1,721,121 research outputs found
Giuseppe Norcio, Epigrammi di Marco Valerio Marziale
No full textKnecht Daniel. Giuseppe Norcio, Epigrammi di Marco Valerio Marziale. In: L'antiquité classique, Tome 52, 1983. p. 380
Studio della formazione di complessi tra alluminio e molecole di interesse ambientale, biologico e farmaceutico
No full texttesi di dottorato di ricerc
Studio della formazione di complessi tra alluminio e molecole di interesse ambientale, biologico e farmaceutico
Full text linkIn this thesis work, the coordination properties of several ligands with pharmaceutical, biological and toxicological properties towards Al3+ have been studied. The investigated molecules are 3-hydroxy-2-(1H)-pyridinone (HPyr), 2-hydroxyphenylethanone (HPE), 2-hydroxybenzeneacetic acid (HBA), 2-hydroxynicotinic acid (HNic), 3-hydroxypicolinic acid (HPic), and glutamic acid (Glu).
The reliability of the speciation data has been considered as one of the primary goals. For this reason, each metal-ligand system has been studied by means of a combination of more analytical techniques, so that independent results have been obtained regarding the stoichiometry of the existing complexes and their stability constants. The techniques employed have been potentiometry, UV-Vis spectrophotometry, and 1H-NMR spectroscopy. For HPyr it was also possible to obtain a crystal, so that the structure of an Al-HPyr complex has been evaluated by means of a X-ray diffractometric analysis.
The complexation strength of the studied ligands has been compared each other and with the complexation strength of other ligands previously studied in the literature. The comparison results indicate that Al3+ complexes can be very stable only if the chelating oxygens bear a significant partial negative charge and they can form a 5 or 6-membered chelation ring. HBA forms very weak complexes, as a 7-membered chelation ring is formed by this ligand. In the case of Glu, the complexes are weak because the metal centre is coordinated also by nitrogen, which has a lower affinity towards Al3+ than negatively charged oxygens. HPE bears two oxygens and forms a six-membered chelation ring. However, this ligand forms much weaker complexes than HPyr, HNic, and HPic, because the net negative charge on the HPE oxygens is 0.5, and not (practically) –1 as it is in the other three ligands.
Another aim of this work was the set-up of a new computer programme, PITMAP, which can be used for the elaboration of potentiometric titrations. PITMAP input files are the titration data, and the output results are the stability constants of the species which form in solution at equilibrium, through fitting of experimental parameters
Mathematical functions for the representation of chromatographic peaks
No full textAbout ninety empirical functions for the representation of chromatographic peaks have been collected and tabulated. The table, based on almost 200 references, reports for every function: 1) the most used name; 2) the most convenient equation, with the existence intervals for the adjustable parameters and for the independent variable; 3) the applications; 4) the mathematical properties, in relation to the possible applications. The list includes also equations originally proposed to represent peaks obtained in other analytical techniques (e.g. in spectroscopy), which in many instances have proved useful in representing chromatographic peaks as well; the built-in functions employed in some commercial peak-fitting software packages were included, too. Some of the most important chromatographic functions, i.e. the Exponentially Modified Gaussian, the Poisson, the Log-normal, the Edgeworth/Cramér series and the Gram/Charlier series, have been reviewed and commented in more detail
Effect of instrumental ESI-MS parameters on aluminium(III)-ligand solution equilibria
No full textElectrospray ionization mass spectrometry (ESI-MS) is being increasingly employed in the study of metal-ligand equilibria in aqueous solution [1, 2, 3]. In the present work, the ESI-MS spectral changes due to different settings of the following listed parameters are analysed: the solution flow rate (FS), the nebulizer gas flow rate (FG), the sprayer potential (E), and the temperature of the counter-current gas flow (T). 28 spectra were obtained for each of six samples containing aluminium(III) and 1,6 dimethyl 4 hydroxy 3 pyridincarboxylic acid at various pH, in the absence or in presence of a buffer, triethylamine, and acetic acid. The abundance of relevant ions were fitted versus the value s of FS, FG, E and T. Most of ionic intensities were significantly related to these instrumental parameters. Correlations were interpreted considering the presence of three kinds of perturbations occurring in the ESI ion source: formation of dimers in the droplets, different transfert efficiency from the gas phase for different complexes (according to their surface activity), and subsequent partial thermal decomposition of dimers and of some of the complexes in the gas phase.
Our results show that the evaluation of the effects produced in the ESI-MS spectra by a change of instrumental parameters can allow to identify the perturbation occurring when metal-ligand solutions are studied by ESI-MS.
References:
[1] Valerio B. Di Marco et al., Mass Spectrometry Reviews, 2006; 25, 347-379.
[2] Ray Colton et al., Mass Spectrometry Reviews, 1995; 14, 79-106.
[3] Valerio B. Di Marco et al., Journal of Mass Spectrometry, 2009; 4, 120-127
Parva quidem arbitrio: uno studio sulle "Bucoliche" di Marco Valerio.
No full textCon la tesi in oggetto, che si configura prevalentemente come un lavoro di orientamento esegetico e, in misura minore, filologico-ecdotico, ci si prefigge l’obiettivo di sottoporre ad un’accurata analisi, condotta su più livelli (letterario, metrico, paleografico, ecc.) e concentrata su una serie di passaggi testuali reputati di particolare pregnanza, il testo delle Bucoliche di Marco Valerio, di controversa datazione. Dopo un consistente capitolo introduttivo, in cui vengono illustrati lo stato dell’arte, i dati essenziali su Marco Valerio e sulla tradizione testuale, diretta e indiretta, affiancati ad alcune considerazioni paleografiche e ad una completa disamina metrica del testo, svolta con criteri statistici e comparativi, s’inizia il discorso sull’opera, nella forma di una Quellenforschung ragionata, ripartito in cinque sezioni, una per ciascuna delle quattro ecloghe esametriche e per il prologo in distici elegiaci. Si procederà anche all’integrazione di un insieme di osservazioni innovative, tralasciate o sfuggite all’attenzione dei critici fino ad oggi, principalmente riguardanti la quarta ecloga, in cui sembra possibile cogliere distinte consonanze verbali o tematiche con i trattati di retorica ciceroniani e con quelli filosofici di Boezio, specie quelli appartenenti alla cosiddetta vetus logica, o ancora con il commento al Somnium Scipionis di Macrobio e con certi autori patristici, sia latini (Agostino) che greci (Gregorio di Nazianzo e Apollinare di Laodicea)
Thermodynamic properties of copper complexes used as catalysts in Atom Transfer Radical Polymerization
No full textAtom Transfer Radical Polymerization (ATRP) is one of the most efficient controlled radical polymerization techniques used for the preparation of various polymers with well defined features such as high molecular weights, low polydispersities and precise molecular architectures [1]. The process is catalyzed by transition metal complexes, especially copper(I) complexes with nitrogen-based ligands [2].
Factors that affect the equilibrium between the activation step in which the propagating radicals are generated and the deactivation step in which the latter are converted to dormant species include disproportionation of the metal complex, standard potentials of the catalyst and dormant species and halogenophilicity of the metal complex [3].
In this communication, we report the results of a thermodynamic study of copper complexes with pentamethyl-diethylenetriamine and tris[2-(dimethylamino)ethyl]amine in acetonitrile. In particular, we determined the stability constants of Cu(II) and Cu(I) complexes as well as the standard potentials of the Cu(II)/Cu(I) and Cu(I)/Cu couples.
1. Braunecker, W.A.; Matyjaszewski, K. Prog. Polym. Sci. 2007, 32, 93-146. 2. Pintauer, T.; Matyjaszewski, K. Coord. Chem. Rev. 2005, 249, 1155-1184. 3. Tsarevsky, N.V; Braunecker, W.A; Matyjaszewski, K. J. Organomet. Chem. 2007, 3212-3222
New possible chelating agents of clinical interest for iron(III): 2-hydroxynicotinic acid and 3-hydroxypicolinic acid. A thermodynamic study
No full textThe formation of complexes between iron(III) and two ligands of possible relevance to chelation therapy, 2-hydroxynicotinic acid and 3-hydroxypicolinic acid, in aqueous 0.6 m (Na)Cl at 25 °C, has been investigated by means of potentiometric titrations and UV measurements. In both cases several mononuclear complexes and their deprotonation products are formed
Complex formation between aluminium(III) and two hydroxy-aromatic ligands: 2-hydroyphenylethanone and 2-hydroxybenzeneacetic acid.
No full textThe formation of complexes between aluminium(III) and two hydroxy-aromatic ligands of possible environmental and biological relevance, 2-hydroxy-phenylethanone (HPE) and 2-hydroxybenzeneacetic acid (HBA), in aqueous 0.6 m (Na)Cl at 25 °C has been investigated by means of potentiometric titrations.
In both systems, the formation of two complexes, AlL and AlLH–1, has been observed, and the following stability constants have been evaluated: for HPE (pKa = 10.027 ± 0.004), log (beta)AlL = 7.34 ± 0.01 and log (beta)AlLH–1 = 1.97 ± 0.04; for HBA (pKa1 = 4.116 ± 0.004 and pKa2 = 10.507 ± 0.008), log (beta)AlL = 8.06 ± 0.03 and log (beta)AlLH–1 = 3.11 ± 0.07. The qualitative and quantitative results obtained have been partially confirmed by UV-spectrophotometry and 1H NMR spectroscopy
- …
