Spontaneous magnetization in Ni-Al and Ni-Fe layered double hydroxides

Layered double hydroxides containing paramagnetic Ni (II) and diamagnetic/paramagnetic Al (III)/Fe (III) ions have been prepared and characterized. Ni 2Al(OH) 6(NO 3). nH 2O ( 1), Ni 2Fe(OH) 6(NO 3). nH 2O ( 2), Ni 2Fe(OH) 6(C 6H 8O 4) 0.5. nH 2O ( 3), and Ni 2Fe(OH) 6(C 10H 16O 4) 0.5. nH 2O ( 4) were prepared by coprecipitation at controlled pH as polycrystalline materials with the typical brucite-like structure, with alternating layers of hydroxide and the corresponding anions, which determine the interlayer separation. Magnetic studies show the appearance of spontaneous magnetization between 2 and 15 K for these compounds. Interestingly, the onset temperature for spontaneous magnetization follows a direct relationship with interlayer separation, since this is the only magnetic difference between compounds 2, 3, and 4. Magnetic and calorimetric data indicate that long-range magnetic ordering is not occurring in any of these materials, but rather a freezing of the magnetic system in 3D due to the magnetic disorder and competing intra- and interlayer interactions. Thus, these hydrotalcite-like magnetic materials can be regarded as spin glasses.     

Synthesis of novel tetrahydroindeno[1,2-b]pyrrolidines via Ugi multicomponent and palladium-catalyzed aerobic oxidative cyclization

Novel tetrahydroindeno[1,2-b]pyrrolidines were conveniently prepared in moderate to good yields via a sequential Ugi multicomponent reaction or Staudinger/aza-Wittig/Ugi combination, followed by the palladium-catalyzed aerobic oxidative cyclization of the resulting Ugi adducts.     

Electrochemical and spectroscopic characterisation of amphetamine-like drugs: application to the screening of 3,4-methylenedioxymethamphetamine (MDMA) and its synthetic precursors

A complete physicochemical characterisation of MDMA and its synthetic precursors MDA, 3,4-methylenedioxybenzaldehyde (piperonal) and 3,4-methylenedioxy-β-methyl-β-nitrostyrene was carried out through voltammetric assays and Raman spectroscopy combined with theoretical (DFT) calculations. The former provided important analytical redox data, concluding that the oxidative mechanism of the N-demethylation of MDMA involves the removal of an electron from the amino-nitrogen atom, leading to the formation of a primary amine and an aldehyde. The vibrational spectroscopic experiments enable to afford a rapid and reliable detection of this type of compounds, since they yield characteristic spectral patterns that lead to an unequivocal identification.Moreover, the rational synthesis of the drug of abuse 3,4-methylenedioxymethamphetamine (MDMA or “ecstasy”) from one of its most relevant precursors 3,4-methylene-dioxyamphetamine (MDA), is reported. In addition, several approaches for the N-methylation of MDA, a limiting synthetic step, were attempted and the overall yields compared.     

Structural, thermal, and magnetic study of solvation processes in spin-crossover [Fe(bpp)(2)][Cr(L)(ox)(2)](2).nH(2)O complexes

The influence of lattice water in the magnetic properties of spin-crossover [Fe(bpp)2]X2.nH2O salts [bpp = 2,6-bis(pyrazol-3-yl)pyridine] is well-documented. In most cases, it stabilizes the low-spin state compared to the anhydrous compound. In other cases, it is rather the contrary. Unraveling this mystery implies the study of the microscopic changes that accompany the loss of water. This might be difficult from an experimental point of view. Our strategy is to focus on some salts that undergo a nonreversible dehydration-hydration process without loss of crystallinity. By comparison of the structural and magnetic properties of original and rehydrated samples, several rules concerning the role of water at the microscopic level can be deduced. This paper reports on the crystal structure, thermal studies, and magnetic properties of [Fe(bpp)2][Cr(bpy)(ox)2]2.2H2O (1), [Fe(bpp)2][Cr(phen)(ox)2]2.0.5H2O.0.5MeOH (2), and [Fe(bpp)2][Cr(phen)(ox)2]2.5.5H2O.2.5MeOH (3). Salt 1 contains both high-spin (HS) and low-spin (LS) Fe2+ cations in a 1:1 ratio. Dehydration yields the anhydrous spin-crossover compound with T1/2 downward arrow = 353 K and T1/2 upward arrow = 369 K. Rehydration affords the dihydrate [Fe(bpp)2][Cr(bpy)(ox)2]2.2H2O (1r) with 100% HS Fe2+ sites. Salt 2 also contains both HS and LS Fe2+ cations in a 1:1 ratio. Dehydration yields the anhydrous spin-crossover compound with T1/2 downward arrow = 343 K and T1/2 upward arrow = 348 K. Rehydration affords [Fe(bpp)2][Cr(phen)(ox)2]2.0.5H2O (2r) with 72% Fe2+ sites in the LS configuration. The structural, magnetic, and thermal properties of these rehydrated compounds 1r and 2r are also discussed. Finally, 1 has been dehydrated and resolvated with MeOH to give [Fe(bpp)2][Cr(bpy)(ox)2]2.MeOH (1s) with 33% HS Fe2+ sites. The influence of the guest solvent in the Fe2+ spin state can anticipate the future applications of these compounds in solvent sensing.     

Computation of the stabilization parameter for the finite element solution of advective–diffusive problems

In a previous paper a general procedure for deriving stabilized finite element schemes for advective type problems based on invoking higher order balance laws over finite size domains was presented. This provides an expression for the element stabilization parameter in terms of the solution residual and its first derivatives in a kind of iterative or adaptative manner. Details of the application of this procedure to 1D and 2D advective–diffusive problems are given. Some examples of applications showing the potential of the new approach are presented. © 1997 John Wiley & Sons, Ltd.     

Compared EC-AFM Analysis of Laser-Induced Graphene and Graphite Electrodes in Sulfuric Acid Electrolyte

Flexible and economic sensor devices are the focus of increasing interest for their potential and wide applications in medicine, food analysis, pollution, water quality, etc. In these areas, the possibility of using stable, reproducible, and pocket devices can simplify the acquisition of data. Among recent prototypes, sensors based on laser-induced graphene (LIGE) on Kapton represent a feasible choice. In particular, LIGE devices are also exploited as electrodes for sensing in liquids. Despite a characterization with electrochemical (EC) methods in the literature, a closer comparison with traditional graphite electrodes is still missing. In this study, we combine atomic force microscopy with an EC cell (EC-AFM) to study, in situ, electrode oxidation reactions when LIGE or other graphite samples are used as anodes inside an acid electrolyte. This investigation shows the quality and performance of the LIGE electrode with respect to other samples. Finally, an ex situ Raman spectroscopy analysis allows a detailed chemical analysis of the employed electrodes.     

Semiclassical regime of Regge calculus and spin foams

Recent attempts to recover the graviton propagator from spin foam models involve the use of a boundary quantum state peaked on a classical geometry. The question arises whether beyond the case of a single simplex this suffices for peaking the interior geometry in a semiclassical configuration. In this paper we explore this issue in the context of quantum Regge calculus with a general triangulation. Via a stationary phase approximation, we show that the boundary state succeeds in peaking the interior in the appropriate configuration, and that boundary correlations can be computed order by order in an asymptotic expansion. Further, we show that if we replace at each simplex the exponential of the Regge action by its cosine—as expected from the semiclassical limit of spin foam models—then the contribution from the sign-reversed terms is suppressed in the semiclassical regime and the results match those of conventional Regge calculus.     

Synthesis and characterization of a soluble bimetallic oxalate-based bidimensional magnet: [K(18-crown-6)]3[Mn3(H2O)4{Cr(ox)3}3

The "templating" K crown ether cation allows for the preparation of soluble layered oxalate-based bimetallic magnets, as in [K(18-crown-6]3{Mn3(H2O)4[Cr(ox)3]3}, with an unprecedented bidimensional polymeric anionic network that involves both oxalato bridges and H bonds. As in other 2D oxalate-bridged compounds, the compound behaves as a soft ferromagnet, with the onset of magnetic ordering occurring at 3.3 K.     

Synthesis and anti-HIV activity of novel cyclopentenyl nucleoside analogues of 8-azapurine

Novel nucleoside analogues of structure 3-5 were synthesized starting from (+/-)-cis-2-amino-3-cyclopentenylmethanol (1). The chlorine derivative 3 inhibited both HIV-1 and HIV-2 replication in MT-4 cells with IC(50) values of 10.67 microM and of 13.79 microM, respectively.