1,720,966 research outputs found
Selective Complexation by p-tert-Butylcalix[6]arene in Monolayers at the Water-Air Interface
No full textCalixarene molecules are very powerful ligands for ions and small molecules and for this reason they have been studied with several techniques as models for host-guest systems. In this paper we report the results of a study on the complexation and structural properties of p-tert-butylcalix[6]arene (CAL6) in monolayer at the water-air interface as a function of temperature and subphase composition. The monolayer properties of CAL6 films are fully studied by recording the pi/A spreading isotherms and surface potentials and by calculating the related parameters [limiting area (A(o)), compressibility modulus (C-s(-1)), dipole moment (mu cos theta)]. Changing the temperature (between 20 and 35 degrees C) and the composition of the aqueous subphase (NaCl, KCl, CsCl, guanidinium thiocyanate) produces strong variations on the monolayer parameters, indicating a different selectivity of the CAL6 ligand for the different monovalent cations. In particular, high selectivity in the case of cesium is found. Surface potential measurements as well as limiting area values, compared to CPK model calculations, are discussed in relation to the orientation of the cone-shaped molecules at the water-air interface
Incorporation of sunscreen agents in textile grafted with beta-ciclodestrin
No full textThe present study describes a different approach for the coating of sunscreen agents on cloting . The procedure involves the covalent binding of cyclodextrin onto the cloth fibres foloowed by inclusion compelxation of the UV filters in the cyclodextrin cavities grafted on teh textile surfac
Complexation properties of calixarenes in Langmuir films at the water-air interface
No full textCalixarene molecules possess very interesting properties as ligands for ions and small organic molecules, and are used as models for host-guest systems. This paper reports the results of a study on the complexation properties of three calixarenes: p-tert-butylcalix[6]arene (CALIX6), p-tert-butylcalix[8]arene (CALIX8) and p-tert-butylcalix[6]arene hexamide (C6AM), in Langmuir films at the water-air interface, in the presence of Na+, K+, Cs+ and [C(NH2)3]+ (guanidinium) and in mixed monolayers with fullerene C60. This study shows that the calixarenes' monolayers are strongly affected by the subphase composition. The analysis of the spreading isotherms shows the high selectivity of CALIX6 and C6AM for caesium and guanidinium cations, respectively. The comparison of the limiting area values with CPK model calculation shows that CALIX6 and C6AM possess a rigid truncated-cone conformation, with different orientation at the water-air interface. The limiting areas found for CALIX8 monomolecular films agree with a perpendicular “pleated loop” conformation at the water-air interface. Electronic spectra on Langmuir-Blodgett films, and also spreading isotherms, show that the CALIX8-C60 1:1 complex is stable at the water-air interface. The complex is also formed after spreading an equimolecular mixture of CALIX8 and C60 on the water surface
Complexation Properties of p-tert-Butylcalixarene Hexamide in Monolayers at the Water-Air Interface
No full textp-tert-Butylcalix[6] arene, CAL6, has been functionalized by the introduction of amide moieties (OCH2-CONEt(2)) on the six phenolic OH groups to give the corresponding hexamide, HXAM, which shows an interesting selectivity toward the guanidinium cation. The present study reports the behavior of HXAM monolayers at the water-air interface as a function of temperature and subphase composition. The parameters obtained from the spreading isotherms (limiting areas, A(0), compressibility moduli, C-s(-1) = (IIA)(partial derivative pi/partial derivative A), and changes in the Gibbs free energy upon passing from water to salt subphase, Delta G(salt-water)) and the surface potential data show that the HXAM assumes a ''cone-shaped'' conformation. The molecules are in a parallel orientation at the water-air interface with the six amide groups in the water phase. Changes in the subphase from water to salt solutions (NaCl, KCl, CsCl, guanidinium thiocyanate) affect the spreading isotherms but not the surface potential behavior. The results are discussed in terms of the two-dimensional phases of the monomolecular films, the stoichiometry of the complexes with the cations, and the conformations of uncomplexed and complexed HXAM molecules. The comparison of these results with those of the unsubstituted CAL6 behavior shows the high selectivity of HXAM monolayers toward the guanidinium cation
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
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