1,721,024 research outputs found
Methods in biotechnology: enzymes in nonaqueous solvents
No full textIn Enzymes in Nonaqueous Solvents: Methods and Protocols, leading chemists, biochemists, biotechnologists, and process engineers summarize for the first time a wide range of methods for executing enzymatic transformations under nonaqueous conditions. Each method includes detailed step-by-step instructions for its successful completion, a list of materials, and ancillary notes that explain the scientific basis of the procedure, as well as troubleshooting. Also provided are a generic description of key reactions, advice on biocatalyst preparation, discussion of reaction conditions, and instructions on bioreactor design. Comprehensive and state-of-the-art, Enzymes in Nonaqueous Solvents: Methods and Protocols offers today's synthetic chemists, biochemists, and process engineers all the essential information needed to carry out enzymatic reactions in nonaqueous media, as well as to successfully scale up to production quantities
Very high activity biocatalysts for low water systems : propanol rinsed enzyme preparations (PREPs)
No full textDepending on the preparation method used enzymes under low water conditions can exhibit differences in catalytic activity that vary by several orders of magnitude. Since this can make the difference between whether a particular biotransformation is practically useful or not it is important to control enzyme history carefully. The basic problem is simple: how to transfer the enzyme from an aqueous environment to one where it is dehydrated whilst ensuring firstly it remains in a native conformation and secondly the active site residues are in the correct protonation state. Although the importance of retaining native structure is well recognised potential detrimental changes to protonation state are often not considered. Usually it is assumed that the enzyme will exhibit 'pH memory' of the previous aqueous solution. As discussed in detail in chapter ?? [sic] Partidge this is not always a valid assumption
Enzymatic solid-to-solid peptide synthesis
No full textSolid-to-solid peptide synthesis is an enzyme-catalyzed reaction carried out in a mixture consisting of solid substrates and up to 20% (w/w) of enzyme solution in water. No organic solvents are necessary for the preparation of the initial reaction mixtures. Generally, solid-to-solid synthesis is considered to be a low-water reaction system because of the very high overall concentration of substrates used. However, from the enzyme's 'viewpoint,' the reaction mixture is just an aqueous solution saturated with substrates, as this is where the actual biotransformation takes place. Therefore, this approach combines advantages of both water- and solvent-based systems (i.e., high enzyme activity, high substrate concentration, and high degree of conversion to the final product). Another attraction of solid-to-solid synthesis is that it enables improved volumetric productivity in the reactor to be achieved. The avoidance of organic solvents is often advantageous too, especially for applications in the pharmaceutical and food industry
Control of acid-base conditions in low-water media
No full textThe catalytic activity of an enzyme is profoundly affected by its ionisation state, whether it is dissolved in aqueous solution or suspended in low water organic media. In aqueous solution, counter ions can freely move around in solution. Since they are not closely associated with opposite charges, their identity does not effect the protonation state of the enzyme and so pH alone governs the protonation state. When a biocatalyst is suspended in low water organic solvent, the situation is more complex. In this case, counter ions are in closer contact with the opposite charges on the enzyme because of the lower dielectric constant of the medium. Thus, protonation of ionisable groups on the enzyme will be controlled by the type and availability of these ions as well as hydrogen ions. Changes in ionisation state of the protein can therefore be described by 2 equilibria which can, in theory, be controlled independently
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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