1,721,007 research outputs found
Production of D-Phenylglycine from racemic (D,L)-Phenylglycine via isoelectrically trapped penicillin G acylase
No full textPenicillin G acylase (PGA) is exploited for producing pure D-phenylglycine from a racemate mixture, via an acylation reaction onto a cosubstrate, the ester methyl-4-hydroxyphenyl acetate. The reaction, when carried in a batch, is severely hampered by the reverse process, by which the product, 4-hydroxyphenylacetyl-(L)phenyl glycine, upon consumption of L-phenylglycine, is converted by the enzyme back into free substrate and 4-hydroxyphenyl acetic acid via lysis of the amido bond. To prevent this noxious reaction, a multicompartment electrolyzer with isoelectric membranes (MIER) is used as enzyme reactor, operating in an electric field. PGA is trapped between pI 5.5 and pI 10.5 membranes, together with an amphoteric, isoelectric buffer (lysine). As the 4-hydroxyphenylacetyl-(L)phenyl glycine product is formed, it vacates the reaction chamber by electrophoretic transport and is collected close to the anode, in a chamber delimited by pI 2.5 and 4.0 membranes. The same fate occurs to the free acid 4-hydroxyphenyl acetic acid, formed upon spontaneous (and enzyme-driven) hydrolysis of the methyl ester in the reaction chamber. These combined processes leave behind, in the enzyme reaction chamber, the desired product, pure D-phenylglycine. The advantages of the MIER reactor over batch operations: the consumption of the L-form in the racemate is driven to completion and the enzyme is kept in a highly stable form, maintaining 100% activity after one day of operation, during which time the PGA enzyme, in the batch reactor, has already lost >75% catalytic activity
Self-Assembling Peptide Hydrogels for 3D Microarrays
No full textRecent advances in biosensing analytical platforms have brought relevant outcomes for novel diagnostic and therapy-oriented applications. In this context, hydrogels have emerged as appealing matrices to locally confine biomolecules onto sensing surfaces under solution mimetic conditions, preserving their structural integrity and function. Here, we describe the application of a self-assembling peptide hydrogel as a suitable matrix for 3D microarray bioassays. The hydrogel is printable and self-adhesive and allows for fast analyte diffusion. As a showcase example, we describe its application in a diagnostic immunoassay for the detection of arbovirus infection
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
Peptide microarrays for the characterization of antigenic regions of human chromogranin A
No full textMicroarraying peptides is a powerful proteomics technique for studying molecular recognition events. Since peptides have small molecular mass, they are not easily accessible when adsorbed onto solid supports. Moreover, peptides can lack a well-defined three-dimensional structure, and therefore a correct orientation is essential to promote the interaction with their target. In this work, we investigated the suitability as a peptide array substrate of a glass slide coated with a copolymer of N,N-dimethylacrylamide, N,N-acryloyloxysuccinimide, and [3-(methacryloyl-oxy)propyl]trimethoxysilyl. This polymeric surface was used as substrate for peptides in the characterization of linear antigenic sites of human chromogranin A, a useful tissue and serum marker for neuroendocrine tumors and a precursor of many biologically active peptides. The microarray support provided sufficient accessibility of the ligand, with no need for a spacer, as the polymer chains prevent interaction of immobilized peptides with substrate. In addition, the polymeric surface constitutes an aqueous micro-environment in which linear epitopes are freely exposed despite peptide random orientation. The results reported in this article are in accordance with those obtained in conventional ELISA assays using biotinylated and non-biotinylated peptides
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