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Hybrid Nanostructured Materials for Application in Catalysis and Molecular Recognition
Full text linkThis Ph.D. thesis describes the versatility of amine triphenolate complexes to be used either as self-assembling molecular scaffolds with applications in material sciences and molecular recognition, like titanium (IV) μ-oxo TPA complexes, or as active catalysts in homogeneous and heterogeneous catalysis, mainly vanadium (V) TPA complexes.
In Chapter 1, the principles of self-assembly are listed, i.e. control on the electronic properties and size discrimination for the realization of supramolecular structures, error-checking, and efficiency, in the way of building up ordered and highly-structured entities under mild conditions. Different examples are proposed, but the analysis is mainly focused on the possibility of applying self-assembly in metal coordination chemistry in order to design highly ordered and functional systems, that may find applications in catalysis or material sciences. In this view, the coordination chemistry and the behaviour in solution of Ti(IV) TPA complexes are presented and in particular the possibility to switch between mononuclear and dinuclear μ-oxo species, depending on the steric nature of peripheral substituents, as well as the feasibility to build up highly functional Ti(IV) molecular scaffolds. A brief introduction on V(V) TPA complexes is reported as well, especially on their Lewis acid nature and structural characteristics that make them be considered as functional models of natural vanadium-dependent haloperoxidases and be used as active catalysts in oxygen transfer reactions.
As the realization of new efficient and functional supramolecular systems supposes the design of the right building blocks, in Chapter 2, the modification of amine triphenolate skeleton is proposed. The functionalization strategy that has been adopted is based on a click-type oxime bond formation upon reaction of an aldehyde group, which can be effectively and selectively inserted on TPA ligands through the so-called Duff reaction, and a wide variety of alkoxyamines. In this way, the ligand skeleton has been efficiently decorated with polar and positively charged moieties, such as TEG arms and imidazolinium residues, and with pyrene groups. The functionalization has interested diverse positions of the ligand and even a double functionalization of two different positions on the same tri-phenolamine can be achieved.
Chapter 3 deals with titanium (IV) amine triphenolate complexes and with the thermodynamic stability in solution of a Ti(IV) complex obtained by complexation with tris-(2-hydroxy-3-phenylbenzyl)amine. In more details, the reaction gives rise to a mononuclear complex, which upon reaction with water stereoselectively self-assembles into a highly stable, inert, dinuclear, heterochiral S6-symmetric μ-oxo TPA complex. Highly decorated Ti(IV) μ-oxo TPA complexes can be efficiently obtained by effecting the complexation reaction on functionalized ligands reported in Chapter 2, or by directly functionalizing Ti(IV) μ-oxo TPA complexes, which bear six aldehyde groups in para and/or meta positions, with the appropriate alkoxyamine. The functionalization strategy enables to construct stable and spatially ordered materials. In particular, two different Ti(IV) μ-oxo TPA complexes, bearing pyrene groups in para and meta positions, respectively, have been used as molecular receptors for fullerene. Fluorescence spectroscopies and DOSY-NMR analyses clearly indicate that pyrene groups on titanium complexes interact with fullerene through π-π interactions. Additionally, interactions between pyrene groups in para position on Ti(IV) μ-oxo TPA complex and SWCNTs (single walled carbon nanotubes) has been studied as well. Even in this case, fluorescence studies have been carried out and AFM images clearly show that CNTs are covered from Ti(IV) μ-oxo TPA complexes, highlighting the possibility to use such these systems for the design of ordered and functional supramolecular structures.
Finally, in Chapter 4, the catalytic activity of V(V) TPA complexes is studied, both in sulfoxidation and aerobic oxidative C-C cleavage reactions. Firstly, the activity of an electron-poor V(V) TPA complex, bearing six chloro groups in ortho and para positions, is investigated in sulfoxidation reactions in presence of hydrogen peroxide as terminal oxidant. The reactions are performed with high yields and selectivities (catalyst loading down to 0.001% and TONs up to 89000). Both reaction rates and selectivities confirm the higher activity of the new catalyst with respect to the ones reported in literature. Moreover, modification of V(V) complexes through oxime bond formation has also led to the realization of organogelator-derived complexes, which have been found to form organogels in dioxane. Lastly, functionalization of V(V) complexes with positively charged moieties makes it possible to obtain water-soluble micelles, upon solubilisation with SDS (sodium dodecyl sulphate). The micellar like system has been tested in aerobic oxidative C-C cleavage of vicinal diols, with high selectivity and quite short reaction times. The compartmentalization of the catalytic system allowed its recycling and reuse for three times by extraction of products with organic solvents.Questa tesi di dottorato descrive la sintesi e la funzionalizzazione di complessi amminotrifenolati di titanio (IV) e vanadio (V) per applicazioni in reazioni di riconoscimento molecolare e in catalisi.
Nel Capitolo 1, sono illustrati i principi che regolano il self-assembly, quali controllo, correzione degli errori ed efficienza. E’ mostrato come questi possano essere applicati per la realizzazione di entità ordinate e strutturate in chimica di coordinazione, per la costruzione di sistemi metallo-supramolecolari, con applicazione in catalisi o scienze dei materiali. In quest’ottica, sono studiati la chimica di coordinazione e il comportamento in soluzione di complessi TPA di titanio (IV) e in particolare la capacità di fornire specie mono- o dinucleari a seconda dell’ingombro sterico dei sostituenti periferici e la possibilità di costruire scaffolds molecolari di titanio (IV) altamente funzionalizzati. Inoltre, è riportata una breve introduzione sui complessi TPA di vanadio (V), in particolar modo sulla loro proprietà di acidi di Lewis e sulle loro caratteristiche strutturali, che fanno sì che vengano considerati dei modelli funzionali delle aloperossidasi naturali vanadio-dipendenti e quindi vengano utilizzati come catalizzatori in reazioni di trasferimento di ossigeno.
Nel Capitolo 2, viene proposta una strategia sintetica per modificare lo scheletro trifenolamminico. La funzionalizzazione prevede la formazione di un legame ossimico, mediante una reazione click-simile tra un’aldeide, che può essere selettivamente introdotta sul legante mediante reazione di Duff, e una varietà di alcossiammine. In questo modo, lo scheletro del legante può essere efficientemente decorato con residui polari e carichi positivamente, come residui TEG o imidazolinio, e con gruppi pirene. La funzionalizzazione può coinvolgere diverse posizioni del legante, così come una doppia derivatizzazione di posizioni differenti sulla stessa trifenolammina.
Nel Capitolo 3, è presentata la possibilità di ottenere dei complessi dinucleari μ-oxo amminotrifenolati di titanio (IV) per reazione di complessazione della tri-(2-idrossi-3-fenilbenzil)ammina con Ti(Oi-Pr)4. Più in dettaglio, il complesso mononucleare, che si forma dalla reazione, in presenze di tracce d’acqua è in grado di auto-assemblarsi in maniera stereoselettiva, dando origine a un complesso dinucleare, altamente stabile, inerte, eterochirale, con simmetria S6. La funzionalizzazione del complesso può essere ottenuta efficacemente mediante una duplice via: effettuando la reazione di complessazione sui leganti funzionalizzati riportati in Capitolo 2, oppure funzionalizzando direttamente complessi TPA μ-oxo di titanio (IV), che portano sei gruppi aldeidici in para e/o meta, con un’appropriata alcossiammina. La strategia di funzionalizzazione permette di costruire dei materiali stabili e spazialmente ordinati. In particolare, due complessi μ-oxo di titanio che portano gruppi pirene rispettivamente in para e meta sono stati utilizzati come recettori molecolari per il fullerene. Spettroscopie di fluorescenza ed esperimenti DOSY-NMR indicano chiaramente che i gruppi pirene sui complessi di titanio interagiscono con il fullerene mediante interazioni π-π. Come ulteriore applicazione, sono state studiate le interazioni tra gruppi pirene dei complessi TPA μ-oxo di titanio e nanotubi di carbonio (SWCNTs). Anche in questo caso, sono stati condotti studi di fluorescenza e analisi AFM mostrano chiaramente che i nanotubi sono rivestiti dai complessi di titanio, evidenziando la possibilità di usare questi sistemi per generare strutture supramolecolari ordinate e funzionali.
Infine, nel Capitolo 4, è studiata l’attività catalitica di complessi TPA d vanadio (V), sia in reazioni di solfossidazione che in reazioni di cleavage aerobico ossidativo di legami C-C. Prima di tutto, viene analizzata l’attività catalitica di un complesso di vanadio (V) elettron-povero, portante sei atomi di cloro in posizioni orto e para, in reazioni di solfossidazione in presenza di perossido d’idrogeno come ossidante terminale. Le reazioni sono condotte con alte rese e selettività, anche in presenza dello 0.001% di catalizzatore, con TON fino a 89000. Le velocità di reazione e le selettività confermano una attività maggiore del catalizzatore rispetto ai catalizzatori riportati in letteratura. In più, la modificazione di complessi TPA di vanadio (V) mediante formazione di un’ossima ha portato anche alla realizzazione di complessi funzionalizzati con catene organogelator e alla formazione di organogel in diossano. In conclusione, la funzionalizzazione di complessi TPA di vanadio (V) con residui carichi positivamente permette di ottenere micelle solubili in acqua, in seguito a solubilizzazione con SDS (sodio dodecil solfato). Il sistema micellare è stato poi testato in reazioni di cleavage aerobico ossidativo di legami C-C di dioli vicinali, con elevate selettività e tempi di reazione relativamente bassi. Il sistema catalitico può essere inoltre riciclato e riutilizzato fino a tre volte in seguito a estrazione dei prodotti con solventi organic
Vanadium catalyzed aerobic carbon-carbon cleavage
No full textIn recent years, the use of vanadium complexes as catalysts and air or oxygen as oxidants has emerged as a new method for the effective oxidative carbon-carbon bond cleavage in a series of substrates, including 1,2-diols and α-hydroxy ethers. In addition to the advantageous use as a synthetic tool, vanadium catalyzed aerobic C. C bond cleavage becomes even more appealing if applied to the degradation of lignocellulosic biomass and in particular in the oxidative depolymerization/degradation of lignin or cellulose. In this review, this chemistry, the most recent advances and the role played by homogeneous vanadium complexes are presented and discussed.SCOPUS: re.jinfo:eu-repo/semantics/publishe
Viral nano-hybrids for innovative energy conversion and storage schemes
No full textTypical rod-like viruses (the Tobacco Mosaic Virus (TMV) and the Bacteriophage M13) are biological nanostructures that couple a 1D mono-dispersed morphology with a precisely defined topology of surface spaced and orthogonal reactive domains. These biogenic scaffolds offer a unique alternative to synthetic nano-platforms for the assembly of functional molecules and materials. Spatially resolved 1D arrays of inorganic-organic hybrid domains can thus be obtained on viral nano-templates resulting in the functional arrangement of photo-triggers and catalytic sites with applications in light energy conversion and storage. Different synthetic strategies are herein highlighted depending on the building blocks and with a particular emphasis on the molecular design of viral-templated nano-interfaces holding great potential for the dream-goal of artificial photosynthesi
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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