1,720,962 research outputs found
COPPER(II) COMPLEXES OF LACTOBIONIC ACID - LACTONE-ACID EQUILIBRIUM AND PROTON DISSOCIATION
No full textPotentiometric, polarographic, and spectroscopic data allowed us to establish the coordination equilibria in the Cu(II) lactobionic acid system. At lower pH regions the equilibrium between acid and lacton forms is also described. The stability constants of the cupric species are about a hundred or more times higher when compared to the galacturonic acid complexes, although the coordination modes in both systems are exactly the same. The obtained results clearly indicate that lactobionic acid is a very efficient chelating agent for metal ions most likely due to secondary interactions between protonated hydroxyl groups and metal ions, as well as possible interligand interactions. These interactions are likely to favor lactobionic acid rather than uronic acids, due to its higher flexibility
Oxovanadium(IV) complexes of phosphonic derivatives of iminodiacetic and nitrilotriacetic acids
No full textThe complex formation between (VO)-O-IV and phosphonic derivatives of iminodiacetic (Ida) and nitrilotriacetic acids (Nta) has been studied by combined application of pH-potentiometric and spectroscopic (EPR and electronic absorption) techniques. Differently from aminomonophosphonates, which are able to bind the metal ion rather weakly forming five-membered chelated rings, the mixed carboxylic-phosphonic and pure phosphonic derivatives of Ida and Nta form chelated systems resulting in very stable complexes mostly of the 1 : 1 type. Substitution of CO2- by PO32- increases the stability of the complexes due to the higher basicities of the phosphonic functions. However, the higher spatial requirement of the phosphonate groups and the greater electrostatic repulsion between the dinegative phosphonate arms would mostly compensate this effect. Spectroscopic evidence has been found for a considerable distortion in the geometry of the aminophosphonate complexes. The differences in the observed stability trends between the corresponding copper(II) and (VO)-O-IV complexes are also discussed
POTENTIOMETRIC, POLAROGRAPHIC AND SPECTROSCOPIC STUDIES OF THE CU(II)-D-GLUCOSAMINE-D-LACTOBIONIC ACID TERNARY-SYSTEMS
No full textOur recent work on Cu(II) and VO(IV) interactions with lactobionic acid have shown1,2 that this sugar acid has an unusually high ability to coordinate both metal ions. The carboxyl group is not a very effective donor for cupric ions3,4 and metal interations with the set of the protonated hydroxyl groups should have considerable effects on complex stability. This high stability of the lactobionic acid complexes can lead to the involvement of this ligand in formation of ternary complexes with ligands such as aminosugars.3-6 Both ligands are important chelating agents for Cu(II) ions in medicine, agriculture and food chemistry.7-9 Since ternary complexes may play an important role in natural systems we have decided to follow complex formation in solutions containing lactobionic acid and one an aminosugar, D-glucosamine. The anchoring group in D(+)-glucosamine (2-amino-2-deoxy-D-glucose) is an amino group which is much more effective donor than carboxylate which acts as an anchor in sugar acids. Thus in our study we have used excess lactobionic acid to promote the formation of ternary complexes as major species in the solutions studied
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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