1,720,969 research outputs found
Coordination Driven Capture of Nicotine Inside a Mesoporous MOF
Full text linkMetal organic frameworks (MOFs) are a wide class of crystalline porous polymers studied in many fields, ranging from catalysis to gas storage. In the past few years, MOFs have been studied for the encapsulation of organic or organometallic molecules and for the development of potential drug carriers. Here, we report on the study of two structurally-related mesoporous Cu-MOFs, namely PCN-6 and PCN-6′ (PCN stands for Porous Coordination Network), for nicotine trapping. Nicotine is a well-known alkaloid liquid molecule at room temperature, whose crystalline structure is still unknown. In this work, the loading process was monitored by electron ionization mass spectrometry by using a direct insertion probe (DIP-EI/MS), infrared (IR), and ultraviolet/visible (UV/VIS) analysis. Both nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric (TGA) analysis showed evidence that nicotine trapping reaches remarkable uptakes up to 40 wt %. In the case of PCN-6@nicotine, X-ray structural resolution revealed that the guest uptake is triggered by coordination of the pyridine ring of nicotine to the copper nuclei of the paddle-wheel units composing the framework of PCN-
Mononuclear and polynuclear complexes ligated by an iminodiacetic acid derivative: synthesis, structure, solution studies and magnetic properties
No full textTwo novel families of coordination polymers, [Ln(bzlida)(Hbzlida)]·H2O (Ln = La, Nd) and [Ln2(bzlida)3]·3H2O (Ln = Nd, Sm, Eu, Gd) were prepared by hydrothermal reaction of Ln2O3 with benzyliminodiacetic acid (H2bzlida). The conditions of synthesis, in particular the pH value, were selected on the basis of previous speciation studies reported in this work. The first type of complex consists of 1D chains built by a fully deprotonated ligand bridging two lanthanide ions and protonated Hbzlida− ligands connecting three cations. The second type is formed by [Ln2(bzlida)3] bimetallic units in which the ligand has a tridentate NOO coordination mode. This is expanded to a 2D network through carboxylate linkers. Under similar synthetic conditions but including copper acetate in the reaction mixture, a new compound was also obtained and characterized: [Cu(bzlida)2{Er(AcO)(H2O)5}2][Cu(bzlida)2]·6H2O (AcO = acetate). This salt is made up of the [Cu(bzlida)2{Er(AcO)(H2O)5}2]2+ heterotrimetallic complex cation containing an acetato bridge, and the [Cu(bzlida)2]2− anion. The same reaction produces the monomeric [Cu(Hbzlida)2]·4H2O whose structure was also elucidated. Magnetic properties of the Gd(III) derivative were studied and analyzed experimentally and theoretically. The results are compared and discussed with respect to those reported in the literature and a magnetostructural correlation is suggested
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Liquid Nicotine Tamed in Solid Forms by Cocrystallization
Full text linkWe address the problem of stabilizing liquid nicotine in solid forms at ambient conditions by cocrystallization. An intriguing aspect of nicotine lies in the fact that its crystal structure has never been reported in the literature, and this peculiarity may be ascribed to the liquid-glass transition that occurs when nicotine is supercooled under its melting point (-79 °C). Even though nicotine was considered a rigid molecule, its glass forming nature could be due to a certain extent of conformational variability, which has been assessed by a conformer search of the Cambridge Crystallographic Data Centre software. The design of cocrystals forms of nicotine is approached by analyzing its molecular electrostatic potential. On the basis of these considerations, three coformers have been identified, and their crystal structure shows that nicotine adapts to the packing features dictated by the coformers. The tool of packing energy frameworks has been used to discuss the stabilization of the cocrystals
- …
