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The Journal of Physical Chemistry C 03/2013; · 4.80 Impact Factor
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ABSTRACT: ABSTRACT: The initial steps of the reaction between ZnO
and (001)-oriented Al2O3 single crystals have been investigated
with X-ray diffraction, atomic force microscopy, and Xray
absorption spectroscopy at the Zn−K edge starting from
45 nm thick zincite films. The reaction eventually yields the
ZnAl2O4 spinel on this interface but via a complex mechanism
involving side and intermediate nonequilibrium compounds,
the spinel initially forming with a distribution of lattice
parameters. Evidence is given of the fact that one of the side
compounds has a crystal structure close to that of the Zn3In2O6 compound. The results are discussed in the general context of
the same reaction on different single-crystal substrates and different film thicknesses.
The Journal of Physical Chemistry C 03/2013; · 4.80 Impact Factor
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ABSTRACT: High-pressure single-crystal X-ray diffraction measurements of lattice parameters of the compound Li2VOSiO4, which crystallises with a natisite-type structure, has been carried out to a pressure of 8.54(5) GPa at room temperature.
Unit-cell volume data were fitted with a second-order Birch-Murnaghan EoS (BM-EoS), simultaneously refining V
0 and K
0 using the data weighted by the uncertainties in V. The bulk modulus is K
0=99(1) GPa, with K′ fixed to 4. Refinements of third order equations-of-state yielded values of K′ that did not differ significantly from 4. The compressibility of the unit-cell is strongly anisotropic with the c axis (K
0(c)=49.7±0.5 GPa) approximately four times more compressible than the a axis (K
0(a)=195±3 GPa).
Physics and Chemistry of Minerals 04/2012; 35(2):71-76. · 1.73 Impact Factor
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American Mineralogist 02/2012; 96:374. · 2.17 Impact Factor
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ABSTRACT: Benzoyl radicals are generated directly from (hetero)aromatic aldehydes upon tetrabutylammonium decatungstate ((n-Bu(4)N)(4)W(10)O(32)), TBADT) photocatalysis under mild conditions. In the presence of alpha,beta-unsaturated esters, ketones and nitriles radical conjugate addition ensues and gives the corresponding beta-functionalized aryl alkyl ketones in moderate to good yields (stereoselectively in the case of 3-methylene-2-norbornanone). Due to the mild reaction conditions the presence of various functional groups on the aromatic ring is tolerated (e.g. methyl, methoxy, chloro). The method can be applied to hetero-aromatic aldehydes whether electron-rich (e.g. thiophene-2-carbaldehyde) or electron-poor (e.g. pyridine-3-carbaldehyde).
Organic & Biomolecular Chemistry 09/2010; 8(18):4158-64. · 3.70 Impact Factor
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ABSTRACT: A specific preparation procedure makes possible to obtain in one shot structural and compositional characterization of a buried interface at the nanometre scale using a micrometre scale probe. A specific example based on dispersive mu-XAS, micro X-ray absorption spectroscopy, shows that nearly-atomic scale changes in local structure, composition, as well as local disorder are faithfully detected. The approach could in principle be applied to any probe with a micrometric resolution.
Physical Chemistry Chemical Physics 06/2010; 12(21):5547-50. · 3.57 Impact Factor
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ABSTRACT: The title compound crystallizes in the trigonal space group R-3, with unit-cell parameters: a=23.261(4), c=9.537(2)Å; λ(MoKα)=0.71073Å, V=4469(2)Å3, and Z=6. The structure has been solved by direct methods using X-ray diffraction techniques. The final reliability index for
the computed structure is 0.0826 for 929 observed reflections and 121 refined parameters. Crown ether adopts an almost circular
shape and macrocycles are piled up in a columnar arrangement forming tubular nanochannels. The channels are filled with guest
CDCl3 molecules, characterised by rotational disorder.
Journal of Chemical Crystallography 07/2007; 37(8):537-541. · 0.57 Impact Factor
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ABSTRACT: In addition to the known bioactive triterpene cucurbitacin B (1), two new cucurbitane triterpenoids, namely, leucopaxillones A (3) and B (4), exhibiting a new oxygenation pattern among cucurbitacins, have been isolated from the mushroom Leucopaxillus gentianeus (syn. L. amarus). Cucurbitacin B (1) imparts a bitter taste to the flesh of the fungus; however, it occurs in the fruiting bodies mainly esterified as tasteless fatty acid esters 2a-c. In vitro growth inhibitory effects of compounds 1-4 on proliferation of four different human tumor cell lines (A549, CAKI-1, HepG2, MCF-7) were evaluated by using a 1-day MTT assay. Only cucurbitacin B was highly active on all lines. Free cucurbitacin B is presumed to be formed in vivo by an enzyme-mediated scission of esters 2a-c, thus constituting a chemical weapon that protects the mushrooms against parasites and predators. Compounds 1-4 are structurally different from the other few cucurbitacins isolated from Basidiomycetes, being, instead, more similar to those occurring in plants. In particular, cucurbitacin B (1) seems to represent an interesting example of secondary metabolite convergence between distant taxa such as fungi and vascular plants, where they likely exert a similar role of protection. The structures of the compounds were established by means of spectroscopic methods and X-ray diffraction on a single crystal. The absolute configuration of leucopaxillone A has been assigned on the basis of CD chirality rules.
Journal of Natural Products 12/2004; 67(11):1823-8. · 3.13 Impact Factor
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ABSTRACT: The demetallation in acidic solution of the Cu(II) complexes with open-chain and cyclic tetramines containing a piperazine unit (2 and 3) has been investigated in terms of its kinetic aspects and compared with the behaviour of unsubstituted counterparts (tetramines 1 and 4). The presence of the piperazine fragment slows demetallation of the open-chain-ligand complex owing to the activation barrier associated with the conformational change from boat-to-half-boat; however, it does not affect the demetallation of the macrocyclic complex, which involves the spontaneous boat-to-twist conformational change. Thus, lateral reinforcement of a cyclam-like ligand does not add any further contribution to the typical inertness in demetallation of macrocyclic complexes.
Chemistry 08/2004; 10(13):3209-16. · 5.93 Impact Factor
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ABSTRACT: We describe the synthesis and characterization of C(2) symmetrical double chromophores, in which two identical chromophores are linked through ethylene glycol spacers of increasing lengths. The complexation ability of the trans stereopure form for each diastereoisomeric pair showed how the two chromophores, when the spacer unit is comprised of a diethylene or a triethylene glycol moiety, are able to interact in a positive way, stabilizing the resulting complexes when compared with single chromophore analogous compounds.
Organic & Biomolecular Chemistry 07/2004; 2(12):1764-9. · 3.70 Impact Factor
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ABSTRACT: The nickel(II) complex with an open chain tetramine containing a piperazine fragment (1) displays an unusual resistance to demetallation in acidic solution and exhibits a lifetime of about five minutes in a solution 0.1 M in HClO4 and 7.0 M in NaClO4. Sluggishness with respect to the demetallation is ascribed to the occurrence of the boat-to-chair conformational conversion of the piperazine fragment, which implies the passage through the highly energetic half-boat transition state. The use of a high concentration of the inert electrolyte induces a 'salting out' effect on both thermodynamics (stability of metal complexes is enhanced) and kinetics (resistance to demetallation is increased).
Dalton Transactions 03/2004; · 3.84 Impact Factor
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ABSTRACT: The new ligands R,R-trans-S,S'-bis[methyl(2'-quinolyl)]-1,2-dithiacyclohexane, cis-S,S'-bis[methyl(2'-quinolyl)]-1,2-dithiacyclohexane, and 1,6-bis(2'-quinolyl)-2,5-dithiahexane have been synthesized and their complexes with Cu(I) and Cu(II) prepared. The ligand/metal systems are bistable, as the complexes with copper in both its oxidation states are stable under the same conditions as solids and in solution. The crystal and molecular structure of [Cu(I)(1,6-bis(2'-quinolyl)-2,5-dithiahexane)]ClO(4) has been determined by X-ray diffraction and reveals that the complex is monomeric, with the ligand folding around the Cu(+) cation, imparting to it a tetrahedral coordination. UV-vis, MS-ESI, and NMR data indicate that the same is found for the Cu(I) complexes of all three ligands. Also, the Cu(II) complexes are monomeric, but with a square arrangement of the ligands around Cu(2+). On changing the oxidation state, the change in the geometrical arrangement is fast and complete in less than 80 ms, as demonstrated by cyclic voltammetry experiments. In the CV profiles, the oxidation and reduction events take place at separated E(ox) and E(red) values, with no return wave even at the fastest scan rates. In the E(ox)-E(red) interval (which ranges from 450 to 650 mV, depending on the ligand), the ligand/copper system can thus exist in one of its two states, depending on its history, and thus display electrochemical hysteretical behavior. The electrochemical cycle leading from the tetrahedral [Cu(I)(ligand)](+) to the square [Cu(II)(ligand)](2+) complex (and vice versa) is reversible and repeatable without degradation, as checked by coupled UV-vis-controlled potential coulometry experiments.
Inorganic Chemistry 10/2003; 42(19):6056-62. · 4.60 Impact Factor
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ABSTRACT: The NO(2)(-) ion, in the trans-octahedral [Ni(II)(N,N'-dimethylethylenediamine)(2)(NO(2))(2)](H(2)O) complex, coordinates the metal through the nitrogen atom (nitro form). On heating the solid complex, the anion rotates to give nitrito coordination (oxygen bound), according to a reversible process. The coordination mode of NO(2)(-) to Ni(II) is related to the steric interplay between the anion and the alkyl substituents on the diamine.
Inorganic Chemistry 03/2003; 42(3):664-6. · 4.60 Impact Factor
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ABSTRACT: The water soluble Ni(II) complexes of the cyclam derivatives with 1,3-benzodioxole and 1,2,3-trimethoxybenzene display the fluorescent emission typical of the covalently linked fluorophores, which results from a charge transfer excited state. On oxidation to Ni(III), the fluorescence is completely quenched due to the occurrence of an electron transfer (eT) process from the excited fluorogenic fragment Fl to the oxidized metal. Thus, fluorescence can be switched off/on at will, for several cycles, by consecutively oxidizing and reducing the metal center, in controlled potential electrolysis experiments both in acetonitrile and in aqueous 0.1 M HClO4. Occurrence of an eT process from Fl to Ni(III) ultimately depends upon the easy oxidation of Fl to Fl+, whereas failure of the occurrence of an eT process from Ni(II) to Fl has to be ascribed to the particular resistance of Fl fragments to the reduction.
Inorganic Chemistry 12/2002; 41(23):6129-36. · 4.60 Impact Factor
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ABSTRACT: A cyclam-like macrocycle has been synthesized with a pendant arm containing a dansylamide group. In the corresponding nickel(II) complex, binding of the pendant arm to the metal is pH controlled. In particular, at pH 4.3, the sulfonamide group deprotonates and coordinates the NiII center, giving rise to a complex of trigonal bipyramidal stereochemistry, as shown by X-ray diffraction studies performed on the crystalline complex salt. At pH 7.5, an OH- ion binds the metal and a six-coordinate species forms. The binding-detachment of the pendant arm to/from the NiII center is signaled by changes in the emission properties of the dansyl subunit in the side chain; the fluorescence of this side chain is high when the pendant arm is not coordinated and low when the sulfonamide group is bound to the metal. The system investigated represents the prototype of a light-emitting molecular machine, driven by a pH change.
Chemistry 12/2002; 8(21):4965-72. · 5.93 Impact Factor
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ABSTRACT: The water soluble NiII complexes of the cyclam derivatives with 1,3-benzodioxole and 1,2,3-trimethoxybenzene display the fluorescent emission typical of the covalently linked fluorophores, which results from a charge transfer excited state. On oxidation to NiIII, the fluorescence is completely quenched due to the occurrence of an electron transfer (eT) process from the excited fluorogenic fragment Fl* to the oxidized metal. Thus, fluorescence can be switched off/on at will, for several cycles, by consecutively oxidizing and reducing the metal center, in controlled potential electrolysis experiments both in acetonitrile and in aqueous 0.1 M HClO4. Occurrence of an eT process from Fl* to NiIII ultimately depends upon the easy oxidation of Fl to Fl+, whereas failure of the occurrence of an eT process from NiII to Fl* has to be ascribed to the particular resistance of Fl fragments to the reduction.
10/2002;
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04/2002;
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ABSTRACT: The easily attainable quadridentate ligand bis-N,N′-(2-methylquinoline)-1,2-trans-cyclohexanediimine forms double helical dimeric complexes with CuI and monomeric complexes with CuII, which are air- and moisture-stable and whose structures have been determined through X-ray diffraction. In an acetonitrile solution, it is possible to cycle electrochemically between the two forms, through a fast process which can be repeated at will (see diagram).
Chemistry 11/1999; 5(12):3679 - 3688. · 5.93 Impact Factor
