1,720,986 research outputs found
Amination of benzylic C-H bonds by aryl azides catalysed by Co-II(porphyrin) complexes : a new reaction leading to secondary amines and imines
No full textCo-II(porphyrin) complexes catalyse the reaction of aromatic azides, ArN3, with hydrocarbons containing a benzylic group, (RRRCH)-R-1-R-2-C-3, to give the corresponding amines, (RRRC)-R-1-R-2-C-3-NHAr. When at least one of the R-1-R-3 substituents is hydrogen, the catalytic reaction proceeds further to give the imines (RRC)-R-1-C-2=NAr in good yields
Enantiorecognition towards L- and D-DOPA on easy-to-prepare inherently chiral film electrodes
No full textWe have recently shown [1,2] that oligomers endowed with “inherent chirality” display high chirality manifestations plus a pool of unprecedented properties. In particular, in the very last months we have demonstrated that electrooligomerization (especially in ionic liquids) of our inherently chiral monomers on screen-printed electrodes and on glassy carbon tip electrodes affords inherently chiral electroactive films of outstanding enantiodiscrimination ability towards a series of chiral probes of quite different bulkiness and chemical nature (also of pharmaceutical interest like DOPA, common antibiotics and FANS) [3]. The general validity of the "inherent chirality" concept has been confirmed by characterizing monomers and related films based on different atropisomeric biheteroaromatic scaffolds (i.e. bis-benzothiophene, bis-indole, and “all thiophene” core). In this work the enantiorecognition ability of our smart films towards L- and D-DOPA will be presented focusing on the variation in voltammetric peak separation of the probe enantiomers when changing i) the medium (e.g. increasing pH, figure below), ii) the nature of electrode material and iii) the probe carboxylic unit (i.e. DOPA methyl ester). The impressive enantiomer peak potential separation combined with the peak current linear dynamic ranges enables to estimate enantiomeric excesses in probe enantiomeric
mixtures. Such synthetic electrode surfaces able to neatly discriminate the antipodes of chiral probes as separate peaks are unprecedented in literature, opening the way to the development of
efficient chiral voltammetric sensors. This work was supported by Fondazione Cariplo (Grant no. 2011-0417)
[1] F. Sannicolò, S. Arnaboldi et al. Angewandte Chemie Int. Ed., 53 (2014),
2623
[2] F. Sannicolò, P. R. Mussini, S. Arnaboldi et al. Chemistry-A European Journal
10, (2014), 15261
[3] S. Arnaboldi et al. Chemical Science, 6 (2015), 170
Highly Enantioselective “Inherently Chiral" Film Electrodes at Work
Full text linkThe usual approaches to chiral electroactive molecular materials, relying on attaching chiral pendants to an electroactive polyconjugated backbone, generally result in modest chirality manifestations; other approaches, such as chiral templating agents, chiral counteranions, etc. actually imply the chirality source to be external to the electroactive material.
Very recently, our research group has unveiled by electrochemical experiments the unprecedented enantioselectivity properties of molecular films based on a new family of "inherently chiral" polyheterocycles, where chirality is not external to the electroactive backbone, but inherent to it, resulting from a tailored torsion produced by the periodical presence of atropoisomeric, conjugatively active biheteroaromatic scaffolds (e.g. 3,3'-bithiophene [as in the monomers (R)- and (S)-BT2T4 represented in Figure 1], 2,2'-biindole and 3,3' bithiophene). [1]
The electroactive films obtained by electrooligomerization mostly consist of cyclic electroactive oligomers, constituted by several fully conjugated thiophene units.
These ringlets, which can also be obtained by chemical oligomerization, are endowed with an outstanding pool of attractive properties both as racemates and as enantiopure antipodes. [1,2] The neat peak separation for two enantiomers of electroactive chiral probes (Figure 2) together with the linearity of the peak currents with enantiomer concentration affords estimation of the enantiomeric excess when both enantiomers are present [3].
The new electrodes have been tested with very good results towards several chiral probes, quite different in molecular structure and of applicative interest, on different supports, and in different media. Moreover, we have verified that the same spectacular enantioselectivity is obtained on surfaces prepared starting from monomers designed according to the same structural concept but chemically different, which demonstrates the general validity of the new strategy.
Albeit preliminary, such unprecedented outstanding results open the way to chiral voltammetry.
References
[1] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P. R. Mussini, M. Panigati, M. Pierini and S. Rizzo, Angewandte Chemie Int. Ed., 2014, 53, 2623
[2] F. Sannicolò, P. R. Mussini, T. Benincori, R. Cirilli, S. Abbate, S. Arnaboldi, S. Casolo, E. Castiglioni, G. Longhi, R. Martinazzo, M. Panigati, M. Pappini, E. Quartapelle Procopio and S. Rizzo, Chemistry-A European Journal, 2014, 10, 15261
[3] S. Arnaboldi, P. Mussini, M. Magni, F. Sannicolò, T. Benincori, R. Cirilli, K. Noworyta and W. Kutner, Chemical Science, 2015, 6, 170
Regioselective Formation of Six- and Seven-Membered Ring by Intramolecular Pd-catalyzed Amination of N-allyl-anthranilamides
No full textA divergent synthesis of quinazolin-4-ones and l,4-benzodiazepin-5-ones by Pd(II)-catalyzed intramolecular amination of tosylated N-allyl-anthranilamides is described. Both kinds of products were available in high yields depending on the different reaction conditions
Enantiorecognition towards L- and D-DOPA on easy-to-prepare inherently chiral film electrodes
No full textWe have recently shown1,2 that oligomers endowed with “inherent chirality” display high chirality manifestations plus a pool of unprecedented properties. In particular, in the very last months we have
demonstrated that electrooligomerization (especially in ionic liquids) of our inherently chiral monomers on screen‐printed electrodes and on glassy carbon tip electrodes affords inherently chiral electroactive films of outstanding enantiodiscrimination ability towards a series of chiral probes of quite different bulkiness and chemical nature (also of pharmaceutical interest like DOPA, common antibiotics and FANS)3. The general validity of the "inherent chirality" concept has been confirmed by characterizing monomers and related films based on different atropisomeric biheteroaromatic scaffolds (i.e. bis‐benzothiophene, bis‐indole, and “all thiophene” core). In this work the enantiorecognition ability of our smart films towards L‐ and D‐DOPA will be presented focusing on the variation in voltammetric peak separation of the probe enantiomers when changing i) the medium (e.g. increasing pH), ii) the nature of electrode material and iii) the probe carboxylic unit (i.e. DOPA
methyl ester). The impressive enantiomer peak potential separation combined with the peak current linear dynamic ranges enables to estimate enantiomeric excesses in probe enantiomeric mixtures. Such synthetic electrode surfaces able to neatly discriminate the antipodes of chiral probes as separate peaks are unprecedented in literature, opening the way to the development of efficient chiral voltammetric sensors.
Figure. Effect of the variation in the pH medium on the enantiorecognition ability of our bithianaphthene‐based (BT2‐T4)n inherently chiral electrodes with L‐ and D‐DOPA probes, superimposed on a speciation plot of DOPA.
This work was supported by Fondazione Cariplo (Grant no. 2011‐0417)
References
[1] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P. R. Mussini, M.
Panigati, M. Pierini and S. Rizzo, Angewandte Chemie Int. Ed., 53 (2014), 2623
[2] F. Sannicolò, P. R. Mussini, T. Benincori, R. Cirilli, S. Abbate, S. Arnaboldi, S. Casolo, E. Castiglioni, G. Longhi, R.
Martinazzo, M. Panigati, M. Pappini, E. Quartapelle Procopio, S. Rizzo, Chemistry‐A European Journal 10, (2014), 15261
[3] S. Arnaboldi, P. Mussini, M. Magni, F. Sannicolò, T. Benincori, R. Cirilli, K. Noworyta and W. Kutner, Chemical
Science, 6 (2015), 170
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Photochemical and photocatalytic reduction of nitrobenzene in the presence of cyclohexene
No full textIrradiation with light of wavelength higher than 350 nm of deaerated mixtures of nitrobenzene and cyclohexene leads to the reduction of the nitro-compound, with the formation of C6H5N(O)=NC6H5 (32%), C6H5N=NC6H5 (21%), C6H5NH2 (15%), C6H5N(H)C6H9 (32%). The same stable reduction products are obtained when the photochemical experiments are carried out in the presence of powder dispersions of TiO2 or WO3 or CdS. On the other hand, the photocatalytic contribution of these semiconductors plays an important role in the relative product distribution, which is observed to depend on both competitive adsorption-desorption equilibria of the involved reagents and intermediates on the solid surface and the different reducing power of the photoexcited semiconductors. Cyclohexene participates in the photoinduced reduction of nitrobenzene, undergoing oxidation, and producing the required electrons and protons. Experimental evidence for the formation of radical species deriving from the oxidation of this alkene is obtained by ESR spin trapping investigation. We report here for the first time, the photoinduced allylic amination of cyclohexene with nitrobenzene to give the important building block of synthetic interest C6H5N(H)C6H9. © 2000 Elsevier Science S.A. All rights reserved
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