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A Combined Experimental and Theoretical Study on the Stereodynamics of Monoaza[5]helicenes: Solvent-Induced Increase of the Enantiomerization Barrier in 1-Aza-[5]helicene
Get PDFHelicenes and heterohelicenes are attractive compounds with great potential in materials sciences to be used in optoelectronics as ligand backbones in enantioselective catalysis and as chiral sensors.[1] Synthetic protocols were developed to obtain helicenes with skeletons consisting of ortho-fused benzene rings or analogue structures incorporating a heteroatom, as in thiophene-, furane-, or pyridine-containing helicenes.[2] In recent years, a repertoire of synthetic strategies was developed to access all monoaza[5]helicenes as well as some diaza[ 5]helicenes.[3] The properties of these materials are related to the stereodynamics of these helical chiral compounds. By exploration of the unexpected broad range of physicochemical properties of aza[n]helicenes it was realized that there is an opportunity to modulate a specific property by controlled design of the position of the N atoms in the helical molecular frame. In this contribution, we show a complete stereodynamic characterization of monoaza[5]-helicenes combining enantioselective dynamic HPLC and DFT calculations. At variance with previous theoretical calculations[4], 1-aza[5]helicene shows a surprisingly high enantiomerization barrier, which is triggered by specific solvent interactions. [5]
References
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[2] a) M. Gingras, Chem. Soc. Rev. 2013, 42, 968–1006; b) M. Gingras, G. F_lix, R. Peresutti, Chem. Soc. Rev. 2013, 42, 1007 –1050; c) Y. Shen, C.-F. Chen, Chem. Rev. 2012, 112, 1463– 1535.
[3] a) C. Bazzini, S. Brovelli, T. Caronna, C. Gambarotti, M. Giannone, P. Macchi, F. Meinardi, A. Mele, W. Panzeri, F. Recupero, A. Sironi, Eur. J. Org. Chem. 2005, 1247 – 1257; b) S. Abbate, C. Bazzini, T. Caronna, F. Fontana, C. Gambarotti, F. Gangemi, G. Longhi, A. Mele, I. Natali Sora, W. Panzeri, Tetrahedron 2006, 62,139 –148; c) T. Caronna, F. Fontana, A. Mele, I. Natali Sora, W. Panzeri, L. Vigan_, Synthesis 2008, 413– 416; d) T. Caronna, S. Gabbiadini, A. Mele, F. Recupero, Helv. Chim. Acta 2002, 85, 1 –8; e) T. Caronna, F. Castiglione, F. Fontana, D. Mendola, I. Natali Sora, Molecules 2012, 17, 463 –479.
[4] S. Abbate, C. Bazzini, T. Caronna, F. Fontana, F. Gangemi, F. Lebon, G. Longhi, A. Mele, I. Natali Sora, Inorg. Chim. Acta 2007, 360, 908 –912.
[5] T. Caronna, A. Mele, A. Famulari, D. Mendola, F. Fontana, M. Juza, M. Kamuf, K. Zawatzky, and O. Trapp, Chem. Eur. J. 2015, 21, 1–7
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Radiolytic degradation of hydrophilic PyTri ligands for minor actinide recycling
No full textThe 2,6-bis[1H-1,2,3-triazol-4-yl]-pyridine (PyTri) chelating unit has already shown promising properties for application to advanced hydrometallurgical processes aimed at recovering minor actinides from highly active raffinate. Radiolytic stability is an undeniable key requirement for chemicals involved in highly radioactive solutions partitioning, since radiolysis can have a huge impact on system safety and performances. In this work, the radiolytic degradation of two hydrophilic PyTri complexing agents was investigated by different analytical techniques. The radiation damage was delivered by a 60Co source. The main radiation-induced ligand degradation by-products were hypothesized. Unprecedented PyTri ligands radiolytic stability was proved, further recommending their implementation in future partitioning processes
Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study
Get PDFThe chemical cross-linking of β-cyclodextrin (β-CD) with ethylenediaminetetraacetic dianhydride (EDTA) led to branched polymers referred to as cyclodextrin nanosponges (CDNSEDTA). Two different preparations are described with 1:4 and 1:8 CD-EDTA molar ratios. The corresponding cross-linked polymers were contacted with 0.27 M aqueous solution of ibuprofen sodium salt (IP) leading to homogeneous, colorless, drug loaded hydrogels. The systems were characterized by high resolution magic angle spinning (HR-MAS) NMR spectroscopy. Pulsed field gradient spin echo (PGSE) NMR spectroscopy was used to determine the mean square displacement (MSD) of IP inside the polymeric gel at different observation times td. The data were further processed in order to study the time dependence of MSD: MSD = f(td). The proposed methodology is useful to characterize the different diffusion regimes that, in principle, the solute may experience inside the hydrogel, namely normal or anomalous diffusion. The full protocols including the polymer preparation and purification, the obtainment of drug-loaded hydrogels, the NMR sample preparation, the measurement of MSD by HR-MAS NMR spectroscopy and the final data processing to achieve the time dependence of MSD are here reported and discussed. The presented experiments represent a paradigmatic case and the data are discussed in terms of innovative approach to the characterization of the transport properties of an encapsulated guest within a polymeric host of potential application for drug delivery
Applications of ionic liquids in biocatalysis
No full textIonic liquids (ILs), a class of organic salts with melting points below 100 °C, have attracted a great deal of attention as possible replacement for conventional molecular solvents in catalysis. Indeed, the choice of reaction medium is considered as important in the set-up of a reaction as the catalyst itself. ILs have initially been proposed as neoteric solvents for sustainable chemistry due to their peculiar properties, such as negligible vapour pressure (thus eliminating VOC release in the environment), non-flammability, high dissolving power, the possibility of modulating physico-chemical properties (e.g., hydrophilicity/hydrophobicity balance) and, in some cases, their relatively low toxicity. Although these factors do not represent per se sufficient conditions for intrinsically green processes, they are considered advantageous starting points for the design of environmentally friendly chemical transformations. Along with their benign characteristics as solvents, ILs offer the chemist new and promising media for synthesis and catalysis on both a laboratory and an industrial scale. Over the past decade, the use of ILs in biocatalysis has been extensively studied [1].
In this work, we will illustrate the use of ILs as solvents in two different biocatalytic processes involved in the conversion of natural biomolecules: the enzymatic one-pot depolymerization of cellulose [2] and the enzymatic transformation of natural phosphatidylcholine in high value phospholipids [3]. Both processes are characterized by a high potential commercial interest, in the framework of environmentally friendly chemistry
TEMPO-Oxidized Cellulose Cross-Linked with Branched Polyethyleneimine: Nanostructured Adsorbent Sponges for Water Remediation
Get PDFAdsorbent sponges for water remediation were prepared using TEMPO-oxidized cellulose nanofibers (TOCNFs) as three-dimensional scaffolds, and branched polyethyleneimine (bPEI, 25 KDa) as the cross-linking agent. TOCNFs were suspended in aqueous solution in the presence of variable amounts of bPEI. The mixtures were first freeze-dried and then thermally treated (from 60 to 102 °C over 10 h) promoting the formation of amide bonds between the carboxylic groups of TOCNF and the primary amines of bPEI. The resulting materials, which were characterized by FTIR and 13C CP-MAS NMR spectroscopy, scanning electron microscopy, and elemental analysis, showed higher chemical and mechanical stability in water than non-reticulated cellulose composites. The high adsorption capability of the new sponges was verified for different organic pollutants (p-nitrophenol, 2,4,5-trichlorophenol, and amoxicillin), and heavy metal ion pollutants (Cu, Co, Ni, Cd), indicating their potential for water decontamination
Improvements in the enzymatic synthesis of phosphatidylserine employing ionic liquids
No full textThe aim of this work was to investigate innovative reaction media such as ionic liquids for enzymatic phospholipids transformations in order to get a higher selectivity in the enzymatic transphosphatidylation reactions of natural phosphatidylcholine catalyzed by phospholipase D (PLD) from Streptomyces PMF. The stability and the activity of the PLD in the ionic liquid [BMIM][PF6] was tested. This ionic liquid used as a cosolvent in the synthesis of phosphatidylserine lead surprisingly to the almost quantitative suppression of unwanted hydrolytic side reaction, thus providing a great improvement in the final product purification
Variations on the Author
Get PDF“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
Get PDFWe 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
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