Mechanism of Alkyl Migration in Diorganomagnesium 2,6-Bis(imino)pyridine Complexes: Formation of Grignard-Type Complexes with Square-Planar Mg(II) Centers

Dialkylmagnesium compounds [MgR2L2] (R = n-Bu, L = none or R = Bn, L = THF) react with 2,6-bis(imino)pyridines (BIP) to afford different types of Mg(II) alkyl complexes, depending on the nature of R. For R = n-Bu, thermally stable products resulting from selective alkyl transfer to the pyridine nitrogen (N1) atom are obtained. However, NMR studies showed that the reaction of [Mg(Bn)2THF2] with iPrBIP at −65 °C leads to a thermally unstable product arising from benzyl migration to position C2 in the pyridine ring. Above +5 °C, this compound rearranges, cleanly yielding a mixture of two isomeric complexes, in which the benzyl group has migrated to positions C3 or C4 of the central ring, respectively. Similar isomeric mixtures were obtained when [Mg(Bn)2THF2] was reacted with iPrBIP or MesBIP at room temperature. Such mixtures are thermally stable below 80 °C, but at this temperature, the 3-benzyl isomer converts into the thermodynamically favored 4-benzyl product, albeit not quantitatively. An alternate route was devised for the selective syntheses of the latter type of compounds. The X-ray diffraction structure of one of them provided an unusual example of a square-planar alkylmagnesium(II) center.Ministerio de Economía e Innovación CTQ2015-68978-

Oxygen-Induced Dimerization of Alkyl-Manganese(II) 2,6-Bisiminopyridine Complexes: Selective Synthesis of a New Ditopic NNN-Pincer Ligand

The outcome of the reaction of manganese(II) dialkyls with 2,6-bisiminopyridine (BIP) ligands is dramatically altered by the presence of very small amounts of oxygen (< 0.5 mol %), leading to binuclear species. These arise from the dimerization of the initial product, a Mn(II) 4-alkyl-2,6-bisiminodihydropyridinate alkyl complex. Cleavage of the binuclear Mn products with methanol affords the free dimeric bases, which can be regarded as a special type of ditopic NNN pincer ligand with an unusual tricyclic framework. The coordinative ability of the new ligands has been probed with the syntheses of Zn and Pd organometallic derivativesMinisterio de Economía e Innovación TQ2015- 68978-

Finding of Gordius austrinus De Villalobos, Zanca & Ibarra - Vidal, 2005 (Gordiida, Nematomorpha) in the stomach of Salmo trutta (Salmoniformes) in Patagonia

Field observations revealed, for the first time, cases of predation on Gordius austrinus by Salmo trutta in Risopatrón Lake, Aysén Region, Chile. Reinvestigation by SEM of the characteristics of the posterior end and of the cuticle of the specimens of horsehair worms collected inside the stomach of brown trout allow us to assign the specimens to the species Gordius austrinus. Also we could show that in some specimens the cuticle of mid body and terminal end presented structural alterations, due to the action of the digestive juices of the fish. This finding implies the extension of the distribution range of G. austrinus.Facultad de Ciencias Naturales y Muse

Finding of Gordius austrinus De Villalobos, Zanca & Ibarra - Vidal, 2005 (Gordiida, Nematomorpha) in the stomach of Salmo trutta (Salmoniformes) in Patagonia

Field observations revealed, for the first time, cases of predation on Gordius austrinus by Salmo trutta in Risopatrón Lake, Aysén Region, Chile. Reinvestigation by SEM of the characteristics of the posterior end and of the cuticle of the specimens of horsehair worms collected inside the stomach of brown trout allow us to assign the specimens to the species Gordius austrinus. Also we could show that in some specimens the cuticle of mid body and terminal end presented structural alterations, due to the action of the digestive juices of the fish. This finding implies the extension of the distribution range of G. austrinus.Facultad de Ciencias Naturales y Muse

Examen único nacional para acceder a las residencias médicas. Un instrumento poco conveniente para el sistema de salud del NEA

El Examen Único de Ingreso a las Residencias Médicas (EUM) fue desarrollado a propuesta de las provincias patagónicas, que buscaban alternativas para mejorar la cobertura y la gestión de ese examen que hasta el año 2010 se tomaba aisladamente en las diferentes provincias en esa región donde había una sola facultad de medicina, las plazas de residencia estaban muy distantes entre sí y los candidatos a las mismas eran mayoritariamente del centro del país. En ese contexto, se realizó en 2011 la primera experiencia regional de EUM con los propósitos de promover una mayor cobertura de vacantes, mejorar la accesibilidad a los concursos, y simplificar la gestión de la prueba

Epigenetic Disruption of the Piwi Pathway in Human Spermatogenic Disorders

Epigenetic changes are involved in a wide range of common human diseases. Although DNA methylation defects are known to be associated with male infertility in mice, their impact on human deficiency of sperm production has yet to be determined. We have assessed the global genomic DNA methylation profiles in human infertile male patients with spermatogenic disorders by using the Infinium Human Methylation27 BeadChip. Three populations were studied: conserved spermatogenesis, spermatogenic failure due to germ cell maturation defects, and Sertoli cell-only syndrome samples. A disease-associated DNA methylation profile, characterized by targeting members of the PIWI-associated RNA (piRNA) processing machinery, was obtained. Bisulfite genomic sequencing and pyrosequencing in a large cohort (n = 46) of samples validated the altered DNA methylation patterns observed in piRNA-processing genes. In particular, male infertility was associated with the promoter hypermethylation-associated silencing of PIWIL2 and TDRD1. The downstream effects mediated by the epigenetic inactivation of the PIWI pathway genes were a defective production of piRNAs and a hypomethylation of the LINE-1 repetitive sequence in the affected patients. Overall, our data suggest that DNA methylation, at least that affecting PIWIL2/TDRD1, has a role in the control of gene expression in spermatogenesis and its imbalance contributes to an unsuccessful germ cell development that might explain a group of male infertility disorders

Electronic structure of rhombus-shaped nanographenes: system size evolution from closed- to open-shell ground states

We theoretically study and characterize a set of rhombus-shaped nanographenes of increasing size, or n-rhombenes, where n = 2–6, displaying zigzag edges leading to an enhancement of the (poly)radicaloid nature and the appearance of intrinsic magnetism as a function of n. Due to that system-dependent radicaloid nature, we employ spin-flip methods able to capture the challenging physics of the problem, thus providing accurate energy differences between high- and low-spin solutions. The theoretical predictions agree with the experimentally available magnetic exchange coupling for the recently synthesized 5-rhombene, as well as with the size at which the transition from a closed-shell to an open-shell ground-state solution occurs. We also investigate if standard DFT methods are able to reproduce the trend disclosed by spin-flip methods and if the results are highly dependent on the functional choice and/or the intrinsic spin contamination.This work is supported by projects PID2019-106114GB-I00 (“Ministerio de Ciencia e Innovación”), AICO/2021/093 and PROMETEO/2021/017 (“Generalitat Valenciana”)

Correlation vs. exchange competition drive the singlet-triplet excited-state inversion in non-alternant hydrocarbons

In this work, we focus on the understanding of the driving force behind the S1 - T1 excited-state energy inversion (which would thus violate the Hund’s rule, situating the S1 state lower in energy than the T1 state) of two non-benzenoid non-alternant hydrocarbons, composed of odd-membered rings. The molecules considered here have identical chemical composition but different atomic configuration in space. The delicate interplay between structural and electronic factors that might induce the inversion and its energy extension, only by few meV, are systematically investigated here by state-of-the-art calculations. Qualitative and quantitative accurate predictions are obtained employing post-HF methods, thanks to the balanced and careful inclusion of electron correlation effects. The obtained results might guide and rationalize new searches of molecules violating Hund’s rule, concomitantly advising the importance of key contributions from the theoretical method of choice.The work in Alicante is supported by project PID2019-106114GB-I00 (“Ministerio de Ciencia e Innovación”). M.E.S.-S. acknowledges the funding by the United Kingdom Research and Innovation (U.K.R.I.) under the U.K. government’s Horizon Europe funding guarantee (grant number EP/X020908/1). Y.O. acknowledges the funding by the “Fonds de la Recherche Scientifique-FNRS” under Grant n. F.4534.21 (MIS-IMAGINE). G.R. acknowledges a grant from the “Fonds pour la formation a la Recherche dans l’Industrie et dans l’Agriculture” (F.R.I.A.) of the F.R.S.-F.N.R.S. Computational resources were also provided by the “Consortium des Équipements de Calcul Intensif” (C´ECI), funded by the “Fonds de la Recherche Scientifiques de Belgique” (F.R.S.-F.N.R.S.) under Grant No. 2.5020.11. D.C. acknowledges funding by projects PID2019-109555GB-I00 and RED2018-102815-T (“Ministerio de Ciencia e Innovación”) and from project No. PIBA19-0004 (“Eusko Jaularitza”)

Shot noise in magnetic tunneling structures with two-level quantum dots

We analyze shot noise in a magnetic tunnel junction with a two-level quantum dot attached to the magnetic electrodes. The considerations are limited to the case when some transport channels are suppressed at low temperatures. Coupling of the two dot's levels to the electrodes are assumed to be generally different and also spin dependent. To calculate the shot noise we apply the approach based on the full counting statistics. The approach is used to account for experimental data obtained in magnetic tunnel junctions with organic barriers. The experimentally observed Fano factors correspond to the super-Poissonian statistics, and also depend on relative orientation of the electrodes' magnetic moments. We have also calculated the corresponding spin shot noise, which is associated with fluctuations of spin current