1,720,977 research outputs found
Understanding Enzyme Immobilisation
No full textEnzymes are versatile catalysts in the laboratory and on an industrial scale. To broaden their applicability in the laboratory and to ensure their (re)use in manufacturing the stability of enzymes can often require improvement. Immobilisation can address the issue of enzymatic instability. Immobilisation can also help to enable the employment of enzymes in different solvents, at extremes of pH and temperature and exceptionally high substrate concentrations. At the same time substrate-specificity, enantioselectivity and reactivity can be modified. However, most often the molecular and physical–chemical bases of these phenomena have not been elucidated yet. This tutorial review focuses on the understanding of enzyme immobilisation
Specific ion effects on the electrochemical properties of cytochrome c
No full textThe range of salts used as supporting electrolytes in electrochemical studies of redox proteins and enzymes varies widely, with the choice of an electrolyte relying on the assumption that the electrolyte used does not affect the electrochemical properties of the proteins and enzymes under investigation. Examination of the electrochemical properties of the redox protein cytochrome c (cyt c) at a 4,4′-bipyridyl modified gold electrode demonstrates that both the redox potential (E o′) and the faradaic current are influenced by the nature of the electrolyte used, in a manner explained primarily by Hofmeister effects. The faradaic peak currents display an atypical trend on switching from kosmotropic to chaotropic anions, with a maximum current observed in the presence of Cl -. For a series of cations, the peak current increased in the sequence: Li + (0.34 μA) Br - (0.35 μA) > ClO 4 - (0.35 μA) > SCN - (0.31 μA) > F - (0.30 μA). E o′ decreased by a total of 24 mV across the series F - > Cl - > Br - > ClO 4 - > SCN - whereas no specific ion effect on E o′ was observed for cations. Factorisation of E o′ into its enthalpic and entropic components showed that while no specific trends were observed, large changes in ΔH o′ and ΔS o′ occurred with individual ions. The effect of anions on the faradaic peak current can be qualitatively explained by considering Collins' empirical rule of 'matching water affinities'. The effect of cations cannot be explained by this rule. However, both anion and cation effects can be understood by taking into account the cooperative action of electrostatic and ion dispersion forces. The results demonstrate that the choice of a supporting electrolyte in electrochemical investigations of redox proteins is important and emphasize that care needs to be taken in the determination and comparison of E o′, ΔH o′ and ΔS o′ in different solutions
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
Hofmeister phenomena in bioelectrochemistry: the supporting electrolyte affects the response of glucose electrodes
No full textAbstract
The faradaic response of ferrocene-methanol when used as a mediator for the catalytic oxidation of glucose by glucose oxidase was examined in a range of electrolytes. The response was modulated by the nature of the salt used. A two-fold difference was observed with the sodium salts of fluoride and thiocyanate, with a 24% difference between NaCl and KCl. The changes in the response can be explained by the Hofmeister effect, with specific ion effects arising between the mediator and the co-substrate binding pocket of the enzyme. Such differences can significantly affect the response of electrochemically mediated glucose biosensors and biofuel cells and emphasise the importance of carefully considering the solution conditions when evaluating the properties of glucose oxidase based biosensors and biofuel cell
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
Rapid In Situ Immobilization of Enzymes in Metal–Organic Framework Supports under Mild Conditions
No full textThe use of a metal–organic framework (MOF) as a support for the in situ immobilization of enzymes was explored. The MOF support, a Basolite F300-like material, was prepared from FeCl3 and the tridentate linker trimesic acid. Immobilization of alcohol dehydrogenase, lipase, and glucose oxidase was performed in situ under mild conditions (aqueous solution, neutral pH, and at room temperature) in a rapid and facile manner with retention of activity for at least 1 week. The catalytic activities of lipase and glucose oxidase were similar to the activities of the free enzymes; with alcohol dehydrogenase, there was a substantial decrease in activity on immobilization that may arise from diffusion limitations. The approach demonstrates that a MOF material, prepared from cheap and commercially available materials, can be successively utilized to prepare stable and catalytically active biocatalysts in a rapid and facile manner
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