1,720,991 research outputs found
Alkyl glucopyranoside-based niosomes containing methotrexate for pharmaceutical applications: Evaluation of physico-chemical and biological properties
No full textWe designed novel niosomes based on alkyl glucopyranoside surfactants and containing methotrexate as anticancer drug, to be used in the pharmaceutical field. The effects of surfactants with chains of different length on niosome size and their distribution, drug entrapment efficiencies and in vitro drug release were determined. Systems made of alkyl glucopyranosides and cholesterol form vesicles whose average size scales with the alkyl chains length of such surfactants. Vesicles size ranges between 300 and 500 nm, with low polydispersity index. In addition, the hemolytic activity of alkyl glucopyranosides as surfactant solutions or vesicular formulations was studied and compared, to identify possible structure-activity relationships. High methotrexate entrapment efficiency was obtained, confirming significant interactions between the drug and the niosomal matrices. After 24 h the amount of methotrexate released from niosomal formulations is effectively delayed, compared to the free drug in solution. Hemolytic tests show that sugar-based surfactants are more hemolytic the longer is their alkyl chain. When the surfactants are in vesicular form, the reverse behavior holds. It was also inferred that vesicle formation reduces the surfactant toxicity. These niosomal formulations can be used as methotrexate delivery systems in anticancer therapy. (C) 2013 Elsevier B. V. All rights reserved
Niosomes containing hydroxyl additives as percutaneous penetration enhancers: Effect on the transdermal delivery of sulfadiazine sodium salt
No full textThe aim of this study was to improve the transdermal permeation of sulfadiazine sodium, employing synergistic combination of surfactants (in the form of niosomes) and additives with different number of hydroxylic groups, (following referred to as "alcohol"), as component of the bilayer. In particular the effect of different concentration of each alcohol (ethanol, propylene glycol or glycerol, from 5%, to 40% v/v) on niosomes size and distribution, drug entrapment efficiencies and ex vivo drug percutaneous permeation were evaluated, identifying formulations giving the best performances. The findings revealed that the presence of alcohol critically affect the physico-chemical properties of niosomes, with regards to dimensions, drug encapsulation and permeation. Vesicular size increased with the amount of alcohol and at the same alcohol concentration, follow the sequence ethanol. >. propylene glycol. >. glycerol. Loaded niosomes were larger than empty ones. Low E% values were found for ethanol, even less in propylene glycol and glycerol based samples, confirming that the chemical structure of the alcohol and its physico-chemical properties, affected the sulfadiazine entrapment efficiency. The comparative evaluation of percutaneous permeation profiles showed that the cumulative amount of permeated drug increases with alcohol concentration up to 20% v/v. Higher concentration (40% v/v) resulted in a strong decrease of the potential skin permeation. Best performances were obtained with glycerol. In all cases ex vivo sulfadiazine percutaneous permeations are controlled and improved respect to the corresponding free drug solutions and traditional niosomes used as controls
Interaction of bovine serum albumin with gemini surfactants
No full textThe interactions between bovine serum albumin and cationic gemini surfactants were investigated as a function of concentration, under different pH conditions. The investigation deals with dielectric relaxation, dynamic light scattering, zeta-potential, circular dichroism, and UV spectroscopy. The interactive behavior of the anionic form is quite different from the cationic species. It indicates that protein-surfactant interactions are mostly electrostatic in nature and depend on the state of charge of bovine serum albumin. The results indicate the presence of both hydrophobic and electrostatic contributions in the interactions of gemini with bovine serum albumin. Comparison of dynamic light scattering, dielectric relaxation, electrophoretic mobility, and optical circular dichroism allows drawing some preliminary hypotheses on the different contributions to surfactant binding and supports former studies on the formation of complexes between the bovine serum albumin and the above species. (C) 2010 Elsevier Inc. All rights reserved
Preparation and characterization of bolaform surfactant vesicles
No full textVesicular formulations (liposomes and niosomes) play an increasingly important role since they can be used as drug delivery and targeting systems. We described the formation of two niosomal systems based on synthetic bolaform surfactants (4,7,10,13-pentaoxa-16-aza-cyclooctadecane)hexadecanedioc acid diamide (BD-16) and alpha,-omega-(4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecane (BC-16). Systems containing BD-16 or BC-16 and different amount of cholesterol (CH) were prepared by aqueous dispersion of films, followed by examination of methylene blue (MB) entrapment, particle size and morphology. Indeed, we also studied the hydration in the distilled water and physiological solution, in order to investigate the complexing ability on vesicle formation. The results obtained in this study show a high encapsulation capacity and this ability and the size depends on cholesterol content. (c) 2005 Elsevier B.V. All rights reserved
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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