Aromatic Ouroboroi: Heterocycles Involving a Sigma-Donor-Acceptor Bond and 4n+2 Pi-Electrons

The aromaticity and dynamics of a set of recently proposed neutral 5- and 6-membered heterocycles that are closed by dative (donor–acceptor) or multi-center s bonds, and have resonance forms with a Hu¨ckel number of p-electrons, are examined. The donors and acceptors in the rings include N, O, and F, and B, Be, and Mg, respectively. The planar geometry of the rings, coupled with evidence from different measures of aromaticity, namely the NICSzz, and NICSpzz components of the conventional nucleus independent chemical shifts (NICS), and ring current strengths (RCS), indicate non-trivial degrees of aromaticity in certain cases, including the cyclic C3B2OH6 and C3BOH5 isomers, both with three bonds to the O site in the ring. The former is lower in energy by at least 17.6 kcal mol1 relative to linear alternatives obtained from molecular dynamics simulations in this work. Some of the other systems examined are best described as non-aromatic. Ring opening, closing, and isomerization are observed in molecular dynamics simulations for some of the systems studied. In a few cases, the ring indeed persists

Theoretical design of stable small aluminium-magnesium binary clusters

We explore in detail the potential energy surfaces of the AlxMgy (x, y = 1–4) systems as case studies to test the utility and limitations of simple rules based on electron counts and the phenomenological shell model (PSM) for bimetallic clusters. We find that it is feasible to design stable structures that are members of this set of small Al–Mg binary clusters, using simple electron count rules, including the classical 4n + 2 Hückel model, and the most recently proposed PSM. The thermodynamic stability of the title compounds has been evaluated using several different descriptors, including the fragmentation energies and the electronic structure of the systems. Three stable systems emerge from the analysis: the Al4Mg, Al2Mg2 and Al4Mg4 clusters. The relative stability of Al4Mg is explained by the stability of the Al42- subunit to which the Mg atom donates its electrons. Here the Mg2+ sits above the aromatic 10 π-electron Al42- planar ring. The Al2Mg2 and Al4Mg4 clusters present more complicated 3D structures, and their stabilities are rationalized as a consequence of their closed shell nature in the PSM, with 10 and 20 itinerant electrons, respectively

Stabilizing carbon-lithium stars

We have explored in silico the potential energy surfaces of the C5Linn-6 (n = 5, 6, and 7) clusters using the Gradient Embedded Genetic Algorithm (GEGA) and other computational strategies. The most stable forms of C5Li5-- and C5Li6 are two carbon chains linked by two lithium atoms in a persistent seven membered ring capped by two Li atoms. The other Li atoms are arrayed on the edge of the seven membered ring. In contrast, the global minimum structure for C5Li7+ is a bicapped star of D5h symmetry. The molecular orbital analysis and computed magnetic field data suggest that electron delocalization, as well as the saturation of the apical positions of the five-membered carbon ring with lithium atoms in C5Li7+ plays a key role in the stabilization of the carbon-lithium star. In fact, the planar star sub-structure for the carbon ring are unstable without the apical caps. This is also what has been found for the Si analogues. The split of the Bindz in its σ- and π-contribution indicates that C5Li7+ is a p-aromatic and σ-nonaromatic system

Estudio teórico de la evolución estructural y energética de los sistemas Si5-n(AlnHn)2- (n=0-5)

53 p.La nanotecnología comprende el estudio, diseño y creación de nuevos materiales a través del control de la materia a nivel de nanoescala. Un ejemplo de estos avances tecnológicos, es la elaboración de biochips para detectar proteínas, una metodología basada en inmovilizar y orientar proteínas sobre la superficie de zagregados atómicos preparados por medios físicos.Los clústeres atómicos se definen como cúmulos o agregados de átomos de tamaño intermedio entre el nivel molecular y el bulk de un sólido. Comprendiendo la estabilidad y enlace químico de estos sistemas, es posible en un futuro predecir y comprender de manera más adecuada los sitios de unión de algunas proteínas sobre estos agregados. La naturaleza química y física de los agregados atómicos puede ser descrita mediante el uso de métodos de la mecánica cuántica.Dentro del estudio químico y físico de los agregados atómicos, el estudio de la isovalencia es un área abierta y necesaria para comprender la estabilidad de estos sistemas. Un ejemplo de estos estudios, es la relación que existe entre los compuestos NaSi5 - y Si5 2- con B5H5 2- y NaB5H5 -, respectivamente, donde cada átomo de Si se comporta de la misma manera que una unidad BH. En esta investigación, se explora la isovalencia y la química que existe en clústeres atómicos conformados por átomos pertenecientes al grupo 13 y 14 de la tabla periódica. Concretamente, se estudia la evolución estructural del enlace químico en la transformación del clúster Si5 2- al Al5H5 2- , al intercambiar sucesivamentex un átomo de silicio por una unidad AlH. Utilizando el análisis de los Orbitales Naturales de Enlace (NBO), en conjunto con el análisis de enlace químico basado en el particionamiento de la densidad electrónica (AdNDP), la Función de Localización Electrónica (ELF) y los Orbitales Moleculares, se obtiene que la estructura tridimensional de los sistemas al realizar la transformación se conserva, y que los patrones de enlace, son acordes con los de los sistemas Si5-n(BnHn)2-(n = 0-5). 7 5. /ABSTRACT: Rol at the nanoscale level. An example of these technological advances is the development of biochips for detecting proteins, a methodology based on immobilize and guide proteins on the surface of atomic aggregates prepared by physical means. Atomic clusters are defined as aggregates of atoms of intermediate size between the molecular level and the bulk of a solid. Understanding the stability and chemical bonding of these systems will enable in the future, the prediction and proper understanding of the binding sites of some proteins on these aggregates. The chemical and physical nature of atomic clusters can be described using quantum mechanics methods. Within the chemical and physical study of atomic clusters, the study of isovalence is an open area and necessary to understand the stability of these systems. An example of these studies is the existing relationship between the NaSi5 - and Si5 2- with the NaB5H5 - and B5H5 2- compounds, respectively, where each Si atom behaves the same way as a unit of B-H. In this research, we explore the isovalence and the existing chemistry in atomic clusters built by atoms from the 13 and 14 group of the periodic table, especially compounds of B- and C as well as Al- and Si, which have the same number of valence electrons. Specifically, we study the structural evolution of the chemical bond in the transformation from the Si5 2- to the Al5H5 2- cluster by exchanging a silicon atom by an Al-H unit. Analysis using Natural Bond Orbital (NBO), chemical bond based on the partitioning of the electron density (AdNDP), the Electronics Location Function (ELF) and the Molecular Orbitals, indicate that the three-dimensional structure of the systems when performed the transformation is preserved, and that the bond patterns are consistent with the systems Si5-n (BnHn)2- (n = 0-5)

Stop rotating! One substitution halts the B19- motor

The B19- anion and other boron species have been dubbed ‘Wankel motors’ for the almost barrierless rotation of inner and outer concentric rings relative to each other in these compounds. A single substitution in B19- is shown to shut down the well-established fluxionality in the anion. A carbon atom substituted in the structure to give a neutral CB18 species is shown computationally to enforce bond localization

Quercetin Affects Erythropoiesis and Heart Mitochondrial Function in Mice

Copyright © 2015 Lina M. Ruiz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Quercetin, a dietary flavonoid used as a food supplement, showed powerful antioxidant effects in different cellular models. However, recent in vitro and in vivo studies in mammals have suggested a prooxidant effect of quercetin and described an interaction with mitochondria causing an increase in O2 (∙-) production, a decrease in ATP levels, and impairment of respiratory chain in liver tissue. Therefore, because of its dual actions, we studied the effect of quercetin in vivo to analyze heart mitochondrial function and erythropoiesis. Mice were injected with 50 mg/kg of quercetin for 15 days. Treatment with quercetin decreased body weight, serum insulin, and ceruloplasmin levels as compared with untreated mice. Along with an impaired antioxidant capacity in plasma, quercetin-treated mice showed a significant delay on erythropoiesis progression. Heart mitochondrial function was also impaired displaying more protein oxidation and less activity for IV, respectively, than no-treated mice. In addition, a significant reduction in the protein expression levels of Mitofusin 2 and Voltage-Dependent Anion Carrier was observed. All these results suggest that quercetin affects erythropoiesis and mitochondrial function and then its potential use as a dietary supplement should be reexamined.Peer reviewe

Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins

Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π-conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine-type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins.M.A. and I.C.R. wish to acknowledge the VUB for a Strategic Research Program awarded to ALGC. The resources and services used in this work were provided by the Flemish Supercomputer Center (VSC), funded by the Research Foundation - Flanders (FWO), and the Flemish Government. I.C.R. acknowledges co-funding from the European Union′s Horizon 2020 research and innovation Maria Skłodowska-Curie Actions, under grant agreement number 945380. It has been also supported by grants from the Spanish government MICINN (PGC2018-098212-B-C21, PID2019-104772GB, PID2019-105488GB-I00, and PCI2019-103657), Diputación Foral de Gipuzkoa (2019-CIEN-000092-01), Gobierno Vasco (IT1346-19, IT1254-19, and PIBA19-0004), and the DIPC (DIPC_INV_003132). Open Access funding provided by University of Basque Country

In Silico Study of Coumarins and Quinolines Derivatives as Potent Inhibitors of SARS-CoV-2 Main Protease

The pandemic that started in Wuhan (China) in 2019 has caused a large number of deaths, and infected people around the world due to the absence of effective therapy against coronavirus 2 of the severe acute respiratory syndrome (SARS-CoV-2). Viral maturation requires the activity of the main viral protease (Mpro), so its inhibition stops the progress of the disease. To evaluate possible inhibitors, a computational model of the SARS-CoV-2 enzyme Mpro was constructed in complex with 26 synthetic ligands derived from coumarins and quinolines. Analysis of simulations of molecular dynamics and molecular docking of the models show a high affinity for the enzyme (∆Ebinding between −5.1 and 7.1 kcal mol−1). The six compounds with the highest affinity show Kd between 6.26 × 10–6 and 17.2 × 10–6, with binding affinity between −20 and −25 kcal mol−1, with ligand efficiency less than 0.3 associated with possible inhibitory candidates. In addition to the high affinity of these compounds for SARS-CoV-2 Mpro, low toxicity is expected considering the Lipinski, Veber and Pfizer rules. Therefore, this novel study provides candidate inhibitors that would allow experimental studies which can lead to the development of new treatments for SARS-CoV-2The authors express their thanks to Grant RC-FP44842-212-2018 Colombia científica and Universidad de Ibagué and for the financial support of the ANID/PIA/ACT192144. OG-B Thank funding from the Ministry of Science, Technology and Innovation, the Ministry of Education, the Ministry of Industry, Commerce and Tourism, and ICETEX, Programme Ecosistema Científico-Colombia Científica, from the Francisco José de Caldas Fund, Grant RC-FP44842–212-2018S

Analysis of Local and Global Aromaticity in Si3C5 and Si4C8 Clusters. Aromatic Species Containing Planar Tetracoordinate Carbon

The minimum energy structures of the Si3C5 and Si4C8 clusters are planar and contain planar tetracoordinate carbons (ptCs). These species have been classified, qualitatively, as global (π) and local (σ) aromatics according to the adaptive natural density partitioning (AdNDP) method, which is an orbital localization method. This work evaluates these species’ aromaticity, focusing on confirming and quantifying their global and local aromatic character. For this purpose, we use an orbital localization method based on the partitioning of the molecular space according to the topology of the electronic localization function (LOC-ELF). In addition, the magnetically induced current density is analyzed. The LOC-ELF-based analysis coincides with the AdNDP study (double aromaticity, global, and local). Moreover, the current density analysis detects global and local ring currents. The strength of the global and local current circuit is significant, involving 4n + 2 π- and σ-electrons, respectively. The latter implicates the Si-ptC-Si fragment, which would be related to the 3c-2e σ-bond detected by the orbital localization methods in this fragment.Fil: Torres Vega, Juan J.. Universidad Nacional Mayor de San Marcos; PerúFil: Alcoba, Diego Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Oña, Ofelia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Vasquez Espinal, A.. Universidad Andrés Bello; ChileFil: Baez Grez, R.. Universidad Andrés Bello; ChileFil: Lain, Luis. Universidad del País Vasco; EspañaFil: Torre, Alicia. Universidad del País Vasco; EspañaFil: García, Victor Raúl. Universidad Nacional Mayor de San Marcos; Perú. Universidad Andrés Bello; ChileFil: Tiznado, William. Universidad Andrés Bello; Chil

Estudios de reactividad química en cicloadiciones 1,3 dipolar mediante herramientas de mecánica cuántica

68 p.Los derivados de pirazol son compuestos químicos muy importantes en la industria farmacéutica debido a que muestran un amplio espectro de actividades biológicas, además de ser utilizados como agentes reductores del colesterol, antiinflamatorios, anticancerígenos, antidepresivos y antipsicóticos. Una de las principales formas de obtener experimentalmente pirazoles funcionalizados ha sido mediante reacciones de cicloadición 1,3 dipolar (1,3-DC). Las reacciones de cicloadición 1,3 dipolar son reacciones químicas entre un dipolo y un dipolarófilo (esquema 1). Existe la necesidad de controlar la regioselectividad de estas reacciones debido a la diversidad de productos que se pueden obtener al variar los sustituyentes R unidos a estos sistemas. Figura 1. Posible mecanismo de reacción para una cicloadición 1,3 dipolar. Imagen extraída de (Rolf, 1963).Estudios teóricos recientes, utilizando herramientas de mecánica cuántica han mostrado que algunos índices de reactividad local, derivados de la Teoría de los Funcionales de la Densidad (DFT) como son la electrofilia y el análisis de la función de Fukui, han permitido la predicción y postulación de algunos modelos para explicar la competitividad regioselectiva en cicloadiciones 1,3 dipolar, dando explicación a las observaciones experimentales para este tipo de reacciones. Sin embargo, aún es poca la información y escasos los resultados acerca de los perfiles de reacción para este tipo de procesos. En esta investigación se desea evaluar algunos índices de reactividad teóricos derivados de la DFT conceptual, así como analizar los perfiles de reacción sobre reacciones de ciclación 1,3 dipolar./ABSTRACT:Pyrazole derivatives are chemical compounds very important in the pharmaceutical industry because they exhibit a broad spectrum of biological activities. In addition, they are used as cholesterol-lowering agents, anti-inflammatory, anticarcinogenic, antidepressants, and antipsychotics. One of the main ways to obtain experimentally functionalized pyrazoles has been through 1,3 dipolar cycloaddition reactions (1,3-DC). 1,3 dipolar cycloaddition are chemical reactions between a dipole and a dipolarophile (Scheme 1). There is a need to control the regioselectivity of these reactions due to the variety of products that can be obtained by varying the R substituents attached to these systems.Scheme 1. Possible reaction mechanism for a 1,3 dipolar cycloaddition. Image from (Rolf, 1963).Recent theoretical studies, using quantum mechanics tools have shown that some local reactivity indices derived from Density Functional Theory (DFT) such as the electrophilicity and analysis of the Fukui function, allow the prediction and application of some models to explain regioselective competitiveness in 1,3 dipolar cycloaddition, yielding explanations to the experimental observations for this type of reactions. However, there is little information and few results about the reaction profiles for these reactions. In this research we want to evaluate some theoretical reactivity indices derived from conceptual DFT, and analyze the reaction profiles on 1,3 dipolar cyclization reactions