Photoelectron diffraction study of ultrathin film growth of Ni on Pt(111)

X-ray photoelectron diffraction (PD) based on a forward scattering approach (FS-PD) has been used to study the growth mode of the first few Ni monolayers deposited on the Pt(111) surface, with a particular attention to the initial stages of epitaxy, i.e. the formation of the first atomic layer. Strong evidences for a layer-by-layer (or Frank-Van der Merwe) growth mode are reported, substantiated also by theoretical simulations carried out with the single scattering cluster-spherical wave (SSC-SW) framework. The first Ni monolayer grows strained in-plane to match the substrate pseudomorphically even if there is a 10% mismatch between the lattice parameters of Ni and Pt. The multilayer (up at least to six monolayers) maintains the horizontal strain and consequently shows a vertical spacing contraction (tetragonal distorsion). It retains the overall threefold symmetry and azimuthal orientation of the substrate, indicative of a single-domain epitaxial fcc stacking. There is also some evidence (even if it is not conclusive) for the fact that the Ni atoms of the first monolayer occupy hcp sites of the substrate surface.     

Coumarin as dipolarophile towards 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide

The reaction of coumarin with the title nitrile oxide gives a single regioisomer in high yield. This result is compared with the dipolarophilic behavior of cinnamic acid esters.     

Steiner systems andn −1-isomorphisms

In this work we introduce the concept of n ^–1-isomorphism between Steiner systems (this coincides with the concept of isomorphism whenever n=1).Precisely two Steiner systems S₁ and S₂ are said to be n^–1-isomorphic if there exist n partial systems S _i ⁽¹⁾ ,...,S _i ⁽ⁿ⁾ contained in Si, i.{1,2},such that S ₁ ^(k) and S ₂ ^(k) are isomorphic for each k{1,..., n}.The n^–1-isomorphisms are also used to study nets replacements, see Ostrom [8], and to study the transformation methods of designs and other incidence structures introduced in [9] and generalized in [1] and [10].Work done under the auspicies of G.N.S.A.G.A. supported by 40% grants of M.U.R.S.T.     

The second acidic constant of salicylic acid

The second dissociation constant of salicylic acid (H2L) has been determined, at 25 degrees C, in NaCl ionic media by UV spectrophotometric measurements. The investigated ionic strength values were 0.16, 0.25, 0.50, 1.0, 2.0 and 3.0 M. The protolysis constants calculated at the different ionic strengths yielded, with the Specific Interaction Theory, the infinite dilution constant, log beta1(0) = 13.62 +/- 0.03, for the equilibrium L2- + H+ <==> HL-. The interaction coefficient between Na+ and L2-, b(Na+, L2-) = 0.02 +/- 0.07, has been also calculated.     

Reaction between 2,2′ -dithiodianiline and acetylenic ketones or esters. A new synthesis of 4H-1,4-benzothiazines

The title compounds ( 3a-c ) together with the benzothiazolines ( 4b-c ) were obtained by reaction between 2,2′ -dithiodianiline ( 1 ) and acetylenic ketone ( 2a ) or esters ( 2b-c ). A possible pathway involving the formation and subsequent cyclization to 3 of enamine intermediates A and/or B , is suggested.     

Site chirality as a messenger in chain-end stereocontrolled propene polymerization

The origin of stereoselectivity in the chain-end controlled syndiospecific polymerization of propene with octahedral Ti-catalysts is unclear. We present a possible mechanism which is based on the site chirality as a messenger of information between the chirality of the chain-end and the chirality of monomer insertion which can operate for secondary propagation. This mechanism could be operative also for the industrially relevant V-based homogeneous catalysts.     

Sodium Chloride Molar Conductance in Different Poly(ethylene glycol)–Water Mixed Solvents

The molar conductivities of NaCl in several poly(ethylene glycol)(PEG)–water “mixed solvents” are presented as a function of the PEG content in solution. Three different PEG samples, a monodispersed one and two polydispersed ones, have been used. The comparison between the molar conductivity values in the mixed solvents and the corresponding ones in pure water shows that the only effect of PEG on the ions’ motions is an obstruction effect despite the variation of the macroscopic dielectric constant induced by PEG itself. A comparison between the molar conductivities and the corresponding mutual main diffusion coefficients shows a tight correlation between the two quantities. This correlation is possible only in the absence of electrostatic effects due to the presence of PEG.     

Resolution of tryptophan-ANS fluorescence energy transfer in apomyoglobin by site-directed mutagenesis

Resonance energy transfer between tryptophanyl residues and the apolar fluorescent dye 1-anilino-8-naphthalene sulfonate (ANS) occurs when the fluorophore is bound to native folded sperm whale apomyoglobin. The individual transfer contribution of the two tryptophanyl residues (W7 and W14, both located on the A-helix of the protein) was resolved by measuring the tryptophan-ANS transfer efficiency for the ANS-apomyoglobin complexes formed by wild-type protein and protein mutants containing one or no tryptophanyl residues, i.e. W7F, W14F and W7YW14F. The transfer efficiency of W14 residue was found to be higher than that of W7, thus indicating that W14 acts as the main energy donor in the ANS-apomyoglobin complex. This suggests that the plane containing the anilinonaphthalene ring of the extrinsic fluorophore has a spatial orientation similar to that of W14 and, hence, to the heme group in the holoprotein.     

Non-Linear Electrodynamics in Blandford–Znajek Energy Extraction

Non-linear electrodynamics (NLED) is a generalization of Maxwell's electrodynamics for strong fields. It has significant implications for the study of black holes and cosmology and has been extensively studied in the literature, extending from quantum to cosmological contexts. In this work, two new ways to investigate these non-linear theories are investigated. First, the Blandford-Znajek mechanism is analyzed in light of this promising theoretical context, providing the general form of the extracted power up to second order in the black hole spin parameter a. It is found that, depending on the NLED model, the emitted power can be extremely increased or decreased, and that the magnetic field lines around the black hole seem to become vertical quickly. Considering only separated solutions, it is found that no monopole solutions exist and this could have interesting astrophysical consequences (not considered here). Last but not least, it is attempted to confine the NLED parameters by inducing the amplification of primordial magnetic fields (“seeds”), thus admitting non-linear theories already during the early stages of the Universe. However, the latter approach proves to be useful for NLED research only in certain models. These (analytical) results emphasize that the behavior of non-linear electromagnetic phenomena strongly depends on the physical context and that only a power-law model seems to have any chance to compete with Maxwell.