1,720,982 research outputs found
Gold nanoparticles incorporated into cryogel walls for efficient nitrophenol conversion
No full textThe past several decades have illustrated an enormous interest in noble metal nanoparticles for their superior catalytic activity, however, their industrial use is very restricted due to inefficient recovery leading to potential contamination of products and the environment. Immobilised nanoparticles illustrate promising results for scaling up processes, and can be successfully applied for various catalytic processes including waste industrial water treatment. The aim of the study was to design and study an easy and economically efficient green chemistry approach of preparation of macroporous material, with well distributed gold nanoparticles within the wall of cryogel. Ionic cryogels containing chitosan and tetrachloroaurate complex was reduced by 1.1.3.3-tetramethoxypropane, concurrently allowing chemical cross-linking of the polymer. A mechanism of reduction of noble gold complexes within the cryogel walls by tetramethoxypropane is also studied. Properties of the composite cryogels were evaluated using; differential scanning calorimetry, FT-IR, NMR, compression tests, SEM, TEM), Energy-dispersive X-ray spectroscopy and low temperature nitrogen adsorption. The catalytic activity of the in-situ synthesised gold nanoparticles was comprehensively studied using a model reduction reaction of 4-nitrophenol. Four different concentrations of gold nanoparticles within the cryogel structure were investigated. The turnover number and the turnover frequency parameters for cryogels containing four different concentrations of gold nanoparticles were calculated. The conversion degree of 4-nitrophenol to 4-aminophenol for cryogel containing the lowest of gold nanoparticles reached 96.8% at room temperature. The catalytic activity of incorporated gold nanoparticles for 4-nitrophenol conversion did not decline over 14 consequent testing cycles
Comparative Toxicity of Interferon Beta-1a Impurities of Heavy Metal Ions
No full textBackground and Objectives: Providing a proper quality control of drugs is essential for efficient treatment of various diseases minimizing the possible side effects of pharmaceutical active substances and potential impurities. Recent in vitro and in vivo studies have shown that certain heavy metalloids and metals interfere with protein folding of nascent proteins in cells and their biological function can be altered. It is unknown whether the drug impurities including heavy metals may affect the tertiary protein structure. Materials and Methods: ReciGen and Rebif are pharmaceutical interferon beta-1a (IFNβ-1a) contained in preparations that are used for parenteral administration. Heavy metal impurities of these samples have been studied by gel electrophoresis, Fourier-transform infrared spectroscopy (FTIR) and inductively coupled plasma mass spectrometry analysis (ICP MS). The concentration of heavy metals including mercury, arsenic, nickel, chromium, iron, and aluminum did not exceed permitted levels established by International Council for Harmonisation guideline for elemental impurities. Results: The ICP MS analysis revealed the presence of heavy metals, moreover zeta potential was significantly different for IFNβ-1a, which can be an indirect indication of the difference in composition of ReciGen and Rebif samples, respectively. FTIR analysis revealed very similar amide I and II bonds at 1654 and 1560 cm−1 attributed to the peptide absorption peaks of IFNβ-1a in Rebif and ReciGen. Conclusions: It was hypothesized that the IFNβ-1a complex binds heavy metals affecting the tertiary protein structure and may lead to some side effects of drug administration. Further testing of IFNβ-1a bioequivalence for parenteral application is necessary
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
Chitosan Glutaraldegyde Cryogels for Wastewater Treatment and Extraction of Silver Nanoparticles
No full textThe discharge of nanoparticles into the environment, such as through industrial plants and municipal wastewater treatment plants, can pose a hazard to aquatic life. This study demonstrates the effective removal of silver nanoparticles (AgNPs) using a chitosan-based cryogel, which has potential applications in agriculture, as well as in water treatment or in industrial plants that discharge into environmentally sensitive water bodies. The adsorbent is economically viable, has high affinity toward metal nanoparticles, is biodegradable and biocompatible, and displays a good removal of nanoparticles. AgNP adsorption was monitored using UV/Vis spectroscopy and TEM analysis. SEM, nitrogen adsorption, TGA, and FTIR analysis were used for cryogel characterization. The BET model of nitrogen adsorption revealed a specific surface area of 7.7 m2/g for chitosan–glutaraldehyde (CHI–GA) cryogels. The elasticity modulus of the CHI–GA cryogel was estimated as 543 ± 54 kPa. The AgNPs were characterized by a negative charge (−38 ± 17 mV) and an average diameter of 64 nm with a polydispersity index of 0.16. The mechanism of AgNP adsorption involved electrostatic interactions between the oppositely charged surfaces of the cryogel and particles. The temperature of the cryogel preparation affected the water permeability and adsorption efficiency. CHI–GA illustrated a capacity of 63 mg/g at a flow rate of 0.8 mL/min under a solution pressure of 500–970 Pa. The increase in pressure of the model plant extract-stabilized AgNP suspension (14 mg/L AgNPs) to 3.42–3.9 kPa led to an increase in the water permeability rate to 10 mL/min and a significant decrease in the efficiency of particle removal. The CHI–GA adsorbent demonstrated up to 96.5% AgNP removal until the breakthrough point due to adsorbent saturation. The CHI–GA cryogel adsorbent (1 g) can be used for efficient filtering of about 4.5 L of contaminated water
Antimicrobial and antioxidant activity of AgNPs stabilized with Calendula officinalis flower extract
No full textThe present research is devoted to optimizing the green synthesis technology of silver nanoparticles (AgNP) with antibacterial properties for further external use. Standardized marigold flowers extract was utilized as reducing and stabilizing agent, which has significantly richer composition of phytochemical groups compared to its aqueous extracts. A comparative analysis of the physicochemical properties and sedimentation stability of AgNPs obtained by exposure of the reaction mixture to: UV radiation, microwave radiation and high temperature using UV–Vis spectrophotometry and Zeta potential analysis were carried out. pH effect of the reaction mixture on size distribution of AgNPs was evaluated. A good stability of AgNPs to aggregation was observed for samples generated under ultraviolet irradiation with continuous stirring. The particle size distribution obtained by UV irradiation with an average size of 80 nm and PDI 0.26. The storage of AgNPs at 4 °C resulted in some aggregation of small size AgNPs that led to the increase the absorbance at 430 nm. Thus, after one month of storage there was no following increase of the absorbance and there was non-significant aggregation over 3 months’ study. Antibacterial activity of AgNPs against S. aureus and E. coli was estimated with and without light irradiation (445 and 635 nm, 14 W). Additionally, the antioxidant activity of the plant extract and the AgNPs stabilized by the extract was estimated
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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