface of polycrystalline MgO to H(2) followed by UV irradiation. We demonstrate that properties of H atom absorbed at surface sites such as step edges (MgO(step)) and reverse corner sites (MgO(RC)), formed at the intersection of two step edges, are compatible with a number of features observed for F(S)(H)(+). Our calculations suggest that (i) H(2) dissociates at the reverse corner site heterolytically and that there is no barrier for this exothermic reaction; (ii) the calculated vibrations of the resulting MgO(RC)(H(+))(H(-)) complex are fully consistent with the measured ones; (iii) desorption of a neutral H atom from the diamagnetic precursor requires UV light and leads to the formation of stable neutral paramagnetic centers at the surface, MgO(step)(H(+))(e(-))(trapped) and MgO(RC)(H(+))(e(-))(trapped). The computed isotropic hyperfine coupling constants and optical transitions of these centers are in broad agreement with the existing experimental data. We argue that these centers, which do not belong to the class of "oxygen vacancies", are two of the many possible forms of the F(S)(H)(+) defect center.     

Partial least-squares modelling of dye fastness to light

Several physicochemical properties (¹³C-n.m.r., spectrophotometric, chromatographic, calorimetric) were measured for a series of 38 azo dyes in order to test the existence of relationships between one or more of these data sets and the fastness of the dyes on polyester fabric. The partial least-squares method was applied; it had previously proved useful in establishing structure/property relationships for the same dyes. It is shown that ¹³C-n.m.r. data can be used successfully to predict dye fastness to light. These data are quickly and cheaply obtained with small amounts of compound.     

Enantioselective epoxidations of alkenes catalyzed by (salen)Mn(III) in aqueous surfactant systems

An aqueous reaction medium, based on a surfactant solution of diethyltetradecylamine N-oxide (AOE-14), was developed for the enantioselective epoxidation of 1,2-dihydronaphthalene and of various cis-β-alkyl styrenes with increasing hydrophobicity, using bleach as oxidant and the Jacobsen chiral (salen)Mn(III) as catalyst. AOE-14 is able to both solubilize all reactants in water and bind the metal of the salen complex acting as coligand. Its use leads to good yields (>75%) and to ee values ranging from 75% up to 91% even in the case of cis-β-alkyl styrenes where lower cis/trans epoxide ratios are observed. The ratio of surfactant/substrate used is 1:1 or 4:1, much lower than those generally used in the literature.     

Development and Validation of Hierarchical Models for the Design of Engine Control Strategies

The development of mathematical models for the design of controlstrategies for spark ignition automotive engines is described. The objectiveof the models, used for both simulation and optimization analysis, is theprediction of the effects of control strategies on fuel consumption andemissions of a vehicle over arbitrary driving cycles. In order to achievethe best compromise between precision, experimental costs, computationaltime and flexibility, a mixed modelling approach is used, withphenomenological and input-output models integrated within a hierarchicalsystem.Mean value models have been used to describe the most significant dynamiceffects: (i) air flow. (ii) two phases fuel flow in the intake manifold, and(iii) thermal flow in the cylinder walls. Stochastic effects due to sensorsand actuators can be also predicted.Two-zone and multizone thermodynamic models for the prediction ofpressure cycle sub-models for engine emissions (HC, CO, andNO _x and mechanical losses have been developed. Experimentaldesign techniques are also under development to optimize the interactionsbetween experimental analysis and models. Most of the models have beenintegrated in a computer code, used by a major automotive supplier.     

Mechanism of the Asymmetric Autocatalytic Soai Reaction Studied by Density Functional Theory

The mechanism of the Soai reaction has been thoroughly investigated at the M05‐2X/6‐31G(d) level of theory, by considering ten energetically distinct paths. The study indicates the fully enantioselective catalytic cycle of the homochiral dimers to be the dominant mechanism. Two other catalytic cycles are shown to both be important for correct understanding of the Soai reaction. These are the catalytic cycle of the heterochiral dimer and the non‐enantioselective catalytic cycle of the homochiral dimers. The former has been proved to be not really competitive with the principal cycle, as required for the Soai reaction to manifest chiral amplification, whereas the latter, which is only slightly competitive with the principal one, nicely explains the experimental enantioselectivity observed in the reaction of 2‐methylpyrimidine‐5‐carbaldehyde. The study has also evidenced the inadequacy of the B3LYP functional for mechanistic investigations of the Soai reaction.     

Study of the reaction of bis- and tris-pyrylium and -thiopyrylium cations with methoxide ion. Electronic effects of the heterocyclic rings as substituents

The bis- and tris-pyrylium and thiopyrylium cations 1-4 were prepared in gram scale by heterocyclization of the corresponding bis- and tris-1,5-pentanediones 6 and 8. Their reaction with CD3ONa in CD3OD was studied by 1H NMR at -40 degrees C and at +25 degrees C. At low temperature, kinetically controlled mixtures of 2H and/or 4H adducts were detected, whereas at room temperature the mixtures equilibrated to yield, in all of the cases, the more stable 2H adducts exclusively. A spectrophotometric study of the reactions with sodium methoxide in methanol was carried out at 25.0 degrees C with the aim of determining the stepwise equilibrium constants for the addition of MeO- at the alpha position of the heteroaromatic rings. The obtained equilibrium constants allowed the evaluation of the electronic effects of chalcogenopyrylium and 2H-chalcogenopyran subunits as substituents. Despite the different sensitivity to electronic effects, pyrylium and thiopyrylium rings have a similar electron-withdrawing effect with a sigma(+)p approximately 0.8 and a sigma(+)m approximately 0.5. Apart from the expected importance of the inductive effect due to the positive charge, the difference between these two values remarks the importance of the resonance contribution. In contrast both the neutral 2H-pyranyl and thiopyranyl rings have a negligible effect as substituents, independently of the position, para or meta, they occupy.     

Unexpected high ordering of a [60]Fullerene nitroxide in the nematic phase of 4-4′-azoxyanisole

A nitroxide [60]fullerene adduct containing a pyrrolidine-1-oxyl group has been synthesized. Its orientational order in the nematic phase of the liquid crystal solvent 4,4′-azoxyanisole (PAA) has been measured from the variation of the EPR spectral parameters on passing from the isotropic to the nematic phase. Highly resolved EPR lines allow for precise evaluation of the shifts of the g, a _N and a _H values. Since the g and the hyperfine tensors are known, the order matrix could be obtained. This is compared with the one calculated with a theoretical model based on short range solute-solvent interactions, which predicts a considerable degree of orientation of the molecular axes, despite the almost spherical shape of the molecule. The agreement with experimental findings is quite good and it is further improved if a bent structure of the pyrrolidine ring is taken into account.