1,721,166 research outputs found
Quantitative Analysis of the Interactions of Metal Complexes and Amphiphilic Systems: Calorimetric, Spectroscopic and Theoretical Aspects
Full text linkMetals and metal-based compounds have many implications in biological systems. They
are involved in cellular functions, employed in the formation of metal-based drugs and present as
pollutants in aqueous systems, with toxic effects for living organisms. Amphiphilic molecules also
play important roles in the above bio-related fields as models of membranes, nanocarriers for drug
delivery and bioremediating agents. Despite the interest in complex systems involving both metal
species and surfactant aggregates, there is still insufficient knowledge regarding the quantitative
aspects at the basis of their binding interactions, which are crucial for extensive comprehension of their
behavior in solution. Only a few papers have reported quantitative analyses of the thermodynamic,
kinetic, speciation and binding features of metal-based compounds and amphiphilic aggregates,
and no literature review has yet addressed the quantitative study of these complexes. Here, we
summarize and critically discuss the recent contributions to the quantitative investigation of the
interactions of metal-based systems with assemblies made of amphiphilic molecules by calorimetric,
spectrophotometric and computational techniques, emphasizing the unique picture and parameters
that such an analytical approach may provide, to support a deep understanding and beneficial use of
these systems for several applications
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
A novel 2,6-bis(benzoxazolyl)phenol macrocyclic chemosensor with enhanced fluorophore properties by photoinduced intramolecular proton transfer
Full text linkMacrocyclic ligand L, in which a 2,6-bis(2-benzoxazolyl)phenol (bis-HBO) group is incorporated in triethylenetetramine, was designed and synthesized with the aim of creating a chemosensor with high selectivity and specificity for metal cations in an aqueous environment. The availability of several proton acceptors and donors, and amine and phenol hydroxy groups, respectively, affects the keto-enol equilibrium in both the ground and excited states, and the ligand properties show dependence on the pH of the solution. L is fluorescent in the visible range, through an excited-state intramolecular proton transfer (ESIPT) mechanism. The results of an exhaustive characterization of L by spectroscopic techniques and DFT calculations, as well as of its Zn(ii), Cd(ii) and Pb(ii) complexes, show promising properties of L as a ratiometric metal cation chemosensor, since metal coordination prevents the ESIPT and gives rise to a peculiar displacement of the fluorescence emission from green to blue with Zn(ii) and Cd(ii), while with Pb(ii) the fluorescence is quenched. © 2023 The Royal Society of Chemistry
Interaction of Cd(II) and Ni(II) terpyridine complexes with model polynucleotides: a multidisciplinary approach
Full text linkTwo metal complexes of 2,2′:6′,2′′-terpyridine (terpy), i.e. Cd(terpy)Cl2 and Ni(terpy)Cl2·3H2O, have been prepared and extensively characterized. The interaction of Cd(terpy)Cl2 with synthetic DNA models, poly(dA-dT)·poly(dA-dT) (polyAT) and poly(dG-dC)·poly(dG-dC) (polyGC), has been studied by CD, fluorescence and UV-vis electronic absorption spectroscopy at several metal/polynucleotide-phosphate ratios and for different NaCl concentrations. All the experimental results indicate an intercalative mechanism of interaction. The optimized geometry of the cadmium complex intercalated between the sixth and seventh base pairs of (AT) and (GC) dodecanucleotide duplexes, obtained by quantum mechanics/molecular mechanics (QM/MM) calculations, lends support to the proposed mechanism. The calculated models provide some additional structural details of the intercalation complex at the molecular level. To evidence the influence of the charge and geometry of the metal complex on the mechanism of interaction with polynucleotides, the nickel complex-polyAT system has been studied to some extent by means of CD and UV-vis spectroscopy, and by thermal melting experiments. The results suggest that the octahedral complex cation [Ni(terpy)(H2O)2Cl]+ interacts with polyAT by partial intercalation assisted by electrostatic interaction with the negative charges of the backbone phosphate groups
How the Metal Ion Affects the 1H NMR Chemical Shift Values of Schiff Base Metal Complexes: Rationalization by DFT Calculations
Full text linkThe chemical shift (CS) values obtained by H-1 NMR spectroscopy for the hydrogen atoms of a tetradentate N2O2-substituted Salphen ligand (H(2)L1) are differently shifted in its complexes of nickel(II), palladium(II), platinum(II), and zinc(II), all bearing the same charge on the metal ions. To rationalize the observed trends, DFT calculations have been performed in the implicit d(6)-DMSO solvent in terms of the electronic effects induced by the metal ion and of the nature and strength of the metal-N and metal-O bonds. Overall, the results obtained point out that, in the complexes involving group 10 elements, the CS values show the greater shift when considering the two hydrogen atoms at a shorter distance from the coordinated metal center and follow the decreasing metal charge in the order Ni > Pd > Pt. This trend suggests a more covalent character of the ligand-metal bonds with the increase of the metal atomic number. Furthermore, a slightly poorer agreement between experimental and calculated data is observed in the presence of the nickel(II) ion. Such discrepancy is explained by the formation of stacked oligomers, aimed at minimizing the repulsive interactions with the polar DMSO solvent
The potential of antimicrobial peptides isolated from freshwater crayfish species in new drug development: A review
Full text linkThe much-publicised increased resistance of pathogenic bacteria to conventional antibiotics has focused research
effort on the characterization of new antimicrobial drugs. In this context, antimicrobial peptides (AMPs)
extracted from animals are considered a promising alternative to conventional antibiotics. In recent years,
freshwater crayfish species have emerged as an important source of bioactive compounds. In fact, these invertebrates rely on an innate immune system based on cellular responses and on the production of important
effectors in the haemolymph, such as AMPs, which are produced and stored in granules in haemocytes and
released after stimulation. These effectors are active against both Gram-positive and Gram-negative bacteria. In
this review, we summarise the recent progress on AMPs isolated from the several species of freshwater crayfish
and their prospects for future pharmaceutical applications to combat infectious agents
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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