Pairing and unpairing electron densities in organic systems: Two-electron three center through space and through bonds interactions

Two-electron three-center bonding interactions in organic ions like methonium (CH + 5 ), ethonium (C2H + 7 ), and protonated alkanes n−C4H + 11 isomers (butonium cations) are described and characterized within the theoretical framework of the topological analysis of the electron density decomposition into its effectively paired and unpaired contributions. These interactions manifest in some of this type of systems as a concentration of unpaired electron cloud around the bond paths, in contrast to the well known paradigmatic boron hydrids in which it is not only concentrated close to the atomic nucleus and the bond paths but out of them and over the region defined by the involved atoms as a whole. This result permits to propose an attempt of classification for these interactions based in such manifestations. In the first type, it is called as interactions through bonds and in the second type as interactions through space type.Fil: Lobayan, Rosana Maria. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bochicchio, Roberto Carlos. 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; Argentin

Computational Strategy for Graphene: Insight from Odd Electrons Correlation

The correlation of odd electrons in graphene turns out to be significant so that the species should be attributed to correlated ones. This finding profoundly influences the computational strategy addressing it to multireference computational schemes. Owing to serious problems related to the schemes realization, a compromise can be suggested by using single-determinant approaches based on either Hartree-Fock or Density-Functional theory in the form of unrestricted open-shell presentation. Both computational schemes enable to fix the electron correlation, while only the Hartree-Fock theory suggests a set of quantities to be calculated that can quantitatively characterize the electron correlation and be used for a quantitative description of such graphene properties as magnetism, chemical reactivity, and mechanical response. The paper presents concepts and algorithms of the unrestricted Hartree-Fock theory applied for the consideration of magnetic properties of nanographenes, their chemical modification by the example of stepwise hydrogenation, as well as a possible governing the electron correlation by the carbon skeleton deformation.Comment: 17 pages, 11 figures, 3 table

Epidemiología de Nematodos Gastrointestinales y resistencia a los antiparasitarios en uso de la zona sur de la Provincia de Misiones

La gastroenteritis verminosa ha sido ampliamente estudiada en las principales zonas ganaderas de nuestro país, como base para el desarrollo de programas de control parasitario sustentables. Los estudios de prevalencia resultan esenciales para determinar la estacionalidad, así como la peligrosidaddel problema. Es así que se realizaron estudios de este tipo en la Pampa Húmeda (Steffan y col, 1982; Fiel y col, 1987; Entrocasso, 1988) y subhúmeda (Suárez y col, 1990; Alvarez, y col, 2000), así como en la región central (Rossanigo y col, 1988; Descarga, 1994) y en el NEA (Lombardero y col, 1976; Bonazzi y col, 1980; Ivancovicc y col 1981; Alvarez y Lombardero, 1989; Daffner y col, 1990; Cardona López y col, 1993). En norte de la Corrientes y el sur de Misiones, se carece de este tipo de estudios por lo que el presente proyecto presenta gran relevancia. Para el mismo se realizó un muestreo sistemático en terneros destetes de seis rodeos (10 terneros/rodeo) de cría sobre campo natural. Las variables medidas fueron: número de huevos por gramo de materia fecal (Hpg), y la proporción de los géneros parasitarios. En el conteo de huevos tubo una mediana de 65 Hpg, el 81% de las muestras presentó una mediana de 95 Hpg. Por productor muestreado las medianas variaron entre 10 Hpg y 290 Hpg. La mediana fue de 50 Hpg en otoño, 55 Hpg en invierno, 290 Hpg en primaveray 150 Hpg en verano. En el cultivo de invierno los géneros observados fueron: Trichostrongylus spp, con 30,83%; Oesophagostomum spp, con 29,83%, Cooperia spp con 23%, y Hemonchus spp con 16%. Trichostrongylus spp. Presentó la menor variación entre productores. En una muestra apareció un huevo de Trichuris spp. y en otra aparecieron 90 huevos de Toxocara spp. Trichostrongylus spp y Oesophagostomum spp variaron entre invierno y primavera, aumentando el primero y disminuyendo el segundo. Cooperia spp y Haemonchus spp no mostraron diferencias entre invierno y primavera

Donor-acceptor interactions as descriptors of the free radical scavenging ability of flavans and catechin

Interest in food phenolics has increased in recent years largely due to their antioxidant capacity, free radical scavenging, and potential health benefits. In literature two main reaction mechanisms have been proposed for their role as free radical (FR) scavengers, i.e., the mechanism of a hydrogen atom transfer (HAT) governed by the O H bond dissociation enthalpy (BDE), and the mechanism of single electron transfer (SET) governed by an electron transfer process, the ionization potential (IP) playing an important role. Thirty nonplanar structures were analyzed. The study of (+)-catechin (CTQ) and (4α → 6″, 2α → O → 1″)-phenylflavans with a R′ = H, R = OH; R′ = OH, R = H, and R′ = OH, R = OH substitution is performed herein. Catechol, phenol, and resorcinol are also included as references. Results obtained with B3LYP hybrid functional with 6-311++G(d,p) and 6-31G(d,p) basis set are analyzed. Two new indicators arising from electron delocalizations are presented herein, thus showing that there is a different set of donor-acceptor interactions to explain FR scavenging mechanisms.Fil: Bentz, Erika Natalia. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; ArgentinaFil: Pomilio, Alicia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Bioquímica y Medicina Molecular. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Bioquímica y Medicina Molecular; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Hospital de Clínicas General San Martín; ArgentinaFil: Lobayan, Rosana Maria. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; Argentin

Theoretical studies and vibrational spectra of 1H -indole-3-acetic acid: Exploratory conformational analysis of dimeric species

Theoretical studies on 1H-indole-3-acetic acid (IAA) were performed to investigate the conformational properties of dimeric species and vibrational spectra. Experimental infrared spectra at 100 K and 297 K and Raman spectrum at 297 K were analyzed and compared against calculations performed at B3LYP/6-31G** level. A exploratory study of the conformational space of dimeric species was performed. Our analysis showed that dimeric forms predicted theoretically contribute distinctively to the assignments of experimental results. These structures are defined by the orientation of the acetyl moieties with respect to the plane of indole ring. The dimers are formed by two symmetrical IAA monomers (one of them with the acetyl moiety upward oriented, Re-face, and the other isomer having the acetyl moiety downward oriented, Si-face) in tail-to-tail way. The X-ray geometry and FTIR vibrational frequencies were compared with the results of DFT calculations. A conformational equilibrium involving the non-equivalent IAA dimers: CCT-CCT, A+A+T-A-A-T, A+A-T-A-A+T, and A+CT-A-CT was found. The relation of the conformational properties of the IAA molecule with the features of the vibrational spectra was described in detail. The band assignments were discussed as related to the conformations properties. Our analysis shows the significance of the theoretical study of the conformational space of the monomeric molecule in the rationalization of experimental results.Centro de Química InorgánicaFacultad de Ingenierí

Structural and electronic properties of Z isomers of (4α→6´´,2α→O→1´´)-phenylflavans substituted with R=H, OH and OCH₃ calculated in aqueous solution with PCM solvation model

In the search for new antioxidants, flavan structures called our attention, as substructures of many important natural compounds, including catechins (flavan-3-ols), simple and dimeric proanthocyanidins, and condensed tannins. In this work the conformational space of the Z-isomers of (4α→6´´, 2α→O→1´´)-phenylflavans substituted with R = H, OH and OCH₃ was scanned in aqueous solution, simulating the solvent by the polarizable continuum model (PCM). Geometry optimizations were performed at B3LYP/6-31 G** level. Electronic distributions were analyzed at a better calculation level, thus improving the basis set (6-311++G**). A topological study based on Bader´s theory (atoms in molecules) and natural bond orbital (NBO) framework was performed. Furthermore, molecular electrostatic potential maps (MEPs) were obtained and thoroughly analyzed. The stereochemistry was discussed, and the effect of the solvent was addressed. Moreover, intrinsic properties were identified, focusing on factors that may be related to their antioxidant properties. Hyperconjugative and inductive effects were described. The coordinated NBO/AIM analysis allowed us to rationalize the changes of MEPs in a polar solvent. To investigate the molecular and structural properties of these compounds in biological media, the polarizabilities and dipolar moments were predicted which were further used to enlighten stability and reactivity properties. All conformers were taken into account. Relevant stereoelectronic aspects were described for understanding the stabilization and antioxidant function of these structures.Centro de Química Inorgánic

Conformational and stereoelectronic investigation of tryptamine : An AIM/NBO study

Due to the free radical scavenger properties of Tryptamine (TRA), as well as of others indole derivatives, it is in our interest to explore deeply the stereoelectronic aspects that would be relevant in their stabilization and antioxidant activity. In this work the conformational space of TRA was scanned using molecular dynamics complemented with functional density calculations at B3LYP/6-31 + G** level. Twenty one conformers of lowest energy were obtained, their electronic distributions were analyzed at a higher calculation level, thus improving the basis set (B3LYP/6-311++G**). A topological study based on Bader’s theory (AIM: atoms in molecules) and natural bond orbital (NBO) framework was performed. The study was enriched by a deep analysis of maps of molecular electrostatic potential (MEP) through a coordinated NBO/AIM analysis. The conformational preferences were explained by hyperconjugative interactions, which were revealed by NBO data. Because radical scavenging by indolic compounds is strongly modulated by their functional residues our study was related to similar analysis done previously on Indole and 1H-indole-3-acetic acid (IAA). Therefore, the conformational space of TRA was studied from a new perspective focusing on a deep analysis of the geometric and electronic properties of TRA conformers. The changes of the electronic distribution introduced by the substituent and the conformational flexibility of the side chain were addressed. The results reported contribute to the understanding of the structure, stability and reactivity of TRA and others indole derivatives.Centro de Química Inorgánic

Conformational and electronic (AIM/NBO) study of unsubstituted A-type dimeric proanthocyanidin

The conformational space of the unsubstituted Atype dimeric proanthocyanidin was scanned using molecular dynamics at a semiempirical level, and complemented with functional density calculations. The lowest energy conformers were obtained. Electronic distributions were analysed at a higher calculation level, thus improving the basis set. A topological study based on Bader’s theory (AIM: atoms in molecules) and natural bond orbital (NBO) framework was performed. Furthermore, molecular electrostatic potential maps (MEPs) were obtained and analysed. NMR chemical shifts were calculated at ab initio level and further compared with previous experimental values; coupling constants were also calculated. The stereochemistry of the molecule is thoroughly discussed, revealing the key role that hyperconjugative interactions play in defining experimental trends. These results show the versatility of geminal spin–spin coupling 2 J(C-1′,O) as a probe for stereochemical studies of proanthocyanidins.Fil: Lobayan, Rosana Maria. Universidad de la Cuenca del Plata; ArgentinaFil: Jubert, Alicia Haydee. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Vitale, Martín G.. 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: Pomilio, Alicia Beatriz. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Programa de Radicales Libres; Argentin

Study of the structural and electronic properties Valproic Acid and new derivatives used as anticonvulsant agents

The conformational and electronic characteristics of the polar O 9=C8-X10 moiety in the anticonvulsant valproic acid (Vpa) drug and some of their amides and ester derivatives are analyzed at the B3LYP level using the 6-31+G(d,p) and 6-311++G(d,p) 6d,10f basis sets. Exploring the delocalization of the electron density of the O9=C 8-X10 moiety by means of ELF, NBO, and AIM calculations, we found that the bending away from coplanarity of the atoms in O 9=C8-X10 is accompanied by a three-dimensional arrangement of donor and acceptor proton units closing nearly planar pseudorings of four, five, and six members arising from stabilizing interactions around the O9=C8-X10 backbone. From the structure-property relationship analysis, we explain the origin of the change in the structural parameters and atomic charges in the polar moiety.Fil: Comelli, Nieves Carolina. 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: Lobayan, Rosana Maria. Universidad de la Cuenca del Plata. Facultad de Ingeniería. Departamento de Ciencias Basicas; ArgentinaFil: Castro, Eduardo Alberto. 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: Jubert, Alicia Haydee. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentin

Evaluación de la gastroenteritis verminosa de los rumiantes en los sistemas silvopastoriles

Dentro de las enfermedades parasitarias que afectan a los bovinos en pastoreo, la gastroenteritis verminosa constituye un grave problema a nivel mundial. Es ocasionada por diferentes tipos de parásitos nematodos que afectan el cuajar e intestinos delgado y grueso, provocando importantes pérdidas económicas en la producción de carne, leche y, ocasionalmente, también la muerte en los animales muy afectados. En las principales zonas forestales del norte de Argentina, ya desde fines de la década de 1990, se está incorporando la actividad ganadera al monte, implantado como alternativa al pastoreo tradicional (también denominado a cielo abierto —CA—). Estos sistemas se denominan sistemas silvopastoriles (SSP), donde se reúnen en un mismo manejo a dos actividades diferentes: ganadería y forestal. Se caracterizan por favorecer el desarrollo de escarabajos coprófagos que participan activamente en los procesos de descomposición de la materia fecal con la consiguiente disminución del número de larvas infectivas de nematodos gastrointestinales (NGI). Este beneficio agroecológico logra una mayor sustentabilidad ambiental y podría contribuir al manejo de los parásitos. Diversos estudios locales e internacionales informaron una menor pérdida en la producción en animales parasitados que pastorean en SSP con respecto al pastoreo a CA. El objetivo de este trabajo fue describir la dinámica poblacional de los NGI de los bovinos en ambos sistemas productivos en la región noreste de la provincia de Corrientes (Argentina), y comprobar si existen diferencias productivas entre ambos. Para comprobar la hipótesis de investigación, en cada sistema se midieron y compararon mensualmente variables parasitológicas (recuento de huevos por gramo de materia fecal —HPG— y porcentaje de géneros parasitarios —GP—) y productivas (peso corporal —PC—). El período de estudio abarcó los años 2017 y 2018, durante los que se utilizaron diseños de investigación observacionales y estudios experimentales. En referencia al HPG, al comienzo del primer año de estudio se pudieron observar diferencias estadísticamente significativas (p<0,05) a favor del SSP en 4 de los 5 meses evaluados, mientras que en los siguientes 6 meses no se observaron diferencias significativas en ambos sistemas productivos. En el estudio experimental se encontraron diferencias significativas (p<0,05) a favor del SSP en solo 1 de las 6 observaciones efectuadas. En el segundo año de estudio, se observaron diferencias significativas (p<0,05) en 3 de las 6 observaciones analizadas, mientras que en el estudio experimental no se observaron diferencias entre ambos sistemas. En cuanto al peso corporal, las diferencias a favor del SSP recién se evidenciaron al final del segundo año. En referencia a los géneros de parásitos predominantes, en ambos sistemas se observó un marcado predominio del género Haemonchus spp., seguido por Cooperia spp., sin diferencias entre ambos sistemas.A modo de conclusión, se puede afirmar que si bien hubo algunas observaciones que demostraron diferencias estadísticas de la variable HPG entre ambos sistemas, estas no fueron biológicamente relevantes como factores de contaminación e infectividad de las pasturas. La variable PC evidenció diferencias a favor del SSP, probablemente debidas al mejor bienestar de los animales bajo la cubierta arbórea. Los porcentuales de géneros parasitarios hallados coinciden con lo reportado en estudios previos en sistemas pastoriles tradicionales. Se sugiere continuar con nuevas investigaciones tendientes a estudiar la sobrevivencia de las larvas infectivas en los SSP, considerado como un factor importante para el mantenimiento de la enfermedad en el sistema productiv