1,721,145 research outputs found
Dataset of Combined Computational-Experimental Study of Ru(0)-Catalyzed Guerbet Reaction
No full textThe present dataset contains data collected in order to computationally disclose the reaction mechanism of the Guerbet reaction in the presence of a Ru(0)-NHC catalyst and NaEtO as co-catalyst. The dataset is composed by cartesian coordinates of optimized geometries of the stationary points characterized with the density functional theory (DFT) calculations
Theoretical Study of Mechanism and Stereoselectivity of Catalytic Kinugasa Reaction
No full textThe mechanism of the catalytic Kinugasa reaction is investigated by means of density functional theory calculations. Different possible mechanistic scenarios are presented using phenanthroline as a ligand, and it is shown that the most reasonable one in terms of energy barriers involves two copper ions. The reaction starts with the formation of a dicopper-acetylide that undergoes a stepwise cycloaddition with the nitrone, generating a five-membered ring intermediate. Protonation of the nitrogen of the metalated isoxazoline intermediate results in ring opening and the formation of a ketene intermediate. This then undergoes a copper-catalyzed cyclization by an intramolecular nucleophilic attack of the nitrogen on the ketene, affording a cyclic copper enolate. Catalyst release and tautomerization gives the final beta-lactamic product. A comprehensive study of the enantioselective reaction was also performed with a chiral bis(azaferrocene) ligand. In this case, two different reaction mechanisms, involving either the scenario with the two copper ions or a direct cycloaddition of the parent alkyne using one copper ion, were found to have quite similar barriers. Both mechanisms reproduced the experimental enantioselectivity, and the current calculations can therefore not distinguish between the two possibilities.</p
Catalytic Asymmetric Reactions of 4-Substituted Indoles with Nitroethene: A Direct Entry to Ergot Alkaloid Structures
Full text linkA domino Friedel-Crafts/nitro-Michael reaction between 4-substituted indoles and nitroethene is presented. The reaction is catalyzed by BINOL-derived phosphoric acid catalysts, and delivers the corresponding 3,4-ring-fused indoles with very good results in terms of yields and diastereo- and enantioselectivities. The tricyclic benzo[cd]indole products bear a nitro group at the right position to serve as precursors of ergot alkaloids, as demonstrated by the formal synthesis of 6,7-secoagroclavine from one of the adducts. DFT calculations suggest that the outcome of the reaction stems from the preferential evolution of a key nitronic acid intermediate through a nucleophilic addition pathway, rather than to the expected "quenching" through protonation
Combined computational-experimental study of Ru(0)-catalyzed Guerbet reaction
Full text linkThe homologation of bioethanol to higher alcohols by means of the Guerbet reaction is a promising way to obtain biofuels. Herein, we present an efficient ruthenium-catalyzed process and a detailed investigation of the reaction mechanism using a combined experimental-computational approach. Density functional theory calculations of the free energy profiles are corroborated by designed experiments. Microkinetic simulations are performed based on the calculated energies, providing good agreement with experimental observations of the time-evolving ethanol conversion and product distribution. Analysis of the kinetics network elucidates the key steps governing the conversion and selectivity of the Guerbet process, pointing out the unexpected role of the molecular hydrogen evolution step and suggesting strategies to design new catalysts for the Guerbet reaction
Challenges in Computational Enzymology
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Development of an Organoautocatalyzed Double σ‐Bond C(sp2)‐N Transamination Metathesis Reaction
Full text linkThe transamination reaction, which involves the conversion of one amine to another, traditionally relies on biological enzyme catalysts. Although chemists have recently developed a few transition metal‐catalyzed methods, mimicking these enzymes to interconvert amine groups in acyclic substrates via transamination metathesis of a single C(sp 2 )─N bond, transamination of cyclic tertiary amines has remained a challenge in synthetic chemistry. Here, we present the development of organoautocatalyzed transamination metathesis of two C(sp 2 )─N bonds in a cyclic substrate that allows for the challenging transformation to take place with up to 95% yield under exceptionally mild reaction conditions at room temperature without external catalysts and/or additives. The reaction mechanism has been studied in detail through time‐resolved 1 H‐NMR, 2D NMR, and computational methods. Remarkably, in situ‐formed pyrrolidinium salt acts as a hydrogen bond donor (HBD) organoautocatalyst in this multi‐step domino process. The new organoautocatalyzed methodology gives environmentally friendly, atom‐economical, straightforward, and rapid access to N ‐substituted 3,5‐dinitro‐1,4‐dihydropyridines (DNDHPs), thus offering facile entry to privileged bioactive compounds.Organoautocatalyzed transamination metathesis of cyclic tertiary amines is disclosed as a high‐yielding, scalable reaction that proceeds under mild, catalyst‐free conditions. It operates via a multi‐step domino reaction mechanism, where an in situ‐formed pyrrolidinium salt functions as a HBD organoautocatalyst. The reaction opens the door for the efficient synthesis of novel N‐substituted DNDHPs of interest in both life and materials sciences. imageDeutsche Forschungsgemeinschaft 10.13039/501100001659Volkswagen Foundation 10.13039/501100001663Swedish Research Council 10.13039/50110000435
Enantioselective organocatalytic hydrophosphination of ?,?-unsaturated aldehydes
No full textOptically active phosphine derivatives can be obtained in high yields and in up to 99?%?ee by using simple chiral amines to catalyze the hydrophosphination of ?,?-unsaturated aldehydes (see scheme, green sphere=chiral group). The synthetic utility of this highly chemo- and enantioselective transformation was exemplified by the one-pot asymmetric synthesis of ?-phosphine oxide acids
Catalytic and Electronic Properties of Redox-Active Metalloenzymes and Transition-Metal Complexes: Insights from the Computational Chemistry.
No full textCharles University in Prague Faculty of Science Department of Modeling of Chemical Properties of Bio- and Nanostructures Catalytic and Electronic Properties of Redox-Active Metalloenzymes and Transition- Metal Complexes: Insights from the Computational Chemistry Dissertation Thesis Abstract RNDr. Martin Srnec Supervisor: Mgr. Lubomír Rulíšek, CSc. Institute of Organic Chemistry and Biochemistry AS CR Center for Biomolecules and Complex Molecular Systems Praha 2010 Introduction Metals and their ions play a key role in maintaining life. They frequently promote protein folding, the stabilization of protein scaffolds, enzymatic activity, energy conversion, intra- and intercellular signals etc. Several decades ago, metalloproteins were considered as a rather small group of proteins. Nowadays, one-third of enzymes are estimated to contain one or more metal ions, whose presence is crucial for their enzymatic functionality. Metalloenzymes participate most often in the catalysis of difficult chemical reactions (e.g. the hydroxylation of methane, decomposition of H2 into protons and electrons, N2 and O2 bond cleavage and many other examples), in oxidation-reduction and electron-transfer reactions, and in the catalysis of spin-forbidden reactions, where relativistic effects (i.e. spin-orbit coupling) are necessary...
Katalytické a elektronové vlastnosti "redox-aktivních" metaloproteinů a komplexů přechodných kovů z pohledu výpočetní chemie.
Full text linkUniversita Karlova v Praze Přírodovědecká fakulta Obor modelování chemických vlastností bio- a nanostrutkur Katalytické a elektronové vlastnosti "redox-aktivních" metaloenzymů a komplexů přechodných kovů z pohledu výpočetní chemie Autoreferát k disertační práci RNDr. Martin Srnec Školitel: Mgr. Lubomír Rulíšek, CSc. Ústav organické chemie a biochemie AV ČR Centrum biomolekul a komplexních molekulárních systémů Praha 2010 Úvod Kovy a jejich ionty hrají v biochemických procesech významnou úlohu. Jejich přítomnost bývá nepostradatelná například při sbalování (folding) bílkovin a stabilizaci jejich struktur. Bývají běžně hnací silou enzymové aktivity, přeměny energie, či buněčných signálů. Ještě před několika desítkami let byly metaloenzymy považovány za nevýznamnou podskupinu bílkovin. Dnes se však odhaduje, že alespoň jedna třetina všech enzymů obsahuje jeden či více kovových iontů, které jsou pro funkčnost enzymu zásadní. Metaloenzymy obvykle katalyzují energeticky náročné chemické reakce jako například hydroxylaci metanu, rozklad molekulového vodíku na protony a elektrony, štěpení vazby molekulového dusíku a kyslíku atp. Dále se účastní redoxních reakcí, přenosu elektronů či spinově zakázaných reakcí, u nichž jsou nezbytné relativistické efekty, zesílené právě přítomností kovu. Biochemická úloha mnoha...Charles University in Prague Faculty of Science Department of Modeling of Chemical Properties of Bio- and Nanostructures Catalytic and Electronic Properties of Redox-Active Metalloenzymes and Transition- Metal Complexes: Insights from the Computational Chemistry Dissertation Thesis Abstract RNDr. Martin Srnec Supervisor: Mgr. Lubomír Rulíšek, CSc. Institute of Organic Chemistry and Biochemistry AS CR Center for Biomolecules and Complex Molecular Systems Praha 2010 Introduction Metals and their ions play a key role in maintaining life. They frequently promote protein folding, the stabilization of protein scaffolds, enzymatic activity, energy conversion, intra- and intercellular signals etc. Several decades ago, metalloproteins were considered as a rather small group of proteins. Nowadays, one-third of enzymes are estimated to contain one or more metal ions, whose presence is crucial for their enzymatic functionality. Metalloenzymes participate most often in the catalysis of difficult chemical reactions (e.g. the hydroxylation of methane, decomposition of H2 into protons and electrons, N2 and O2 bond cleavage and many other examples), in oxidation-reduction and electron-transfer reactions, and in the catalysis of spin-forbidden reactions, where relativistic effects (i.e. spin-orbit coupling) are necessary....Department of Physical and Macromolecular ChemistryKatedra fyzikální a makromol. chemieFaculty of SciencePřírodovědecká fakult
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