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Eventi Molecolari in uno Spazio Confinato
No full textThe scope of this Ph.D. thesis deals with the synthesis of molecular cages based on tris(2-pyridylmethyl)amines (TPMAs) scaffold and characterized by the presence of metals having a non-saturated coordination sphere in the inner part of the system. The new molecular architectures were synthesized taking advantage of Dynamic Covalent Chemistry DCC, in particular imine condensation, on opportunely functionalized TPMA metal complexes. The main objective was to control the self-assembly of the TPMA metal complexes in order to obtain new functional systems. The cages obtained have allowed to describe several molecular events within a confined space.
In the Introduction chapter, after a brief overview of TPMAs synthesis and the coordination chemistry, the supramolecular applications of TPMAs complexes are reported. The latter is mainly focused on chirality sensing and recent supramolecular structures involving these ligands. A part of the survey is dedicated to the applications of TPMAs complexes as metal receptor and anion sensor and the capability of this ligand to coordinate the metal center in helical fashion which allowed the use of these ligands as molecular switches. Afterwards, this property is further analyzed toward the application of these metal complexes in the determination of enantiomeric excess (e.e) and other functions. In the last section, TPMAs are envisaged as capping agents to obtain several supramolecular structures.
In Chapter 1 the synthesis of a novel supramolecular cage built from the self-assembly of TPMA zinc complexes through imine condensation chemistry is reported. The cage recognition properties over a variety of structurally related dicarboxylic acid guests, together with the kinetic study of the template assembly and disassembly, have been investigated in detail. This knowledge has been used to selectively modulate the rate of both assembly and disassembly processes. In particular, a novel disassembly method induced by strain release of the guest has been developed.
In Chapter 2 is reported the extension of the cage series varying the structural parameter and the metal ion coordinated to the TPMA unit. These cages have been obtained through the self-assembly of modified tris(pyridylmethyl)amine complexes and different diamines have been chosen to vary their size and flexibility. The recognition properties of this cage series were characterized with a novel rapid method based on ESI-MS therefore the determination of binding profiles for linear saturated dicarboxylic acids within the cage series was studied. This methodology has allowed to gather how small changes in the structure of the host and guest can contribute to the recognition events. Moreover, it was possible to study molecular systems which contains paramagnetic metals that are not suitable for classical binding constant determination by 1H NMR.
In Chapter 3 is discussed the synthesis of a novel chiral supramolecular cage and the capability of this structure to control the helicity of a perfluorinated carbon chain are reported. The helix configuration of the perfluoroalkyl chain was evaluated with a combination of theoretical calculations of the host-guest complex and the support of Vibrational Circular Dichroism (VCD) experiments
In Chapter 4 a detailed study on homo and hetero co-encapuslation processes within a supramolecular cage is reported. In particular, the model case under study regards the possibility to have different p-substituted benzoic acid, within a supramolecular cage containing two metals. While electron-withdrawing EWG substituents are preferential guests, it has been possible to evaluate the conditions in which hetero co-encapuslation is favoured. This part of the study has been carried out in part at the University of Cambridge (UK) in the group of Prof. C.A. Hunter. In the Appendices are contained the experimental information related to each chapter
Supramolecular cage encapsulation as a versatile tool for the experimental quantification of aromatic stacking interactions
No full textSupramolecular cages as differential sensors for dicarboxylate anions: Guest length sensing using principal component analysis of ESI-MS and 1 H-NMR raw data
No full textTris(2-pyridylmethyl)amines as emerging scaffold in supramolecular chemistry
No full texttris-(2-Pyridylmethyl)amine (usually abbreviated as TPA or TPMA) are ligands which are emerging in many fields of chemistry because of their ability to form stable and catalytically active complexes with a wide variety of metals. While the applications in catalysis began soon after the synthesis of the first metal complexes, studies in supramolecular chemistry are more recent and they often take advantage from their stereodynamic nature. This review surveys TPMA applications as: i) anion sensors, ii) biochemical sensors, iii) molecular switches, iv) chiral probes and as v) building blocks in the synthesis of supramolecular cages
Helicity control of a perfluorinated carbon chain within a chiral supramolecular cage monitored by VCD
Full text linkConfinement within supramolecular systems is the leading technology to finely tune guest functional properties. In this communication we report the synthesis of a chiral supramolecular cage able to bias the helicity of a perfluorinated carbon chain hosted within the cage. We monitor the phenomenon of chiral induction by Vibrational Circular Dichroism (VCD) experiments complemented by DFT calculations over the possible conformers
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
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