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Materiali Organici p-Coniugati Chirali
No full textThe research conducted during the Ph.D. is divided into two main lines, both joined together by the key role played by chiral p-conjugated synthons within novel supramolecular systems. The first part involved the synthesis and utilization of 1,1'-binaphthylic derivatives. Starting from them, new chiral molecular cages capable of acting as chiroptical sensors for an important radioactive environmental pollutant (99TcO4-) were synthesized and studied (Chapter 2, in collaboration with Prof. Valeria Amendola, Pavia). The interaction between the cage and anion, mainly caused by hydrogen bonds, is transduced into a large modulation of the chiroptical signal.1 In chapter 3, in collaboration with Prof. Dominique Armspach (University of Strasbourg), new cyclodextrins "capped" with atropoisomeric 1,1'-biphenylic systems were synthesized. The process of chirality transfer from cyclodextrin (point chirality) to the biphenyl moiety (axial chirality) was investigated in detail, both in solution and in the solid state. The key role of intramolecular hydrogen bonds responsible for the efficient chirality transfer was demonstrated, and finally the temperature-dependent chiroptical activity of such systems was studied. The second research line involved the synthesis and utilization of triptycene synthons.2 New triptycene-fused quinacridone dyes were synthesized and studied, following our general strategy of merging nonplanar p-conjugated synthons and high-performance pigments (Chapter 4). Subsequently, after several unsuccessful attempts to resolve crucial chiral triptycene intermediates, such resolution was achieved by using chiral HPLC, in collaboration with the research group of Prof. Roberto Cirilli (chapter 5).2 Finally (chapter 6), in collaboration with Prof. Amendola's research group, new triptycene-fused benzimidazoles were synthesized. These derivatives were successfully used for the self-assembly via hydrogen bonding of chiral polymers consisting of triptycene-benzimidazoles and chiral (non-chromophoric) carboxylic acids. In this case, chirality is transferred via non-covalent interactions from simple chiral carboxylic acids to an equilibrating mixture (resulting from tautomeric equilibria) of triptycene/benzimidazole isomers. The resulting supramolecular structures proved to be capable of emitting circularly polarized light with glum dissymmetry factors up to 6*10-3.
References and Pubblications
1) R. Mobili ±, G. Preda ±,S. La Cognata, L. Toma, D. Pasini, V. Amendola, Chem. Commun., 2022, 58, 3897–3900.
2) G. Preda, A. Nitti, D. Pasini, ChemistryOpen 2020, 9, 719–727.
3) A. Rosetti, G. Preda, C. Villani, M. Pierini, D. Pasini, R. Cirilli, Chirality, 2021; 33, 883–890.La ricerca condotta durante il dottorato è divisa in due filoni principali, entrambi accumunati dal ruolo chiave rivestito da sintoni -coniugati chirali all’interno nuovi sistemi supramolecolari. Il primo filone ha riguardato la sintesi e l’utilizzo di derivati 1,1’-binaphthylic. A partire da essi, sono stati sintetizzati e studiati nuove gabbie molecolari in grado agire come sensori chirottici per un importante inquinante ambientale radioattivo (99TcO4-) (capitolo 2, in collaborazione con la Prof.ssa Valeria Amendola, Pavia). L’interazione tra gabbia e anione, causata principalmente da legami a idrogeno, viene tradotta in ampio cambiamento del segnale (chir)ottico.1 Nel capitolo successivo, in collaborazione con il Prof. Dominique Armspach (Università di Strasburgo) sono stati sintetizzate ciclodestrine “cappate” con sistemi atropoisomerici di tipo 1,1’-bifenilico. Il processo di trasferimento di chiralità dalla ciclodestrina (chiralità puntuale) alla prozione bifenilica (chiralità assiale) è stato studiato in dettaglio, sia in soluzione che a stato solido. Il ruolo chiave dei legami legami idrogeno intramolecolari responsabili dell’efficiente trasferimento di chiralità è stato dimostrato ed infine la attività chirottica temperatura dipendente di tali sistemi è stata studiata. Il secondo filone di ricerca ha riguardato la sintesi e l’utilizzo di sintoni tripticenici.2 Sono stati sintetizzati e studiati nuovi coloranti triptycene-fused quinacridone, seguendo la nostra strategia generale che prevede la fusione di sintoni -coniugati non planari e pigmenti ad altre prestazioni. Successivamente (capitolo 5), dopo diversi tentativi di risoluzione falliti, la risoluzione di cruciali sintoni tripticenici chirali è stata ottenuta mediante utilizzo di HPLC chirale, in collaborazione con il gruppo di ricerca del Prof. Roberto Cirilli (Università La Sapienza, Roma).3 Infine, in collaborazione con il gruppo di ricerca della Prof. Amendola, sono stati sintetizzati nuovi derivati di tripticene/benzimidazolo. Tali derivati sono stati impiegati con successo per l’autoassemblaggio via legame a idrogeno di polimeri chirali costituiti da derivati tripticene/benzimidazolo e acidi carbossilici chirali (non cromoforici). In questo caso la chiralità viene trasferita tramite interazioni non covalenti da semplici acidi carbossibili chirali a una miscela in equilibrio (derivante da equilibri tauromerici) di isomeri tripticene/benzimidazolo. Le strutture supramolecoalri così ottenute si sono rivelate in grado emettere luce polarizzata circolarmente con fattori di disimmetria glum fino a 6*10-3.
Referenze e Pubblicazioni
1) R. Mobili ±, G. Preda ±,S. La Cognata, L. Toma, D. Pasini, V. Amendola, Chem. Commun., 2022, 58, 3897–3900.
2) G. Preda, A. Nitti, D. Pasini, ChemistryOpen 2020, 9, 719–727.
3) A. Rosetti, G. Preda, C. Villani, M. Pierini, D. Pasini, R. Cirilli, Chirality, 2021; 33, 883–890
Homoconjugation and Tautomeric Isomerism in Triptycene-Fused Pyridylbenzimidazoles
No full textThe facile, metal-free synthesis and characterization of three new series of triptycene-fused pyridylbenzimidazoles are reported; such compounds possess an imidazole moiety fused within the benzene rings of the trypticene and a pyridine ring installed at position 2 of the imidazole rings. The position of the nitrogen atom of the pyridyl moiety linked to position 2 of the fused benzimidazole scaffold is systematically changed from the ortho to para position. The number of substituted blades bearing the pyridyl-substituted fused benzimidazole scaffolds has been increased from one to three. Such a library of compounds allowed us to evaluate the enhancement of two main effects: tautomeric isomerism and homoconjugation. The characteristic dynamic equilibrium between different isomers induced by prototropic tautomerization was examined by 1H nuclear magnetic resonance spectroscopy. By comparison of the photophysical properties of the new compounds with those of classical planar pyridylbenzimidazoles, the presence of the homoconjugation effect between the different triptycene blades was demonstrated. Fine details of the electronic structure of the new derivatives were unraveled by a computational analysis. The novel compounds can be employed for the construction of intriguing self-assembled supramolecular architectures
TAX RELIEF FOR CHARITABLE GIVING: NEW EVIDENCE FROM THE ITALIAN PERSONAL INCOME TAX RETURNS
No full textChiral Triptycenes in Supramolecular and Materials Chemistry
Full text linkTriptycenes are an intriguing class of organic molecules with several unusual characteristics, such as a propeller-like shape, saddle-like cavities around a symmetrical scaffold, a rigid π-framework. They have been extensively studied and proposed as key synthons for a variety of applications in supramolecular chemistry and materials science. When decorated with an appropriate substitution pattern, triptycenes can be chiral, and, similarly to other popular chiral π-extended synthons, can express chirality robustly, efficiently, and with relevance to chiroptical spectroscopies. This minireview highlights and encompasses recent advances in the synthesis of chiral triptycenes and in their introduction as molecular scaffolds for the assembly of functional supramolecular materials
Synthesis of 2,6-Diaminotriptycene Conjugates with Chiral Auxiliaries: Towards the Scalable Resolution of Crucial Triptycene Intermediates
No full textTriptycenes are tridimensional molecular scaffolds with interesting properties for applications in materials science: molecular rigidity and preorganization, tailorable chromophores, and, with an appropriate substitution pattern, chirality. The separation of the two enantiomers of chiral triptycenes has been the subject of increasing interest in recent years, with limited success. Here, we report the synthesis and characterization of a series of new organic compounds, in which a chiral triptycene scaffold, derivatized in the 2 and 6 positions with amino groups, has been functionalized with different enantiopure chiral auxiliaries, forming diastereoisomeric couples. The properties of such compounds, in terms of the optimization of their chromatographic separation, are elucidated with the aid of computational calculations of preferred conformations and molecular polarities
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
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