172,736 research outputs found
Catalytic Applications of Pyridine-Containing Macrocyclic Complexes
No full textPolyazamacrocycles are a common class of macrocyclic compounds, utilized across a number of fields, including, but not limited to, catalysis, selective metal recovery and recycling, therapy and diagnosis, and materials and sensors.1 Worth of note is their ability to form stable complexes with a plethora of both transition, especially late, and lanthanide metal cations.2 Deviation of the macrocycle donor atoms from planarity often leads to rather uncommon oxidation states.3 Both the thermodynamic properties and the complexation kinetics are strongly affected by the introduction of a pyridine moiety into the skeleton of polyazamacrocycles by increasing the conformational rigidity and tuning the basicity.4 Pyridine-containing ligands engender great interest due to various potential field of applications. They have been successfully employed in biology, Magnetic Resonance Imaging, molecular recognition, supramolecular chemistry and self-assembly, molecular machines and mechanically interlocked architectures.5 In this lecture, I will provide a perspective on the catalytic applications of metal complexes of pyridine-containing macrocyclic ligands (Pc-L’s) which have been studied in our group (Figure), with a focus interest on the structural features relevant to catalysis.6 The increased conformational rigidity imposed by the pyridine ring allowed for the isolation and characterization of metal complexes which showed a rich coordination chemistry.7 The very different conformations accessible upon coordination and the easy tuneable synthesis of the macrocyclic ligands have been exploited in stereoselective syntheses.8
References:
1 L. F. Lindoy, G. V. Meehan, I. M. Vasilescu, H. J. Kim, J.-E. Lee, S. S. Lee, Coord. Chem. Rev. 2010, 254, 1713.
2 T. Ren, Chem. Commun. 2016, 52, 3271.
3 A. Casitas, X. Ribas, Chem. Sci. 2013, 4, 2301.
4 K. M. Lincoln, M. E. Offutt, T. D. Hayden, R. E. Saunders, K. N. Green, Inorg. Chem. 2014, 53, 1406.
5 M. Rezaeivala, H. Keypour, Coord. Chem. Rev. 2014, 280, 203.
6 B. Castano, S. Guidone, E. Gallo, F. Ragaini, N. Casati, P. Macchi, M. Sisti, A. Caselli, Dalton Trans. 2013, 42, 2451.
7 a) G. Tseberlidis, M. Dell'Acqua, D. Valcarenghi, E. Gallo, E. Rossi, G. Abbiati, A. Caselli, RSC Adv. 2016, 6, 97404; b) T. Pedrazzini, P. Pirovano, M. Dell'Acqua, F. Ragaini, P. Illiano, P. Macchi, G. Abbiati, A. Caselli, Eur. J. Inorg. Chem. 2015, 2015, 5089.
8 a) M. Dell’Acqua, B. Castano, C. Cecchini, T. Pedrazzini, V. Pirovano, E. Rossi, A. Caselli, G. Abbiati, J. Org. Chem. 2014, 79, 3494; b) M. Trose, M. Dell’Acqua, T. Pedrazzini, V. Pirovano, E. Gallo, E. Rossi, A. Caselli, G. Abbiati, J. Org. Chem. 2014, 79, 7311; c) B. Castano, E. Gallo, D. J. Cole-Hamilton, V. Dal Santo, R. Psaro, A. Caselli, Green Chem. 2014, 16, 3202
Designing new Ligands: Catalytic Applications of Pyridine-Containing Macrocyclic Complexes
No full textThe introduction of a pyridine moiety into the skeleton of a polyazamacrocyclic ligand affects both the thermodynamic properties and the coordination kinetics of the resulting metal complexes. These features have engender a great interest in the scientific community and the applications of pyridine-containing macrocyclic ligands ranges from biology to supramolecular chemistry, encompassing MRI, molecular recognitions, materials and catalysis. In this lecture, I will provide a perspective on the catalytic applications of metal complexes of pyridine-containing macrocyclic ligands (Pc-L’s) which have been studied in our group (Figure 1), with a focus interest on the structural features relevant to catalysis.1 The increased conformational rigidity imposed by the pyridine ring allowed for the isolation and characterization of metal complexes which show a rich coordination chemistry.2 The very different conformations accessible upon coordination and the easy tuneable synthesis of the macrocyclic ligands have been exploited in stereoselective syntheses.3
References
1 B. Castano, S. Guidone, E. Gallo, F. Ragaini, N. Casati, P. Macchi, M. Sisti, A. Caselli, Dalton Trans. 2013, 42, 2451.
2 a) G. Tseberlidis, M. Dell'Acqua, D. Valcarenghi, E. Gallo, E. Rossi, G. Abbiati, A. Caselli, RSC Adv. 2016, 6, 97404; b) T. Pedrazzini, P. Pirovano, M. Dell'Acqua, F. Ragaini, P. Illiano, P. Macchi, G. Abbiati, A. Caselli, Eur. J. Inorg. Chem. 2015, 2015, 5089.
3 a) M. Dell’Acqua, B. Castano, C. Cecchini, T. Pedrazzini, V. Pirovano, E. Rossi, A. Caselli, G. Abbiati, J. Org. Chem. 2014, 79, 3494; b) M. Trose, M. Dell’Acqua, T. Pedrazzini, V. Pirovano, E. Gallo, E. Rossi, A. Caselli, G. Abbiati, J. Org. Chem. 2014, 79, 7311; c) B. Castano, E. Gallo, D. J. Cole-Hamilton, V. Dal Santo, R. Psaro, A. Caselli, Green Chem. 2014, 16, 3202
Special matchings and permutations in Bruhat orders
No full textFor any permutation v, we show that the special matchings of v generate a Coxeter system. This gives new necessary conditions on an abstract poset to be isomorphic to a lower Bruhat interval of the symmetric group, and also answers in the affirmative, in the symmetric group case, a problem posed in [F. Brenti, F. Caselli, M. Marietti, Special matchings and Kazhdan-Lusztig polynomials, Adv. Math. 202 (2006) 555601]. (c) 2006 Elsevier Inc. All rights reserved
Selective oxidation of alkenes by H2O2 catalysed by well-defined [Iron(III)(Pyridine-Containing Ligand)] complexes
No full textThe introduction of a pyridine moiety into the skeleton of a polyazamacrocyclic ligand affects both thermodynamic properties and coordination kinetics of the resulting metal complexes (1). These features have engendered a great interest of the scientific community in recent years. The applications of pyridine-containing macrocyclic ligands ranges from biology to supramolecular chemistry, encompassing MRI, molecular recognitions, materials and catalysis. Much of the efforts in the use of macrocyclic pyridine containing ligands have been devoted to the study of catalytic oxidation reactions. We report here the synthesis and characterization of [Fe(III)Pc-L’s)] complexes (Pc-L = Pyiridine-Containing Ligand) and their catalytic applications in alkene epoxidation or cis-dihydroxylation reactions using H2O2 as the terminal oxidant under mild conditions (Figure). Depending on the anion employed for the synthesis of the iron(III) metal complex, we observed a completely reversed selectivity. When X = OTf, a selective cis-dihydroxylation reaction was observed. On the other hand, employing X = Cl, we obtained the epoxide as the major product (traces of aldehyde were observed at very high conversions). It should be pointed out that under otherwise identical reaction conditions, using FeCl3·6H2O as catalyst in the absence of the ligand, no reaction was observed.
References:
1 a) B. Castano, S. Guidone, E. Gallo, F. Ragaini, N. Casati, P. Macchi, M. Sisti, A. Caselli, Dalton Trans. 2013, 42, 2451; b) G. Tseberlidis, M. Dell'Acqua, D. Valcarenghi, E. Gallo, E. Rossi, G. Abbiati, A. Caselli, RSC Adv. 2016, 6, 97404; c) T. Pedrazzini, P. Pirovano, M. Dell'Acqua, F. Ragaini, P. Illiano, P. Macchi, G. Abbiati, A. Caselli, Eur. J. Inorg. Chem. 2015, 2015, 5089
Amination of C-H Bonds by Metal Porphyrins Catalysed Nitrene Transfer Reaction
No full textThe biological and pharmaceutical activities of organonitrogen compounds prompted the scientific community to develop new methods for the direct and selective C-N bond formation, working within restricted financial parameters and environmentally friendly requirements.In the last few years we have reported on the catalytic activity of metal porphyrin complexes in a wide range of reactions, such as olefin epoxidation,1 hydrocarbon amination and olefin aziridination. For these last reactions arylazides, a versatile class of starting material, was employed as atom-efficient aminating agents.2 ArN3 generate a nitrene functionality “ArN” and the eco-friendly molecular nitrogen is the only side product.
The selective insertion of “ArN” into C–H bonds of benzylic substrates or olefins yields benzylic amines, benzylic imines or allylic amines. To clarify the mechanism of the C-H amination reactions, the ruthenium bis-imido porphyrin complex (1) was isolated and characterised by X-ray analysis.
The role of 1 in catalytic nitrene insertions into C H bonds was studied in the reaction of ArN3 with several hydrocarbons proving that 1 is an active reaction intermediate. It also appears to have equilibrium between stability and reactivity.3 To the best of our knowledge, complex 1 is the first structurally characterized bis-imido porphyrin complex that shows a good catalytic activity in this class of reactions.
References: [1] S. Fantauzzi, E. Gallo, E. Rose, N. Raoul, A. Caselli, S. Issa, F. Ragaini, S. Cenini, Organometallics , 2008, 27, 6143; [2] For a review see: S. Fantauzzi, A. Caselli and E. Gallo, Dalton Trans., 2009, 5434; [3] S. Fantauzzi, E. Gallo, A. Caselli, F. Ragaini, N. Casati, P. Macchi and S. Cenini Chem. Commun., 2009, 3952–395
Relazioni tra gesti, azioni comprensione e produzione di parole: uno studio longitudinale tra i 10 e 17 mesi.
No full textDiversi studi hanno mostrato come il periodo tra i 10 e i 17 mesi sia fondamentale per l’emergenza delle competenze gestuali e verbali e hanno individuato l’esistenza di relazioni nel loro sviluppo (Caselli et al., 2009; Fenson et al., 1994). Studi recenti hanno indicato la rilevanza di indagare in maniera più approfondita tali relazioni, ipotizzando l’esistenza di processi comuni sottostanti a queste competenze (Bates & Dick, 2002; Volterra et al., 2005). L’obiettivo di questo studio è indagare longitudinalmente con rilevazioni intensive il primo sviluppo di gesti, azioni, comprensione e produzione di parole e le loro relazioni in bambini con sviluppo tipico. I partecipanti dello studio sono 22 bambini italiani monolingui, osservati mensilmente da 10 a 17 mesi mediante l’uso del questionario “Gesti e Parole nel Primo Vocabolario del Bambino” forma breve (Caselli et al. in preparazione). I risultati hanno mostrato un aumento significativo di gesti, azioni e comprensione di parole dai 10 ai 17 mesi e un incremento della produzione di parole dai 12 mesi. Un’ampia variabilità interindividuale è emersa in tutte le competenze, che tuttavia si riduce verso la fine del periodo considerato per quanto riguarda gesti, azioni e comprensione di parole. Sono emerse strette relazioni tra azioni e comprensione di parole a tutte le età e relazioni tra gesti e comprensione delle parole soprattutto nei primi mesi di rilevazione; la produzione appare invece meno legata alle altre competenze. In conclusione, il nostro studio mostra come, tra 10 e 17 mesi, gesti, azioni e comprensione di parole abbiano traiettorie evolutive caratterizzate da una crescita costante e relazioni reciproche. Questi risultati confermano l’ipotesi dell’esistenza di una stretta connessione tra competenze comunicative, motorie e cognitive e sviluppo del vocabolario
Lipschitz continuity results for a class of obstacle problems
No full textWe prove Lipschitz continuity results for solutions to a class of obstacle problems under standard growth conditions of p-type, p b 2. The main novelty is the use of a linearization technique going back to [28] in order to interpret our constrained minimizer as a solution to a nonlinear elliptic equation, with a bounded right hand side. This lead us to start a Moser iteration scheme which provides the Ll bound for the gradient. The application of a recent higher di¤erentiability result [24] allows us to simplify the procedure of the identification of the Radon measure in the linearization technique employed in [32]. To our knowdledge, this is the first result for nonautomonous functionals with standard growth conditions in the direction of the Lipschitz regularity
Specificity ratings for English data
No full textA dataset of specificity ratings for English words is hereby presented, analyzed and discussed in relation with other collections of speaker-generated ratings, including concreteness. Both, specificity and concreteness are analyzed in their ability to explain decision latencies in lexical and semantic tasks, showing important individual contributions. Specificity ratings are collected through best–worst scaling method on the words included in the ANEW dataset (Bradley and Lang in Affective norms for English words (ANEW): instruction manual and affective ratings (Tech. Rep.). Technical report C-1, the center for research in psychophysiology, 1999), chosen for its compatibility with many other collections of rating resources, and for its comparability with Italian specificity data (Bolognesi and Caselli in Behav Res Methods 55(7):3531–3548, 2023), allowing for cross-linguistic comparisons. Results suggest that specificity plays an important role in word processing and the importance of taking specificity into consideration when investigating concreteness effects
Synthesis of Biologically Relevant Compounds by Ruthenium Porphyrin Catalyzed Amination of Benzylic C–H Bonds
No full textHerein we report the catalytic activity of ruthenium porphyrin complexes to promote the amination of benzylic C-H bonds by aryl azides, yielding α- and β-amino esters. The catalytic methodology is also effective to synthesize two derivatives of methyl l-3-phenyllactate in order to convert one of them into the corresponding β-lactam. The catalytic experimental conditions have been optimized on the basis of a preliminary mechanistic investigation which underlines the pivotal role of the substrate concentration to maximize the reaction productivity. © 2014 American Chemical Society
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