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In this work, a systematic investigation on the mechanism and kinetics of the reactions of t-amyl methyl ether (TAME) and t-amyl ethyl ether (TAEE) with OH radicals in the gas phase has been performed within the Density Functional Theory (DFT) framework. The potential energy surfaces were obtained at the M06-2X/6-311++G(d,p) level. Kinetic data for the initial step in the oxidative degradation of TAME and TAEE were obtained, as well as branching ratios between the possible reaction channels. The calculated total rate constants are 3.9 × 10−11 cm3 molecules−1 s−1 and 1.3 × 10−12 cm3 molecules−1 s−1, for TAME and TAEE, respectively. Contrary to what occurs in the case of the MTBE and ETBE oxidation initiated by OH radicals, for TAME and TAEE the H-abstraction from α methoxy or ethoxy groups is not favored. For both molecules, the contribution of the reaction channels involving H-abstraction from the t-amyl group amounts to about 70% of the total rate coefficients. Using our calculated rate constants and a chosen OH tropospheric concentration of 1 × 106 molecule cm−3, lifetimes of ∼43 and ∼128 min were obtained for TAME and TAEE, respectively.

The highly porous metal–organic framework based on copper-benzenetricarboxylate (HKUST-1, Cu3(BTC)2, MOF-199) is used for a loading study of basic fuchsin (BF, neutral charge, ϕ = 12.40 A molecular diameter, 50 ppm solution), crystal violet (CV, cationic charge, ϕ = 15.10 A, 50 ppm solution) and Eriochrome Black T (EBT, anionic charge, ϕ = 15.50 A, 80 ppm solution), as chosen molecular probes for physicochemical analysis and interactions. Characterization is carried out using XRD, FTIR, SEM, and TGA, and UV-Vis is used to determine the differential concentration of loaded dye in the MOF. The adsorption process is evaluated by three incorporation methodologies: post-synthesis (PS) and one-pot in organic (OPO) or metallic (OPM) solution. XRD cell parameters reveal the general compactness of the net through ionic (CV and EBT), dipolar (BF, CV and EBT) and van der Waals (BF, CV and EBT) dye–MOF interactions. Enhanced compactness is observed for CV due to its cationic nature and medium size; the effect is not as strong in EBT, which is anionic in nature but bigger in size, and the least compactness is observed for BF, which lacks ionic interaction with the net. The samples have crystal sizes between 34 and 57 nm, which indicate the generation of nanomaterials. The employed procedures yield crystallite size in the following order: PS < OPO < OPM. The (%) adsorption of all the dyes is above 86.93%, which is observed for the EBT-PS sample as the lowest and 99.42% for BF-PS as the highest, which evidences the high displacement of equilibrium in the studied systems to the Cu3(BTC)2·dye occluded state. Thus, MOFs can be suggested as potential adsorbents/loaders of BF/CV/EBT dyes for composite material generation as well as MOF·molecule interaction studies because of their high loading ability and obtained stability as well as facile synthesis.

In this work, a systematic investigation on the reactions of methyl t-butyl ether (MTBE) and ethyl t-butyl ether (ETBE) with OH radicals in the gas phase has been performed, within the Density Functional (DFT) framework. The potential energy surfaces were obtained at the M06-2X/6-311++G(d,p) level. Specific emphasis was given to obtain kinetic data for MTBE and ETBE oxidative degradation and to identify and quantify the intermediate products formed. The values of the calculated rate constants reproduce remarkably well the available experimental data. The calculated total rate constants for the MTBE + OH and ETBE + OH reactions, in the gas phase at 298.15 K, are 2.79 × 10−12 and 7.38 × 10−12 cm3 molecules−1 s−1. Thus, ETBE reacts more than 2 times faster with OH radicals than MTBE. In both molecules, the hydrogen atoms that are most easily abstracted are the ones occupying an α position with respect to the ether oxygen atom. The contribution of the reaction channels involving H-abstraction from the tert-butyl group amounts to about 24–27% of the total rate coefficient. The results obtained in this work may improve the reliability and precision of the OH radical kinetic data required to predict the lifetime of aliphatic ethers and their contribution to urban and regional pollution.

In recent years, metal organic frameworks (MOF) have received considerable interest due to their physicochemical properties, such as structures’ flexibility, high surface area, tuna‐ ble pore size, and topologies, among others, which have lead to promising applications, particularly in the area of catalysis. In this chapter, we present the most important results of research conducted with MOF in catalytic applications; mainly in the design of its structure, synthesis, characterization, and possible limitations.

In this work, we have performed a theoretical study on the mechanisms and kinetics of the •OH initiated oxidation of selected ethylene glycol vinyl ethers, using quantum chemistry and computational kinetics methods. We have found that the main reaction path is the •OH-addition to vinyl double bonds, and especially to the vinyl terminal carbon atom. Branching ratios for addition at C1 are larger than 94%. Although divinyl ethers could be expected to react approximately twice as fast as monovinyl ethers, it was found that, in fact, •OH rate constants of monovinyl and divinyl ethers are very similar, in agreement with experimental results. This effect is attributed to the sharing of the oxygen lone pairs effect, when the molecule contains two vinyl groups. Thus, in EGMVE, the vinyl group is more reactive than the one in divinyl ethers. The energy of its highest occupied molecular orbital (HOMO) is closer to that of the OH radical, thus favoring the interaction with the single occupied molecular orbital (SOMO) of the radical. Negative activation enthalpies are obtained for the three molecules studied, implying that the rate constant decreases as temperature increases. This anti-Arrhenius behavior is commonly observed in •OH addition to alkenes. An excellent correlation is observed between experimental and calculated rate constants. © 2012 Wiley Periodicals, Inc.

In this work, we report a quantum chemistry mechanistic study of the hydroxyl (•OH) and hydroperoxyl (•OOH) radicals initiated oxidation of indigo, within the density functional theory framework. All possible hydrogen abstraction and radical addition reaction pathways have been considered. We find that the reaction between a free indigo molecule and an •OH radical occurs mainly through two competing mechanisms: H-abstraction from an NH site and •OH addition to the central C═C double bond. Although the latter is favored, both channels occur, the indigo chromophore group structure is modified, and thus the color is changed. This mechanism adequately accounts for the loss of chromophore in urban air, including indoor air such as in museums and in urban areas. Regarding the reactivity of indigo toward •OOH radicals, only •OOH-addition to the central double bond is thermodynamically feasible. The corresponding transition state free energy value is about 10 kcal/mol larger than the one for the •OH initiated oxidation. Therefore, even considering that the •OOH concentration is considerably larger than the one of •OH, this reaction is not expected to contribute significantly to indigo oxidation under atmospheric conditions.

This work shows that indigo's high stability can be attributed both to the large π conjugation inside the molecule and to intra- and intermolecular hydrogen bonds. The theoretical investigation of indigo's electronic structure has been performed using high-level methods. To understand the interactions in solid state, calculations of the dimer system with both molecules in the same plane was carried out. In the monomer, two intramolecular hydrogen bridges between amino and carbonyl groups occupy positions that would otherwise be the most reactive ones for nucleophilic and electrophilic attacks. In the dimer, amino and carbonyl groups on different monomers form intermolecular multicentred non-linear hydrogen bonds in six-member rings, protecting again the same reactive centres and explaining the limited solubility of indigo. The addition of the free radical OH breaks the central C = C double bond, the conjugation and the hydrogen bridges as a first step. The Gibbs energy calculation favours the addition of ...

Recently it has been shown that very accurate exchange and correlation potentials may be predicted from the properties of the one- and two-particle density matrices for a system with a finite number of electrons. The charge density dependence of the exchange potential thus derived is the same as that of a free electron gas (homogeneous system). In order to take into account the inhomogeneity effects, we have carried out an expansion of the charge density around the center of the Fermi hole. This leads to an exchange potential of the same form as that of the Xαβ theory. The value of β predicted for a modified Wigner form of the pair correlation function of electrons with parallel spin, f (1,2), when the number of electrons goes to infinity is 0.0020, in agreement with the theoretical value found by Liberman. Exchange, correlation, and total energies of atoms Li through Ar predicted from several models, corresponding to different forms of f (1,2), are in very good agreement with the exact values.

We present a theoretical study of the piezoelectric polymer poly(vinylidene fluoride), PVDF. By density functional theory calculations, some of the distinct properties of this material have been obtained. Among such properties are hardness, capacitance, dipolar moment and energy associated with the conformational structural changes. For the calculations, we employed the B3LYP functional and the 6311+G(d,p) basis set. Five chain molecules of varying length were studied, H–(CH2–CF2) x –H, where x = 1–4 and 6 for the four different PVDF conformations, namely, I = Tp, II = TGa, III = TGp and IV = T3G, where T means trans and G means gauche.

The applicability of naturally available low-cost and eco-friendly adsorbent materials for the removal of hazardous dyes from aqueous waste is of increasing environmental interest. Among the adsorption treatments available, clays seem to be economically attractive due to their abundance and adsorption capabilities. Indeed, many ancient coloring materials utilized clays mixed with natural dyes (e.g., indigo in Maya Blue). In this work, we performed a quantum-mechanical theoretical study of the adsorption of the indigo molecule onto the (001) surface of a phyllosilicate. Different methods and approaches were applied and compared. We found that the presence of a tetrahedral charge and a sodium counterion significantly increased the adsorption energy of the indigo molecule. The vibrational spectrum of the dye-surface system was also studied, and some interesting shifts in the frequencies of the main vibrational modes of indigo due to its interaction with the surface of the clay mineral were identified.

The non-rigid group (NRG) for the wagging and torsion motions in methylamine is deduced in terms of rotation and inversion operations. The group is compared to that of LonguetHiggins for the same molecule expressed in terms of permutations and permutations-inversion. It is seen that the NRG is isomorphic to that of Longuet-Higgins and the C6v symmetry point group. The character table is deduced, as well as the symmetry eigenvectors in terms of products of trigonometric functions. Selection rules for the infrared torsional-wagging transitions are given, and the band profiles of the spectrum discussed.

A theoretical study of poly(vinylidene flouride-trifluoroethylene) and poly(vinylidene fluoride-chlorotrifluoroethylene, is presented. By density functional theory calculations, some of the properties of these materials have been obtained. Among such properties, the dipolar moment and the energies associated to the structural changes. The B3LYP functional and 6311+G(d,p) bases set were used with Gaussian program. Calculations associated to different conformations were carried out to get insight about the involved phase changes. The energetic, charges, and dipole moment were calculated. The conformations, namely, I = Tp, II = TGa, and III = TGp, where T means trans and G means gauche, for the two polymers aforementioned were compared with the poly(vinilydene fluoride) studies previously obtained. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2411–2417, 2010

Quantum Chemical Investigations of Structural Parameters of PVDF-based Organic Ferroelectric Materials

This paper proposes a Markov observation based model, where the transition matrix is formulated using air quality monitoring data for specific pollutant emissions, with the primary objective to analyze the corresponding stationary distributions and evaluate sceneries for the air quality impact of pollution control policies. The model is non predictive and could be applied to every source of pollutant emissions included in air monitoring data. Two cases of study are presented, ozone and sulfur, over central zone of Mexico City for a seven years span from 2000 to 2006. For presentation purposes each year were divided in two semesters. In ozone case, the stationary distribution for both semesters shows a probability diminution of the higher ozone concentrate levels, with tendency to ”piston effect”. In the sulfur case, the first semester displays an oscillatory behavior with a little tendency to diminution of the higher sulfur concentrate levels, the second semester had decreasing probabilities of the higher sulfur levels. The results support an small improvement of air quality and then a favorable evaluation of the diverse pollution control policies that had been implemented in Mexico City over the last several years. En este trabajo se propone un modelo de Markov basado en observaciones, donde la matriz de transición se formula empleando información del monitoreo de la calidad del aire para ciertos contaminantes específicos, con el objetivo principal de analizar las distribuciones estacionarias correspondientes y evaluar escenarios del impacto de las medidas de control anticontaminantes de la calidad del aire. El modelo no es predictivo y puede aplicarse a cualquier fuente de emisiones contaminantes incluidas en el sistema de monitoreo ambiental. Se presentan dos casos de estudio, ozono y azufre, sobre la zona central de la Ciudad de México para un intervalo de siete años del 2000 al 2006. Para propósitos de presentación, cada año se dividió en dos semestres. En el caso del ozono, la distribución estacionaria para ambos semestres mostró una disminución en la probabilidad de ocurrencia de los niveles de alta concentración de ozono, con cierta tendencia al ”efecto pistón”. En el caso del azufre, el primer semestre mostró un comportamiento oscilatorio con una pequeña tendencia a la disminución de los niveles de alta concentración y en el segundo semestre disminuyeron las probabilidades de altos niveles de azufre. Los resultados establecen una ligera mejoŕıa en la calidad del aire y por lo tanto una evaluación favorable de las diversas medidas de control de contaminantes que han sido implementadas en la Ciudad de México en los últimos años.

"La producción de biocombustible a partir de cultivos agrícolas no sólo trae consigo una reducción en la disponibilidad de los alimentos, sino que podría causar una disminución de la calidad del aire afectando a la salud de la población expuesta. El propósito de este trabajo es el evaluar el efecto que tendría la sustitución de gasolina Magna por la mezcla gasolina-etanol en la flota vehicular mediante la simulación de la reactividad fotoquímica de la calidad del aire en la Ciudad de México. Adicionalmente, se analizará el efecto de esta sustitución sobre la producción de tóxicos como acetaldehído, peroxiacetil nitratos (PAN) y benceno, así como de otros contaminantes tales como hidrocarburos totales y óxido de nitrógeno. La evaluación de esta estrategia se llevará a cabo mediante la aplicación de modelos de calidad del aire CIT en su versión trayectoria, en donde se relacionan las emisiones del parque vehicular con las concentraciones del biocombustible. La información generada en diversos estudios de campo como IMADA-AVER /1-3/ se empleará como bases de datos que alimenten a los modelos fotoquímicos. Así también, se empleará el inventario de emisiones de la Zona Metropolitana de la Ciudad de México (ZMVM) del año 2006 para generar la proyección a futuro a al 2020."

The exchange energy density functional of an N electron atom is approximated by a combination of the Dirac and the Fermi–Amaldi approximations. The unknown coefficients of the combination are estimated by requiring that the sum of the Coulombic and exchange energies vanish when evaluated with the exact one‐electron density. Evaluating the present functional with the Hartree–Fock densities of 1785 atoms and ions, and comparing the resulting exchange energies with the corresponding Hartree–Fock values gave an average error of 2%. The functional derivative has the correct long‐range behavior, and leads to an Euler–Lagrange equation whose solutions gave energies which were in very good agreement with the Hartree–Fock values.

The Z−1 perturbation expansion is used to derive a formula of the energy of an ion in the limit of large nuclear charge Z and number of electrons N of the form E=∑nZ(7−n)/3 fn(q) where q=N/Z and fn(q)=q(1−n)/3[b0n+b 1nq+b2nq2] with b1n≂[(7−n)/3]Cn−2b0n and b2n≂b0n −[(4−n)/3]Cn. The constants b0n correspond to the asymptotic expansion of the zero‐order perturbation coefficient e0(N) and the constants Cn correspond to the neutral atom binding energy E=∑nCnZ(7−n)/3. The first function f0(q), which corresponds to the Thomas‐Fermi limit, is then used to obtain approximate analytical expressions for the first derivative at the origin S(q) and the radius of the ion, χ0(q), of the Thomas‐Fermi screening function. The expressions for f0(q), S(q), and χ0(q) provide an excellent representation of the numerical solutions. The function f1(q) is used to show that the value of the coefficient of the leading correction to the Thomas‐Fermi energy C1 is 1/2. Finally, it is shown that the description of the ratio of the tot...

The exchange potential is separated into self-interaction and interelectronic exchange components which are modeled through the properties of the cne- and two-particle density matrices. The resulting functional has the correct asymptotic behaviour.

A Taylor series expansion of the energy of an atomic system around the neutral atom value, which introduces the first and second derivatives of the energy with respect to the number of electrons (electronegativity χ, and hardness η, respectively) is proposed. The relaxed first derivative and the unrelaxed second derivative of the Xα and hyper‐Hartree–Fock methods are used to relate χ and η with the Lagrange multiplier ei, and the self‐repulsion integral J(i) of the highest occupied atomic orbital for the case of an open shell. A simple model, based on screening effects, is developed to get a better representation of a relaxed second derivative. This model replaces J(i) by 1/2 〈r−1〉i and leads to η= 1/4 〈r−1〉i. The use of this relation, together with the Xα expression for electronegativity, χ=−ei, and a simple charge transfer model for electronegativity equalization leads to values of molecular electronegativities which are in very good agreement with the values obtained through the use of atomic or molecu...

The Z-1 perturbation expansion is used to derive an expression for the atomic binding energy E in the limit of large nuclear charge Z and number of electrons N. The coefficients appearing in this expression are determined from conditions related to the general behavior of E as a function of N. It is shown that through this expression one can: 1) obtain an excellent representation of Thomas-Fermi ions; 2) derive an expression for the chemical potential of neutral atoms in the limit of large Z, which accounts for the general behavior of this property in atoms of the periodic table; and 3) describe rather well ratios between different energy components.