Palladium nanoparticles stabilized by alkylated polyethyleneimine as aqueous biphasic catalysts for the chemoselective stereocontrolled hydrogenation of alkenes

Palladium nanoparticles were prepared, stabilized, and dispersed in water by alkylated branched polyethyleneimine. The palladium nanoparticles were effective aqueous biphasic catalysts for the chemoselective hydrogenation of alkenes with preferential reduction of less hindered double bonds, such as reduction of 3-methylcyclohexene in the presence of 1-methylcyclohexene and 1-octene in the presence of 2-methyl-2-heptene. [structure: see text].     

An H2-Type Norm of a Discrete-Time Linear Stochastic System with Periodic Coefficients Simultaneously Affected by an Infinite Markov Chain and Multiplicative White Noise Perturbations

This article investigates the problem of the definition and computation of an H₂-type norm for discrete-time time-varying periodic stochastic linear systems simultaneously affected by multiplicative white noise perturbations and random jumping according to a Markov chain with an infinite countable number of states. Also, we solve an optimization problem that contains, as a special case, the H₂ optimal control problem for the considered class of stochastic systems under the assumption of perfect state measurements.     

Periodic solutions of affine stochastic differential equations

We discuss the problem of the existence of periodic and stationary solutions of affine stochastic differential equations. We prove that under a controllability condition the system has a periodic solution if and only if the linear part is eyponentially stable in mean square.

It is also shown that the controllability assumption is necessary for the existence of a “unique” weakly periodic solution with nondegenerate covariance.     

Exponential Stability in Mean Square for a General Class of Discrete-Time Linear Stochastic Systems

Abstract

The problem of the mean square exponential stability for a class of discrete-time linear stochastic systems subject to independent random perturbations and Markovian switching is investigated. The case of the linear systems whose coefficients depend both to present state and the previous state of the Markov chain is considered. Three different definitions of the concept of exponential stability in mean square are introduced and it is shown that they are not always equivalent. One definition of the concept of mean square exponential stability is done in terms of the exponential stability of the evolution defined by a sequence of linear positive operators on an ordered Hilbert space. The other two definitions are given in terms of different types of exponential behavior of the trajectories of the considered system. In our approach the Markov chain is not prefixed. The only available information about the Markov chain is the sequence of probability transition matrices and the set of its states. In this way one obtains that if the system is affected by Markovian jumping the property of exponential stability is independent of the initial distribution of the Markov chain.

The definition expressed in terms of exponential stability of the evolution generated by a sequence of linear positive operators, allows us to characterize the mean square exponential stability based on the existence of some quadratic Lyapunov functions.

The results developed in this article may be used to derive some procedures for designing stabilizing controllers for the considered class of discrete-time linear stochastic systems in the presence of a delay in the transmission of the data.     

Influence of surfactants on the fading of malachite green

The kinetics of the reaction between malachite green (MG) and sodium hydroxide (MG fading) was studied using a spectrophotometric method in the presence of two cationic surfactants, cetyl-benzyl-dimethyl-ammonium chloride (CBDAC) and hexadecyl-trimethylammonium bromide (HTAB) and one anionic surfactant, sodium dodecyl sulphate (SDS) at concentrations below and above critical micellar concentrations. The cationic surfactants have a catalytic effect, while the anionic surfactant has an inhibitory effect on the reaction. A kinetic model describing the influence of surfactant on reaction rate was developed. The results are discussed on the basis of electrostatic and hydrophobic interactions between the kinetic micelles and malachite green.      

Crystal and Molecular Structure of [2,6‐(Me2NCH2)2C6H3]2SnF2, an Intramolecularly Coordinated Diorganotin Difluoride

Single‐crystal X‐ray diffraction analysis of [2,6‐(Me₂NCH₂)₂C₆H₃]₂SnF₂ reveals that only one of the two dimethylaminomethyl groups of each pincer‐type ligands [2,6‐(CH₂NMe₂)₂C₆H₃]^? is coordinated to the tin atom at Sn‐N distances of 2.576(2) and 2.470(2) Å, inducing chirality of the latter. The tin atom exhibits a distorted octahedral trans(C,C)cis(N,N)cis(F,F) configuration. Extensive intra‐ and intermolecular C‐H···F hydrogen bonding is observed with the latter giving rise to formation of polymeric chains.     

An Easy Way Toward ε‐Caprolactone Macromonomers by Microwave Irradiation Using Early Lanthanide Halides as Catalysts

Poly(ε‐caprolactone) macromonomers were synthesized under microwave irradiation from commercial caprolactone, using commercial hydrated lanthanide halides as catalysts. The molecular weight of the polymers was in the range 3 000–5 000. Higher molecular weights (5 000–20 000) and lower polydispersity indices were obtained with THF adducts of the lanthanide halides as catalysts and also by applying longer reaction times or using diethylene glycol as a coupling reagent.     

Scanning tunneling microscopy and spectroscopy of graphene layers on graphite

We report low temperature scanning tunneling microscopy and spectroscopy on graphene flakes supported on a graphite substrate. The experiments demonstrate that graphite is exceptionally well suited as a substrate for graphene because it offers support without disturbing the intrinsic properties of the charge carriers. The degree of coupling of a graphene flake to the substrate was recognized and characterized from the appearance of an anomalous Landau level sequence in the presence of a perpendicular magnetic field. By following the evolution of the Landau level spectra along the surface, we identified graphene flakes that are decoupled or very weakly coupled to the substrate. From the Landau level sequence in this flake, we extract the local Fermi velocity and energy of the Dirac point and find extremely weak spatial variation of these quantities confirming the high quality and non invasive nature of the graphite substrate.     

An example of lipophiloselectivity: the preferred oxidation, in water, of hydrophobic 2-alkanols catalyzed by a cross-linked polyethyleneimine-polyoxometalate catalyst assembly

A cross-linked polyethyleneimine polymer containing the [ZnWZn2(H2O)2(ZnW9O34)2]12- polyoxometalate was prepared from branched polyethyleneimine (Mw = 600), the polyoxometalate, and a n-octylamine-epichlorohydrin cross-linking reagent. This catalytic assembly was active for the selective oxidation of 2-alkanols to 2-alkanones with aqueous H2O2 with reactions presumably occurring at a hydrophobic domain. Most importantly, the catalyst showed distinctive lipophiloselectivity, that is selectivity as a function of the lipophilic nature of a reaction substrate. The lipophiloselectivity was proportional to the relative partition coefficient (1-octanol/water) of the substrates.     

Early Aptian carbon and sulphur isotope signatures at ODP site 765

Current carbon and sulphur isotope ratios (δ(13)C and δ(34)S) suggest there were major shifts in partitioning between reduced and oxidised reservoirs of carbon and sulphur during the Early Cretaceous. However, the δ(13)C and δ(34)S records are composed from different Ocean Drilling Program sites and are hard to correlate at high resolution. We present high-resolution Aptian δ(13)C(org) and δ(34)S(barite) values derived from the same set of samples, enabling a higher certainty correlation than previously possible. Two major hypotheses aim to explain the Early Aptian S-isotope excursion: increased volcanic degassing and/or fluctuations in the marine sulphate concentration. Our S-isotope data provide tight constraints on the timing and magnitude of volcanic flux required. We show that the observed S-isotope signature can be explained by a 2?Ma pulse of increased volcanic flux, injecting ～4.5×10(18)?mol C into the atmosphere. Further work is needed to evaluate whether these fluxes are compatible with the existing C-isotope record.