389 research outputs found

    Trapping Elusive Cp*Co(III) Metallacycles: Implications in C-H Functionalization Processes

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    La conversi√≥ d'enlla√ßos carboni‚Äďhidrogen en enlla√ßos carboni‚Äďcarboni o carboni‚Äďhetero√†tom √©s una de les reaccions m√©s atractives dins de la qu√≠mica org√†nica. Entre les diferents estrat√®gies desenvolupades al llarg de les √ļltimes d√®cades, l'activaci√≥ selectiva d'enlla√ßos C‚ÄďH, promoguda per metalls de transici√≥, amb l'ajuda d'un grup director, s'ha convertit en una alternativa molt atractiva a les tradicionals reaccions d'acoblament creuat. El desenvolupament d'aquest camp ha estat dominat per l'√ļs de catalitzadors de metalls nobles. No obstant aix√≤, en els √ļltims anys, catalitzadors de metalls m√©s barats i abundants, com el cobalt, han esdevingut una alternativa molt interessant. En aquest context, l'√ļs de complexos de Cp*CoIII ha rebut especial atenci√≥ a causa de la seva capacitat per a promoure una gran varietat de reaccions de formaci√≥ d'enlla√ßos C‚ÄďC i C‚ÄďX. Malgrat els avan√ßos realitzats, aquests sistemes encara estan en la seva inf√†ncia en comparaci√≥ amb els catalitzadors de Rh i Pd, a causa de la falta de coneixement fonamental. L'estudi sobre la naturalesa de les esp√®cies reactives o el mecanisme implicat en aquestes transformacions s'ha vist obstaculitzat per la dificultat de detectar intermedis de reacci√≥. Intrigats per aquesta problem√†tica, en aquesta tesi doctoral hem explorat: i) el desenvolupament de noves estrat√®gies per a accedir a aquests intermedis de reacci√≥; ii) l'√ļs d'aquests metal¬∑lacicles de Cp*CoIII, no sols per a obtenir informaci√≥ del mecanisme sobre diferents reaccions catalitzades per aquests compostos, sin√≥ tamb√© per a millorar la seva efici√®ncia; i finalment, iii) l'estudi de l'efecte d'alguns additius en les etapes elementals involucrades en els cicles catal√≠tics. El coneixement fonamental generat durant aquesta tesi doctoralLa conversi√≥n de enlaces carbono‚Äďhidr√≥geno en enlaces carbono‚Äďcarbono o carbono‚Äďhetero√°tomo es una de las reacciones m√°s atractivas dentro de la qu√≠mica org√°nica. Entre las diferentes estrategias desarrolladas a lo largo de las √ļltimas d√©cadas, la activaci√≥n selectiva de enlaces C‚ÄďH, promovida por metales de transici√≥n, con la ayuda de un grupo director, se ha convertido en una alternativa muy atractiva a las tradicionales reacciones de acoplamiento cruzado. El desarrollo de este campo ha estado dominado por el empleo de catalizadores de metales nobles. Sin embargo, en los √ļltimos a√Īos, catalizadores de metales m√°s baratos y abundantes, como el cobalto, se han convertido en una alternativa muy interesante. Dentro de este contexto, el uso de complejos de Cp*CoIII ha recibido especial atenci√≥n debido a su capacidad para promover a una gran variedad de reacciones de formaci√≥n de enlaces C‚ÄďC y C‚ÄďX. A pesar de los avances realizados, estos sistemas a√ļn est√°n en su infancia en comparaci√≥n con los catalizadores de Rh y Pd, debido a la falta de conocimiento fundamental. El estudio sobre la naturaleza de las especies reactivas o el mecanismo implicado en estas transformaciones se ha visto obstaculizado por la dificultad de detectar intermedios de reacci√≥n. Intrigados por esta problem√°tica, en esta tesis doctoral hemos explorado: i) el desarrollo de nuevas estrategias para acceder a estos intermedios de reacci√≥n; ii) el uso de estos metalaciclos de Cp*CoIII, no s√≥lo para obtener informaci√≥n mecan√≠sitica sobre diferentes reacciones catalizadas por estos compuestos, sino tambi√©n para mejorar su eficiencia; y finalmente, iii) el estudio del efecto de la adici√≥n de algunos aditivos en las etapas elementales involucradas en los ciclos catal√≠ticos. El conocimiento fundamental generado durante esta tesis doctoral ha supuesto un gran avance en la cat√°lisis de cobalto, especialmente a nivel molecular.The conversion of ubiquitous and typically inert C‚ÄďH bonds into C‚ÄďC and C‚Äďheteroatom bonds is one of the most attractive transformation in organic chemistry. Among the different strategies developed over the past decades, ligand-directed transition-metal-catalyzed transformations have achieved remarkable progress, becoming an attractive alternative to traditional cross-coupling reactions. During decades, these catalytic systems required noble transition metals for the efficient construction of organic molecules. However, in the past few years, more cost-effective first-row metals, such as cobalt, have emerged as an appealing alternative to precious metals. In this context, the employment of Cp*CoIII complexes have represented a tremendous advance in cobalt catalysis, since they have the potential to promote a wide variety of C‚ÄďC and C‚Äďheteroatom bond-forming reactions, via putative cyclometalated cobalt(III) species. Despite this significant progress, these cobalt systems are still at their infancy compared to Rh- or Pd-based ones, essentially due to the limited fundamental organometallic understanding of these systems. The investigation of the underlying reaction mechanisms of these transformations has been hampered by the difficulty to detect/isolate key intermediates. Challenged by the lack of fundamental knowledge of these transformations, in this Doctoral thesis we explore: i) the design and development of novel synthetic routes for accessing well-defined and stable cobalt metallacycles, analogous to proposed key reactive intermediates; ii) the employment of these Cp*CoIII metallacycles not only for unravelling previous inaccessible mechanistic intricacies of selected Cp*CoIII-catalyzed processes but also for improving their efficiency; and finally, iii) the participation and/or effect of some additives in different benchmark transformations. The fundamental knowledge generated during this Doctoral Thesis has led to important breakthroughs in cobalt catalysis, specially at molecular level

    Impact of the first wave of the SARS-CoV-2 pandemic on the outcome of neurosurgical patients: A nationwide study in Spain

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    Objective To assess the effect of the first wave of the SARS-CoV-2 pandemic on the outcome of neurosurgical patients in Spain. Settings The initial flood of COVID-19 patients overwhelmed an unprepared healthcare system. Different measures were taken to deal with this overburden. The effect of these measures on neurosurgical patients, as well as the effect of COVID-19 itself, has not been thoroughly studied. Participants This was a multicentre, nationwide, observational retrospective study of patients who underwent any neurosurgical operation from March to July 2020. Interventions An exploratory factorial analysis was performed to select the most relevant variables of the sample. Primary and secondary outcome measures Univariate and multivariate analyses were performed to identify independent predictors of mortality and postoperative SARS-CoV-2 infection. Results Sixteen hospitals registered 1677 operated patients. The overall mortality was 6.4%, and 2.9% (44 patients) suffered a perioperative SARS-CoV-2 infection. Of those infections, 24 were diagnosed postoperatively. Age (OR 1.05), perioperative SARS-CoV-2 infection (OR 4.7), community COVID-19 incidence (cases/10 5 people/week) (OR 1.006), postoperative neurological worsening (OR 5.9), postoperative need for airway support (OR 5.38), ASA grade =3 (OR 2.5) and preoperative GCS 3-8 (OR 2.82) were independently associated with mortality. For SARS-CoV-2 postoperative infection, screening swab test <72 hours preoperatively (OR 0.76), community COVID-19 incidence (cases/10 5 people/week) (OR 1.011), preoperative cognitive impairment (OR 2.784), postoperative sepsis (OR 3.807) and an absence of postoperative complications (OR 0.188) were independently associated. Conclusions Perioperative SARS-CoV-2 infection in neurosurgical patients was associated with an increase in mortality by almost fivefold. Community COVID-19 incidence (cases/10 5 people/week) was a statistically independent predictor of mortality. Trial registration number CEIM 20/217

    Optimasi Portofolio Resiko Menggunakan Model Markowitz MVO Dikaitkan dengan Keterbatasan Manusia dalam Memprediksi Masa Depan dalam Perspektif Al-Qur`an

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    Risk portfolio on modern finance has become increasingly technical, requiring the use of sophisticated mathematical tools in both research and practice. Since companies cannot insure themselves completely against risk, as human incompetence in predicting the future precisely that written in Al-Quran surah Luqman verse 34, they have to manage it to yield an optimal portfolio. The objective here is to minimize the variance among all portfolios, or alternatively, to maximize expected return among all portfolios that has at least a certain expected return. Furthermore, this study focuses on optimizing risk portfolio so called Markowitz MVO (Mean-Variance Optimization). Some theoretical frameworks for analysis are arithmetic mean, geometric mean, variance, covariance, linear programming, and quadratic programming. Moreover, finding a minimum variance portfolio produces a convex quadratic programming, that is minimizing the objective function √į√į¬•with constraints√į √į √į¬• ¬• √įand√į¬ī√į¬• = √į. The outcome of this research is the solution of optimal risk portofolio in some investments that could be finished smoothly using MATLAB R2007b software together with its graphic analysis

    Odderon Exchange from Elastic Scattering Differences between pp and pp‚ąí^{-} Data at 1.96 TeV and from pp Forward Scattering Measurements

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    We describe an analysis comparing the p¬Įp elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96 TeV to that in pp collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeV using a model-independent approach. The TOTEM crosssections, extrapolated to a center-of-mass energy of ‚ąös=1.96‚ÄČ‚ÄČTeV, are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the pp cross section. The two data sets disagree at the 3.4ŌÉ level and thus provide evidence for the t-channel exchange of a colorless, C-odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of the same C-odd exchange based on the total cross section and the ratio of the real to imaginary parts of the forward elastic strong interaction scatteringamplitude in pp scattering for which the significance is between 3.4ŌÉ and 4.6ŌÉ. The combined significance is larger than 5ŌÉ and is interpreted as the first observation of the exchange of a colorless, C-odd gluonic compound

    Search for heavy resonances decaying to two Higgs bosons in final states containing four b quarks