Kinetic and Product Study of the S-oxidation vs HAT Chemoselectivity in Reactions Promoted by Nonheme Iron(IV)-oxo Complex/NHPI Mediator System

The chemoselectivity between S-oxidation and hydrogen atom transfer (HAT) from C−H bonds has been investigated in the oxidations of a series of aryl sulfides, alkyl aromatic compounds and benzylic alcohols promoted by the iron(IV)-oxo complex [(N4Py)Fe^IV(O)]²⁺ (N4Py: N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)-methylamine) either alone or in the presence of the N-hydroxyphthalimide (NHPI) mediator via kinetic and product studies. Kinetic analyses indicate a generally higher reactivity of [(N4Py)Fe^IV(O)]²⁺ for S-oxidation process while HAT is favored in the reactions promoted by phthalimide-N-oxyl radical (PINO) deriving from NHPI oxidation. Product analysis in intermolecular competitive oxidations confirms the kinetic results with sulfoxides obtained as major products in the oxidation promoted by [(N4Py)Fe^IV(O)]²⁺. Conversely, when NHPI is employed as a mediator, significant differences in terms of chemoselectivity are observed, and HAT-derived products are obtained in higher yields which translate into an inversion of selectivity in the case of the substrates containing activated C−H bonds like diphenylmethane, triphenylmethane and benzylic alcohols. A similar change of chemoselectivity is also observed in the oxidation of aromatic substrates containing both a sulfur atom and α to OH benzylic C−H bonds, with the sulfoxide product more abundant in the absence of NHPI and carbonyl products prevailing with the [(N4Py)Fe^IV(O)]²⁺/NHPI system.     

Aluminum,calcium and zinc complexes supported by potentially tridentate iminophenolate ligands: synthesis and use in the ring‐opening polymerization of lactide

The coordination chemistry of the potentially tridentate phenoxyethyl‐ and benzylaminoethyl‐iminophenol pro‐ligands {ONO}H and {ONN}H on to calcium, zinc and aluminum centers has been studied. {ONO}Ca(N(SiMe₃)₂)(THF) (1) was prepared by a one‐pot salt metathesis procedure but the analogous reaction with {ONN}H led to intractable mixtures. Reaction of {ONO}H and {ONN}H with ZnEt₂ (0.5 or 1 equiv.) systematically led to isolation of the corresponding homoleptic complexes {ONO}₂Zn (2) and {ONN}₂Zn (3). The dimethylaluminum complexes {ONO}AlMe₂ (4) and {ONN}AlMe₂ (5) were readily prepared by treatment of AlMe₃ with 1 equiv. of the corresponding pro‐ligands. Compounds 2 and 4 both feature monomeric structures in the solid state, with chelating iminophenolate ligands and free‐hanging phenoxyethyl arms. The amido complex 1 was shown to be a moderately active initiator for the controlled ring‐opening polymerization (ROP) of racemic lactide at room temperature, yielding polylactides with high initiation efficiencies, relatively narrow polydispersities and a slight heterotactic bias. Immortal polymerizations were achieved by combining excess isopropanol to 1, offering up to 50 macromolecules per metal center, with well‐controlled molecular features. The dimethylaluminum compounds 4 and 5 initiated the controlled ROP of lactide in the presence of 1 equiv. of benzyl alcohol as a co‐initiator but required higher temperatures. Copyright © 2012 John Wiley & Sons, Ltd.     

Contrasting chaos with noise via local versus global information quantifiers

At issue here is the distinction between noise and chaos. They are different phenomena but sometimes produce results that resemble each other. From a numerical viewpoint, in particular, subtle differences that exist between them are often difficult to discern. We present here a conceptual scheme, based on Information Theory, that successfully distinguishes between these two regimes. The idea is to look for the location of the pertinent signal on a special plane, called the information-one, whose axes are entropic-like measures. Using these quantifiers (one local, the other global), the contrast between the two dynamical regimes becomes apparent.     

Temperature Dependence of Photoinduced Birefringence in Polystyrene Doped with Disperse Red‐1

A theoretical model on the basis of the free‐volume concept is presented explaining the temperature dependence of photoinduced birefringence in polystyrene films that contain Disperse Red‐1. Birefringence increases with temperature up to 180 K as the free volume for isomerization increases, and then decreases as thermally activated processes dominate. The fast process of birefringence decay has a time constant that increases with temperature at low temperatures, due to the change in photoisomerization.

Temperature dependence of the birefringence amplitude measured at 300 s. The amplitude increases with temperature up to 180 K and then decreases. The solid line is for guiding the eye.     

A test statistic whose derivation is simple and unusual

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A test statistic whose derivation is simple and unusual

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Isospin symmetry breaking in double-beta-decay processes

The nuclear structure physics of double-beta-decay transitions is reviewed starting from the consideration of the isospin symmetry breaking in the nuclear many body problem. The difficulties found in the use of the QRPA and related approximations, in dealing with the calculation of nuclear double-beta-decay observables, are understood in terms of the mixing between isospin collective and intrinsic variables and in terms of isospin breaking approximations.     

Europium Luminescent Polymeric Microspheres Fabricated by Spray Drying Process

The spray drying method was used to prepare luminescent microspheres. These microspheres were prepared by spraying an aqueous solution of dextrin and an europium(III) complex with subsequent drying in a hot medium. The spray dried powder was characterized by scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). Particle size distribution was estimated from SEM images. The ultrasonic spray drying technique was successfully applied to yield a microparticulated and red luminescent powder composed by the [Eu(dpa)(3)](3-) (dpa = dipicolinic acid) complex incorporated in dextrin microspheres.     

Boundedness of fractional operators in weighted variable exponent spaces with non doubling measures

In the context of variable exponent Lebesgue spaces equipped with a lower Ahlfors measure we obtain weighted norm inequalities over bounded domains for the centered fractional maximal function and the fractional integral operator.     

Performance of encryption schemes in chaotic optical communication: A multifractal approach

From the estimation of the Hurst exponent and the multifractality degree we discriminate the security levels of two typical encoding schemes usually applied in chaos-based communication systems. We also analyze the effects that the sampling period and the message amplitude have on the goodness of these techniques. We compare our results with those obtained by considering an information theory approach [O.A. Rosso, R. Vicente, C.R. Mirasso, Phys. Lett. A 372 (2007) 1018]. The Hurst exponent seems to be a sensitive and powerful tool for discriminating the presence of a message embedded in a chaotic carrier.