Estudios teóricos sobre la estructura y reactividad química de complejos de molibdeno. Importancia del cruzamiento entre estados electrónicos

El estudio de la Química de compuestos de Mo esta adquiriendo una gran relevancia debido a su importancia en catalizadores biológicos e industriales. En este sentido, la presente Tesis Doctoral versa sobre el estudio teórico de cuatro casos de compuestos de Mo (mononucleares o clústeres trinucleares) con el objeto de determinar su reactividad química y la influencia de los diferentes tipos de ligandos utilizados, ya sea hidruros, ditiolenos y disulfuros, prestanto especial atención al posible cruzamiento entre estados electrónicos. El estudio de cuatro situaciones tan diversas proporciona una visión global del problema, permitiendo identificar diferentes tipos de procesos redox en los cuales puede estar involucrado el átomo de Mo, y, en consecuencia, es posible el cruce entre superficies de energía potencial de distinto espín

Synthesis of Silver nanoparticles (AgNPs) with Antibacterial Activity

The synthesis of nanomaterials is currently one of the most active in nanoscience branches; especially those help improve the human quality life. Silver nanoparticles (AgNPs) are an example of this as it is known to have inhibitory and bactericidal effects. In this work, we report the synthesis of silver nanoparticles by chemical reduction method of silver nitrate (AgNO3) from aqueous solution, using a mix of polivinyl pyrrolidone (PVP) - Aloe Vera as reducing agent and for stabilization and control of particle size. Silver nanoparticles obtained were characterized by Scanning Electron Microscopy (SEM), UV-visible spectroscopy and measurements using Zetasizer Nano ZS were applied to size estimation. The existence of surface plasmon resonance peak at λmax ∼ 420 nm is evidence of silver nanoparticles formation. It was possible to standardize an appropriate protocol for the evaluation of bactericidal activity of the nanoparticles, for mesophilic microorganisms. Bactericidal activity above 90% against these kinds of bacteria was demonstrated. © Published under licence by IOP Publishing Ltd

Termólisis de ß-hidroxicetonas-ß-aril sustituidas. un estudio computacional.

Estudios teóricos de la termólisis de 9-hidroxicetonas-9-aril sustituidas (m,p) para producir mezclas de aldehídos aromáticos y acetona a 429,15K se llevaron a cabo utilizando métodos ab-initio a niveles MP2/6- 31G(d)//HF/6-31G(d). Los perfiles de reacción para los sustituyentes m y p estudiados muestran en todos los casos que la segunda etapa de la reacción tautomerización de acetona (9G≠=217.6 kJmol-1) es la etapa mas lenta. La primera etapa incluye un estado de transición cíclico de seis miembros y sobre ésta se centraron los estudios de una posible relación lineal de energía libre. Los resultados muestran que no hay una buena correlación Hammett indicativo de efecto perpendicular a la coordenada de reacción

A DFT study on natural sensitizers with donor-p-acceptor architecture based on 1,7-diazaheptametine for applications in Dye-Sensitized Solar Cells (DSSC)

Nature offers a wide range of organic dyes with potential as sensitizers in DSSC technology. Among them, some natural dyes contain a 1,7-diazaheptamethine system, influencing their chromatic properties. In this investigation, we computationally analyzed 21 natural betalain dyes featuring a common structural moiety through Density Functional Theory calculations. Among them, eight dyes were classified under the betacyanin subfamily, while the remaining thirteen were attributed to the betaxanthin subfamily. These dyes were examined both in isolation and when bound to titanium dioxide (dye@TiO2). The betaxanthin subfamily showed more twisted geometries, while the betacyanin subfamily exhibited a smaller energy gap. All isolated dyes or dyes@TiO2 exhibit maximum absorption peaks within the visible region (350–700 nm), showcasing their light-capturing capacity. Stability, evidenced by negative adsorption energies, suggests the spontaneity of the adsorption process. Furthermore, our results indicate that the nature of bonding significantly influences the electronic properties of dye@TiO2 complexes. Collectively, these results underscore the importance of the 1,7-diazaheptamethine system in imparting color and structure to these dyes. Our thorough analysis, encompassing molecular interactions, geometric attributes—especially the configuration of donor groups—electronic properties, and absorption spectra, provides valuable insights into the potential applications and effectiveness of these dyes for incorporation in dye-sensitized solar cells (DSSC)

Gas-Phase Elimination Reaction of Ethyl (5-cyanomethyl-1,3,4-thiadiazol-2-yl)carbamate: A Computational Study

The gas‐phase elimination reaction of ethyl (5‐cyanomethyl‐1,3,4‐thiadiazol‐2‐yl)carbamate has been studied computationally at the MP2/6–31++G(2d,p) level of theory. The values of the activation parameters and rate constants for the thermal decomposition were evaluated over a temperature range from 405.0 to 458.0 K. The temperature dependence of the rate constants was used to deduce the modified Arrhenius expression: log k405–458 K = (9.01 ± 0.49) + (1.32 ± 0.16) log T – (6946 ± 30) 1/T, which is in good agreement with the expression obtained from experimental data. The results confirm that the mechanism is a cis‐concerted elimination that occurs in two steps: The first one corresponds to the formation of ethylene and an intermediate, 5‐(cyanomethyl)‐1,3,4‐thiadiazol‐2‐yl‐carbamic acid, via a six‐membered cyclic transition state, and the second one is the decarboxylation of this intermediate via a four‐membered cyclic transition step, leading to carbon dioxide and the corresponding 1,3,4‐thiadiazole derivative (5‐amino‐1,3,4‐thiadiazole‐2‐acetonitrile). The connectivity of transition states with their respective minima was verified through intrinsic reaction coordinate calculations, and the progress of the reaction was followed by means of Wiberg bond indices, resulting that both transition states have an “early” character, nearer to the reactants than to the products

Understanding the reaction mechanism of the oxidative addition of ammonia by (PXP)Ir(i) complexes: The role of the X group

An analysis of the electronic rearrangements for the oxidative addition of ammonia to a set of five representative (PXP)Ir pincer complexes (X = B, CH, O, N, SiH) is performed. We aim to understand the factors controlling the activation and reaction energies of this process by combining different theoretical strategies based on DFT calculations. Interestingly, complexes featuring higher activation barriers yield more exothermic reactions. The analysis of the reaction path using the bonding evolution theory shows that the main chemical events, N-H bond cleavage and Ir-H bond formation, take place before the transition structure is reached. Metal oxidation implies an electron density transfer from non-shared Ir pairs to the Ir-N bond. This decrement in the atomic charge of the metal provokes different effects in the ionic contribution of the Ir-X bonding depending on the nature of the X atom as shown by the interacting quantum atoms methodology. © 2017 the Owner Societies

Dissociation Mode of the O–H Bond in Betanidin, pKa-Clusterization Prediction, and Molecular Interactions via Shape Theory and DFT Methods

Betanidin (Bd) is a nitrogenous metabolite with significant bioactive potential influenced by pH. Its free radical scavenging activity and deprotonation pathway are crucial to studying its physicochemical properties. Motivated by the published discrepancies about the best deprotonation routes in Bd, this work explores all possible pathways for proton extractions on that molecule, by using the direct approach method based on pKa. The complete space of exploration is supported by a linear relation with constant slope, where the pKa is written in terms of the associated deprotonated molecule energy. The deprotonation rounds 1, …, 6 define groups of parallel linear models with constant slope. The intercepts of the models just depend on the protonated energy for each round, and then the pKa can be trivially ordered and explained by the energy. We use the direct approximation method to obtain the value of pKa. We predict all possible outcomes based on a linear model of the energy and some related verified assumptions. We also include a new measure of similarity or dissimilarity between the protonated and deprotonated molecules, via a geometric–chemical descriptor called the Riemann–Mulliken distance (RMD). The RMD considers the cartesian coordinates of the atoms, the atomic mass, and the Mulliken charges. After exploring the complete set of permutations, we show that the successive deprotonation process does not inherit the local energy minimum and that the commutativity of the paths does not hold either. The resulting clusterization of pKa can be explained by the local acid and basic groups of the BD, and the successive deprotonation can be predicted by using the chemical explained linear models, which can avoid unnecessary optimizations. Another part of the research uses our own algorithm based on shape theory to determine the protein’s active site automatically, and molecular dynamics confirmed the results of the molecular docking of Bd in protonated and anionic form with the enzyme aldose reductase (AR). Also, we calculate the descriptors associated with the SET and SPLET mechanisms

Kalanchoe daigremontiana leaf extract: A green stabilizing agent in synthesis of Silver Nanoparticles

The synthesis of silver nanoparticles (AgNPs) has been increasingly extended due to its potential applications in fields such as optics, environmental, catalysis, electronics and as an antibacterial agent. In this way it is necessary to develop methods framed in green chemistry to achieve greater stability over time of the AgNPs. The present work aims to show the synthesis of AgNPs using Kalanchoe daigremontiana leaf extract, as a reducing and stabilizing agent. UV-vis and transmission electron microscopy (TEM) were used to characterize AgNPs obtained. The absorbance of solutions was measured, evidencing of the formation of AgNPs due to the existence of plasmon resonance at that ?max ? 417 nm. The size distribution and morphology of the AgNPs by TEM shows stable, spherical and nomodispersar nanoparticles with a size between 4 and 12 nm. The measurements were carried out immediately after the synthesis procedure, then the AgNPs solutions were stored at room temperature and darkness by 27 months and it could be corroborated the stabilizing capacity of Kalanchoe daigremontiana leaf extract, since the ?max and the size of particle did not vary significatively in this period of time. © Published under licence by IOP Publishing Ltd

Experimental and computational thermochemical study of 3-hydroxypropanenitrile

This paper reports the values of the standard (p∘ = 0.1 MPa) molar enthalpy of formation in the gas phase, at T = 298.15 K, for 3-hydroxypropanenitrile derived from the respective enthalpy of combustion in oxygen, measured by static bomb combustion calorimetry and the standard molar enthalpy of vaporization, at T = 298.15 K, determined using the transference (transpiration) method in a saturated N2 stream, the value of the gas-phase enthalpy of formation being. Furthermore, we have performed high-level ab initio molecular orbital calculations at the G3 level. Four different conformations corresponding to local minima of the potential energy surface have been found for 3-hydroxypropanenitrile. The optimised molecular and electronic structure of the most stable conformer of 3-hydroxypropanenitrile shows a gauche arrangement with a weak intramolecular hydrogen bond from OH hydrogen to the π-bond charge cloud of the nitrile group. The calculated values for the enthalpy of formation of the most stable conformer using atomization and isodesmic bond separation reactions, −94.7 and −95.0 kJ · mol−1, respectively, are in very good agreement with the experimental value.The support of the Spanish MEC/DGI under Projects CTQ2006-12745 and FIS2004-02954-C03-01 and the Colombian DIME, Dirección General de Investigaciones Medellı´n, Sede Medellı´n under Project 030802749 and Vicerrectoria de Investigación, Universidad Nacional de Colombia, Convocatoria Nacional de Investigacion, Modalidad 1, is gratefully acknowledged. M.T. thanks MEC/SEUI, FPU AP2002-0603, Spain, for financial support. A.G. thanks CSIC, I3PCPG-06-00062 for financial support

Testing industrial laboratory dispersion method of Multi-Walled Carbon Nanotubes (MWCNTs) in aqueous medium

The carbon nanotubes (CNTs) dispersion has gained interest in recent years due to its multiple applications in fields such as electronics, concrete, optics, environmental, automotive, marine and aeronautics coatings. In this sense it is necessary to develop stable dispersions of CNTs. On a laboratory scale the method of preparation of the CNTs is usually done using sonication, but this method is not appropriate to obtain CNTs dispersions on a larger scale. This work studies Multiwalled Carbon Nanotubes (MWCNTs) in aqueous medium comparing an industrial laboratory dispersion method vs traditional sonication. A factorial experimental design was performed, considering as variables: dispersion method, type of surfactant and use of a rheological modifier. The samples were prepared according to the full factorial DoE and properties such as electrical conductivity and pH were studied. Stability measurements were carried out over time and charge stability studies were performed using zeta potential measurements. The results shown the best combination of variables for the electrical conductivity was: dispersion method, sonication; dispersant, TX-100; rheological modifier, present. Although the results show that an improvement in CNTs dispersion is not achieved with the grinding and the use of industrial additives, the additive Disperbyk 2012 presented the highest value of electrical conductivity as a lonely compound, but the final electrical conductivity obtained when using it was not so high, it indicates that this additive must have specific conditions of activation, which implies that a further experimental work is required in order to get a suitable working window that allows a combination of variables with greater industrial application. © Published under licence by IOP Publishing Ltd