126,261 research outputs found
Comprendere le immagini: segni iconici e segni plastici
No full textQuesto scritto corrisponde al primo dei tre capitoli di cui sono autrice all’interno del volume. Si tratta del capitolo quinto, intitolato "Comprendere le immagini: segni iconici e segni plastici". Avvalendosi dei contributi teorici e metodologici offerti da svariate discipline (l’iconologia, la semiotica e la retorica visiva), esso affronta la complessa questione delle modalità attraverso le quali riconosciamo e comprendiamo le immagini, siano esse le immagini artistiche o quelle presenti nei manifesti pubblicitari. In particolare, vengono indagati i seguenti problemi: il rapporto tra visuale e verbale; il rapporto tra immagini e oggetti del mondo; l’esistenza di una “grammatica” dell’immagine, con le sue peculiari relazioni tra il piano dell’espressione e il piano del contenuto, così come tra segni iconici e segni plastici; i processi di significazione dell’immagine, fra denotazione e connotazione
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Improving the reliability of MM-PBSA and MM-GBSA binding energy predictions by explicitly considering ligand solvation shells
No full textMolecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) and Molecular Mechanics Generalized Born Surface Area (MM-GBSA) are interesting techniques for drug design/discovery applications, but sometimes the correlation between predicted and experimental binding energies might result unsatisfactory.
Nowadays, a certain effort is focused on ameliorating the solvation term in MM-PB/GBSA calculations and some strategies were applied to obtain a better correlation between calculations and experiments.
Some authors reported that the predictivity of MM-PB/GBSA calculations might be improved by modulating the internal dielectric constant (εin).1 Unfortunately, a universal εin, suitable for all systems was not found and a thorough analysis of the binding pocket is needed to choose the proper value of εin.
MM-PB/GBSA binding energy predictions might also be improved by explicitly considering selected water molecules in the calculation, however this strategy is controversial.2-5
Herein, we report on how the explicit inclusion of variably populated ligand hydration shells might improve the correlation between MM-PB/GBSA computed binding energy and experimental activities.
DNA-topoisomerase, α-thrombin, penicillopepsin, avidin, and neuraminidase complexes with different ligands were considered as test sets, and ligand hydration shells populated by an increasing number of water molecules were systematically evaluated.
We found that the consideration of a hydration shell populated by a number of water residues (Nwat) between 30 and 70 provided in all the considered examples a positive effect on correlation between MM-PB/GBSA calculated binding affinities and experimental activities, with a negligible increment of computational cost.6
REFERENCES
1. Hou, T.; Wang, J.; Li, Y.; Wang, W., J. Chem. Inf. Model. 2011, 51, 69-82.
2. Wong, S.; Amaro, R. E.; McCammon, J. A., J. Chem. Theory Comput. 2009, 5, 422-429.
3. Hayes, J. M.; Skamnaki, V. T.; Archontis, G.; Lamprakis, C.; Sarrou, J.; Bischler, N.; Skaltsounis, A.-L.; Zographos, S. E.; Oikonomakos, N. G., Proteins 2011, 79, 703-19.
4. Freedman, H.; Huynh, L. P.; Le, L.; Cheatham, I. I. I. T. E.; Tuszynski, J. A.; Truong, T. N., J. Phys. Chem. B 2010, 114, 2227-2237.
5. Checa, A.; Ortiz, A. R.; de Pascual-Teresa, B.; Gago, F., J. Med. Chem. 1997, 40 (25), 4136-45.
6. Maffucci, I.; Contini, A., J. Chem. Theory Comput. 2013, 9 (6), 2706-2717
Tautomeric equilibria of benzopyranoimidazoles: useful insights from quantum chemical calculation and NMR
No full textThe development of novel syntetic strategies for achieving compounds containing the coumarin nucleus condensed to several heterocycles has been the subject of our research for the latter few years. [1] Such heterocycles are pharmacologically relevant as CNS depressants, [2] growth inhibitors of mammalian cancer [3] and also phosphodiesterase VII inhibitors for treatment of immunity-associated diseases. [4]
Recently we reported the synthesis of some substituted benzopyranoimidazolones, and we pointed out the possibility of such heterocycles to exist in solution in at least two tautomeric forms, the N3-H and the N1-H tautomers (Fig. 1). [5] The study and quantitative evaluation of prototropic tautomerism in heterocyclic compounds is of primary interest, influencing both reactivity and biological behavior, for example the ability of a drug to bind the active site of a target enzyme [6]. Unfortunately literature does not report any reliable structural information and neither experimental data concerning tautomerism on pyranoimidazolone nucleus. Furthermore RT NMR experiments conducted by us so far were able to evidence the presence of at least two tautomers only for compound 4d and the attempts previously reported by us to unequivocally assign the preferred tautomeric structure by NMR were unsuccessful. The only result was obtained by N-methylation of compound 4d, were just the N3-CH3 product was isolated both at high and low reaction temperatures. However the reaction condition adopted could have influenced the tautomeric equilibrium. On the other hand tautomerism has been successfully described on various substituted imidazoles by ab-initio and DFT calculations in both gas-phase and solution within the continuum solvent model or evaluating explicit solvent interactions. [7]
In our previous work, where the main object was the development of a synthetic strategy for benzopiranoimidazoles, preliminary quantum chemical calculations explained only in part the tautomeric behavior observed, thus the need of a throughout theoretical and experimental investigation. The relative stability of all the possible tautomers for [1]benzopyrano[3,4-d]imidazol-4(3H)-ones, namely the N3-H (alpha tautomer), N1-H (beta tautomer), coumarin O-H (gamma tautomer) and C2-H (delta tautomer), has been evaluated by mean of HF and B3LYP calculations, including the solvent contribution by the SCRF PCM model. Furthermore the 13C and 1H chemical shifts were calculated by GIAO technique at the HF/6-311+G(2d,p) and B3LYP/TZVP levels of theory both in gas phase and in solution by using the PCM model for DMSO. The calculation of 13C chemical shifts by GIAO technique and the comparison with the experimental has been reported as one of the most reliable methods for the investigation of tautomeric equilibria in solution [8]. Finally, 1H NMR spectra were recorded in CD3COCD3 at 500 Mhz at variable temperature in a range from RT to –60°C in order to evidence the presence of the most probable tautomers by progressively lowering their interconversion rates.
The combination of the above mentioned theoretical techniques and experimental NMR allowed us to demonstrate that:
1.The only relevant tautomeric equilibrium for benzopyranoimidazolones is between alpha and beta forms.
2.All compounds 4a-e are able to exhibit tautomeric equilibrium in polar solvents.
3.The interconversion rate between alpha and beta tautomers is fast, thus by NMR is possibile to detect the presence of both tautomers only at low temperatures, otherwise averaged signals are recorded.
Bibliography
1.[a] E.M. Beccalli, A. Contini and P. Trimarco, Eur. J. Org. Chem., 2003, 3976-3984, [b] E.M. Beccalli, A. Contini and P. Trimarco, Tetrahedron Letters, 2004, 45, 3447-3449.
2.V. L. Savel’ev, N. T. Pryanishnikova, V. A. Zagorevskii, I. V. Chernyakova, O.S. Artamonova, V. V. Shavyrina, L. I. Malysheva, Khim. Farm. Zh. 1983, 17, 697-700; see Chem. Abstr. 1983, 99, 158325.
3.M. Trkovnik, V. Kalaj, D. Kitan, Org. Prep. Proced. Int., 1987, 19, 450-455
4.M. Eggenweiler, J. Rochus, M. Wolf, M. Gassen, O. Poeschke, Merck Patent Gmbh, Germany, PCT Int. Appl. 2001; see Chem. Abstr. 2001, 134, 331619.
5.See ref 1a
6.P. Pospisil, P. Ballmer, G. Folkers, L. Scapozza, Tautomerism of nucleobase derivatives and their score in virtual screening to thymidine kinase, Abstracts of Papers, 224th ACS National Meeting, Boston, MA, United States, August 18-22, 2002
7.[a] O. V. Shishkin, O. S. Sukhanov, L. Gorb and J. Leszczynski, PCCP, 2002, 4, 5359-5364. [b] G. -S. Li, M. F. Ruiz-Lopez, M. S. Zhang, B. Maigret, J. Mol. Struct. (Theochem), 1998, 422, 197-204. [c] E. D. Raczyńska, Anal. Chim. Acta, 1997, 348, 431-441. [d] G. A. Worth, P. M. King, W. G. Richards, Biochem. Biophys. Acta, 1989, 993, 134-136. [e] G. -S. Li, M. F. Ruiz-Lopez, M. -S. Zhang, B. Maigret, J. Phys. Chem., 1997, 101, 7885-7892. [f] F. J. Luque, J. M. Lopez-Bes, J. Cemeli, M. Aroztegui, M. Orozco, Theor. Chem. Acc., 1997, 96, 105-113.
8.[a] N. E. Campillo, C. Montero, J. A. Páez, J. Mol. Struct. (Theochem), 2004, 678, 83-89. [b] E. Kleinpeter and A. Koch, J. Phys. Org. Chem., 2001, 14, 566-576
Performing the undiscovered solo piano works of Italian composer Lucia Contini Anselmi (1876-1913)
No full text© 2022 Quilby NelsonLucia Contini Anselmi (b.1876-d.? after 1913) was an Italian composer and pianist. Born in Vercelli, Italy, Contini Anselmi wrote over thirty works, mainly for solo piano. Despite the current surge of research into women composers of the nineteenth and twentieth centuries, there is little known about Contini Anselmi with no major research to date, compounded by the lack of research into Italian female composers of this time period. Therefore, this study will serve to fill both these gaps in the literature. The goal of this research is to present a performance approach to two of Contini Anselmi’s works, Ludentia Op. 11 (1913) and Sibylla Cumaea Op. 15 (1916) through a practice-led research orientation. This will be realised through the application of the writings in Contini Anselmi’s treatise, Della tecnica per l’esecuzione della musica sul pianoforte e sua interpretazione, a previously unknown document published in 1908
Munari, Rodari e Malaguzzi nell’educazione alla creatività
No full textIl capitolo si inserisce in un volume che si propone un duplice obiettivo: 1) individuare i modelli teorici che stanno alla base dell’odierno concetto di creatività; 2) individuare pratiche, metodologie e strategie educative che consentano di promuovere la creatività nei bambini di età prescolare. Il capitolo in questione si rapporta a entrambi gli obiettivi: esso ricostruisce infatti alcuni nodi essenziali delle concezioni della creatività elaborate da Bruno Munari (1907-1998), Gianni Rodari (1920-1980) e Loris Malaguzzi (1920-1994), con particolare riguardo alle idee o alle proposte che hanno avuto più influenza su educatori e istituzioni educative, insegnanti e scuole, e che sembrano tuttora estremamente attuali, in grado di orientare l’esplorazione di nuove strategie di educazione alla creatività.
Il capitolo è stato unitariamente pensato e discusso dalle autrici. Tuttavia, per quanto concerne la stesura del testo, Annamaria Contini ha redatto i paragrafi 4.1, 4.1.1, 4.1.2, 4.1.3, 4. 2, 4.2.1 e 4.2.2, mentre Chiara Bertolini ha redatto i paragrafi 4.2.3, 4.3 e 4.4
- …
