1,721,179 research outputs found
Assemblaggi supramolecolari di Magneti a Singola Molecola con centri redox-attivi: studi sintetici, strutturali e magnetici
No full textI Magneti a Singola Molecola (SMMs)1 sono sistemi molecolari che esibiscono un momento magnetico direzionale-bistabile a bassa temperatura e che in linea di principio possono essere utilizzati per memorizzare ed elaborare informazioni.2 I SMMs sono solitamente isolati come cristalli molecolari e che mostrano deboli interazioni intermolecolari. Tuttavia, possono essere deliberatamente assemblati in vettori ben definiti con varie dimensionalità, dai dimeri alle catene e ai Metal-Organic Frameworks (MOFs) 3D.3 Gli obiettivi centrali in questo settore in rapida crescita sono il controllo del trasporto elettronico attraverso un SMM tramite il suo stato magnetico e, viceversa, la manipolazione del momento magnetico gigante di un SMM utilizzando una corrente elettrica.
Nel mio progetto di dottorato ho esplorato vie di sintesi per combinare SMMs con gruppi redox-attivi con diversi stati di ossidazione, che possono agire come serbatoi di elettroni (ERs).4 A questo scopo, complessi Fe4 (S = 5) sono stati selezionati in quanto SMMs con elevata flessibilità chimica.5 Le strutture supramolecolari così assemblate spaziano da triadi [ER-Fe4-ER] (ER = ferrocene, metalloporfirine) a catene [Fe4-ER]n (ER = dimeri di rutenio) o MOF 3D [(Fe4)2-ER]n (ER = Ag).
La maggior parte di essi contengono un nuovo Fe4(III) funzionalizzato con due gruppi 4-piridile e che funge da sintone ditopico supramolecolare a 180°, ovvero [Fe4(pPy)2(dpm)6] (Fe4pPy) (H3pPy = 2-(idrossimetil)-2-(piridin-4-il)propan-1,3-diolo, Hdpm = dipivaloylmethane).
Questo complesso reagisce facilmente con tetra(p-tert-butylphenyl)porphyrinato(carbonyl) ruthenium(II), [Ru(ptBuTPP)(CO)], dando la triade [Fe4pPy{Ru(ptBuTPP)(CO)}2]. Le misure fotofisiche mostrano che l'emissione dello stato eccitato tipica della metalloporfirina è fortemente spenta a causa di un processo di trasferimento di energia al nucleo Fe4.
Quando Fe4pPy è fatto reagire con AgClO4, si ottiene [(Fe4pPy)2Ag](ClO4), che mostra una struttura diamondoide con gli ioni Ag+ nodi tetraedrici e i cluster Fe4 come linker lineari. Il reticolo cristallino cubico comprende 4 unità Fe4 magneticamente distinte con assi di anisotropia diretti lungo i triplici assi dei tetraedri AgN4. La struttura magnetica noncollineare risultante non ha anisotropia magnetica del secondo ordine, ma mantiene la bistabilità.6
Fe4pPy può reagire con dimeri [Ru2(OAc)4]0/+, ottenendo strutture a catena, come [Fe4pPy{Ru2(OAc)4}]0/+. Qui, la comunicazione magnetica nella catena può essere attivata o disattivata modificando il conteggio degli elettroni sui ponti dimerici. Infatti, le due specie dimeriche hanno una grande anisotropia di tipo asse difficile che genera diverse proprietà magnetiche a bassa T. Con il suo stato fondamentale non magnetico, [Ru2(OAc)4]0 porta ad una comunicazione intracatena trascurabile; al contrario, [Ru2(OAc)4]+ agisce con seff = 1⁄2 e interagisce antiferromagneticamente con le vicine unità Fe4. Di conseguenza, le catene mostrano cicli di isteresi con scambio parziale e rimanenza magnetica migliorata,7 suggerendo la possibilità di utilizzare il trasferimento di elettroni per la comunicazione intermolecolari e modulare vettori di SMMs sensibili alle variazioni redox.
[1] D. Gatteschi et al., Molecular Nanomagnets, Oxford University Press, Oxford, 2006.
[2] (a) L. Bogani, W. Wernsdorfer, Nat. Mater. 2008, 7, 179–186; (b) F. Troiani, M. Affronte, Chem. Soc. Rev. 2011, 40, 3119–3129.
[3] (a) K. Liu et al., Chem. Soc. Rev. 2016, 45, 2423–2439; (b) I.-E. Jeon, R. Clérac, Dalton Trans. 2012, 41, 9569–9586.
[4] J. Otsuki et al., Coord. Chem. Rev. 2008, 252, 32–56.
[5] S. Accorsi et. al., J. Am. Chem. Soc. 2006, 128, 4742–4755.
[6] L. Rigamonti et al., Chem. Eur. J. 2016, 22, 13705–13714.
[7] A. Nava et al., Angew. Chem. Int. Ed. 2015, 54, 8777–8782.Single Molecule Magnets (SMMs)[1] are molecular systems that exhibit a directionally-bistable magnetic moment at low-temperature and that in principle can be used to store and process information.[2] SMMs are normally isolated as molecular crystals entailing weak intermolecular interactions. However, they can be deliberately assembled into topologically well-defined arrays of various dimensionality, ranging from dimers to chains and 3D metal-organic frameworks (MOFs).[3] Central targets in this burgeoning field are controlling electron transport through an SMM via its magnetic state and, conversely, manipulating the giant magnetic moment of an SMM using an electric current.
In my PhD project I have explored synthetic routes to combine, at the supramolecular level, SMMs with redox-active groups capable of spanning different oxidation states, thereby acting as electron reservoirs (ERs).[4] To this aim, Fe4 complexes (S = 5) have been selected as SMM displaying utmost chemical flexibility.[5] The supramolecular structures so assembled range from [ER-Fe4-ER] triads (ER = ferrocene, metalloporphyrin) to [Fe4-ER]n chains (ER = diruthenium paddlewheel) and a [(Fe4)2-ER]n 3D MOF (ER = Ag+).
Most of them contain a new tetrairon(III) complex functionalized with two 4-pyridyl groups and acting as a 180°-ditopic supramolecolar synthon, namely [Fe4(pPy)2(dpm)6] (Fe4pPy) (H3pPy = 2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol, Hdpm = dipivaloylmethane).
This complex readily reacts with tetra(p-tert-butylphenyl)porphyrinato(carbonyl) ruthenium(II), [Ru(ptBuTPP)(CO)], to yield supramolecular triad [Fe4pPy{Ru(ptBuTPP)(CO)}2]. Photophysical measurements show that the typical emission of the metalloporphyrin excited state is strongly quenched due to an energy transfer process to the Fe4 core.
When reacted with silver(I) perchlorate, Fe4pPy affords compound [(Fe4pPy)2Ag](ClO4), which displays an unprecedented diamondoid structure with silver(I) ions as tetrahedral nodes and Fe4 complexes as linear linkers. The cubic crystal lattice comprises four magnetically distinct Fe4 units with anisotropy axes directed along the threefold axes of AgN4 tetrahedra. The resulting highly-noncollinear magnetic structure has no second-order magnetic anisotropy, but retains magnetic bistability.[6]
Fe4pPy can also react with [Ru2(OAc)4]0/+ paddlewheels, affording chain-like structures [Fe4pPy{Ru2(OAc)4}]0/+. Here, magnetic communication within the chains can be switched on/off by changing the electron count on diruthenium bridges. In fact, the two diruthenium species have a huge hard-axis anisotropy which generates very different low-T magnetic properties. With its nonmagnetic ground state, [Ru2(OAc)4] leads to negligible intrachain communication; by contrast, [Ru2(OAc)4]+ acts as an effective s = 1/2 spin and interacts antiferromagnetically with the neighbouring Fe4 units. As a result, the chain exhibits exchange-biased hysteresis loops and enhanced magnetic remanence,[7] suggesting the possibility to use electron transfer to tune intermolecular communication in redox-responsive arrays of SMMs.
[1] D. Gatteschi et al., Molecular Nanomagnets, Oxford University Press, Oxford, 2006.
[2] (a) L. Bogani, W. Wernsdorfer, Nat. Mater. 2008, 7, 179–186; (b) F. Troiani, M. Affronte, Chem. Soc. Rev. 2011, 40, 3119–3129.
[3] (a) K. Liu et al., Chem. Soc. Rev. 2016, 45, 2423–2439; (b) I.-E. Jeon, R. Clérac, Dalton Trans. 2012, 41, 9569–9586.
[4] J. Otsuki et al., Coord. Chem. Rev. 2008, 252, 32–56.
[5] S. Accorsi et. al., J. Am. Chem. Soc. 2006, 128, 4742–4755.
[6] L. Rigamonti et al., Chem. Eur. J. 2016, 22, 13705–13714.
[7] A. Nava et al., Angew. Chem. Int. Ed. 2015, 54, 8777–8782
Signal-averaged electrocardiographic parameter progression as a marker of increased electrical instability in two cases with an overt from of arrhythmogenic right ventricular cardiomyopathy
No full textIn arrhythmogenic right ventricular cardiomyopathy (ARVC) the fibrofatty substitution of the RV myocardium constitutes the substrate for reentrant circuits, leading to the onset of ventricular arrhythmias. This pathological process also accounts for "delayed ventricular potentials" that could be recorded as late potentials using the signal-averaged ECG technique (SAECG). This study examined two patients affected by overt forms of ARVC who showed a worsening of the electrical instability associated with a fast progression of SAECG parameters, while all the other clinical findings remained unchanged. This suggests a possible role of SAECG parameter progression as a marker of increased electrical instability
Letter regarding article by Nasir et al, "Electrocardiographic features of arrhythmogenic right ventricular dysplasia/cardiomyopathy according to disease severity: a need to broaden diagnostic criteria"
No full textabstract not availabl
Letter regarding article by Norman et al, "Novel mutation in desmoplakin causes arrhythmogenic left ventricular cardiomyopathy"
No full textIF JCR 2007: 12.75
The conduction system in corrected transposition with situs inversus.
No full textThe location and course of the conduction system were investigated by serial section in two hearts with corrected transposition of the great arteries in situs inversus. In the first case, characterized by dextrocardia, the interventricular septum was intact, while in the second case with levocardia, a high ventricular septal defect was associated with pulmonary atresia. In both hearts, a regular posterior connecting AV node was present, left-sided in one case and right-sided in the other. The bundle branches were distributed in the morphologically appropriate ventricles. Extensive hemorrhage and coagulation necrosis of the common bundle and bundle branches were observed in the first case, being consequent upon surgical replacement of the right-sided tricuspid valve. The common bundle ran below the membranous septum in this case. In the heart with ventricular septal defect it was related to the postero-inferior rim of the defect. In both cases, an accessory AV node was located anteriorly in the interatrial septum but did not connect with the ventricular musculature. The different position of the atrioventricular conducting tissue in corrected transposition, between cases in situs solitus and situs inversus, is emphasized
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