Ion Association in [bmim][PF6]/Naphthalene Mixtures: An Experimental and Computational Study

Mixtures of room temperature ionic liquids (IL) with neutral organic molecules provide a valuable testing ground to investigate the interplay of the ionic and molecular-dipolar state in dense Coulomb systems at near ambient conditions. In the present study, the viscosity eta and the ionic conductivity a of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6])/naphthalene mixtures at T = 80 degrees C have been measured at 10 stoichiometries spanning the composition range from pure naphthalene to pure [bmim][PF6]. The viscosity grows nearly monotonically with increasing IL mole fraction (x), whereas the conductivity per ion displays a clear peak at x approximate to 15%. The origin of this maximum has been investigated using molecular dynamics simulations based on a classical force field. Snapshots of the simulated samples show that the conductivity maximum is due to the gradual transition in the IL component from an ionic state at high x to a dipolar fluid made of neutral ion pairs at low x. At concentrations x <0.20 the ion pairs condense into molecular-thin filaments bound by dipolar forces and extending in between nanometric droplets of IL. These results are confirmed and complemented by the computation of dynamic and transport properties in [bmim][PF6]/naphthalene mixtures at low IL concentration.

Thermochemistry of Ionic Liquid-Catalyzed Reactions: Theoretical and Experimental Study of the Beckmann Rearrangement-Kinetic or Thermodynamic Control?

A thermodynamic analysis of the experimental conditions of the Beckmann rearrangement reaction of oximes into amides has been undertaken to examine whether the reaction is under thermodynamic or kinetic control. To answer this question, the thermodynamic properties of the typical Beckmann rearrangement reactions in the ideal gaseous state-cyclohexanone oxime to caprolactam and 2-butanone oxime to N-methylpropanarnide-were studied by using the quantum mechanical method. Gibbs energy and equilibrium constants of the Beckmann rearrangement have been assessed in the gaseous and the liquid phases. Results of the thermodynamic analysis have shown that Beckmann rearrange ments are kinetically controlled. Thus, a search for possible active ionic liquid based catalysts for the mild reaction conditions has been performed.

Theoretical and experimental correlations of gas dissolution, diffusion, and thermodynamic properties in determination of gas permeability and selectivity in supported ionic liquid membranes

Supported ionic liquid membranes (SILMs) has the potential to be a new technological platform for gas/organic vapour separation because of the unique non-volatile nature and discriminating gas dissolution properties of room temperature ionic liquids (ILs). This work starts with an examination of gas dissolution and transport properties in bulk imidazulium cation based ionic liquids [C_nmim][NTf2] (n = 2.4, 6, 8.10) from simple gas H₂, N₂, to polar CO₂, and C₂H₆, leading to a further analysis of how gas dissolution and diffusion are influenced by molecular specific gas-SILMs interactions, reflected by differences in gas dissolution enthalpy and entropy. These effects were elucidated again during gas permeation studies by examining how changes in these properties and molecular specific interactions work together to cause deviations from conventional solution–diffusion theory and their impact on some remarkably contrasting gas perm-selectivity performance. The experimental perm-selectivity for all tested gases showed varied and contrasting deviation from the solution–diffusion, depending on specific gas-IL combinations. It transpires permeation for simpler non-polar gases (H₂, N₂) is diffusion controlled, but strong molecular specific gas-ILs interactions led to a different permeation and selectivity performance for C₂H₆ and CO₂. With exothermic dissolution enthalpy and large order disruptive entropy, C₂H₆ displayed the fastest permeation rate at increased gas phase pressure in spite of its smallest diffusivity among the tested gases. The C₂H₆ gas molecules “peg” on the side alkyl chain on the imidazulium cation at low concentration, and are well dispersed in the ionic liquids phase at high concentration. On the other hand strong CO₂-ILs affinity resulted in a more prolonged “residence time” for the gas molecule, typified by reversed CO₂/N₂ selectivity and slowest CO₂ transport despite CO₂ possess the highest solubility and comparable diffusivity in the ionic liquids. The unique transport and dissolution behaviour of CO₂ are further exploited by examining the residing state of CO₂ molecules in the ionic liquid phase, which leads to a hypothesis of a condensing and holding capacity of ILs towards CO₂, which provide an explanation to slower CO₂ transport through the SILMs. The pressure related exponential increase in permeations rate is also analysed which suggests a typical concentration dependent diffusion rate at high gas concentration under increased gas feed pressure. Finally the strong influence of discriminating and molecular specific gas-ILs interactions on gas perm-selectivity performance points to future specific design of ionic liquids for targeted gas separations.

A Theoretical and Experimental Study of Resonance in a High Performance Engine Intake System: Part 1

The unsteady gas dynamic phenomena in engine intake systems of the type found in racecars have been examined. In particular, the resonant tuning effects, including cylinder-to-cylinder power variations, which can occur as a result of the interaction between an engine and its airbox have been considered. Frequency analysis of the output from a Virtual 4-Stroke 1D engine simulation was used to characterise the forcing function applied by an engine to an airbox. A separate computational frequency sweeping technique, which employed the CFD package FLUENT, was used to determine the natural frequencies of virtual airboxes in isolation from an engine. Using this technique, an airbox with a natural frequency at 75 Hz was designed for a Yamaha R6 4-cylinder motorcycle engine. The existence of an airbox natural frequency at 75 Hz was subsequently confirmed by an experimental frequency sweeping technique carried out on the engine test bed. A coupled 1D/3D analysis which employed the engine simulation package Virtual 4-Stroke and the CFD package FLUENT, was used to model the combined engine and airbox system. The coupled 1D/3D analysis predicted a 75 Hz resonance of the airbox at an engine speed of 9000 rpm. This frequency was the induction frequency for a single cylinder. An airbox was fabricated and tested on the engine. Static pressure was recorded at a grid of points in the airbox as the engine was swept through a speed range of 3000 to 10000 rpm. The measured engine speed corresponding to resonance in the airbox agreed well with the predicted values. There was also good correlation between the amplitude and phase of the pressure traces recorded within the airbox and the 1D/3D predictions.

A theoretical and experimental dissociation of two models of decision‐making

La prise de décision est un processus computationnel fondamental dans de nombreux aspects du comportement animal. Le modèle le plus souvent rencontré dans les études portant sur la prise de décision est appelé modèle de diffusion. Depuis longtemps, il explique une grande variété de données comportementales et neurophysiologiques dans ce domaine. Cependant, un autre modèle, le modèle d’urgence, explique tout aussi bien ces mêmes données et ce de façon parcimonieuse et davantage encrée sur la théorie. Dans ce travail, nous aborderons tout d’abord les origines et le développement du modèle de diffusion et nous verrons comment il a été établi en tant que cadre de travail pour l’interprétation de la plupart des données expérimentales liées à la prise de décision. Ce faisant, nous relèveront ses points forts afin de le comparer ensuite de manière objective et rigoureuse à des modèles alternatifs. Nous réexaminerons un nombre d’assomptions implicites et explicites faites par ce modèle et nous mettrons alors l’accent sur certains de ses défauts. Cette analyse servira de cadre à notre introduction et notre discussion du modèle d’urgence. Enfin, nous présenterons une expérience dont la méthodologie permet de dissocier les deux modèles, et dont les résultats illustrent les limites empiriques et théoriques du modèle de diffusion et démontrent en revanche clairement la validité du modèle d'urgence. Nous terminerons en discutant l'apport potentiel du modèle d'urgence pour l'étude de certaines pathologies cérébrales, en mettant l'accent sur de nouvelles perspectives de recherche.

”Nonlinear optical properties of polymers containing azomesogens and chiral molecules: theoretical and experimental evaluations."

The present work emphasizes the use of chirality as an efficient tool to synthesize new types of second order nonlinear materials. Second harmonic generation efficiency (SHG) is used as a measure of second order nonlinear response. Nonlinear optical properties of polymers have been studied theoretically and experimentally. Polymers were designed theoretically by ab initio and semiempirical calculations. All the polymeric systems have been synthesized by condensation polymerization. Second harmonic generation efficiency of the synthesized systems has been measured experimentally by Kurtz and Perry powder method

Fuzzy set Theory and Quantum Chemistry

Es discuteixen breument algunes consideracions sobre l'aplicació de la Teoria dels Conjunts difusos a la Química quàntica. Es demostra aqui que molts conceptes químics associats a la teoria són adequats per ésser connectats amb l'estructura dels Conjunts difusos. També s'explica com algunes descripcions teoriques dels observables quàntics es potencien tractant-les amb les eines associades als esmentats Conjunts difusos. La funció densitat es pren com a exemple de l'ús de distribucions de possibilitat al mateix temps que les distribucions de probabilitat quàntiques

Dinuclear copper and zinc complexes of a hexaazamacrocycle containing p-xylyl spacers and bridging anions: theoretical and spectroscopic studies

The hexaazamacrocycle 7,22-dimethyl-3,7,11,18,22,26-hexaazatricyclo[26.2.2.2(13,16)] tetratriaconta-1(30), 13,15,28,31,33- hexaene (Me-2[30] pbz(2)N(6)) was synthesized and characterised by single crystal X-ray diffraction. The macrocycle adopts a conformation with the two aromatic rings almost parallel at a distance of ca. 4.24 Angstrom, but displaced relative to each other by ca. 1.51 Angstrom. The protonation constants of this compound and the stability constants of its complexes with Cu2+ and Zn2+, were determined in water - methanol (9 : 1 v/v) at 25 degreesC with ionic strength 0.10 mol dm(-3) in KCl. The potentiometric and spectroscopic studies (NMR of zinc, cadmium and lead complexes, and EPR of the copper complexes) indicate the formation of only dinuclear complexes. The association constants of the dinuclear copper complex with anions ( thiocyanate, terephthalate and glyphosate) and neutral molecules (1,4-benzenedimethanol, p-xylylenediamine and terephthalic acid) were determined at 20 degreesC in methanol. The structural preferences of this ligand and of its dinuclear copper(II) complex with a variety of bridging ligands were evaluated theoretically by molecular mechanics calculations (MM) and molecular dynamics (MD) using quenching techniques.

Geometrical isomers of [TEAH][Co(L-Se)(2)]center dot xH(2)O: synthesis, structural, spectroscopic and computational studies

Trans-1, [HNEt3][Co-III(L-Se)(2)]center dot H2O and cis-1, [HNEt3][Co-III(L-Se)(2)]center dot 3H(2)O have been synthesized and characterized by single-crystal X-ray studies. The counter ion Et3NH+ plays a crucial role in the crystal packing leading to the formation of two distinctly different supramolecular assemblies in the two complexes. In trans-1, Co-bisphenolate units and triethylamine molecules are arranged in a linear fashion leading to a supramolecular columnar assembly along the crystallographic a-axis. In this assembly, triethylammonium ions are sandwiched between successive Co-bisphenolate units and act as gluing agents joining Co-bisphenolate units on either side through C-H center dot center dot center dot pi interactions. In sharp contrast to trans-1, Co-bisphenolate units and triethylammonium ions in cis-1 are arranged in a helical supramolecular assembly through similar C-H center dot center dot center dot pi interactions along the crystallographic b-axis. The Se center dot center dot center dot Se van der Waals interactions may be responsible for the predominant occurrence of the cis-isomer. The cyclic voltammetric studies showed quasi-reversible waves for the cobalt(III) -> cobalt(II) reductions with E-1/2 = 0.635 and 0.628 V vs. Ag/AgCl for cis-1 (at similar to 5 degrees C) and trans-1 (at similar to 25 degrees C), respectively. DFT calculations show that the trans-form is the thermodynamic product with higher stability than the cis-one, which is consistent with the variable temperature H-1 NMR studies

C-H...O hydrogen bonding in 4-phenyl-benzaldehyde: a comprehensive crystallographic, spectroscopic and computational study

The crystal structure of 4-phenyl-benzaldehyde reveals the presence of a dimer linked by the C=O and C( 9)-H groups of adjacent molecules. In the liquid phase, the presence of C-(HO)-O-... bonded forms is revealed by both vibrational and NMR spectroscopy. A Delta H value of - 8.2 +/- 0.5 kJ mol(-1) for the dimerisation equilibrium is established from the temperature-dependent intensities of the bands assigned to the carbonyl-stretching modes. The NMR data suggest the preferential engagement of the C(2,6)-H and C(10/12)/C(11)-H groups as hydrogen bond donors, instead of the C(9)-H group. While ab initio calculations for the isolated dimers are unable to corroborate these NMR results, the radial distribution functions obtained from molecular dynamics simulations show a preference for C(2,6)-H and C(10/12)/C(11)-(HO)-O-... contacts relative to the C(9)-(HO)-O-... ones.

Solvent-dependent modulation of metal–metal electronic interactions in a dinuclear cyanoruthenate complex: a detailed electrochemical, spectroscopic and computational study

The dinuclear complex [{Ru(CN)4}2(μ-bppz)]4− shows a strongly solvent-dependent metal–metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH2Cl2. In CH2Cl2 the separation between the successive Ru(II)/Ru(III) redox couples is 350 mVand the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mVand the much broader IVCT transition is characteristic of a class II mixed-valence state. This is consistent with the observation that raising and lowering the energy of the d(π) orbitals in CH2Cl2 or water, respectively, will decrease or increase the energy gap to the LUMO of the bppz bridging ligand, which provides the delocalisation pathway via electron-transfer. IR spectroelectrochemistry could only be carried out successfully in CH2Cl2 and revealed class III mixed-valence behaviour on the fast IR timescale. In contrast to this, time-resolved IR spectroscopy showed that the MLCTexcited state, which is formulated as RuIII(bppz˙−)RuII and can therefore be considered as a mixed-valence Ru(II)/Ru(III) complex with an intermediate bridging radical anion ligand, is localised on the IR timescale with spectroscopically distinct Ru(II) and Ru(III) termini. This is because the necessary electron-transfer via the bppz ligand is more difficult because of the additional electron on bppz˙− which raises the orbital through which electron exchange occurs in energy. DFT calculations reproduce the electronic spectra of the complex in all three Ru(II)/Ru(II), Ru(II)/Ru(III) and Ru(III)/Ru(III) calculations in both water and CH2Cl2 well as long as an explicit allowance is made for the presence of water molecules hydrogen-bonded to the cyanides in the model used. They also reproduce the excited-state IR spectra of both [Ru(CN)4(μ-bppz)]2– and [{Ru(CN)4}2(μ-bppz)]4− very well in both solvents. The reorganization of the water solvent shell indicates a possible dynamical reason for the longer life time of the triplet state in water compared to CH2Cl2.

Bridge-localized HOMO-binding character of divinylanthracene-bridged dinuclear ruthenium carbonyl complexes: spectroscopic, spectroelectrochemical, and computational studies

The electronic properties of four divinylanthracene-bridged diruthenium carbonyl complexes [{RuCl(CO)(PMe3)3}2(μ[BOND]CH[DOUBLE BOND]CHArCH[DOUBLE BOND]CH)] (Ar=9,10-anthracene (1), 1,5-anthracene (2), 2,6-anthracene (3), 1,8-anthracene (4)) obtained by molecular spectroscopic methods (IR, UV/Vis/near-IR, and EPR spectroscopy) and DFT calculations are reported. IR spectroelectrochemical studies have revealed that these complexes are first oxidized at the noninnocent bridging ligand, which is in line with the very small ν(C[TRIPLE BOND]O) wavenumber shift that accompanies this process and also supported by DFT calculations. Because of poor conjugation in complex 1, except oxidized 1+, the electronic absorption spectra of complexes 2+, 3+, and 4+ all display the characteristic near-IR band envelopes that have been deconvoluted into three Gaussian sub-bands. Two of the sub-bands belong mainly to metal-to-ligand charge-transfer (MLCT) transitions according to results from time-dependent DFT calculations. EPR spectroscopy of chemically generated 1+–4+ proves largely ligand-centered spin density, again in accordance with IR spectra and DFT calculations results.

A psychophysical and computational analysis of the spatio-temporal mechanisms underlying the flash-lag effect

Several accounts put forth to explain the flash-lag effect (FLE) rely mainly on either spatial or temporal mechanisms. Here we investigated the relationship between these mechanisms by psychophysical and theoretical approaches. In a first experiment we assessed the magnitudes of the FLE and temporal-order judgments performed under identical visual stimulation. The results were interpreted by means of simulations of an artificial neural network, that wits also employed to make predictions concerning the F LE. The model predicted that a spatio-temporal mislocalisation would emerge from two, continuous and abrupt-onset, moving stimuli. Additionally, a straightforward prediction of the model revealed that the magnitude of this mislocalisation should be task-dependent, increasing when the use of the abrupt-onset moving stimulus switches from a temporal marker only to both temporal and spatial markers. Our findings confirmed the model`s predictions and point to an indissoluble interplay between spatial facilitation and processing delays in the FLE.

Design of novel antituberculosis compounds using graph-theoretical and substructural approaches

The increasing resistance of Mycobacterium tuberculosis to the existing drugs has alarmed the worldwide scientific community. In an attempt to overcome this problem, two models for the design and prediction of new antituberculosis agents were obtained. The first used a mixed approach, containing descriptors based on fragments and the topological substructural molecular design approach (TOPS-MODE) descriptors. The other model used a combination of two-dimensional (2D) and three-dimensional (3D) descriptors. A data set of 167 compounds with great structural variability, 72 of them antituberculosis agents and 95 compounds belonging to other pharmaceutical categories, was analyzed. The first model showed sensitivity, specificity, and accuracy values above 80% and the second one showed values higher than 75% for these statistical indices. Subsequently, 12 structures of imidazoles not included in this study were designed, taking into account the two models. In both cases accuracy was 100%, showing that the methodology in silico developed by us is promising for the rational design of antituberculosis drugs.

Photochemical Generation and Intramolecular Chemistry of β-Alkoxycarbenes

The photolytic phenanthrene-based precursors for both β-methoxycarbene and β-ethoxycarbene were synthesized with and without a deuterium label attached to the a carbon. The incorporation of this deuterium label allowed distinction between a 1, 2-H shift and a 1, 2-O shift pathway to the respective alkyl vinyl ether, without the influence of a primary kinetic isotope effect. Photolyses of these precursors gave rearrangement products of the expected β-alkoxycarbenes. In the case of β-methoxycarbene, no methyl vinyl ether was observed due to its volatility. However, the appearance of aldehyde peaks in the NMR spectra, from an apparent further rearrangement to acetaldehyde through an enol intermediate, indicated that a 1,2-H shift had occurred. Ethyl vinyl ether was isolated following the photolysis of the β-ethoxycarbene precursor. Quantification of the two pathways showed less than 2% undergoing an ethoxy shift to the ethyl vinyl ether. Yield experiments on this photolysis demonstrated a maximum yield of β-ethoxycarbene as 43%, though this decreased as the experiment continued. Computational work on the β-ethoxycarbene system indicates that the triplet scate is more stable than the singlet. In addition, the activation energy to the 1.2-H shift pathway is remarkably low and is clearly consistent with the observed overwhelming preference for this pathway in the experiment.