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Circular dichroism of polyncleotides: Interactions of NiCl2 with poly(dA-dT)center dot poly(dA-dT) and poly(dG-dC)center dot poly(dG-dC) in a water-in-oil microemulsion
No full textThe thermal behavior of the synthetic, high molecular weight, double
stranded polynucleotides poly(dA-dT)poly(dA-dT) [polyAT] and poly(dG-dC)poly(dGdC)
[polyGC] solubilized in the aqueous core of the quaternary water-in-oil cationic
microemulsion CTAB|n-pentanol|n-hexane|water in the presence of increasing amounts
of NiCl2 at several constant ionic strength values (NaCl) has been studied by means of
circular dichroism and electronic absorption spectroscopies. In the microemulsive medium,
both polynucleotides show temperature-induced modifications that markedly vary
with both Ni(II) concentration and ionic strength. An increase of temperature causes
denaturation of the polyAT duplex at low nickel concentrations, while more complex
CD spectral modifications are observed at higher nickel concentrations and ionic
strengths. By contrast, thermal denaturation is never observed for polyGC. At low Ni(II)
concentrations, the increase of temperature induces conformational transitions from BDNA
to Z-DNA form, or, more precisely, to left-handed helical structures. In some
cases, at higher nickel concentrations, the CD spectra suggest the presence of Z0-type
forms of the polynucleotid
INTERACTIONS OF ORGANOTIN(IV) HALIDES WITH REDUCED GLUTATHIONE IN AQUEOUS-SOLUTION
No full textGlutathione (GSH) is a compound extremely common among many living organisms in which it plays a fundamental role in the processes of detoxification. Also, organotin(IV) derivatives are more and more commonly used in technological processes or as antitumor drugs. So it seemed interesting to investigate the possible interactions between GSH and organotin compounds in water. Particularly, it has been studied because of its role in the organic radicals linked to the tin center on the stoichiometry and the structure of the adducts. Information was obtained following the reaction between MenSnCl4-n (n = 1 to 3) and GSH by Mossbauer and NMR spectroscopies on the assumption that changes of the characteristic parameters such as the quadrupole splitting and the chemical shift and coupling constants, respectively, are closely related to modifications in the coordination of the tin atom.
In the case of addition of GSH to a solution of CH3SnCl3 in HEPES, complex equilibria are evidenced, while in the case of Me2SnCl2 and of Me3SnCl only a single species is present. Mossbauer effect data together with point charge calculations and H-1 NMR results point to a 2:1 and a 1:1 complex, respectively; GSH is coordinated by the S(thiolic) atom and the coordination geometry around the tin center appears to be trigonal bipyramida
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
The interaction of native calf thymus DNA with FeIII-dipyrido[3,2-a:2’,3’-c]phenazine
Full text linkThe mono and bis dipyrido[3,2-a:20,30-c]phenazine (dppz) adducts of iron(III) chloride, i.e. [Fe(dppz)]Cl3 and [Fe(dppz)2]Cl3, have been synthesized and characterized. The interaction of the FeIIIdppz hydrolyzed aquo complex with native calf thymus DNA has been monitored as a function of the metal complex–DNA molar ratio, by variable temperature UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The results obtained in solution at various ionic strength values give support for a tight intercalative binding of the FeIIIdppz cation with DNA. In particular, the appearance of induced CD bands, caused by the addition of FeIIIdppz, indicate the existence of a rigid metal complex–DNA-binding leading to dominating chiral organization of FeIIIdppz species within the DNA double helix. The trend of selected CD bands with the molar concentration of FeIIIdppz emphasizes that the presence of high amounts of metal complex induces also the formation of DNA–FeIIIdppz supramolecular aggregates in solution. The analysis of fluorescence measurements allowed us to calculate a value of the intercalative binding constant comparable to that obtained by UV spectrophotometric titration. Finally, the temperature dependence of the absorbance at 258 nm shows that the metal complex strongly increases the DNA melting temperature already at metal complex–DNA molar ratio equal to 0.25 suggesting that metal complex intercalation effectively hinders DNA denaturation. Overall, the results of the present study point out that the FeIIIdppz aquo complex has DNA-binding properties analogous to those previously reported for the tris-chelate FeII(phen)2dppz complex (phen = 1,10-phenantroline)
Natural or synthetic nucleic acids encapsulated in a closed cavity of amphiphiles
No full textIn this review some aspects of the interactions of organized structures of amphiphiles with natural or synthetic DNAs are briefly considered. In particular DNAs encapsulated in closed cavities of amphiphiles, specifically giant vesicles and water-in-oil droplets and reverse micelles, are dealt with. Two main applications of giant vesicles are reviewed in detail, namely their use as microreactors where reactions can be followed by optical microscopy on a single vesicle and in synthetic biology as protocell models or as potential semi-synthetic ‘‘living’’ cells. Water-in-oil droplets uses for rapid and relatively low-cost DNA amplification by PCR reaction are described as well as for in vitro transcription and translation. A large variety of non-Watson–Crick conformations of polynucleotides observed in the aqueous inner core of reverse micelles is illustrated and compared with those observed in matched water solutions
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
1H-NMR RELAXATION STUDY OF THE LIPOSOME - NUCLEI INTERACTION
No full textPhospholipidic liposomes can influence DNA template availability for RNA synthesis when interacting with isolated nuclei by enhancing (when the phospholipids are negatively charged) or by inhibiting (when they are neutral) trascriptional activity. The analysis of the 1H-NMR relaxation behaviour of isolated nuclei, of Small Unilamellar Vesicles (SUV) and of the SUV-Nuclei system has been undertaken to elucidate the mechanism of the interaction between the nuclear core and the phospholipids
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