1,721,077 research outputs found
PHOTOACID SWITCHING IN FUSED-RING N-RICH AROMATICS
No full text[1,2,4]triazolo[3,2-c][1,2,4]triazole is a simple fused-ring N-rich aromatic
system, with remarkable properties with respect to acid-base behavior and
tautomerism1-3. Neutral heterobicycles (HL) exhibit amphoteric behaviour
(they can deliver the N−H proton forming the conjugated base L-
and can
accept up to two protons, forming the species H2L+
and H3L++) and show an
unprecedented tautomeric switching upon protonation, as revealed by single
crystal X-ray analysis and confirmed by theoretical calculations4
. By
varying the groups attached at the heterocycle, a remarkable shift of pKai
values, up to 5-6 units, is observed. The studies of the acid-base properties
in the excited state show that the N-H group in neutral triazolo-triazoles has
an intrinsic photobasic behavior. Singly protonated forms of the system
have instead a photoacid behavior. If a photoacid phenol group is attached at
position 7 of the intrinsically photobasic triazolo-triazole unit, the
interaction between the two complementary photoactive functions in the
same molecule is additive, in such a way that in the ground state N-H is
more acid than O-H while the opposite holds in the excited state. So,
between ground and excited state, the acid proton is delivered by different
sites of the same molecule (photoacid switching).
[1] C-H Zhou, Y. Wang,Current Medicinal Chemistry,19 (2012) N.2, 239-
280.
[2] Y. Murti at all, American Journal of Chemistry1 (2011) 42-46.
[3] R. Centore, S. Fusco, A. Capobianco,V. Piccialli, S. Zaccaria, and A.
PelusoEuropean Journal of Organic Chemistry18 (2013) 3721-3728.
[4] R. Centore, C. Manfredi, S. Fusco, C. Maglione, A. Carella, A.
Capobianco, A. Peluso, D. Colonna, A. Di Carlo,Journal of Molecular
Structure 1093 (2015) 119–124
A THERMODYNAMIC STUDY ON THE RESVERATROL-WATER SYSTEM
No full textResearch on the effects of dietary polyphenols on human health has
developed considerably in the past. It strongly supports a role for
polyphenols in the prevention of degenerative diseases, particularly
cardiovascular diseases and cancers1,2. The antioxidant properties of
polyphenols have been widely studied, but it has become clear that the
mechanisms of action of polyphenols go beyond the modulation of
oxidative stress. In nature we can find resveratrol as two diastereoisomers:
(Z)- resveratrol and (E)- resveratrol that presents a major stability3
Fig1.- trans-resveratrolo
In the present work is presented a thermodynamic study on resveratrol in
aqueous solutions. Acid-base properties of resveratrol have been
investigated. The study has been conducted at 25.00 ± 0.02°C, in constant
ionic medium, NaCl 0.5 M/ethanol 4% (v/v) by using potentiometry, UVVis
spectrophotometry (absorption and emission), chromatography (HPLC).
A chemical investigation on the interaction of the resveratrol with metals of
biological interest, such as Mn2+ and Cu2+has also been carried out. The
study indicated the formation of a predominating Me(II)-resveratrol,
mononuclear complexes.
[1] M. Valko, D. Leibfritz, J. Moncol, M. Cronin, M. Mazur, J. Telser,, The
International Journal of Biochemistry & Cell Biology, 39(2007) 44–84
[2] D. Delmas, Virginie Aires, E. Limagne, P. Dutartre, F. Mazue, F.
Ghiringhelli and N. Latruffe, Ann. N.Y. Acad. Sci.,1215 (2011) 48-59
[3] M. Deak and H. Falk, On the Chemistry of the Resveratrol
Diastereomers, Monatshefte feur Chemie, 134(2003)883–888
HO
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
Thermodynamic Properties of Dopamine in Aqueous Solution. Acid-Base Properties, Distribution, and Activity Coefficients in NaCl Aqueous Solutions at Different Ionic Strengths and Temperatures
No full textThe acid-base properties of dopamine were studied in different experimental conditions by potentiometry, UV-spectrophotometry, and spectrofluorimetry. The distribution measurements between 2-methyl-1-propanol/pure water (or NaCl aqueous solutions up to I = 1.02 mol kg(-1)) were carried out at T = 298.15 K and 310.15 K. The potentiometric measurements were used to calculate the total concentration of the ligand in each phase, and from simple mass balance equations, using the free hydrogen concentration and the protonation constants, it was possible to calculate the ligand neutral species concentration and the distribution coefficient. The salting parameter and the activity coefficient of the neutral species were calculated by means of the Setschenow equation. Independently of the experimental conditions, a good agreement between the protonation constants obtained from the different techniques was obtained. The dependence of the protonation constants on ionic strength was modeled by means of the Debye-Huckel type and Specific ion Interaction Theory (SIT) approaches, and the specific interaction parameters of the ionic species were determined. For the protonation constants, the following thermodynamic values were obtained at T = 298.15 K, log K-1(H0)=10.886 +/- 0.042; log K-2(H0) = 9.107 +/- 0.032; at T = 310.15 K, log K-1(H0) =10.260 +/- 0.024; log K-2(H0) = 8.418 +/- 0.018. From the distribution measurements the following distribution coefficients at infinite dilution were obtained at T = 298.15 K, log K-D0(0) = 0.705 +/- 0.013; at T = 310.15 K, log K-D0(0) = 0.983 +/- 0.014
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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