1,721,088 research outputs found
Fluorescent di-nuclear rhenium(I) complexes bioconjugated with PNA for DNA targeting
No full textNew materials for applications both in diagnosis and gene therapy should posses good affinity with DNA, together with some spectroscopic or radiochemical properties. For diagnostic purposes, the conjugation of peptide nucleic acids (PNA) with luminescent rhenium(I) complexes seems to be an interesting tool. Indeed, the former have a high binding affinity for DNA and RNA while the latter have good photoluminescent properties. We have recently published [1] a new family of dinuclear carbonyl rhenim(I) complexes containing 1,2-diazine ligand, whose high PLQY was strongly correlated with the substituent on the diazine ring. Moreover, we have previously reported the stable adduct between thymine-PNA monomer and the complex [Re2(-Cl)2(CO)6(-4-COOH-pydz)] (1) [2]. Owing to the electron-withdrawing of the carbonylic substituent, the PLQY of this adduct was negligble. In order to increase the quantum yield of the bioconjugated compound, we have now synthetized a much more luminescent complex namely [Re2(-Cl)2(CO)6(-4-(CH2)3-COOH-pydz)] (2). Here we report the synthesis and the photophysical characterization of the adducts obtained by the coupling of the homo-thymine PNA decamer with both metal complexes 1 and 2.
[1] M. Mauro, E. Quartapelle Procopio, Y. Sun, C.H. Chien, D. Donghi, M. Panigati, P. Mercandelli, P. Mussini, G. D’Alfonso, L. De Cola, Adv. Func. Mat., in press
[2] D. Donghi, M. Panigati, G. Prencipe, E. Licandro, S. Maiorana, L. D’Alfonso, Luminescence, 2008, 23, 21
Luminescent tricarbonyl pyridazine-rhenium complexes containing bridging -or/-sr ligands
No full textThere is still a high interest towards the photochemical and photophysical properties of luminescent rhenium(I) diimine tricarbonyl complexes, due to their broad range of applications [1-2].
Recently we reported the synthesis of a series of neutral dinuclear Re(I) complexes suitable for phosphorescent light emitting devices (OLEDs). These compounds, of general formula [Re2(CO)6(-1,2-diazine)(-X)2], where X could be halogen or hydride, exhibit emission in solution from triplet metal-to-ligand charge-transfer (3MLCT) excited states [3-4]. Wavelengths, lifetimes and quantum yields of the emission can be modulated by varying both the diazine substituents and/or the ancillary ligands. Photoluminescent quantum yield (PLQY) up to 0.53 have been measured for di-chloro complexes containing pyridazine (pydz) bearing alkyl substituents in positions [5].
The aim of the work is to understand how the photophysical properties of the complexes can be tuned by modifying the ancillary ligands, estimating the possibility to functionalize these complexes without involving the diazine emitting centre.
The synthesis of a new series of dinuclear complexes with general formula [Re2(CO)6(μ-pydz)(μ-ER)2], (E = S, O) – containing two (thio)phenol-type (or a alcoxo-type) unit as bridging ligands – has therefore been developed. The complexes have been characterized from the spectroscopical, photophysical, electrochemical and structural point of view.
The emisssion - in deareated toluene – is localized in the red region of the visible spectrum (608 < em < 708 nm). The progressive bathochromic shift of both absorption and emission maxima follows the same trend of the oxidation potentials and agrees with the electron-withdrawing character of the alcoxo or phenoxo ligands, with respect to the halogen one. The PLQYs are in the range 0.1-5.5%, and, in agreement with the energy gap law, the highest value, comparable to that of the analogous dichloro derivative, is observed for compound 1, showing the emission at the highest energy.
[1] Lundin, N. J.; Blackman, A. G.; Gordon, K. C.; Officer, D. L. Angew. Chem., Int. Ed. 2006, 45, 2582.
[2] Mak, C. S. K.; Leung, Q. Y.; Li, C. H.; Chan, W. K. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 2311.
[3] Panigati, M.; Donghi, D.; D'Alfonso, G.; Mercandelli, P.; Sironi, A.; D'Alfonso, L. Inorg. Chem. 2006, 45, 10909.
[4] Donghi, D.; D’Alfonso, G.; Mauro, M.; Panigati, M.; Mercandelli, P.; Sironi, A.; Mussini, P.; D’Alfonso, L. Inorg. Chem. 2008, 47, 4243.
[5] Mauro, M.; Quartapelle Procopio, E.; Sun, Y.; Chien, C-H.; Donghi, D.; Panigati, M.; Mercandelli, P.; Mussini, P.; D’Alfonso, G.; De Cola, L. Adv. Funct. Mater. 2009, 19, 2607
Photoluminescent and crystal structure properties of the yellow and orange forms of [Re2(m-Cl)2(CO)6(m- 4,5-trimethyl-silyl-pyridazine]
No full textA series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) has been recently reported1,2. These compounds, of general formula [Re2(μ-Cl)2(CO)6(μ-1,2-diazine)], contain diazines bearing alkyl groups in one or in both the b positions. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess, in solution, high emission quantum yields (F 0.18-0.22 for the derivatives with disubstituted diazines). The excited state responsible for this emission can be confidentially described as a triplet metal-to-ligand charge transfer (3MLCT) level3. Following the DFT computational suggestions we have now synthetized a new complex of this family using the 4,5-bis(trimetylsilyl)-1,2-diazine ligand namely [Re2(m-Cl)2(CO)6(m- 4,5-trimethyl-silyl-pyridazine] (1, see Scheme). This complex has been completely carachterized in solution and it shows an emission maximum batochromically shifted respect to those of the analogous Re(I) compounds with alkyl-substituted diazine, with a lower quantum yield. Slow evaporation at room temperature of a CH2Cl2 solution containing (1) induces the concomitant formation of orange and yellow single crystals (Figure 1, top). X-ray crystal structure determinations performed at room temperature as well as at 100 K, show that they are two different polymorphs of the same compound. The emission spectra recorded on crystalline samples of the two polymorph (Figure 1, bottom) are hypsochromically shifted respect to the solution one and present higher quantum yields (lem = 537 nm and F = 0.30 for the yellow phase, lem = 575 nm and F = 0.50, for the orange one). References
(1) Mauro, M, Quartapelle Procopio, E., Sun,Y., Chien, C-H., Donghi, D., Panicati, M., Mercandelli, P., Mussini, P., D’Alfonso, G., De Cola, L. Adv. Func. Mat. 2009, in press
(2) Donghi, D., D’Alfonso, G., Mauro, M, Panigati, M., Mercandelli, P., Sironi, A., Mussini, P., D’Alfonso, L., Inorg. Chem. 2008, 47, 4243.
(3) Wrighton, M., Morse, D. L., J. Am. Chem. Soc., 1974, 96, 998
Potential-driven Chirality manifestations and impressive enantioselectivity by inherently chiral electroactive films
Full text linkMolecular materials coupling electroactivity with enantiorecognition capability are an attractive objective in materials research. The usual strategy, hinging on attaching chiral pendants to an electroactive polyconjugated backbone, generally results in modest chirality manifestations. We have thus designed electroactive chiral polyheterocycles, where chirality is not external to the electroactive backbone, but inherent to it, resulting from a tailored torsion produced by the presence of atropisomeric, conjugatively active biheteroaromatic scaffolds. The coincidence of the stereogenic element with the whole electroactive backbone affords by electrooligomerization enantiopure electroactive films of impressive chiroptical activity, which can be finely and reversibly tuned by the electric potential, since injection of positive charges results in decrease of the atropisomeric scaffold angle to favour delocalization, as revealed by CD spectroelectrochemistry, suggesting us the image of a "breathing chirality". To test the enantiorecognition ability of the new inherently chiral conducting films we have developed an efficient protocol in ionic liquid affording preparation of very
reproducible electrode surfaces by electrooxidation of the enantiopure monomers on screen printed electrode supports. The resulting specular R and S electrodes have been tested with (R)-(+)- and S-(-)-N,N-dimethyl-1-ferrocenylethylamine specular probes. The response is highly and reproducibly enantioselective (with 100 mV separation between R and S probes with single enantiomers and even more with the racemate), specular for R vs S surfaces with respect to S and R probes, and reversible in repeated alternating sequences of S and R probe sensing on a single electrode.[1] With the contribution of Fondazione Cariplo, grant no. 2011-0417. [1] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P.R. Mussini, M. Panigati, M. Pierini, S. Rizzo, Angew. Chemie 2014, 53, 2623-2627
Dihydrogen bond between a bridging hydride and coordinated HNMe2 : solid state and solution characterization
No full textThe addition of one equivalent of dimethylamine (DMA) to the 44 valence-electron triangular
cluster anion [Re3(μ3-H)(μ-H)3(CO)9]– (1) affords the novel unsaturated derivative [Re3(μ-
H)4(CO)9(DMA)]– (2, 46 valence electrons) which contains a dimethylamine molecule terminally
coordinated to a cluster vertex. Theoretical calculations reveal that in the more stable conformation
the dimethylamine NH proton directs towards the hydride bridging the opposite cluster edge in syn
position, the close proximity of the ligands bound to the cluster surface allowing the formation of
an unconventional N–H...(μ-H)Re2 hydrogen bond. The presence of this conformation in the solid
state has been proven by an X-ray structural analysis of crystalline [PPh4]2. Spectroscopic
evidences (IR and NMR) indicate that the dihydrogen bond is maintained also in solution and, by
the evaluation of the proton spin-lattice relaxation rates at variable temperature, a good estimation
of the H...H distance in solution have been determined
An intramolecular N-H⋯(μ-H)Re2 dihydrogen bond and a novel μ3-η2 coordination mode of the pyrazolate anion on a triangular cluster face
No full textThe quantitative addition of pyrazole (Hpz) to the 44 valence-electron, triangular cluster anion [Re3(μ3-H)(μ-H) 3(CO)9]- gives the novel unsaturated anion [Re3(μ-H)4(CO)9(Hpz)]- (1, 46 valence electrons), which contains a pyrazole molecule that is terminally coordinated on a cluster vertex. Solidstate X-ray and IR analyses reveal a rather weak hydrogen-bonding interaction between the NH proton and one of the hydrides bridging the opposite triangular cluster edge (ΔH° = - 3.1 kcal.mol-1 from the Iogansen equation). Both IR and NMR data indicate that such a proton-hydride interaction is maintained in the major conformer present in CD2Cl2, but also provide evidence of the presence of minor conformers of 1 in which the NH proton is involved in an intermolecular hydrogen bond with the solvent. The μ-H⋯HN bond length evaluated in solution through the T1 minimum value (2.07 Å) and that determined in the solid state by X-ray diffraction (2.05 Å) are in good agreement. NMR experiments show that, in acetone, intermolecular N-H ⋯ solvent interactions replace the intramolecular dihydrogen bond. At room temperature in CH2Cl2, the pyrazole ligand in 1 is labile and 1 slowly "disproportionates" to [Re3(μ3-H)(μ-H) 3(CO)9]- and [Re3(μ-H)3 (CO)9(μ-η2-pz)(Hpz)]-, with H2 evolution. Slow H2 evolution also leads to the formation of the anion [Re3(μ-H)3(CO)9(pz)]- (5), in which the pyrazolate anion adopts a novel μ3-η2-coordination mode, as revealed by a single-crystal X-ray analysis. The analysis of the bond lengths indicates that the pyrazolate anion in 5 acts as a six-electron donor, with loss of the aromaticity. The formation of 5 from 1 is much faster in solvents with a high dielectric constant, such as acetone or DMF. Anion 5 was also obtained from the reaction of pyrazole with [Re3(μ-H)3 (CO)9(μ3CH3)]- through the intermediate formation of two isomeric addition derivatives and following CH4 evolution
Metal fragment rotation in triangular metal clusters: H-1, H-2, and C-13 NMR studies of the fluxional behavior of the anion {[Re-3(mu-H)(3)(mu-eta(2)-NC5H4)(CO)(10)](-)}
No full textVariable-temperature C-13 NMR spectroscopy, 1D SPT, and 2D EXSY
experiments have been used to investigate the fluxionality of the
triangular cluster anion {[Re-3(mu-H)(3)(mu-eta(2)-NC5H4)(CO)(10)](-).
The (CO)-C-13 resonances have been assigned through H-1-C-13 2D HMQC and
C-13 2D DQF-COSY experiments and through the measurement of the
(CO)-C-13 longitudinal relaxation times. The exchange pattern observed
in the C-13 2D EXSY experiments proved the occurrence of a synchronous
axial-axial and equatorial-equatorial carbonyl exchange on the apical
metal. The rate constants at 303 and 313 K compare well with those
previously measured, through H-1 NMR spectroscopy, for the exchange of
the two hydrides bridging the lateral edges of the cluster. The rigid
rotation of the whole apical [H2Re(CO)(4)] moiety around an axis
passing through the midpoint of the basal bimetallic fragment is in
agreement with these results. A deuterium kinetic isotope effect
k(H)/k(D) = 1.45(24) has been measured through H-1 and H-2 2D EXSY
experiments, supporting the involvement of the hydrides in the
rate-determining step of the exchange process.
Synthesis and characterization of a tetrathia[7]helicenebased rhenium(I) complex
Full text linkTetrathia[7]helicenes (7-TH), formed by thiophene and benzene rings ortho-fused in an alternating fashion, are emerging as one of the most popular class of chiral helical-shaped molecules, thanks to their peculiar electronic and chiroptical properties suitable for manifold applications in different areas of science.1 In particular, transition metal-based 7-TH systems are an extremely appealing class of complexes, in which the coordination of metals with the -helical ligand, bearing appropriate coordinating functionalities, provides original chiral architectures. Indeed, the effective functionalization of the -position(s) of the terminal thiophene ring(s) of the 7-TH scaffold allows the introduction of a variety of substituents, including those with efficient coordinating ability (e.g. cyano2, phosphane3, phosphine oxide4). For example, Rh(I)5 and Au(I)6 complexes based on 7-TH phosphanes have been successfully used in the homogenous transition metal catalysis. In our ongoing studies on 7-TH-based organometallic complexes, we have focused on a novel field of investigation concerning the development of rhenium-based polynuclear complexes containing 7-TH phosphine oxide ligands. In this communication, we describe the synthesis and the characterization of a novel dinuclear rhenium(I) complex (Figure 1), along with the elucidation of its tridimensional structure by single crystal X-ray diffraction studies
Thiophene-based helicenes : eclectic scaffolds in organometallic chemistry
Full text linkHelicenes are ortho-annulated polycyclic aromatic compounds, endowed with an inherently chiral π-conjugated system that are intensively studied in different areas of science.1 Among helicenes, thiophene-based helicenes are emerging as an intriguing and promising class of screw-shaped structures, thanks to the presence of the thiophene rings, which confer peculiar chemical, structural, and electronic features.2 For several years, we have been interested in the synthesis and functionalization of tetrathia[7]helicenes (7-TH, Figure 1), which are configurationally stable heterohelicenes, potentially very interesting for applications in optoelectronics,3 catalysis,4 and biology.5 In particular, transition metal-based 7-TH systems are an extremely appealing class of complexes, in which the coordination of metals with the π-helical ligand, bearing proper coordinating groups, provides unusual chiral architectures. Indeed, the selective functionalization of 2 and 13 positions of the 7-TH scaffold allows the introduction of a variety of substituents, including those with efficient coordinating ability (e.g. cyano, phosphane, phosphine oxide). In this communication we report our recent studies on the synthesis and characterization of 7-TH-based organometallic complexes, and their potential applications in optoelectronics and catalysis
Determinazione del contenuto di selenio in diverse varietà di riso mediante analisi voltammetrica
No full textDa diversi anni numerosi studi dimostrano come il Selenio intervenga come cofattore di importanti processi enzimatici antiossidativi e per questo motivo, possa essere considerato un potenziale agente antitumorale, più in generale, quale agente preventivo dei processi di invecchiamento. Il Selenio biodisponibile viene assunto prevalentemente attraverso l’alimentazione ma essendo caratterizzato da un margine di sicurezza ridotto diventa estremamente importante determinarne con la massima accuratezza il contenuto nei diversi alimenti, in particolare nei cereali, che costituiscono la base di molte diete, non solo di quella mediterranea. É stato infatti osservato che, assunto in dosi eccessive, questo micronutriente risulta particolarmente tossico (la dose giornaliera raccomandata U.S. RDA prevede infatti una quantità non superiore a 70 g/giorno per gli uomini e 55 g/giorno per le donne) [1].
L’obiettivo di questo lavoro è stato quello di determinare il contenuto di Selenio in tre diverse varietà di riso coltivate nella zona del Vercellese: nel riso bianco, in una varietà di riso nero ed in una di riso rosso.
Il campione veniva inizialmente mineralizzato e tra i diversi metodi di “digestione” riportati in letteratura è stato utilizzato per la prima volta un metodo “combinato” che ha permesso di ottenere una buona distruzione della matrice e buoni recuperi dell’analita. Il metodo consiste in una prima “digestione” per via umida a caldo con HNO3 concentrato in presenza di Mg(NO3)2, seguita da uno stadio di incenerimento in muffola a 450°C. Il prodotto della calcinazione veniva poi ridisciolto in HCl 6 M a 110°C , diluito con acqua deionizzata e quindi analizzato. Numerosi sono i metodi analitici che si possono utilizzare per determinare il Selenio. In particolare, la tecnica voltammetrica di stripping catodico (CSV) (basata sulla formazione e succesiva riduzione, su goccia di mercurio, di un composto intermetallico HgSe o, in presenza di ioni rame, CuxSe) permette di ottenere limiti di rilevabilità estremamente soddisfacenti (inferiori a 100 pM) [2]. Questo metodo che si raccomanda a causa della sua elevata sensibilità pone però il problema della ottimizzazione di molteplici variabili [3-5], in relazione alla specifica matrice, che può contenere numerose specie interferenti sia derivanti dal campione originario sia dallo specifico metodo di digestione. In particolare accanto all’ottimizzazione dei parametri tipici delle tecniche di stripping (potenziale e tempo di deposizione, tempo di “quiete”, velocità e modalità di stripping, agitazione, dimensioni della goccia di mercurio...) nel caso del Selenio si aggiungono alcuni problemi specifici [2,3] come (a) la scelta di una concentrazione ottimale degli ioni Cu2+ e (b) l’effetto di modulazione da parte dei cloruri (presenti in concentrazione significativa in seguito alla digestione del campione) e del pH. In questa presentazione verrà discussa la procedura di ottimizzazione dei parametri critici d’analisi e riportati i dati relativi al contenuto di Selenio nei differenti campioni di riso da noi considerati. Si tratta del primo caso di applicazione della CSV con aggiunta di rame all’analisi del Selenio in campioni mineralizzati secondo la procedura sopra descritta. I dati elettroanalitici sono stati infine confrontati con quelli ottenuti mediante spettrometria HG-ICP.
[1] A. Kumar, K. Krishnaswamy, J. Agric. Food Chem. (1997), 45, 2565
[2] G. Mattsson, L. Nyholm, Å. Olin, J. Electroanal. Chem. (1994), 379, 49
[3] P.Zuman, G. Somer, Talanta (2000), 51, 645
[4] L. Campanella, T. Ferri, J. Electroanal. Chem. (1984) 164, 241
[5] T. Ferri, C. De Luca, L. Ticconi, Analytical Letters (2001), 34, 97
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