1,720,981 research outputs found
Conformational studies on a medium size cyclopseudopeptide containing the oxazolidin-2-one moiety
No full textAn efficient synthesis of a 24 pseudopeptide membered ring in solution is reported in good yield. The cycle contains four units, all formed by an a-amino acid (Xaa) and a 4-carboxy-5-methyl-oxazolidin-2-one group (4-carboxy-5-methyl- oxazolidin-2-one = Oxd) in the same configuration (L or D). In the final sequence, the four LL or DD units are alternated so that, after cyclization, cyclo-(L-Xaa-L-Oxd-D-Xaa-D-Oxd-L-Xaa-L-Oxd-D-Xaa-D-Oxd) is formed. The conformational analysis of this compound has been performed by means of infrared and 1H NMR spectroscopy and shows that the CHa hydrogens of the a-amino acids retain the very deshielded chemical shifts recorded in the spectra of the free precursors. Furthermore, the NH hydrogen have a weak tendency to form cross peaks, thus suggesting that the cycle lies in a large circle able to host small molecules, thus this compound is a promising candidate for drug delivery studies. Copyright © 2012 John Wiley & Sons, Ltd
Heat recovery potential and electrical performances in-field investigation on a hybrid PVT module
No full textThe aim of the present study is the characterization of PVT modules electrical performance in real operating conditions, as well as the investigation of thermal recovery via a cooling circuit integrated with a third generation PV module. The approach combines both theoretical and experimental tools: a MatLab® simulation model provides a reliable theoretical basis, whose validation is performed on experimental evidences from in-field PV module tests. The model represents the module energy balance, under unsteady operating conditions; a full set of measurements allowed to validate the theoretical approach, thus offering the possibility to evaluate the effects of both variable outdoor air temperature and pressure and wind speed. Water-cooled PV modules electrical performance increases by as much as 33%, with respect to the situation in which no cooling is performed and up to a 20% electric efficiency is achieved, with a 2.0 L/min water flow rate on the back. A major drawback is that thermal recovery for cogeneration purposes is not effective, due to a low thermal gradient (10 K maximum) on the water. When a 10 mm thick glass cover was integrated in the PV module along with a frame to reduce wind circulation over exposed surfaces, a 100â500 W thermal recovery on a day basis could be achieved. Furthermore, a 15â30 K increase in water temperature assures about the higher quality of the recoverable heat. The suitability of organic fluids instead of water to reduce the power absorption by the pump, is addressed as the most effective way to increase PVT electric output: the absorption with R236fa and R245fa is a 60% and 75% lower than with water, respectively. The novelty of the present study lies in the dual theoretical and experimental approach, leading to a validated non-steady-state mockup, easily adjustable to extend the analysis to PV modules arrays for residential applications. Furthermore, the use of an infrared camera, typically confined to post-manufacturing quality control, allows here a continuous monitoring of the module thermal field, key to evaluate the temperature effect on the module performances both in steady and unsteady conditions
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
Foldamers based on oxazolidin-2-ones
No full textFoldamers are artificial molecules capable of organization into well defined secondary structures such as helixes, Î2 sheets and turns. The essential requirement for an oligomer to qualify for inclusion in the foldamer family is to possess a well defined, repetitive secondary structure, imparted by conformational restrictions imposed by the monomeric unit. These compounds may be composed of subunits of any kind, but most of them contain unusual amino acids and/or aromatic units. We describe the synthesis, the conformation analysis and the physical properties (in the solid state) of pseudopeptide foldamers containing imido-type functions, obtained by coupling the nitrogen of a 4-carboxy oxazolidin-2-one unit with the carboxylic acid moiety of the next unit, which may be another 4-carboxy oxazolidin-2-one or an amino acid. Such an imido-type function is characterized by a nitrogen atom connected both to an endocyclic and to an exocyclic carbonyl group, and tends always to adopt the trans conformation. As a consequence of this remarkable property, which causes local constraint, these imido-type oligomers are forced to fold in ordered conformations. In combination with interactions of other kinds (H bond, apolar interactions, etc.), these lead to the formation of supramolecular materials. The synthetic approach is highly tuneable with endless variations, so materials with required properties may be prepared "on demand", simply by changing the design and the synthesis. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Formation of gels in the presence of metal ions
No full textA small library of stereoisomeric pseudopeptides able to make gels in different solvents has been prepared and their attitude to make gels in the presence of several metal ions was evaluated. Four benzyl esters and four carboxylic acids, all containing a moiety of azelaic acid (a long chain dicarboxylic acid) coupled with four different pseudopeptide moieties sharing the same skeleton (a phenyl group one atom apart from the oxazolidin-2-one carboxylic group), were synthesized in solution, by standard coupling reaction. The tendency of these pseudopeptides to form gels was evaluated using the inversion test of 10 mM solutions of pure compounds and of stoichiometric mixtures of pseudopeptides and metal ions. To obtain additional information on the molecular association, the gel samples were left dry in the air to form xerogels that were further analyzed using SEM and XRD. The formation of gel containing Zn(II) or Cu(II) ions gave good results in term of incorporation of the metal ions, while the presence of Cu(I), Al(III) and Mg(II) gave less satisfactory results. This outcome is a first insight in the formation of stable LMWGs formed by stoichiometric mixtures of pseudopeptides and metal ions. Further studies will be carried out to develop similar compounds of pharmacological interest. © 2011 Springer-Verlag
Pseudopeptide Foldamers designed for photoinduced intramolecular electron transfer
No full textWe have designed and prepared three pseudopeptide foldamers, called dyads 1, 2 and 3, equipped with a donor and an acceptor unit to promote intramolecular electron transfer after light excitation. All the three dyads contain the same donor and acceptor, which are a derivative of 1,5-dihydroxynaphthalene and a derivative of pyromellitic diimide, respectively. The donor and acceptor units are separated by hybrid foldamers of different length in order to vary both their distance and relative orientation. Specifically, one, two or three L-Ala-D-Oxd (Ala 1⁄4 alanine, Oxd 1⁄4 4-carboxy-5-methyl-oxazolidin-2-one) units are contained in dyads 1, 2, and 3, respectively. Dyad 1 folds in a bent conformation in which the donor and acceptor units lie one close to the other, while dyads 2 and 3 preferentially assume an extended conformation. In all the three dyads both the donor and acceptor emissions are efficiently quenched via intramolecular electron transfer, as suggested by photophysical and electrochemical investigations. Because of its bent conformation dyad 1 exhibits a charge-transfer (CT) band at 410 nm in CH2Cl2 solution and a photoinduced electron transfer that occurs more efficiently than in dyads 2 and 3. Upon dissolving dyad 1 in DMSO, a competitive solvent for hydrogen bonds that establish in the pseudopeptide
linker, the CT band disappears and the efficiency of electron transfer slightly decreases, in agreement with an unfolded conformation in which donor and acceptor units are no longer in close contact
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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