988 resultados para Lien silylé


Relevância:

10.00% 10.00%

Publicador:

Resumo:

La ricerca ha preso le mosse da tre ipotesi fondamentali: 1) Esiste un legame tra processi cognitivi di basso ed alto livello; 2) Lo spazio senso-motorio è una percezione soggettiva; 3) Lo spazio senso-motorio varia in funzione delle diverse modalità di interazione sociale. La tesi sostiene che lo spazio senso-motorio si lascia modulare dalla semplice co-presenza di un altro agente umano e da interazioni cooperative e non cooperative. I capitoli I, II, III, hanno lo scopo di scomporre e spiegare il significato della prima, seconda e terza ipotesi; giungendo a formulare la tesi centrale che sarà poi dimostrata sperimentalmente nel capitolo IV. Il capitolo V introduce future linee di ricerca nell’ambito dell’etica proponendo una nuova ipotesi sul legame che potrebbe sussistere tra la percezione dello spazio durante l’interazione sociale e i giudizi morali. Il lavoro svolto chiama ad operare insieme diverse discipline che concorrono a formare le scienze cognitive: la storia della filosofia, la filosofia della mente contemporanea, la neuropsicologia sperimentale ed alcuni temi della psicologia sociale.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

In the following chapters new methods in organocatalysis are described. The design of new catalysts is explored starting from the synthesis and the study of ion tagged prolines to their applications and recycle, then moving to the synthesis of new bicyclic diarylprolinol silyl ethers and their use in organocatalytic transformations. The study of new organocatalytic reaction is also investigated, in particular bifunctional thioureas are employed to catalyse the conjugate addition of nitro compounds to 3-yilidene oxindoles in sequential and domino reactions. Finally, preliminary results on photochemical organocatalytic atom transfer radical addition to alkenes are discussed in the last chapter.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

N-metallo ketene imines are attractive for the preparation of a wide range of organic compounds. Our research group has been engaged in the preparation and application of the N-metallo imines (SKIs). In this frame we have studied the uncatalyzed reaction of SKIs with isocyanates to give the corresponding malonamides with good yields. It has been demonstrated that the use of SKIs, instead of simple lithium anion of nitriles, is essential for the success of the reaction. A possible explanation assumes that this new reaction proceeds via a silatropism. In the course of our studies, reported in this thesis, the synthesis and the reactivity of N-silyl ketene imines in the preparation of 2,2-diaryl-3,4- dihydroxy- alcanonitrile in an uncatalyzed adol-type reaction has been performed. Our conception has been to use a chiral aldehyde to introduce asymmetric induction at the β-position and at the α-quaternary stereogenic center in the new forming diols. To achieve this goal, we used diarylacetonitrile as the substrate to form the corresponding N-trimethylsylilketene-imines to be reacted with (S)–lactic aldehyde with different protecting groups on the hydroxyl functionality. A number of 2,2-diaryl-3,4-dihydroxy-pentanenitrile were prepared with good to excellent stereo-control and satisfactory yields. Extension of this protocol to other metallo-ketene imines was performed. Accordingly, the preparation of tin ketene imines was attempted in analogy of the corresponding silyl ketene imine. The reaction of tin ketene imines with aldehydes was tested as a new tool for the synthesis of beta-hydroxynitriles starting from carbonyl compounds (aldehydes and/or ketones). Dialkyl(aryl)silyl nitriles and dialkyl(aryl)tin nitriles presents different reactivity. Finally, N-aluminium-ketene imines, as nucleophilic partner in the opening reaction of epoxides were studied. Preliminary positive results foster us to continue our studies in enlightening the scope and the limitations of this new reaction.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Das Stannylen SnHyp2 (Hyp = Si(SiMe3)3) reagiert mit den Übergangsmetallhydrid-Komplexen Cp2MH2 (Cp = C5H5, M = Mo, W) in einer alpha-Additionsreaktion zu Cp2MSn(H)Hyp2. Ferner bilden sich unter Abspaltung von HSi(SiMe3)3 auch vierkernige Verbindungen der Form [Cp2MSn(H)Hyp]2, welche für M = Mo röntgendiffraktometrisch nachgewiesen wurden. Erhöht man den sterischen Anspruch der Silylreste des Stannylens, so nimmt die Tendenz der Adduktbildung ab, so dass nur die vierkernigen Komplexe nachweisbar sind. Im Fall für SnSit2 (Sit = Si(SiMe3)2SiMe2tBu) konnten sogar Stereoisomere der vierkernigen Verbindungen [Cp2MoSn(H)Sit]2 nachgewiesen werden. Im Gegensatz dazu reagiert das Plumbylen PbHyp2 mit Cp2MoH2 in einer Substitutionsreaktion zu dem nachgewiesenen Cp2Mo(H)Hyp. Bei größer werdendem Silylrest werden andere Reaktionsabläufe bevorzugt. Auf dem Forschungsgebiet der Ein-Elektronen-Reduktion von Halogenstannanen und -plumbanen XER2R´ (X = Halogen; E = Sn, Pb; R = Silylrest; R = Aryl- / Alkylrest) mit dem 19-Elektronen-Komplex Decamethylcobaltocen CoCp*2 (Cp* = C5Me5) konnten Unterschiede zwischen den Verbindungen des Zinns und des Bleis festgestellt werden: Bei der Reduktion von Halogenstannanen fallen die erwarteten Decamethylcobaltocenium-Halogenide [CoCp*2]X aus und ESR-Messungen bestätigen die Anwesenheit von Stannylradikalen, während bei der Reduktion von hypersilylierten Halogenplumbanen unterschiedliche Folgeprodukte entstehen und Plumbylradikale via ESR-Spektroskopie nicht feststellbar sind. Bei alkylhaltigen Halogenplumbanen XPbHyp2R (R = Alkyl) findet eine Spaltung der Pb-C-Bindung statt und es bilden sich Plumbate der Form [CoCp*2][PbHyp2X], während die Reduktion von einem arylhaltigen Halogenplumban IPbHyp2Ph (Ph = Phenyl) das erwartete Decamethylcobaltocenium-Salze ergibt.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Die Reaktion von Kupfertris(trimathylsilyl)silan (= Hypersilylkupfer, CuHyp) mit Iodoorganylverbindungen sollte analog zum Ullmann-Protokoll zum Halogen-Nukleophil-Austausch führen. Tatsächlich beobachteten wir zumeist die Bildung von Cuprio-Organylen, isolierbar in Form von mehrkernigen Neutralkomplexen aus dem Produkt und weiteren Äquivalenten von Hypersilylkupfer. Nach Zugabe von (weichen) Basen wie Trimethylphosphan kam es zur Auflösung dieser Komplexe und zur Bildung der erwarteten Silylorganyle. Von der systematischen Variation der eingesetzten Arene, Alkene und Alkine sowie ihrer Liganden versprachen wir uns tiefere Einsicht in die mechanistischen Zusammenhänge. Neben dem üblichen Halogen-Kupfer-Autausch konnten wir bei orthosubstituierten, bzw. zusätzlich tetramethylsubstituierten Diiodarenen einen einfachen Iod-Siyl-Autausch beobachten (vermutlich über Arinzwischenstufen), für Alkinedukte sogar eine doppelte Silylierung. Tatsächlich zeigen quantenchemische Berechnungen für CuHyp-Iodoorganyl-Systeme eine klare Präferenz von ullmannartigen Verläufen; andererseits führte Basenzugabe erst nachträglich zur Bildung von Ullmann-Produkten über die Auflösung der primären Komplexe. Innerhalb der üblicherweise gebildeten mehrkernigen Komplexe kommen Bindungen durch die Wechselwirkung unbesetzter σ*-Molekülorbitalee am Kupferzentrum von CuHyp und elektronenreichen bindenden Orbitalen in den Kupferorganyleinheiten zustande. Freie Elektronenpaare am Phosphor bei PMe3 könnten analog die Auflösung der Neutralkomplexe und die Bildung von vierkernigen Kupfer(III)-Intermediaten zwischen den Kupferorganyleinheiten und Iodsilan in der Lösung bewirken, die aufgrund ihrer strukturellen und energetischen Besonderheiten zu den erwarteten Ullmann-Produkten weiterreagieren würden. Die beobachteten Primärreaktionen verliefen dann offensichtlich über vergleichbare, aber unterschiedlich strukturierte Intermediate, vermutlich aufgrund der Tatsache, dass das eingesetzte CuHyp als Trimer vorliegt. Diese Annahme wird durch die direkte Silylierung von Iodalkinen gestützt, deren Dreifachbindungen möglicherweise als interne Base die trimeren in monomere CuHyp-Einheiten überführen. In eine ähnliche Richtung wäre die jüngst berichtete direkte Silylierung von Allylen bei Anwesenheit von elektronenreichen CN-Gruppen zu deuten.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Que reste-t-il de Calvin et du calvinisme aujourd’hui ? Treize spécialistes du Réformateur s’intéressent dans cet essai à l’influence de cette figure centrale dans toutes sortes de domaines: sur la tolérance religieuse, le capitalisme, la démocratie moderne et l’éthique, dans les mentalités et les pays où sa pensée s’est traduite (Suisse, Etats-Unis, Europe), sur la foi chrétienne, la manière d’appréhender la Bible ou de définir le lien du religieux et du politique. L’actualité de Calvin reste éminemment prégnante dans le monde aujourd’hui, même si le bilan du calvinisme présente les ombres et les lumières du contraste, ce que les meilleurs connaisseurs actuels de sa pensée s’attachent ici à démontrer.�Une photographie stimulante de Calvin, né il y a 500 ans.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

IkappaB kinase beta (IKKbeta) is involved in tumor development and progression through activation of the nuclear factor (NF)-kappaB pathway. However, the molecular mechanism that regulates IKKbeta degradation remains largely unknown. Here, we show that a Cullin 3 (CUL3)-based ubiquitin ligase, Kelch-like ECH-associated protein 1 (KEAP1), is responsible for IKKbeta ubiquitination. Depletion of KEAP1 led to the accumulation and stabilization of IKKbeta and to upregulation of NF-kappaB-derived tumor angiogenic factors. A systematic analysis of the CUL3, KEAP1, and RBX1 genomic loci revealed a high percentage of genome loss and missense mutations in human cancers that failed to facilitate IKKbeta degradation. Our results suggest that the dysregulation of KEAP1-mediated IKKbeta ubiquitination may contribute to tumorigenesis.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Wohnen und Habitat sind entscheidende Aspekte des Alltagslebens in mikrohistorischer Hinsicht. korrespondierend mit der Ökonomie des Raumes stellen sie relevante Dimensionen und Produkte des Handelns in Gesellschaften auf der Makroebene dar. Die hier versammelten Beiträge zeugen von der Notwendigkeit der Erneuerung des Themenfeldes Wohnen in vielfältigen gesellschaftlichen, kulturellen und praxeologischen Perspektiven. Sie spannen den Bogen vom Spätmittelalter bis zur Gegenwart, von der entlegenen Burg bis zur Metropole. Sie stellen dabei Bezüge her zu den zeitgenössischen «turns and trends» der Forschung, zu den Debatten über Wohn-, Wirtschafts- und Haushaltsformen bis hin zu den Spannungen zwischen Raumökonomie und Sozialreform, Öffentlichkeit und privater Raum sowie Mobilität und Häuslichkeit.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The present study focused on the relations between the self-efficacy, social self-concept, time perspectives, school investment and academic achievement of students in four different European countries and in different adolescence periods. A total of 1623 students completed questionnaires. The relations between the concepts proved not to be specific to the Western or to the former Communist bloc countries studied. The expected general decline in investment and academic achievement over the adolescence period showed up in all four countries studied. Contrary to our hypothesis, however, this decline could not be explained by growing influences of either social self-concept or time perspectives regarding personal development on their investment. In fact, the effects of social self-concept were strongest for the youngest adolescence group. Students’ social self-concept was the best predictor for their investment, while self-efficacy proved to predict academic achievement best in all adolescence periods.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Fitness to drive in elderly drivers is most commonly discussed with a focus on cognitive impairment. Therefore, this article is focussing on mental illness and the use of psychotropic drugs in elderly drivers, which can both interfere with fitness to drive. Based on a detailed literature review and on clinical judgement, we propose signposts and "red flags" to judge the individual risks. Health professionals dealing with elderly patients should in particular be aware of the dangers related to cumulative risks and need to inform the patients appropriately. For medico-legal reasons the information provided to patients must be written down in the medical record. Individual counselling is important as fitness to drive is a complex topic.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

BACKGROUND Observational studies of a putative association between hormonal contraception (HC) and HIV acquisition have produced conflicting results. We conducted an individual participant data (IPD) meta-analysis of studies from sub-Saharan Africa to compare the incidence of HIV infection in women using combined oral contraceptives (COCs) or the injectable progestins depot-medroxyprogesterone acetate (DMPA) or norethisterone enanthate (NET-EN) with women not using HC. METHODS AND FINDINGS Eligible studies measured HC exposure and incident HIV infection prospectively using standardized measures, enrolled women aged 15-49 y, recorded ≥15 incident HIV infections, and measured prespecified covariates. Our primary analysis estimated the adjusted hazard ratio (aHR) using two-stage random effects meta-analysis, controlling for region, marital status, age, number of sex partners, and condom use. We included 18 studies, including 37,124 women (43,613 woman-years) and 1,830 incident HIV infections. Relative to no HC use, the aHR for HIV acquisition was 1.50 (95% CI 1.24-1.83) for DMPA use, 1.24 (95% CI 0.84-1.82) for NET-EN use, and 1.03 (95% CI 0.88-1.20) for COC use. Between-study heterogeneity was mild (I2 < 50%). DMPA use was associated with increased HIV acquisition compared with COC use (aHR 1.43, 95% CI 1.23-1.67) and NET-EN use (aHR 1.32, 95% CI 1.08-1.61). Effect estimates were attenuated for studies at lower risk of methodological bias (compared with no HC use, aHR for DMPA use 1.22, 95% CI 0.99-1.50; for NET-EN use 0.67, 95% CI 0.47-0.96; and for COC use 0.91, 95% CI 0.73-1.41) compared to those at higher risk of bias (pinteraction = 0.003). Neither age nor herpes simplex virus type 2 infection status modified the HC-HIV relationship. CONCLUSIONS This IPD meta-analysis found no evidence that COC or NET-EN use increases women's risk of HIV but adds to the evidence that DMPA may increase HIV risk, underscoring the need for additional safe and effective contraceptive options for women at high HIV risk. A randomized controlled trial would provide more definitive evidence about the effects of hormonal contraception, particularly DMPA, on HIV risk.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A novel synthesis of 2'-deoxypseudoisocytidine as well as of its phosphoramidite building block for oligonucleotide synthesis is presented. The synthesis is based on Heck-coupling between N-protected pseudoisocytosine and a silyl protected furanoid glycal. With this procedure the corresponding phosphoramidite building block is obtained in 5 steps and an overall yield of 28%.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

10.1002/hlca.19900730309.abs In three steps, 2-deoxy-D-ribose has been converted into a phosphoramidite building block bearing a (t-Bu)Me2Si protecting group at the OH function of the anomeric centre of the furanose ring. This building block was subsequently incorporated into DNA oligomers of various base sequences using the standard phosphoramidite protocol for automated DNA synthesis. The resulting silyl-oligomers have been purified by HPLC and selectively desilylated to the corresponding free apurinic DNA sequences. The hexamer d (A-A-A-A-X-A) (X representing the apurinic site) which was prepared in this way was characterized by 1H- and 31P-NMR spectroscopy. The other sequences as well as their fragments, which formed upon treatment with alkali base, were analyzed by polyacrylamide gel electrophoresis.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Wie erklären sich die ungleichen Bildungschancen von Jugendlichen mit und ohne Migrationshintergrund? Der Artikel geht dieser Frage anhand von Daten aus den Städten Bern und Zürich nach. Während Jugendliche aus dem nichtdeutschsprachigen Ausland im Vergleich zu Schweizer Jugendlichen im Nachteil sind, haben Jugendliche aus Deutschland und Österreich sogar einen Vorteil. Dabei zeigt sich, dass diese Unterschiede weniger auf sprachliche Schwierigkeiten als vielmehr auf Effekte der sozialen Herkunft zurückzuführen sind

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The immunogenicity of malignant cells has recently been acknowledged as a critical determinant of efficacy in cancer therapy. Thus, besides developing direct immunostimulatory regimens, including dendritic cell-based vaccines, checkpoint-blocking therapies, and adoptive T-cell transfer, researchers have started to focus on the overall immunobiology of neoplastic cells. It is now clear that cancer cells can succumb to some anticancer therapies by undergoing a peculiar form of cell death that is characterized by an increased immunogenic potential, owing to the emission of the so-called "damage-associated molecular patterns" (DAMPs). The emission of DAMPs and other immunostimulatory factors by cells succumbing to immunogenic cell death (ICD) favors the establishment of a productive interface with the immune system. This results in the elicitation of tumor-targeting immune responses associated with the elimination of residual, treatment-resistant cancer cells, as well as with the establishment of immunological memory. Although ICD has been characterized with increased precision since its discovery, several questions remain to be addressed. Here, we summarize and tabulate the main molecular, immunological, preclinical, and clinical aspects of ICD, in an attempt to capture the essence of this phenomenon, and identify future challenges for this rapidly expanding field of investigation.