排序方式: 共有46条查询结果,搜索用时 31 毫秒
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Andrs Cordn‐Franco Alejandro Fernndez‐Margarit F. Flix Lara‐Martín 《Mathematical Logic Quarterly》2006,52(1):51-70
A well known theorem proved (independently) by J. Paris and H. Friedman states that B Σn +1 (the fragment of Arithmetic given by the collection scheme restricted to Σn +1‐formulas) is a Πn +2‐conservative extension of I Σn (the fragment given by the induction scheme restricted to Σn ‐formulas). In this paper, as a continuation of our previous work on collection schemes for Δn +1(T )‐formulas (see [4]), we study a general version of this theorem and characterize theories T such that T + B Σn +1 is a Πn +2‐conservative extension of T . We prove that this conservativeness property is equivalent to a model‐theoretic property relating Πn ‐envelopes and Πn ‐indicators for T . The analysis of Σn +1‐collection we develop here is also applied to Σn +1‐induction using Parsons' conservativeness theorem instead of Friedman‐Paris' theorem. As a corollary, our work provides new model‐theoretic proofs of two theorems of R. Kaye, J. Paris and C. Dimitracopoulos (see [8]): B Σn +1 and I Σn +1 are Σn +3‐conservative extensions of their parameter free versions, B Σ–n +1 and I Σ–n +1. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The mechanism of nitrogen atom transfer from four-coordinate tris(carbene)borate iron(IV) nitrido complexes to phosphines and phosphites has been investigated. In the absence of limiting steric effects, the rate of nitrogen atom transfer to phosphines increases with decreasing phosphine σ-basicity. This trend has been quantified by a Hammett study with para-substituted triarylphosphines, and is contrary to the expectations of an electrophilic nitrido ligand. On the basis of electronic structure calculations, a dual-nature transition state for nitrogen atom transfer is proposed, in which a key interaction involves the transfer of electron density from the nitrido highest occupied molecular orbital (HOMO) to the phosphine lowest unoccupied molecular orbital (LUMO). Compared to analogous atom transfer reactions from a 5d metal, these results show how the electronic plasticity of a 3d metal results in rapid atom transfer from pseudotetrahedral late metal complexes. 相似文献
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Filippo Carboni Annabel Kitowski Charlotte Sorieul Daniele Veggi Marta C. Marques Davide Oldrini Evita Balducci Barbara Brogioni Linda Del Bino Alessio Corrado Francesca Angiolini Lucia Dello Iacono Immaculada Margarit Maria Rosaria Romano Gonalo J. L. Bernardes Roberto Adamo 《Chemical science》2022,13(8):2440
The introduction of glycoconjugate vaccines marks an important point in the fight against various infectious diseases. The covalent conjugation of relevant polysaccharide antigens to immunogenic carrier proteins enables the induction of a long-lasting and robust IgG antibody response, which is not observed for pure polysaccharide vaccines. Although there has been remarkable progress in the development of glycoconjugate vaccines, many crucial parameters remain poorly understood. In particular, the influence of the conjugation site and strategy on the immunogenic properties of the final glycoconjugate vaccine is the focus of intense research. Here, we present a comparison of two cysteine selective conjugation strategies, elucidating the impact of both modifications on the structural integrity of the carrier protein, as well as on the immunogenic properties of the resulting glycoconjugate vaccine candidates. Our work suggests that conjugation chemistries impairing structurally relevant elements of the protein carrier, such as disulfide bonds, can have a dramatic effect on protein immunogenicity.The introduction of glycoconjugate vaccines marks an important point in the fight against various infectious diseases. 相似文献
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A. Cordón‐Franco A. Fernández‐Margarit F. F. Lara‐Martín 《Mathematical Logic Quarterly》2011,57(5):444-455
We characterize the sets of all Π2 and all $\mathcal {B}(\Sigma _{1})We characterize the sets of all Π2 and all $\mathcal {B}(\Sigma _{1})$ (= Boolean combinations of Σ1) theorems of IΠ?1 in terms of restricted exponentiation, and use these characterizations to prove that both sets are not deductively equivalent. We also discuss how these results generalize to n > 0. As an application, we prove that a conservation theorem of Beklemishev stating that IΠ?n + 1 is conservative over IΣ?n with respect to $\mathcal {B}(\Sigma _{n+1})$ sentences cannot be extended to Πn + 2 sentences. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim 相似文献
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Vicente J. Margarit Marta E. Martínez‐Armero Dr. M. Teresa Navarro Dr. Cristina Martínez Prof. Avelino Corma 《Angewandte Chemie (International ed. in English)》2015,54(46):13724-13728
A two‐dimensional zeolite with the topology of MWW sheets has been obtained by direct synthesis with a combination of two organic structure‐directing agents. The resultant material consists of approximately 70 % single and double layers and displays a well‐structured external surface area of about 300 m2 g?1. The delaminated zeolite prepared by means of this single‐step synthetic route has a high delamination degree, and the structural integrity of the MWW layers is well preserved. The new zeolite material displayed excellent activity, selectivity, and stability when used as a catalyst for the alkylation of benzene with propylene and found to be superior to the catalysts that are currently used for producing cumene. 相似文献
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Smith JM Mayberry DE Margarit CG Sutter J Wang H Meyer K Bontchev RP 《Journal of the American Chemical Society》2012,134(15):6516-6519
The reaction of TEMPO with the iron(I) synthon PhB(MesIm)(3)Fe(COE) leads to formation of the κ(1)-TEMPO complex PhB(MesIm)(3)Fe(TEMPO). Structural and spectroscopic data establish the complex contains divalent iron bound to a nitroxido anion and is isoelectronic to an iron(II) peroxo complex. Thermolysis of the complex results in N-O bond homolysis, leading to the formation of an iron(III) oxo intermediate. The oxo intermediate is active in oxygen atom transfer reactions and can be trapped by the triphenylmethyl radical to give the iron(II) alkoxo complex PhB(MesIm)(3)Fe(OCPh(3)). 相似文献
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