1,720,993 research outputs found
The Structure of Gemini Surfactants Self-Assemblies Investigated by Energy Dispersive X-ray Diffraction
No full textSolid-supported multibilayers of the enantiomers of the cationic gemini surfactant 1, i.e., (2S,3S)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide (la) and (2R,3R)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide (1b), have been studied by means of energy dispersive X-ray diffraction. The effect of substrate on the orientation of the sample has been investigated. Dehydration/hydration kinetics of the samples under enviromental conditions has been followed. Furthermore, we have characterized the structural properties of the meso form, (2S,3R)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide (1c). The reported results indicate that the spontaneous self-assemblies of the meso form present different physical characteristics
Chiral recognition of dipeptides in a biomembrane model
No full textChiral recognition of the enantiomeric couples of ditryptophan and diphenylalanine was observed by 1H NMR spectroscopy in micelles formed by sodium N-dodecanoyl-L-prolinate. Ditryptophan showed a selective association with the Z domains of the amidic aggregates, whereas diphenylalanine did not show any selectivity in the association. Partition coefficients between water and aggregates were evaluated by diffusion NMR experiments. Intramolecular distances of ditryptophan isomers associated with chiral aggregates were obtained by ROESY experiments and were used as constraints in molecular mechanics calculations. From these calculations, information on the conformation of the peptides in the chiral aggregates was obtained
New biphenylic derivatives: synthesis, characterisation and enantiodiscrimination in chiral aggregates
No full textChiral discrimination of racemic 2,2'-diamino-6-(octanoyloxymethyl)biphenyl and 2,3'-diamino-6-(octanoyloxymethyl)biphenyl in micelles formed either by N-alkyl-NN-dimethyl-N-(S)-(1-phenyl)ethylammonium bromide or sodium N-dodecanoyl-L-prolinate has been investigated by H-1 NMR spectroscopy. The rotational barrier of 2,3'-diamino-6-(octanoyloxymethyl)biphenyl has been evaluated by HPLC and by dynamic NMR. The rotational barrier of 2,3-diamino-6-(acetoxymethyl)biphenyl was evaluated by theoretical calculations and compared with the experimental data relative to its analogue. (C) 2004 Elsevier Ltd. All rights reserved
Remote loading of aloe emodin in gemini-based cationic Liposomes
No full textAnthraquinone compound aloe-emodin (AE)
has shown antineoplastic, antibacterial, antiviral, and antiinflammatory
properties and scavenging activity on free
radicals. Because of these therapeutic features, AE has been
attracting increasing interest and could be applied in the curing
of many diseases. However, until now the physicochemical
features of this compound have not been fully investigated;
furthermore, its wide application might be hindered by its
scarce solubility in aqueous media (∼19 μM). The inclusion of
AE in nanocarriers, such as cationic liposomes, could allow its
delivery effectively and selectively to target sites, reducing side
effects in the remaining tissues. In this work, the weak acid nature of AE, because of its two phenolic functions, was exploited to
load it remotely in the internal aqueous phase of liposomes in response to a difference in pH between the inside and outside of
the liposomes, pHin > pHout. The inclusion of AE in gemini-based cationic liposomes b
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
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