1,720,988 research outputs found
Pd(II)/1,10-phenanthroline complexes bearing arene ligands: On the role of N- vs O-coordination to tune their cellular activity and binding ability towards DNA and RNA
No full textThree Pd(II)-based complexes of 1,10-phenanthroline and N- or O-coordinating ligands have been synthesised and tested with different relevant biosubstrates like double-stranded DNA, double and triple helix of RNA, DNA G-quadruplexes of different conformations and bovine serum albumin. Here a correlation between N- vs O-coordinating elements and binding mechanism emerged, where the N-coordinating ligands proved to be the most promising. These outcomes were confirmed also in the cellular experiments. The Pd(II) complex with naphthalene-1,8-diamine is the one that is able to be carried by BSA, to strongly bind nucleic acids, to produce reactive oxygen species (ROS) and to show the best cellular performances (poorly toxic towards healthy cells and highly toxic against the cisplatin-resistant cancer cell line). On the opposite, the complex with benzene-1,2-diolate may be sequestered by BSA, weakly binds nucleic acids, does not produce ROS and shows poor cellular activity. The complex with benzene-1,2-diamine stays in between. Other mechanistic details are discussed which show that the biophysical behaviour is the sum of the contribution of aromaticity, charge and N- or O-coordination
Adding Diversity to a Diruthenium Biscyclopentadienyl Scaffold via Alkyne Incorporation: Synthesis and Biological Studies
Full text linkWe report the synthesis and the assessment of the anticancerpotentialof two series of diruthenium biscyclopentadienyl carbonyl complexes.Novel dimetallacyclopentenone compounds (2-4) were obtained (45-92% yields) from the thermal reaction(PhCCPh exchange) of [Ru2Cp2(CO)(& mu;-CO){& mu;-& eta;(1):& eta;(3)-C(Ph)C(Ph)C(O)}], 1, with alkynes HCCR [R = C5H4FeCp (Fc),3-C6H4(Asp), 2-naphthyl; Cp = & eta;(5)-C5H5, Asp = OC(O)-2-C6H4C(O)Me]. Protonation of 1-3 by HBF4 afforded the corresponding & mu;-alkenyl derivatives 5-7, in 40-86% yields. All productswere characterized by IR and NMR spectroscopy; moreover, cyclic voltammetry(1, 2, 5, 7) andsingle-crystal X-ray diffraction (5, 7)analyses were performed on representative compounds. Complexes 5-7 revealed a cytotoxic activity comparableto that of cisplatin in A549 (lung adenocarcinoma), SW480 (colon adenocarcinoma),and ovarian (A2780) cancer cell lines, and 2, 5, 6, and 7 overcame cisplatin resistancein A2780cis cells. Complexes 2, 5, and 7 (but not the aspirin derivative 6) inducedan increase in intracellular ROS levels. Otherwise, 6 strongly stabilizes and elongates natural DNA (from calf thymus,CT-DNA), suggesting a possible intercalation binding mode, whereas 5 is less effective in binding CT-DNA, and 7 isineffective. This trend is reversed concerning RNA, and in particular, 7 is able to bind poly(rA)poly(rU) showing selectivity forthis nucleic acid. Complexes 5-7 caninteract with the albumin protein with a thermodynamic signature dominatedby hydrophobic interactions. Overall, we show that organometallicspecies based on the Ru2Cp2(CO)( x ) scaffold (x = 2, 3) are activeagainst cancer cells, with different incorporated fragments influencingthe interactions with nucleic acids and the production of ROS
Mg(II) and Ni(II) induce aggregation of poly(rA)poly(rU) to either tetra-aggregate or triplex depending on the metal ion concentration
Full text linkThe ability of magnesium(II) and nickel(II) to induce dramatic conformational changes in the synthetic RNA
poly(rA)poly(rU) has been investigated. Kinetic experiments, spectrofluorometric titrations, melting experiments
and DSC measurements contribute in shedding light on a complex behaviour where the action of metal
ions (Na+, Mg2+, Ni2+), in synergism with other operators as the intercalating dye coralyne and temperature,
all concur in stabilising a peculiar RNA form. Mg2+ and Ni2+ (M) bind rapidly and almost quantitatively to the
duplex (AU) to give a RNA/metal ion complex (AUM). Then, by the union of two AUM units, an unstable tetraaggregate
(UAUA(M2)*) is formed which, in the presence of a relatively modest excess of metal, evolves to the
UAUM triplex by releasing a single AM strand. On the other hand, under conditions of high metal content, the
UAUA(M2)* intermediate rearranges to give a more stable tetra-aggregate (UAUA(M2)). As concerns the role
of coralyne (D), it is found that D strongly interacts with UAUA(M2). Also, in the presence of coralyne, the ability
of divalent ions to promote the transition of AUD into UAUD is enhanced, according to the efficiency sequence
[Ni2+]≫[Mg2+]≫[Na+]
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
Stabilisation and nucleic acids binding of a +3 ion: the Aluminium/Cacodylate/RNA system
No full textMetal ions influence the three-dimensional architecture and function of nucleic acids, can induce folding of nucleic acids strands, or even can aid catalytic mechanism in ribozymes. Therefore, investigations of metal ion binding to specific sites, and of the ability to stabilize local motifs or particular non-canonical structures are of primary interest.
We have recently found that Mg(II) and Ni(II) cations are able to induce quadruplex and triplexes formation starting from duplex poly(rA)poly(rU) under still unexplored high ions concentrations. We have now extended our research to the study of the less explored class of tervalent metal ions. The interaction between aluminium(III) and poly(rA) nucleic acid, both in the form of single or double strand, has been analysed. The Al3+/poly(rU) system has been also investigated for comparison purposes. At the pH range needed for these experiments (pH = 5 - 7) the stability of Al3+ in solution is guaranteed by the cacodylate buffer that also complexes the metal ion. It is shown that the binding occurs indeed, with features that differ on passing from poly(rA) to poly(rA)poly(rA). The fast process of the metal ion binding to RNA is studied by means of the initial rate analysis in different reactants conditions and a binding mechanism is proposed. This enables the main binding species to be individuated. In the case of poly(rA) a slow cooperative aggregation of the single strands is found to occur (figure, right), that is favoured by the presence of the aluminium ion. The different binding features will be discussed
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