Search results for "iOS"
showing 10 items of 8115 documents
Multiple aspects of plasticity in clutch size vary among populations of a globally-distributed songbird.
2013
Plasticity in life-history characteristics can influence many ecological and evolutionary phenomena, including how invading organisms cope with novel conditions in new locations or how environmental change affects organisms in native locations. Variation in reaction norm attributes is a critical element to understanding plasticity in life history, yet we know relatively little about the ways in which reaction norms vary within and among populations. We amassed data on clutch size from marked females in eight populations of house sparrows (Passer domesticus) from North America and Europe. We exploited repeated measures of clutch size to assess both the extent of within-individual phenotypic …
Venenos, cadáveres, excrementos
1999
Microwave-Assisted Organocatalytic Enantioselective Intramolecular aza-Michael Reaction with α,β-Unsaturated Ketones
2011
An organocatalytic enantioselective intramolecular aza-Michael reaction of carbamates bearing conjugated ketones as Michael acceptors is described. By using 9-amino-9-deoxy-epi-hydroquinine as the catalyst and pentafluoropropionic acid as a co-catalyst, a series of piperidines, pyrrolidines, and the corresponding benzo-fused derivatives (indolines, isoindolines, tetrahydroquinolines, and tetrahydroisoquinolines) can be obtained in excellent yields and enantioselectivities. In addition, the use of microwave irradiation at 60 °C improves the efficiency of the process giving rise to the final products with comparable yields and enantiomeric excesses. Some mechanistic insights are also consider…
A combined experimental and theoretical study of the thermal cycloaddition of aryl azides with activated alkenes.
2011
International audience; Reactions were performed from aryl azides on the one hand, and activated alkenes coming from β-dicarbonyl compounds or malonodinitrile on the other hand, either with recourse to conventional heating or to microwave activation, to afford 1-aryl-1H-1,2,3-triazoles. The mechanism and the regioselectivity of the reactions involving β-dicarbonyl compounds have been theoretically studied using DFT methods at the B3LYP/6-31G* level: they are domino processes comprising a tautomeric equilibrium of the β-dicarbonyl compounds with their enol forms, a 1,3-dipolar cycloaddition of the enol forms with the aryl azides (high activation energy), and a dehydration process (lower acti…
The Low-Affinity ATP Binding Site of the Escherichia coli SecA Dimer Is Localized at the Subunit Interface
1997
The homodimeric SecA protein is the ATP-dependent force generator in the Escherichia coli precursor protein translocation cascade. SecA contains two essential nucleotide binding sites (NBSs), i.e., NBS1 and NBS2 that hind ATP with high and low affinity, respectively. The photoactivatable bifunctional cross-linking agent 3'-arylazido-8-azidoadenosine 5'-triphosphate (diN(3)ATP) was used to investigate the spatial arrangement of the nucleotide binding sites of SecA, DiN(3)ATP is an authentic ATP analogue as it supports SecA-dependent precursor protein translocation and translocation ATPase, UV-induced photo-cross-linking of the diN(3)ATP-bound SecA results in the formation of stable dimeric s…
SVILUPPO DI METODICHE PER LA DIAGNOSI DELLA BABESIOSI BOVINA E RICERCA DI CANDIDATI VACCINALI IN BABESIA BIGEMINA
2012
Cattle babesiosis is a tick-borne disease transmitted by haemoparasites belonging to the phylum of Apicomplexa, such as Babesia bovis and B.bigemina. The pathology affects cattle mainly in tropical and subtropical areas, but also in Europe, strongly reducing meat and milk production. The study performed during these three years of PhD was addressed to the molecular characterization of Italian B.bigemina strains isolated from infected animals, with attention to the genes codifying for surface antigens, putative candidates for vaccine and diagnostic tools development. One of the molecules potentially involved in the erythrocyte invasion by B.bigemina is the Apical Membrane Antigen-1 (AMA-1), …
Compartmentalization of biosynthetic enzymes in bacterial cells: the histidine metabolic pathway case
Introduction: It is known that the inner concentration of proteins within the cell cytoplasm is so high that limits the diffusion of enzymes and metabolic intermediates, leading to a loss of time and energy. Therefore, the organization of genes in operons would have enabled to have enzymes involved in the same metabolic pathway physically close to each other. A corollary to this hypothesis in the possibility of physical interactions between the enzymes of the same metabolic pathway, resulting in the formation of a supramolecular complex capable in channeling the intermediates from one enzyme to a physical adjacent one, with restricted diffusion in the surrounding milieu. Objectives: The aim…
The structure and biosynthesis of heinamides A1-A3 and B1-B5, antifungal members of the laxaphycin lipopeptide family.
2021
Laxaphycins are a family of cyclic lipopeptides with synergistic antifungal and antiproliferative activities. They are produced by multiple cyanobacterial genera and comprise two sets of structurally unrelated 11- and 12-residue macrocyclic lipopeptides. Here, we report the discovery of new antifungal laxaphycins from Nostoc sp. UHCC 0702, which we name heinamides, through antimicrobial bioactivity screening. We characterized the chemical structures of eight heinamide structural variants A1-A3 and B1-B5. These variants contain the rare non-proteinogenic amino acids 3-hydroxy-4-methylproline, 4-hydroxyproline, 3-hydroxy-d-leucine, dehydrobutyrine, 5-hydroxyl beta-amino octanoic acid, and O-c…
The Calabrian Stage redefined
2008
The name Calabrian was introduced in the geological literature by the French stratigrapher Maurice Gignoux in 1910, and later described in his important monograph (633 pages) "Les formations marines pliocènes et quaternaires de l'Italie du sud et de la Sicile" published in 1913. Detailed data were provided on several sections (Santa Maria di Catanzaro, Caraffa, Monasterace, Palermo) and on their fossil content. The Calabrian Stage has commonly been used for over fifty years as the oldest subdivision of the Quaternary, notably in the time scales of Berggren & van Couvering (1974) and Haq & Eysinga (1987). However, after the GSSP for the Pliocene/Pleistocene boundary (P/P) was approved by INQ…