Cercant evidències de noves interaccions entre àtom

La natura està constituïda per àtoms, que acostumen a formar molècules més o menys complexes. Els enllaços i interaccions mantenen els àtoms units. Aquest estudi s'ha centrat en uns enllaços molt poc coneguts, els enllaços o interaccions agòstiques.La naturaleza está constituida por átomos que acostumbran a formar moléculas más o menos complejas. Los enlaces e interacciones mantienen a los átomos unidos. Este estudio se ha centrado en uno enlaces muy poco conocidos, los enlaces o interacciones agósticas. Son muy particulares, ya que en lugar de unir dos átomos, unen un átomo y un enlace

Density Functional Theory-Inspired Design of Ir/P,S-Catalysts for Asymmetric Hydrogenation of Olefins

In silico-based optimization of Ir/P,S-catalysts for the asymmetric hydrogenation of unfunctionalized olefins using (E)-1-(but-2-en-2-yl)-4-methoxybenzene as a benchmark olefin has been carried out. DFT calculations revealed that the thioether group has a major role in directing the olefin coordination. This, together with the configuration of the biphenyl phosphite group, has an impact in maximizing the energy gap between the most stable transition states leading to opposite enantiomers. As a result, the optimized catalyst proved to be efficient in the hydrogenation of a range of alkenes with the same substitution pattern and olefin geometry as the benchmark olefin, regardless of the presence of functional groups with different coordination abilities (ee values up to 97%). Appealingly, further modifications at the thioether groups and at the biaryl phosphite moiety allowed the highly enantioselective hydrogenation of olefins with different substitution patterns (e.g., α,β-unsaturated lactones and lactams, 1,1′-disubstituted enol phosphinates, and cyclic β-enamides; ee values up to >99%).We gratefully acknowledge financial support from the Spanish Ministry of Science and Innovation (PID2019-104904GB-I00, PGC2018-100780-B-I00, and PGC2018-096616-B-I00), European Regional Development Fund (AEI/FEDER, UE), the Catalan Government (2017SGR1472), and the University of Alicante (VOGROB-316FI). M.B. also thanks the URV for generous support

Mechanistic study on the asymmetric synthesis of the Wieland-Miescher ketone analogs

The organocatalyzed synthesis of the Wieland‐Miescher ketone (WMK) via N‐sulfonyl‐binamprolinamide catalysis was investigated using experimental and computational tools. A mechanistic proposal is presented describing the origin of the high enantioselectivity, which rivals that of aldolases. The computational study reveals that the role of the prolinamide catalyst is to lower the reaction barrier and determine the stereoselectivity of the product achieved, while the role of the carboxylic acid is to facilitate proton transfer steps. The effect of the acid co‐catalyst was confirmed by experiments. The role of the structure of the BINAM backbone and the effect of the sulfonamide group are uncovered experimentally and computationally. Calculations show that a rigid highly defined catalytic pocket due to covalent and steric interactions induces conformational changes in the triketone substrate to maximize interactions

Virtual simulation of the biomechanics of the abdominal wall with different stoma locations

An ostomy is a surgical procedure by which an artificial opening in the abdominal wall, known as a stoma, is created. We assess the effects of stoma location on the abdominal wall mechanics. We perform three-dimensional finite element simulations on an anatomy model which was generated on the basis of medical images. Our simulation methodology is entirely based on open source software. We consider seventeen different locations for the stoma incision (trephine) and we simulate the mechanical response of the abdominal wall when an intraabdominal pressure as high as 20 kPa is applied. We focus on factors related to the risk of parastomal hernia development such as the deformation experienced by the abdominal wall, the stress levels supported by its tissues and the corresponding level of trephine enlargement. No significant dependence was found between stoma location and the levels of abdominal wall deformations or stress supported by tissues, except for the case with a stoma located on the linea alba. Trephine perimeter and area respectively increased by as much as 44% and 85%. The level of trephine deformation depends on stoma location with considerably higher trephine enlargements found in stomas laterally located with respect to the rectus abdominis muscle.Peer ReviewedPostprint (published version

Case report of a gallbladder agenesis, a diagnostic challenge

Agenesis of the gallbladder is an underdiagnosed entity. It can be an asymptomatic pathology, usually diagnosed incidentally as a finding on imaging techniques or in necropsies. There are symptomatic cases presenting as biliary colic too, attributed to cholecystitis or cholangitis, leading to exploratory surgeries. We present a 14-year-old boy admitted to the outpatient Pediatric Gastroenterology Department with a history of daily abdominal pain for the past 2 months. Blood and fecal tests were normal. Coeliac disease, inflammatory intestinal diseases and Helicobacter pylori infection were ruled out. An abdominal US was informed of a hypodistensed gallbladder with no other findings. A CT scan was performed, which reported of an absent gallbladder. Upon these findings, a Magnetic Resonance Cholangiopancreatography (MRCP) was carried out, confirming the diagnosis of agenesis of the gallbladder. Its diagnosis still poses a challenge, as an absent gallbladder may not always be apparent by US, with the MRCP being the gold-standard test for examining the biliary tract. The prognosis is usually good, and the treatment of choice consists of antispasmodics when needed. There are few cases reported in literature, for this reason, our article discusses the most important aspects of agenesis of the gallbladder in order to suspect it, request the appropriate tests and saving unnecessary surgical interventions. Gallbladder agenesis is a rare entity that can lead to unnecessary diagnostic tests and interventions. The MRCP is the gold-standard test. Despite its benign nature, symptomatic treatment might be required in order to improve the patient's quality of life

P-Stereogenic Ir-MaxPHOX: A Step toward Privileged Catalysts for Asymmetric Hydrogenation of Nonchelating Olefins

The Ir-MaxPHOX-type catalysts demonstrated high catalytic performance in the hydrogenation of a wide range of nonchelating olefins with different geometries, substitution patterns, and degrees of functionalization. These air-stable and readily available catalysts have been successfully applied in the asymmetric hydrogenation of di-, tri-, and tetrasubstituted olefins (ee′s up to 99%). The combination of theoretical calculations and deuterium labeling experiments led to the uncovering of the factors responsible for the enantioselectivity observed in the reaction, allowing the rationalization of the most suitable substrates for these Ir-catalysts

Comportaments no clàssics d'enllaços [sigma] a l'esfera de coordinació de metalls de transcició

Consultable des del TDXTítol obtingut de la portada digitalitzadaVegeu mbbresum1de1.pd

Química de l'espín prohibit: la importància dels intermedis a capa oberta en l'activació d'enllaços C-H

Estudi realitzat a partir d’una estada a la School of Chemistry de la University of Bristol, Gran Bretanya, entre 2006 i 2008. La reacció d’activació del pre-catalitzador CH3-Fe(P(iPr)2CH2)3B-Ph, que es dóna en presència de H2 i P(CH3)3, és una reacció spin-prohibida ja que els reactius i els productes tenen diferents estat d’espín en el seu estat fonamental: el pre-catalitzador és quintet, mentre que el producte format després de l’eliminació de metà, PMe3(H3)-Fe[(P(iPr)2CH2)3B-Ph, és singlet. Un dels intermedis d’aquesta reacció és d’especial interès ja que catalitza la hidrogenació d’olefines. Intermedi que experimentalment s’ha proposat com a H-Fe[(P(iPr)2CH2)3B-Ph] o el Hx-Fe[(P(iPr)2CH2)3B-Ph]. Aquestes espècies han estat estudiades computacionalment, mitjançant la combinació de mètodes del funcional de la densitat calibrats mitjançant càlculs ab initio. Els resultats obtinguts mostren que les superfícies d’energia potencial singlet, triplet i quintet es creuen al llarg de les reaccions descrites. La reacció d’activació del pre-catalitzador és una reacció multi spin-prohibida (més d’un canvi d’espín), en la que el mecanisme preferit addiciona primer hidrogen i després la fosfina, el pas determinant de la velocitat és el creuament de la superfície d’energia potencial quintet a la triplet a la geometria del reactiu, que es produeix amb una barrera d’aproximadament 18 kcal/mol. La reacció d’hidrogenació d’olefines en canvi pot ser o no una reacció espín prohibida depenent de les condicions en que es dugui a terme. En cas de que la reacció es dugui a terme en un excés d’hidrogen, en el mecanisme principal l’espècie activa seria el (H2)H-Fe[(P(iPr)2CH2)3B-Ph] singlet en el seu estat fonamental que hidrogenaria l’olefina sense cap pas espín prohibit. Aquest mecanisme és el de barrera més baixa però s’espera que estigui més desafavorit entropicament. Si les condicions no són d’un important excés d’hidrogen, llavors l’espècie activa s’espera que sigui H-Fe[(P(iPr)2CH2)3B-Ph], la reacció llavors seria multi espín prohibida amb una barrera de unes 13 kcal/mol corresponents al creuament entre la superfície quintet i triplet a la geometria del H-Fe[(P(iPr)2CH2)3B-Ph]

Comportaments no clàssics d'enllaços (sigma) a l'esfera de coordinació de metalls de transició

Consultable des del TDXTítol obtingut de la portada digitalitzadaVegeu mbbresum1de1.pd