Phase and valence transitions in Ba2LnSnxNb1−xO6−δ

The structures of compounds in the perovskite series Ba₂LnSn_xNb_1−xO_6−δ (Ln=Pr and Tb and x=0, 0.1, 0.2, …, 1.0) have been examined using synchrotron X-ray and neutron diffraction. It was found that niobate members of both series feature full B-site cation ordering but that this order is lost with increasing x. X-ray absorption near-edge structure (XANES) and near-infrared spectroscopies indicate that the oxidation state of the lanthanide cations gradually changes from Ln³⁺ to Ln⁴⁺ with increased Sn⁴⁺ doping. This is believed to be the cause of the loss of B-site ordering. Least squares analysis of the XANES spectra suggests that the rate of the transformation of Ln³⁺ cations to the tetravalent state is such that the Pr series contains no oxygen vacancies while the Tb series may contain a very small amount of vacancies, with δ≈0.02.     

1H and 13C NMR data of benzylsulfonic acids-model compounds for lignosulfonate

Although there has been a major progress in the analysis of native lignin using NMR in the recent years, not much attention has been paid to lignosulfonates. Lignosulfonates are more difficult to analyse because of solubility issues and a more complex structure owing to chemical modification during the pulping process. A large database of NMR data is available for the building blocks of native lignin, but no data are available for the corresponding sulfonated compounds. We have prepared 15 monomeric and seven dimeric sulfonated model compounds characterised by NMR. These include models for end groups, as well as beta-beta, beta-5, 5-5 and beta-O-5 linkages in lignosulfonates, and will be important for further structural investigation on lignosulfonate.     

Catecholase activity of a copper(II) complex with a macrocyclic ligand: unraveling catalytic mechanisms

We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1(4,7).1(11,14). 1(17,20)]triacontane-5,7(28),11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tert-butylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu(II) and the Cu(I) complexes are also reported.     

Insider trading equilibrium in a market with memory

We consider the Kyle-Back model for insider trading, with the difference that the classical Brownian motion noise of the noise traders is replaced by the noise of a fractional Brownian motion B ^H with Hurst parameter ${H>\frac{1}{2}}$ (when ${H=\frac{1}{2}, B^H}$ coincides with the classical Brownian motion). Heuristically, for ${H>\frac{1}{2}}$ this means that the noise traders has some ??memory??, in the sense that any increment from time t on has a positive correlation with its value at t. (In other words, the noise trading is a persistent stochastic process). It also means that the paths of the noise trading process are more egular than in the classical Brownian motion case. We obtain an equation for the optimal (relative) trading intensity for the insider in this setting, and we show that when ${H\rightarrow\frac{1}{2}}$ the solution converges to the solution in the classical case. Finally, we discuss how the size of the Hurst coefficient H influences the optimal performance and portfolio of the insider.