Search results for "Lytic cycle"
showing 10 items of 75 documents
ChemInform Abstract: Bioinspired Functional Analogs of the Active Site of Molybdenum Enzymes: Intermediates and Mechanisms
2015
Abstract Molybdenum(VI) complexes of the general type MoVI(L)2(E)O (L = 2-(aryl N CH)-pyrrolylato, E = O, NtBu) and their relevance as bioinspired functional analogs for molybdenum-containing oxotransferases are reviewed. All complexes are capable of transfering oxygen atoms to PR3 (forward oxygen atom transfer) giving OPR3 and phosphane molybdenum(IV) complexes MoIV(L)2(E)(PR3) (with a second equivalent PR3) via the transient phosphoryl complex MoIV(L)2(E)(OPR3) and the five-coordinate intermediate MoIV(L)2(E). Reactivity of MoIV(L)2(E) and the favored stereochemistry of products from excess PR3 MoIV(L)2(E)(PR3) depend on the steric demand of the chelate ligands (L)−, the π donor ligand E …
Bioinspired functional analogs of the active site of molybdenum enzymes: Intermediates and mechanisms
2015
Abstract Molybdenum(VI) complexes of the general type MoVI(L)2(E)O (L = 2-(aryl N CH)-pyrrolylato, E = O, NtBu) and their relevance as bioinspired functional analogs for molybdenum-containing oxotransferases are reviewed. All complexes are capable of transfering oxygen atoms to PR3 (forward oxygen atom transfer) giving OPR3 and phosphane molybdenum(IV) complexes MoIV(L)2(E)(PR3) (with a second equivalent PR3) via the transient phosphoryl complex MoIV(L)2(E)(OPR3) and the five-coordinate intermediate MoIV(L)2(E). Reactivity of MoIV(L)2(E) and the favored stereochemistry of products from excess PR3 MoIV(L)2(E)(PR3) depend on the steric demand of the chelate ligands (L)−, the π donor ligand E …
Stereocontrol in Diphenylprolinol Silyl Ether Catalyzed Michael Additions : Steric Shielding or Curtin-Hammett Scenario?
2017
The enantioselectivity of amine-catalyzed reactions of aldehydes with electrophiles is often explained by simple steric arguments emphasizing the role of the bulky group of the catalyst that prevents the approach of the electrophile from the more hindered side. This standard steric shielding model has recently been challenged by the discovery of stable downstream intermediates, which appear to be involved in the rate-determining step of the catalytic cycle. The alternative model, referred to as Curtin-Hammett scenario of stereocontrol, assumes that the enantioselectivity is related to the stability and reactivity of downstream intermediates. In our present computational study, we examine th…
The catalytic reduction of nitrobenzene at the [MoVIO2(O2CC(S)(C6H5)2)2]2? complex intercalated in a Zn(II)-Al(III) layered double hydroxide host: A …
2001
The heterogeneous reduction of nitrobenzene by thiophenol catalyzed by the dianionic bis(2-sulfanyl-2,2-diphenylethanoxycarbonyl) dioxomolybdate(VI) complex, [MoVIO2(O2CC(S)(C6H5)2)2]2−, intercalated into a Zn(II)–Al(III) layered double hydroxide host [Zn3−xAlx(OH)6]x+, has been investigated under anaerobic conditions. Aniline was found to be the only product formed through a reaction consuming six moles of thiophenol for each mol of aniline produced. The kinetics of the system have been analyzed in detail. In excess of thiophenol, all reactions follow first-order kinetics (ln([PhNO2]/[PhNO2]0) = −kappt) with the apparent rate constant kapp being a complex function of both initial nitrobenz…
Probing protein interactions in the membrane-containing virus PRD1.
2015
PRD1 is a Gram-negative bacteria infecting complex tailless icosahedral virus with an inner membrane. This type virus of the family Tectiviridae contains at least 18 structural protein species, of which several are membrane associated. Vertices of the PRD1 virion consist of complexes recognizing the host cell, except for one special vertex through which the genome is packaged. Despite extensive knowledge of the overall structure of the PRD1 virion and several individual proteins at the atomic level, the locations and interactions of various integral membrane proteins and membrane-associated proteins still remain a mystery. Here, we demonstrated that blue native PAGE can be used to probe pro…
The presence of conifer resin decreases the use of the immune system in wood ants.
2008
5 pages; International audience; 1. Wood ants ( Formica paralugubris ) incorporate large amounts of solidified conifer resin into their nest, which reduces the density of many bacteria and fungi and protects the ants against some detrimental micro-organisms. By inducing an environment unfavourable to pathogens, the presence of resin may allow workers to reduce the use of their immune system. 2. The present study tested the hypothesis that the presence of resin decreases the immune activity of wood ants. Specifically, three components of the humoral immune defences of workers kept in resin-rich and resin-free experimental nests (antibacterial, lytic, and prophenoloxidase activities) were com…
Increase in midgut microbiota load induces an apparent immune priming and increases tolerance to Bacillus thuringiensis
2010
Summary The insect immune system is comprised of both humoral and cellular components that are mobilized in response to parasitic or pathogenic infections. Activation of the immune response implies a consid- erable expenditure of energy and that is why insects rely on inducible pathways that are activated after coming into contact with the pathogenic agent. Known as immune priming, insects can prolong the activation of the immune response and transmit their immune status to the next generation. Starting from a laboratory colony of the lepidopteran Spodoptera exigua and using the lytic zone assay as a measure of the immune status, we selected for a sub-colony with high levels of immune activ…
High resolution crystal structures of triosephosphate isomerase complexed with its suicide inhibitors: The conformational flexibility of the catalyti…
2011
The key residue of the active site of triosephosphate isomerase (TIM) is the catalytic glutamate, which is proposed to be important (i) as a catalytic base, for initiating the reaction, as well as (ii) for the subsequent proton shuttling steps. The structural properties of this glutamate in the liganded complex have been investigated by studying the high resolution crystal structures of typanosomal TIM, complexed with three suicide inhibitors: (S)-glycidol phosphate ((S)-GOP, at 0.99 A resolution), (R)-glycidol phosphate, ((R)-GOP, at 1.08 A resolution), and bromohydroxyacetone phosphate (BHAP, at 1.97 A resolution). The structures show that in the (S)-GOP active site this catalytic glutama…
Heterogeneously catalyzed Suzuki-Miyaura conversion of broad scope
2012
The reaction tolerates a broad range of functional groups in the coupling partners and is usually performed in solution under homogeneous conditions at T ¢ 60 uC using 2–3 mol% catalytic amounts. The catalyst is often a Pd(0) complex with triarylphosphane ligands. 2 The catalytic cycle (Scheme 2) begins with the oxidative addition of an aryl halide to a Pd(0) species formed in situ to form an arylpalladium(II) halide intermediate. 3 Chloroarenes, especially nonactivated aryl chlorides, are notoriously less reactive due to the stability of the C–Cl bond (the relative reactivity of Ar–X is correlated to the respective bond dissociation energy: Ph–Cl: 96 kcal mol 21 ,P h–Br: 81 kcal mol 21 ,P …
Enantioselective Protonation of the Lithium Transient Enolate of2-Methyltetralone with 2-Sulfinyl Alcohols
2005
A new catalytic cycle for the enantioselective protonation of cyclic ketone enolates with sulfinyl alcohols has been developed. An enol trifluoroacetate that can be easily obtained from the corresponding ketone is used for the first time as an enolate precursor of a cyclic ketone enolate. In this method, the achiral alcohol plays two roles: it is involved, as is usual in catalytic asymmetric protonation reactions, in the turnover of the chiral proton source and also in the generation of a transient enolate through the reaction of its corresponding alkoxide with the enol trifluoroacetate precursor. Stereoselectivity is highly dependent on the structure of the achiral alcohol. High levels of …