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排序方式: 共有336条查询结果,搜索用时 343 毫秒
21.
Guangcan Xu Sbastien Leloux Pinglu Zhang Jorge Meijide Surez Yongmin Zhang Etienne Derat Mickaël Mnand Olivia Bistri‐Aslanoff Sylvain Roland Tom Leyssens Olivier Riant Matthieu Sollogoub 《Angewandte Chemie (International ed. in English)》2020,59(19):7591-7597
The encapsulation of copper inside a cyclodextrin capped with an N‐heterocyclic carbene (ICyD) allowed both to catch the elusive monomeric (L)CuH and a cavity‐controlled chemoselective copper‐catalyzed hydrosilylation of α,β‐unsaturated ketones. Remarkably, (α‐ICyD)CuCl promoted the 1,2‐addition exclusively, while (β‐ICyD)CuCl produced the fully reduced product. The chemoselectivity is controlled by the size of the cavity and weak interactions between the substrate and internal C?H bonds of the cyclodextrin. 相似文献
22.
We describe the development, fabrication, and characterization of a novel two‐electrode nanosensor contained within the tip of a needle‐like probe. This sensor consists of two, vertically aligned, carbon structures which function as individual electrodes. One of the carbon structures was modified by silver electrodeposition and chlorination to enable it to function as a pseudo‐reference electrode. Performance of this pseudo‐reference electrode was found to be comparable to that of commercially available Ag/AgCl reference electrodes. The unmodified carbon structure was employed as a working electrode versus the silver‐plated carbon structure to form a two‐electrode sensor capable of characterizing redox‐active analytes. The nanosensor was demonstrated to be capable of electrochemically characterizing the redox behavior of para‐aminophenol (PAP) in both bulk solutions and microenvironments. PAP was also measured in cell lysate to show that the nanosensor can detect small concentrations of analyte in heterogenous environments. As the working and reference electrodes are contained within a single nanoprobe, there was no requirement to position external electrodes within the electrochemical cell enabling analysis within very small domains. Due to the low‐cost manufacturing process, this nanoprobe has the potential to become a unique and widely accessible tool for the electrochemical characterization of microenvironments. 相似文献
23.
The electrophilic ipso-reactions of a tBu-calix[6]arene that presents alternate O-methyl and O-2-methylen-N-methyl-imidazolyl groups (1) at the small rim have been studied. Whereas 1 underwent per-sulfonation in sulfuric acid, it selectively reacted with nitric acid to yield a tris-nitro derivative. The ipso-nitration occurred regioselectively on the calixarene anisol units. The reaction has been studied with various tBu-calixarenes (2-11) presenting alternate anisol and phenol ether units. The regioselectivity of the process appeared to be correlated to the presence of a protonable site on the O-substituent. It is proposed that the corresponding protonated heteroatom (N for the amines, O for the amides and the carboxylic acid), situated in the gamma or epsilon position of the phenoxy moieties, deactivates the corresponding aromatic ring by removing electron density through intramolecular hydrogen bonding. The high control operated by the O-substituents at the small rim even allowed the selective ipso-nitration of partially detertiobutylated calixarene 1(H3). Hence, these findings open new routes to a wide range of nonsymmetrically substituted calixarenes at the large rim. 相似文献
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Carole Diederichs David Taj Thimothe Lecomte Crisitiano Ciuti Philippe Roussignol Claude Delalande Aristide Lemaître Ludovic Largeau Olivia Mauguin Jacqueline Bloch Charles Leyder Alberto Bramati Elisabeth Giacobino Jrme Tignon 《Comptes Rendus Physique》2007,8(10):1198-1204
We report the realization of a monolithic vertical-cavity, surface emitting micro-optical parametric conversion nanostructure, triply resonant with the parametric frequencies, allowing parametric oscillation with ultra-low pump power threshold. The photonic phase-space naturally provides triple resonance for the parametric frequencies, together with built-in cavity phase-matching for the pump wave at normal incidence. Parametric oscillation is observed in both the strong and weak exciton–photon coupling regime, allowing a high operating temperature. Signal and idler beams can be collected at 0° or at finite angles. The OPO threshold is low enough to envisage the realization of an all-semiconductor electrically-pumped micro-parametric oscillator. To cite this article: C. Diederichs et al., C. R. Physique 8 (2007). 相似文献
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Wolfram J. Horneff Raimond H. Maurer Olivia S. Mitchell Ivica Dus 《Insurance: Mathematics and Economics》2008,42(1):396-408
Financial advisers have developed standardized payout strategies to help Baby Boomers manage their money in their golden years. Prominent among these are phased withdrawal plans offered by mutual funds including the “self-annuitization” or default rules encouraged under US tax law, and fixed payout annuities offered by insurers. Using a utility-based framework, and taking account of stochastic capital markets and uncertain lifetimes, we first evaluate these rules on a stand-alone basis for a wide range of risk aversion. Next, we permit the consumer to integrate these standardized payout strategies at retirement and compare the results. We show that integrated strategies can enhance retirees’ well-being by 25%-50% for low/moderate levels of risk aversion when compared to full annuitization at retirement. Finally, we examine how welfare changes if the consumer is permitted to switch to a fixed annuity at an optimal point after retirement. This affords the retiree the chance to benefit from the equity premium when younger, and exploit the mortality credit in later life. For moderately risk-averse retirees, the optimal switching age lies between 80 and 85. 相似文献
29.
Effectiveness of Photodynamic Therapy in Elimination of HPV‐16 and HPV‐18 Associated with CIN I in Mexican Women
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Elizabeth Maldonado Alvarado Martha Olivia Osorio Peralta Alejandra Moreno Vázquez Lydia Alejandra Martínez Guzmán Maria Eugenia Melo Petrone Zulma Iveth Enriquez Mar Dora Estela Jovel Galdamez Bárbara Carrión Solana Guadalupe Balderas Martínez Eduarda Parra Rossana Inés Castellanos Oliveros Rosa Linda Bello Leiva Araceli Espinosa Montesinos Citlalli Barrera Mendoza Selma Eugenia Medina García Eva Ramón Gallegos 《Photochemistry and photobiology》2017,93(5):1269-1275
This study aimed to determine the effectiveness of photodynamic therapy (PDT), using δ‐aminolevulinic acid (5‐ALA), in the elimination of premalignant cervical lesions in Mexican patients with human papillomavirus (HPV) infection and/or cervical intraepithelial neoplasia (CIN). Thirty women diagnosed with CIN I and/or positive for HPV participated in the study. Topical 6% 5‐ALA in gel form was applied to the uterine cervix; after 4 h, the lesion area was irradiated with a light dose of 200 J cm?2 at 635 nm. This procedure was performed three times at 48‐h intervals. Clinical follow‐up was performed at 3, 6, and 12 months after the initial PDT administration, by colposcopy, cervical cytology, histopathological analysis, polymerase chain reaction, and hybrid capture. Of HPV‐infected patients without evidence of CIN I, 80% cleared the infection, while HPV associated with CIN I was eliminated in 83% of patients (P < 0.05). At 12 months, CIN I had regressed in 57% of patients, although this response was not statistically significant. PDT using 6% 5‐ALA is concluded to be effective in eliminating HPV infection associated or not with CIN I. 相似文献
30.
Gomila A Le Poul N Cosquer N Kerbaol JM Noël JM Reddy MT Jabin I Reinaud O Conan F Le Mest Y 《Dalton transactions (Cambridge, England : 2003)》2010,39(48):11516-11518
We report the self-induced "electroclick" immobilization of the [Cu(II)(6-ethynyl-TMPA)(H(2)O)](2+) complex, by its simple electro-reduction, onto a mixed azidoundodecane-/decane-thiol modified gold electrode. The redox response of the grafted [Cu(II/I)(TMPA)] at the modified electrode is fully reversible indicating no Cu coordination change and a fast electron transfer. 相似文献