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Dithiolene and thiolate transition metal complexes: towards an exploration of their multi-functional properties
Full text linkThis work has dealt with the synthesis and characterization of transition metal complexes with two types of sulphur based ligands: 1,2 dithiolato ligands and thiol-carboxylate ligands.
The electronic features related to the metal-sulphur interaction, such as the rich redox behaviour associated to the interplay between the sulphur and a redox active metal, the better overlap between sulphur and metal orbitals, the ability of forming coordination compounds in different topologies, from discrete complexes to extended 1-D network, make sulphur-based coordination compounds. We have explored these features starting from non redox innocent metal bis-dithiolene complexes as possible molecular precursors in the field of molecular magnetism, as paramagnetic centers able to organize in more complex coordination compounds.
In the first part of this work, “classical” metal bis-dithiolene complexes have been investigated as metallo-ligands towards the coordination of “acceptor” metal complexes, in order to build up coordination compounds of higher nuclearities with paramagnetic centers. Particularly, the investigated dithiolenes were [Cu(mnt)2]2- ,[Cu(tfadt)2]2-and [Ni(dmid)2].- while the “acceptor” metal complexes are Mn(III) porphinato ,Mn(III) salen-like complexes and finally a mixed valence Mn(II)Mn(III) complex.
We have observed that the reactivity in solution of metal-bis –dithiolene together with the Mn-based complexes employed has lead to co-crystallization salts where the coordinating group of the dithiolene does not coordinate the Mn center.
From these observation, we have decided to synthesize a series of new 1,2 dithiolato ligands bearing a potential coordinating functional group. We have choosen to functionalize them with crown-ether macrocycles with different sizes, in order modulate their selectivity for transition metal ions or lanthanide ions. The corresponding radical nickel(dithiolene) complexes have been synthesized and polymetallic Ni-Na and Ni-Ni chains have been obtained as well as a bimetallic Ni-Ni discrete complex. We have provided their physico-chemical characterizations in order to understand their rich redox behaviour and their magnetic properties. The investigation on these new 1,2 dithiolato ligands is still in progress in order to build up polymetallic assemblies also with lanthanide ions.
We have then switched to another class of sulphur-based ligands, the thiol-carboxylate ligands. 2-mercaptonicotinic acid has been considered as versatile ligand towards the synthesis of sulphur-based metal complexes. This polyfunctional ligand can coordinate with N, O or S donor atoms. Under hydrothermal conditions, Zn(II) and 2-mercaptonicotinic acid afforded a coordination polymer where 2-mercaptonicotinic acid is S,O chelating. The electronic properties were studied by means of theoretical calculations and experimental measurments.
Under the same reaction conditions, Ni(II) did not led to any crystalline material. By switching the reaction conditions, it has been observed a mononuclear S,O chelated Ni bis(mercaptonicotinate).Questo lavoro di dottorato ha riguardato la sintesi e la caratterizzazione di complessi di metalli di transizione con leganti donatori allo zolfo.
In particolare sono stati considerati i leganti 1,2 ditiolato e un legante tipo tiol-carbossilato, l’acido 2-mercaptonicotinico.
Lo zolfo presenta una variabilità maggiore di stati di ossidazione rispetto all’ossigeno e a questo si riconduce il particolare comportamento redox dei complessi con legami M-S. Per questo motivo la sintesi di complessi implicanti il legame metallo-zolfo è un’area di ricerca attiva soprattutto per quanto riguarda la progettazione di materiali con proprietà di conduzione, ottiche o magnetiche.
In questo contesto sono stati considerati i complessi dei metalli di transizione con i leganti 1,2 ditiolato, altresi detti metallo bis-ditioleni.
Nei metallo bis-ditioleni la variabilità degli stati di ossidazione del complesso senza grandi variazioni della geometria di coordinazione li rende adatti per la sintesi di materiali molecolari. In particolare, una via sintetica per l’ottenimento di tali materiali consiste nell’organizzare questi complessi via coordinazione ad un altro centro metallico, in maniera da ottenere composti a più alta nuclearità. Soprattutto per quanto riguarda il magnetismo molecolare, vi è la necessita di organizzare nella stessa molecola più centri paramagnetici.
In questo lavoro di tesi, inizialmente dithioleni paramagnetici “classici” come [Cu(mnt)2]2- ,[Cu(tfadt)2]2-and [Ni(dmid)2].-, contenenti gruppi funzionali potenzialmente coordinanti sono stati impiegati come metallo-leganti verso complessi paramagnetici di Mn(III) o a valenza mista Mn(II)/Mn(III). Durante gli esperimenti condotti, è risaltata la reattività in soluzione dei metallo bis-ditioleni verso lo scambio di leganti che non ha condotto alla formazione del complesso polunucleare sperato, sebbene siano stati isolati composti potenzialmente interessanti.
Alla luce di tutto cio, è stata intrapresa la sintesi di nuovi leganti 1,2 ditiolato opportunamente funzionalizzati con gruppi coordinanti quali gli eteri corona.
La versatilità dei ditioleni verso la funzionalizzazione ha permesso di realizzare una serie di leganti con diverse dimensioni del macrociclo, in modo da poter modulare la selettività verso metalli di transizione ma anche verso ioni di lantanidi trivalenti.
Sono stati sintetizzati a partire da questi leganti i complessi ditioleni di nickel, isolandoli in forma di anioni e aventi spin S=1/2. Sono state ottenuti complessi polimetallici Ni-Ni e Ni-Na. Inoltre è stato ottenuto un complesso bimetallico Ni-Ni.
Tutti i complessi sono stati caratterizzati chimicamente. Inoltre, le proprietà magnetiche sono state indagate tramite misure di suscettività magnetica in funzione della temperatura, rivelando per il complesso polimetallico Ni-Ni una forte interazione fra le unità ditiolene costituenti il complesso.
Il legante tiol-carbossilato acido 2- mercaptonicotinico è stato considerato per la sua versatilità alla coordinazione. In condizioni idrotermali e in presenza di Zn(II) e acido 2-mercaptonicotinico, è stato ottenuto un polimero di coordinazione dove il legante mercaptonicotinato funge da chelante S,O e lega a ponte monoatomico i vicini centri metallici. La stessa topologia non è stata ottenuta con il Ni(II). Cambiando le condizioni di reazione, finora solo il complesso monometallico Ni(II) bis-mercaptonicotinato è stato ottenuto.
Le proprietà elettroniche correlate alla situazione di coordinazione S-Zn-O del polimero di coordinazione di Zn(II) sono state investigate per mezzo di calcoli teorici e misure sperimentali
Nanocrystalline Cellulose from the Solitary Tunicate Phallusia Mammillata, a Valuable Nanocellulose Precursor
Full text linkAscidians are ubiquitous filter-feeding marine invertebrates, the only animals producing cellulose in their outer tunic, in the form of a composite structure of cellulose microfibrils linked to a protein matrix. This study reports the successful processing of Phallusia mammillata, a species prevalent in the Northern Adriatic Sea, into high-quality nanocellulose (NC). An optimized extraction method followed by chemical modification is applied to produce suitable precursors for cellulose-based products. Structural, compositional, and thermal characterization demonstrated the high degree of crystallinity of the extracted cellulose, which is further processed into both cationic and anionic forms by direct reaction of nanofibril suspensions. High-aspect-ratio nanofibrillated cellulose (NFC) with a fibrils diameter of 10 ± 2 nm is directly obtained from purified tunics. Anionic nanocrystals and cationic nanofibrils with a mean diameter of 8 ± 2 nm are obtained from pristine nanofibrillated cellulose suspensions. To the best of the authors’ knowledge, this is the first report on the extraction and processing of cellulose from Phallusia mammillata, opening new possibilities toward high-grade cellulose-based materials exploiting an abundant local resource
Molecular, Electronic, and Crystal Structures of Self-Assembled Hydrothermally Synthesized Zn(II)−Mercaptonicotinate: A Combined Spectroscopic and Theoretical Approach
No full textA Zn(II) 2-mercaptonicotinate coordination polymer (Zn1), with Zn(II) ions chelated by both sulfur and oxygen in a
distorted square pyramidal environment, and a molecular Zn(II) 2-hydroxynicotinate complex (Zn2) were synthesized
by the reaction of zinc acetylacetonate with 2-mercaptonicotinic (Zn1) and 2-hydroxynicotinc (Zn2) acid, respectively, under hydrothermal conditions. The crystal structures of Zn1 and Zn2 were determined by single crystal X-ray diffraction measurements. Dispersion-corrected density functional theory (DFT) calculations reproduce very well the
experimental structures and show that Zn1 is stable against hydration, whereas Zn2 is stable against dehydration over wide ranges of temperature and pressure, in agreement with thermogravimetric analysis results. The electronic structure of the two compounds is computed with the DFT+U method. The theoretical valence band agrees well with the X-ray photoelectron spectroscopy experiments. Furthermore, the band gap of Zn1 is found to be narrower than that of Zn1 and is characterized by the presence of sulfur lone pairs at the edge of the valence band
Nuovo metodo di sintesi per l'ottenimento di ossido di zinco nanocristallino da precursori con leganti bidentati.
Full text linkopenTESI.3540La copia a stampa della tesi e' disponibile presso la biblioteca con la collocazione indicat
Nuovo metodo di sintesi per l'ottenimento di ossido di zinco nanocristallino da precursori con leganti bidentati.
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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
Functional bioglass/carbon nanocomposite scaffolds from vat photopolymerization of a novel preceramic polymer-based nanoemulsion
Full text linkSilicone polymers are already known as feedstock for a variety of silicate bioceramics, in the form of scaffolds with complex shapes, obtained by Vat Photopolymerization. Printing is enabled by using silicone blended with photocurable acrylates. The development of a particular silicate composition that functions as a glass or glass-ceramic precursor is possible by the addition of suitable oxide fillers (especially carbonate powders), suspended in the polymer blend. Oxides, from the fillers, easily react with silica left by the thermal transformation of the silicone. The fillers, however, also determine complications in Vat Photopolymerization, due to light scattering; in addition, local oxide concentrations generally impede the obtainment of glassy products. The present paper illustrates a simple solution to these issues, based on the inclusion of a Ca salt in nano-emulsion within a silicone-containing blend. Homogeneous printed samples are later converted into crack-free, fully amorphous ceramic composites, by firing at only 700 °C. The glass matrix, resembling 70S30C (70 % SiO2 and 30 % CaO) bioglass, is achieved according to the quasi-molecular CaO distribution. The secondary phase, promoted by treatment in N2 atmosphere and consisting of pyrolytic carbon, provides a marked photothermal effect.Fil: Stábile, Franco Matías. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Famengo, Alessia. Consiglio Nazionale delle Ricerche; ItaliaFil: Pedron, Danilo. Università di Padova; ItaliaFil: Elsayed, Hamada. Università di Padova; Italia. National Research Centre. Ceramics and Building Materials Department; EgiptoFil: Bernardo, Enrico. Università di Padova; Itali
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
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