1,721,020 research outputs found
IDENTIFICAZIONE E CARATTERIZZAZIONE STRUTTURALE DI UNA NUOVATIPOLOGIA DI G-QUADRUPLEX DI ORDINE SUPERIORE
No full textInsight Into the Conformational Arrangement of a Bis-THF DiolCompound Through 2D-NMR Studies and X-Ray StructuralAnalysis
No full textThe conformational arrangement of an all-threo
bis-THF diol compound, synthesized through the RuO4-
catalysed oxidative bis-cyclization of farnesyl acetate, was
determined via crystallographic analysis and detailed 2DNMR
solution studies. The bis-THF compound crystallizes
in the orthorhombic Pbca space group, with unit cell parameters
a = 10.496(1), b = 17.974(1), c = 19.777(2) A ° ,
Z = 8. The final refinement converged to R1 = 0.0484 for
4714 independent observed reflections having I[2r(I).
There is a good agreement between the solution molecular
conformation determined by 2D-NMR and the X-ray
molecular conformation. The molecule adopts a folded, horse
shoe-type conformation both in solution and in the crystal,
that suggests aptitude to coordinate cations. Additionally, in
the crystals, the molecular conformation is stabilized by
intramolecular and intermolecular H-bonding
DNA-based nanostructures: the effect of the base sequence on octamer formation from d(XGGYGGT) tetramolecular G-quadruplexes
No full textIn a previous work we have demonstrated that the DNA sequence CGGTGGT folds into a higher order G-quadruplex structure (2Q), obtained by the 5'-5' stacking of two unusual G(:C):G(:C):G(:C):G(:C) planar octads belonging to two identical tetra-stranded parallel quadruplexes, when annealed in the presence of ammonium or potassium ions. In the present paper, we discuss the role played by the title nucleosides X and Y (where X and Y stand for A, C, G, or T) on the formation and stability of 2Q structures formed by the XGGYGGT oligodeoxynucleotides. We found that the above mentioned dimerization pathway is not peculiar to the CGGTGGT sequence, but is possible for all the remaining CGGYGGT sequences (with Y = A, C, or G). Furthermore, we have found that the TGGAGGT sequence, despite the absence of the 5'-ending C, is also capable of forming a 2Q-like higher order quadruplex by using a slightly different dimerization interface, as characterized by NMR spectroscopy. To the best of our knowledge, this is the first characterization of a quadruplex multimer formed by an oligodeoxynucleotide presenting a thymine at its 5'-end. Examples of such structures were observed previously only in crystals and in the presence of non-physiological cations. Our results expand the repertoire of DNA quadruplex nanostructures of chosen length and add further complexity to the structural polymorphism of G-rich DNA sequences
Evaluating the potential of Hydrophilic Interaction Liquid Chromatography for collagen peptide mapping analysis
No full textThis study presents a systematic approach for developing an innovative hydrophilic interaction liquid chromatography (HILIC) method for collagen peptide mapping analysis. The predominant post-translational modification (PTM) of collagen, proline hydroxylation, introduces polar hydroxyl groups throughout the collagen sequence, making HILIC a promising alternative to classical reversed-phase liquid chromatography (RPLC) approaches. This study employs sixteen model peptides, selected from in silico predicted tryptic peptides with zero missed cleavages and representing diverse physicochemical properties and structural motifs of collagen. The peptides were used as standards to conduct detailed chromatographic evaluation. Various HILIC stationary phases and mobile phases were systematically examined to identify optimal separation conditions for collagen peptides, contributing to a better understanding of peptide behavior in HILIC. The study also explores the effects of sample diluent and injection mode, comparing classical injection with the Performance Optimizing Injection Sequence (POISe), to determine their impact on HILIC performance. Introducing a plug of weak solvent (acetonitrile) prior to sample injection, effectively mitigates the mismatch in eluent strength between the fully aqueous sample diluent (resulting from tryptic digestion) and the mobile phase, addressing issues of peak distortion. Different injection volumes (from 0.5 to 8 μL) and acetonitrile ratios (1:1, 1:2, 1:5 and 1:10) were tested to optimize sample injection and increase sensitivity of collagen tryptic peptides. Following method optimization, HILIC was coupled with mass spectrometry (MS) to evaluate its effectiveness in analyzing collagen-digested samples. This evaluation included the assessment of peptide sequence coverage and the method ability to identify hydroxylation patterns, thereby demonstrating its potential for detailed peptide analysis
Synthesis of 2,6-Dialkyl(aryl)purine Nucleosides by Exploiting the Reactivity of NebularineN1-Oxide towards Grignard Reagents
No full textThe synthesis of 2,6-dialkyl(aryl)purine nucleosides by appli- cation of a double addition of Grignard reagents to N1-oxide purine nucleosides is described. The synthetic protocol ex- ploits the reactivity of both the C6–N1–O– and C2–N1–O– moieties of the purine base. The overall process consists of initial Grignard reagent addition to the C6 of nebularine N1-oxide followed by aromatization to give a C6-substituted nu- cleoside. Regeneration of the N1-oxide is then followed by a second Grignard addition at C2 causing the opening of the pyrimidine ring. Cyclization of the transiently opened pyrim- idine is then driven by aromatization of the system to afford the final purine system
Insight into Pyridinium Chlorochromate Chemistry: Catalytic Oxidation of Tetrahydrofuran Compounds and Synthesis of Umbelactone
No full texthe catalytic system PCC (cat.)/H 5IO 6 has been used to oxidise mono- and polytetrahydrofuran compounds. New oxidative pathways are disclosed. 2,2,5-Trisubstituted THF rings are converted into dicarbonyl compounds through oxidative cleavage of the C2-C3 bond. Cyclic enol ethers appear to be intermediate species in this process. Oxidation of 2,2,5-trisubstituted α-keto-THF compounds proceeds with the oxidative cleavage of the C2(THF)-C=O bond to give 1,4-diketones with degraded carbon backbones. Attack of the oxidant on 2,5-disubstituted THF rings leads to 1,4-diketones containing intact THF carbon frameworks. Oxidation of complex poly-THF substrates, containing up to five THF rings, allows access to new poly-THF compounds through regioselective THF oxidation along the poly-THF backbones. A mechanistic explanation of the new processes consistent with the reported reactivity of PCC and the isolation of some minor products of the process is provided. The synthesis of racemic umbelactone, an antiviral natural butenolide metabolite, has been carried out by use of the developed chemistry. The catalytic oxidation of mono- and polytetrahydrofuran compounds has been carried out with chlorochromatoperiodate (CCP), generated by the combination of PCC and H 5IO 6. New synthetically useful oxidative transformations are disclosed. Umbelactone, an antiviral natural butenolide metabolite, has been synthesized by use of the developed chemistry
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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