1,721,117 research outputs found
Insights on some controversial issues of the catalytic mechanism of [NiFe] hydrogenases
No full textControversial issues of the catalytic mechanism of NiFe hydrogenases are investigated through high level DFT calculations on a model cluster
A mechanistic relativistic DFT study of alkynes cyclotrimerization catalyzed by Rh(I) half-sandwich complexes
No full textThe mechanism of alkyne cyclotrimerization catalyzed by RhCp and RhInd fragments is investigated through high level relativistic DFT calculations
A DFT investigation of the structural and electronic properties ofCo(I) and Rh(I) half-sandwich complexes with heteroaromatic Pi ligands
No full textCo(I) and Rh(I) half-sandwich complexes of the heteroaromatic 1,2-azaborolyl and 3a,7a-azaborindenyl anions with the
ancillary ligand COD (1,5-cycloctadiene) are designed by using accurate state-of-the-art Density Functional Theory (DFT)
calculations. Their structural and electronic properties are compared to those of the analogous compounds containing the
classic hydrocarbon isoelectronic ligands, i.e. cyclopentadienyl and indenyl anions. A comparison is made between the
catalytic ability of (η5-C5H5)-Co and (1,2-azaborolyl)-Co fragments toward alkyne [2+2+2] cyclizations, a class of reactions
of paramount importance in industrial and pharmaceutical research for the synthesis of substituted benzenes, polycyclic and
heterocyclic compounds, by theoretically addressing the fundamental mechanistic steps
Ring slippage and catalytic activity of RhCp and RhInd fragments
No full textIndenyl effect in acetylene cyclotrimeriazions is investigated through accurate DFT calculations
200 years of selenium: aspects of the chemistry and biochemistry of the moon element disclosed in silico
No full textOxidative stress is a condition in which cell defense mechanisms cannot cope with oxidant processes. It is associated to an unbalanced concentration of chemical compounds in the cell, defined as ROS (reactive oxygen species) and RNS (reactive nitrogen species), which can react with important cell components and damage DNA, proteins and lipids, leading to severe pathologies including cancer. Aerobic organisms possess powerful anti-oxidant systems, among which an important class of enzymes, i.e. glutathione peroxidases (GPXs). Their activity relies on the REDOX chemistry of selenium. It is no coincidence that the importance of this oligoelement is claimed by many nutritionists! Yet, exactly 200 years after the discovery of selenium by the Swedish chemist Berzelius, many aspects of its chemistry and its biological role are not fully understood. Given that a complex machinery is required to insert Se in a protein in the form of selenocysteine, the 21st amino acid, it is challenging to explain apparently contradictory evidences in biology: in GPx, the presence of Se leads to an increased efficiency over sulfur; in other proteins, the presence of Se seems not justified. In addition, PRXs (peroxiredoxins, another important class of anti-oxidant enzymes) have a GPX like anti-oxidant mechanism and contain only sulfur.
Recently, much effort has been devoted to the design and synthesis of molecular GPXs mimics containing Se and even the heavier tellurium, which might be employed as drugs. The task of assessing the specific role of a different chalcogen (S, Se, Te) in these molecules and in the whole enzyme is intriguing and can be exquisitely tackled in silico. Selected results on the reactivity of model chalcogenides and of GPX active site and of its S and Te mutants are presented and discussed, disclosing some clear advantages of selenium in chemistry and biology
Interdisciplinarietà, co-progettazione ed altro ancora nel PLS: verso un’efficace sincronizzazione tra la scuola secondaria e l’università
No full textIl Piano Lauree Scientifiche (PLS) attraverso le sue quattro linee di azione principali (laboratori, autovalutazione-orientamento, formazione insegnanti, riduzione del tasso di abbandono fra il primo e il secondo anno di università) è potenzialmente uno strumento efficace per sincronizzare la scuola secondaria e l’università. Al fine di favorire nei giovani la maturazione di una scelta di un corso di laurea chimico consapevole, condizione essenziale per una carriera di studi di successo, è necessario uno sforzo congiunto dei docenti della scuola e dell’università, che può concretizzarsi proprio nella pluralità di attività del PLS Chimica.
L’esperienza di questi due anni a Padova, che si innesta in una tradizione consolidata del PLS nel nostro dipartimento e ha beneficiato negli ultimi anni di un efficiente coordinamento a livello nazionale, sta dimostrando che interdisciplinarietà e co-progettazione sono elementi coesivi alla base del successo dei nuovi progetti realizzati. Cosa può nascere dall’incontro di matematica, geologia e chimica? Cosa succede se 25 insegnanti di scuole diverse sono coinvolti nella realizzazione di un gioco da tavolo didattico? Insegnare chimica con passione! non è uno slogan, ma il nome del convegno autunnale degli insegnanti delle scuole secondarie del Veneto che presentano e condividono le loro esperienze didattiche in classe
Organochalcogen peroxidase mimetics as potential drugs: a long story of a promise still unfulfilled
No full textOrganochalcogen compounds have attracted the interest of a multitude of studies to design potential therapeutic agents mimicking the peroxidase activity of selenium-based glutathione peroxidases (GPx's). Starting from the pioneering ebselen, various compounds have been synthesized over the years, which may be traced in three major classes of molecules: cyclic selenenyl amides, diaryl diselenides, and aromatic or aliphatic monoselenides. These compounds share common features and determinants needed to exert an efficient GPx-like activity, such as polarizing groups in close proximity to selenium and steric effects. Nonetheless, the reactivity of selenium, and tellurium as well, poses serious problems for the predictability of the biological effects of these compounds in vivo when used as potential drugs. These molecules, indeed, interfere with thiols of redox-regulated proteins and enzymes, leading to unexpected biological effects. The various chemical aspects of the reaction mechanism of peroxidase mimetics are surveyed here, focusing on experimental evidence and quantum mechanics calculations of organochalcogen representatives of the various classes
Toward a Rational Design of Half-Sandwich Group 9 Catalysts for [2+2+2] Alkynes Cycloadditions
No full textFilling the gap between molecular structure and reactivity is a well-known challenging task in chemistry. The rational design of catalysts may greatly benefit of computational aid, provided state-of-the-art methodologies are employed. The case of metal catalyzed [2+2+2] cycloaddition of alkynes/alkynes-nitriles to benzene/pyridine is investigated in detail, due to the paramount importance of these reactions for the synthesis of cyclic and polycyclic organic compounds. Catalysts of general formula Cp’M are considered, where Cp’ is the cyclopentadienyl anion or the cyclopentadienyl moiety of larger polycyclic aromatic/heteroaromatic ligands, and M=Co, Rh, Ir. Energy profiles of the whole cycles with a number of intermediates ranging from 5 to 9 connected by the corresponding transition states are computed and the catalyst performance is evaluated based on its turnover frequency (TOF), by implementing the equations of the energy span model. TOF values are related to peculiar structural features of the Cp’M fragment, i.e. to the M-Cp’ bonding mode which results in slippage phenomena during the catalytic cycle. In fact, the metal is never coordinated to the five carbon atoms ring in highly symmetric fashion (eta5), but is slipped and the amount of this distortion changes during the various steps of the catalysis. This fluxionality is found to affect importantly the efficiency of the catalyst
Peroxidase Activity of Organic Selenides: Mechanistic Insights from Quantum Chemistry
Full text linkOrganoselenium compounds can reduce H2O2 and organic hydroperoxides mimicking the antioxidant activity of glutathione peroxidase (GPx). This catalytic process reduces the peroxides, which play a key role in oxidative stress, thus inhibiting their harmful action. Thus, it is not surprising that a lot of effort has been devoted toward the synthesis and design of numerous GPx mimics, which, nevertheless, show minor efficiency when compared to the native enzyme. In this context, quantum chemistry tools are an important support to rational drug design, because they allow to investigate in detail the structural and electronic properties of the organochalcogen compound with the aim of establishing links with its potential catalytic activity. In this review, we have collected the information from the available quantum chemistry studies about the reactivity of organic selenides with peroxides and thiols, delineating the analysis on monoselenides and ebselen, which will be critically discussed and gathered for a more complete overview of their GPx-like activity; few novel results will be presented to interpret very recent experimental mechanistic findings
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