1,720,993 research outputs found
Accurate computational prediction of the structural and vibrational properties of s-triazine derivatives in vacuo. A DFT approach
No full textThe well-known class of herbicides, s-triazine derivatives, are commonly used as reagents in the manufacture of resins and pharmaceuticals, and also of solvent-refined coals. Recently, triazine derivatives have been observed to form self-assembling nanostructures on metallic surfaces. In this paper, we present a study using a DFT approach for the computational prediction of the structural and vibrational properties in vacuo of three s-triazine derivatives, viz., atrazine (N,. N'-ethyl-isopropyl-6-chloro-1,3,5-triazine,2,4-diamine), prometryn (N,. N'-diisopropyl-6-methyl-thio-1,3,5-triazine,2,4-diamine) and simetryn (N,. N'-diethyl-6-methyl-thio-1,3,5-triazine,2,4-diamine). In particular we show that the employment of the Becke three-parameter Lee-Yang-Parr (B3-LYP) exchange-correlation functional using the aug-cc-pVQZ basis set provides an accurate prediction of the structural and vibrational properties of atrazine, prometryn, and simetryn
Rapid gaschromatografic method for determination of carbamazepine and unrearranged carbamazepine-10,11-epoxide in human plasma
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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
Studio spettroscopico della cimetidina.
No full textSono stati studiati gli spettri elettronici e vibrazionali della cimetidina (cim) e dei suoi complessi con ioni metallici, sia allo stato solido, sia in soluzione acquosa diluita. Lo spettro UV del sistema cim-Cu2+ evidenzia un intenso doppietto a 320 e 370 mn che puo’ essere utilizzato a scopo analitico
Combined experimental and theoretical study on electronic and vibrational states of cimetidine.
No full textCimetidine is a drug used in the treatment of peptic ulcer, and acts as a powerful histamine H2-receptor antagonist. The study of electronic and vibrational states of cimetidine, with a combined theoretical and experimental investigation on structural and electronic properties, is of prime importance because of/since the high flexible structure and the presence of different functional groups in the molecule. The aim of this work is to use a multidisciplinary approach, involving theoretical and computational methods, photochemistry and vibrational spectroscopy, to better explain the biological and physiological effects of this drug. Quanto-mechanical (HF, DFT and semi-empirical) methods were employed to estimate the energetic stability and the vibro-electronic properties of cimetidine. In the first part of the work, the experimental vibrational spectra of cimetidine alone and after the interaction with silver particles (obtained with traditional and surface enhanced Raman spectroscopies respectively) were compared with extensive ab initio calculations. In the second part, the study of the singlet excited states and the consequent electronic spectra calculations in vacuum and in different solvents with semi-empirical and ab initio methods, were presented with experimental UV-vis absorption and fluorescence spectra in order to understand the nature of excited states and to evaluate the effects of the solvent on the electronic properties of cimetidine
Spectrophotometric study on the interaction of cimetidine with Co(II), Cu(II), Ni(II) and Zn(II) metal ions.
No full textCimetidine (cim) is a drud largely used in medicine for its blocking effect on histamine H2 receptors. Its pharmacological action appeared related to the interaction with metal ion leading to the formation of metallo-complexes; for this purpose 4 cim-metal systems were studied by the mole ratio method. A further spectrophotometric analysis was performed in order to obtain reliable spectra of 2:1 and 1:1 cim-metal complexes. The UV-vis spectra of all cim-metal complexes exhibit one band at 220 nm, whose wavelength does not shift upon complexation with cim. Nevertheless, they changes in intensity, supporting the existence of both 1:2 and 1:1 metal complexes. Moreover, the spectra of the Cu(II) complex clearly shows the formation of two new bands at about 332 and 368 nm and a third weak, broad absorption at 619 nm. The effect of the counter-ion was considered too, extending the measurements to chlorides, nitrates and perchlorates of the selected cations.
The analysis of the spectrophotometric data suggests that Cu(II)-cim complexes are the most stable and therefore confirms the results already obtained by SERS (Surface Enhanced Raman Spectroscopy) technique on the same systems
Theoretical and Raman spectroscopic study on the interaction of cimetidine (cim) with Mg++ and Ca++ ions.
No full textCimetidine (cim), a widely used drug for peptic ulcer disease, was found to affect serum levels of calcium and magnesium. The complexes of cim with Mg++ ions have been previously studied by nuclear magnetic resonance and we deepened this study by using a combined theoretical (computational analysis) and experimental (spectroscopic techniques) approach. The theoretical analysis of complexes between cim and Mg++ or Ca++ ions showed that cim is a flexible molecule, acting as a bidentate ligand toward divalent ions, using nitrogen atoms. Moreover, it suggested that Mg(Cim)2++ complex is the most stable; its structure is probably a distorted octahedron in which thè two S atoms complete the coordination shell. Raman study on the solid 2:1 cim/Mg++ and cim/Ca++ complexes supported the theoretically provided interaction sites, as suggested by the noticeable wavenumbers shift observed in vC-H and vC-N vibrations. The study was extended in the very diluted solutions (ppm) range by using the Surface Enhanced Raman Spectroscopy (SERS), mimicking the physiological active concentrations of cim. SERS spectra suggested, upon the binding of cim to silver colloids (with a mechanism that mimics the binding to a protein), the formation of a 1:1 adduct, as cim acts as a monodentate ligand. Thus, Mg++ con bridge the substrato with other bioactive structures
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