Magnetic force microscopy characterization of heat and current treated Fe40Ni38Mo4B18 amorphous ribbons

The domain structure of a magnetostrictive Fe₄₀Ni₃₈Mo₄B₁₈ amorphous ribbon has been studied using magnetic force microscopy (MFM) at room temperature. First, the evolution of the magnetic domain patterns as a function of the annealing temperature has been investigated. In samples heat treated at 250 and 450 °C for 1 h, a transformation from 90° to 180° domain wall has been clearly observed, while the sample heat treated at 700 °C for 1 h showed a magnetic phase fixed by the crystalline anisotropy. Additionally, the evolution of the magnetic domain structure by applying a DC current was recorded by the MFM technique. For current annealed samples at 1 A for 1, 30 and 60 min, a transformation between different domain patterns has been observed. Finally, in samples treated by the current annealing method under simultaneous stress, an increase of the annealing time gives rise to a different magnetic structure arising from the development of transverse magnetic anisotropy.     

Stereoselective synthesis of eight-membered cyclic ethers by tandem Nicholas reaction/ring-closing metathesis: a short synthesis of (+)-cis-Lauthisan

[STRUCTURE: SEE TEXT] Cis-2,8-disubstituted oxocanes and the parent unsaturated precursors were prepared from the corresponding Co2(CO)6-cycloalkynic ethers. Key steps in such synthesis were the ether linkage formation by intermolecular Nicholas reaction, RCM of the suitable acyclic dienyl ether and montmorillonite K-10 induced isomerization of the complexed cycloalkyne. A short synthesis of (+)-cis-lauthisan taking advantage of the developed methodology is described.     

Special jordan H*-triple systems

This work, jointly with [9], completes the structure theory and classification of the Jordan H ^*- triple systems. The problem of describing the Jordan H ^*-triple systems is reduced in [5] to that of describing the topologically simple ones. Ruling out the finite-dimensional case, we have that any of these H ^*-triples has an underlying triple system structure of quadratic type (and these can be fully described), or it is the H ^*-triple system associated to the odd part of a topologically simple Z₂-graded Jordan H ^*-algebra, whose classification is given in [13].     

Quenching of the Singlet and Triplet Excited States of Pterin by Amino Acids

Unconjugated oxidized pterins accumulate in the skin of patients suffering from vitiligo and, under UVA irradiation, photosensitize the oxidation of amino acids. In this work, we study the interaction of the singlet and triplet excited states of pterin (Ptr), the parent compound of oxidized pterins, with four oxidizable amino acids: tryptophan (Trp), tyrosine (Tyr), histidine (His) and methionine (Met). Steady‐state and time‐resolved fluorescence measurements and laser flash photolysis experiments were performed to investigate the quenching of the Ptr excited states by the amino acids in aqueous solution. The singlet excited states of Ptr are quenched by Met mainly via a dynamic process and by Trp via a combination of dynamic and static processes. His does not quench singlet excited states of Ptr, and quenching by Tyr could not be investigated due to the low solubility of this amino acid. The triplet excited states of Ptr are quenched by the four studied amino acids, and the corresponding bimolecular quenching rate constants are in the range of diffusion controlled limit. The assessment of the results in the context of the Ptr‐photosensitization of amino acids suggests that triplet excited state of Ptr is the species that initiates the photochemical processes.     

Hydrophobization and evaluation of absorption capacity of Aloe vera,Opuntia ficus-indica and Gelidium for oil spill cleanup

Natural sorbent materials have practical advantages for the oil spill cleanup, whose advantages are their low-cost, feasibility for real-life applications and environmental adaptability. In this work, absorption capacity was determined for lyophilized aloe, nopal and agar and their composites with silica, Fe₃O₄/polysterene and multi-wall carbon nanotubes (MWCNTs). Freeze-drying was performed in order to preserve the structure and increase the internal volume of sorbents. The structures of lyophilized sorbents and composites were analyzed by scanning electron microscopy (SEM). SEM images for lyophilized sorbents show a tridimensional arrangement formed by plant-derived materials, which allows the oil absorption. The composites keep their tridimensional structure after freeze-drying and composite formation and exhibit coupling between both materials. Absorption capacity of aloe, nopal and agar are 9?g/g, 3?g/g, and 26?g/g, respectively without any pretreatment. Composites with Fe₃O₄/polysterene own capacities of 5.8?g/g, 2.8?g/g, and 14?g/g, respectively. Finally, for MWCNT composites, capacities are 7.8?g/g, 2.9?g/g and 23?g/g. A significant difference of adsorption capacity between lyophilized sorbents and composites is attributed to lyophilized materials absorbing oil, water and other compounds. Meanwhile, for composites the absorption is a more selective process, since the hydrophobization does not allow the absorption of water.     

Dynamic ion pairs in the adsorption of isolated water molecules on alkaline-earth oxide (001) surfaces

Low coverage water adsorption on alkaline-earth oxides is studied by first principles methods and ab initio molecular dynamic simulations. On CaO and BaO(001), water dissociation is thermodynamically favored in contrast with the molecular adsorption found for MgO(001). On CaO(001), the barrier for water splitting is very small leading to a tight ion pair H-OH that exhibits a dynamic character with the hydroxyl group able to visit four equivalent adsorption sites while remaining attached to the proton. In contrast, ion pair separation is endothermic by 0.8 eV. These results are common to other basic surfaces such as BaO(001) and have important implications in the chemistry of partially hydroxylated oxide surfaces.     

Dihydrogen Catalysis of the Reversible Formation and Cleavage of CH and NH Bonds of Aminopyridinate Ligands Bound to (η5‐C5Me5)IrIII

This study focuses on a series of cationic complexes of iridium that contain aminopyridinate (Ap) ligands bound to an (η⁵‐C₅Me₅)Ir^III fragment. The new complexes have the chemical composition [Ir(Ap)(η⁵‐C₅Me₅)]⁺, exist in the form of two isomers ( 1⁺ and 2⁺ ) and were isolated as salts of the BAr_F^? anion (BAr_F=B[3,5‐(CF₃)₂C₆H₃]₄). Four Ap ligands that differ in the nature of their bulky aryl substituents at the amido nitrogen atom and pyridinic ring were employed. In the presence of H₂, the electrophilicity of the Ir^III centre of these complexes allows for a reversible prototropic rearrangement that changes the nature and coordination mode of the aminopyridinate ligand between the well‐known κ²‐N,N′‐bidentate binding in 1⁺ and the unprecedented κ‐N,η³‐pseudo‐allyl‐coordination mode in isomers 2⁺ through activation of a benzylic C?H bond and formal proton transfer to the amido nitrogen atom. Experimental and computational studies evidence that the overall rearrangement, which entails reversible formation and cleavage of H?H, C?H and N?H bonds, is catalysed by dihydrogen under homogeneous conditions.     

Shedding Light on the Origin of Solid-State Luminescence Enhancement in Butterfly Molecules

Different molecular strategies have been carefully evaluated to produce solid-state luminescence enhancement (SLE) in compounds that show dark states in solution. A set of α-phenylstyrylarene derivatives with a butterfly shape have been designed and synthesised, for the first time, with the aim of improving the solid-state fluorescence emission of their parent styrylarene compounds. Although these butterfly molecules are not fluorescent in solution, one of them (1,2,4,5-tetra(α-phenylstyryl)benzene) exhibits a fluorescence quantum yield as high as 68 % in a drop-cast sample and 31 % in its crystalline form. In contrast, 1,3,5-tris(α-phenylstyryl)benzene and 4,6-bis(α-phenylstyryl)pyrimidine do not show SLE. A range of fluorescence spectroscopy experiments and DFT calculations were carried out to unravel the origin of different photophysical behaviour of these compounds in the solid state. The results indicate that a rational strategy to control the SLE effect in luminogens depends on a delicate balance between molecular properties and inter-/intramolecular interactions in the solid state.