Hybrid Silsesquioxane/Benzoate Cu7-Complexes: Synthesis,Unique Cage Structure,and Catalytic Activity

A series of phenylsilsesquioxane-benzoate heptacopper complexes 1–3 were synthesized and characterized by X-ray crystallography. Two parallel routes of toluene spontaneous oxidation (into benzyl alcohol and benzoate) assisted the formation of the cagelike structure 1. A unique multi-ligation of copper ions (from (i) silsesquioxane, (ii) benzoate, (iii) benzyl alcohol, (iv) pyridine, (v) dimethyl-formamide and (vi) water ligands) was found in 1. Directed self-assembly using benzoic acid as a reactant afforded complexes 2–3 with the same main structural features as for 1, namely heptanuclear core coordinated by (i) two distorted pentameric cyclic silsesquioxane and (ii) four benzoate ligands, but featuring other solvate surroundings. Complex 3 was evaluated as a catalyst for the oxidation of alkanes to alkyl hydroperoxides and alcohols to ketones with hydrogen peroxide and tert-butyl hydroperoxide, respectively, at 50 °C in acetonitrile. The maximum yield of cyclohexane oxidation products as high as 32% was attained. The oxidation reaction results in a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone. Upon the addition of triphenylphosphine, the cyclohexyl hydroperoxide is completely converted to cyclohexanol. The specific regio- and chemoselectivity in the oxidation of n-heptane and methylcyclohexane, respectively, indicate the involvement of of hydroxyl radicals. Complex 3 exhibits a high activity in the oxidation of alcohols.     

Analysis of a time-dependent scheduling problem by signatures of deterioration rate sequences

In the paper a single machine time-dependent scheduling problem is considered. The processing time p_j of each job is described by a function of the starting time t of the job, p_j=1+α_jt, where the job deterioration rate α_j?0 for j=0,1,…,n and t?0. Jobs are nonpreemptable and independent, there are no ready times and no deadlines. The criterion of optimality of a schedule is the total completion time.First, the notion of a signature for a given sequence of job deterioration rates is introduced, two types of the signature are defined and their properties are shown. Next, on the basis of these properties a greedy polynomial-time approximation algorithm for the problem is formulated. This algorithm, starting from an initial sequence, iteratively constructs a new sequence concatenating the previous sequence with new elements, according to the sign of one of the signatures of this sequence.Finally, these results are applied to the problem with job deterioration rates which are consecutive natural numbers, α_j=j for j=0,1,…,n. Arguments supporting the conjecture that in this case the greedy algorithm is optimal are presented.     

Reduction of the shrinkage of thermosets by the cationic curing of mixtures of diglycidyl ether of bisphenol A and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione)

Ytterbium and lanthanum triflates were used as initiators to cure mixtures of diglycidyl ether of bisphenol A and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione) in several proportions. The evolution of the epoxy and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione) bands during curing and the linear ester groups in the final materials were evaluated with Fourier transform infrared in the attenuated‐total‐reflection mode. The use of a conventional cationic initiator, boron trifluoride monoethylamine, was also studied to test the advantages of lanthanide triflates. The shrinkage after curing and the thermal degradability of the materials with variations in the comonomer ratio and the initiator were evaluated and related to the chemical structure of the final network. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6869–6879, 2006     

Comparison of agarose and cross-linked protein gels as magnetic resonance imaging phantoms

Measurements of the magnetic field dependence of spin-lattice relaxation rates and the response of the water-proton signal intensity to off-resonance radio frequency fields show that the commonly used agarose phantom provides a less faithful representation for the magnetic response of tissue than does a cross-linked protein system. The origin of these differences lies in the structure and intramolecular dynamics of the macromolecular system used to make the gel. These distinctions will also cause differences in the magnetic response of the water spin system when paramagnetic relaxation agents or contrast agents are incorporated. Use of a thermally cross-linked bovine serum albumin phantom is suggested.     

Experimental results on diffractive one-pion production at the CERN ISR

New experimental results are reported on diffractive dissociation of protons into (nπ⁺) in proton-proton collisions at a centre-of-mass energy of $\text{s}\text{= 45}\text{GeV}$. The data were obtained using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. We have searched for resonance contributions and found peaks at mass values of 1.5 GeV, 1.65 GeV, and 2.1 GeV. A dip in $\text{d}\text{σ}\text{d}\text{t}$ is observed at low t and low mass; it is most pronounced for events with neutrons emitted at 90° in the Gottfried-Jackson frame. The correlation between mass and slope depends strongly on θ_J. The cross section of the channel pp → pnπ⁺ is 400 ± 110 μb at $\text{s}\text{= 45}\text{GeV}$, giving an energy dependence of s^?0.30±0.07 for isospin exchange zero in this channel.     

Micellar effects on a ligand substitution reaction: Kinetics of the formation of [Fe(CN)5(μ‐pz)Ru(NH3)5]−, from [Fe(CN)5H2O]3− and [Ru(NH3)5pz]2+, in the presence of anionic micelles

The kinetics of substitution of H₂O by Ru(NH₃)₅pz²⁺ (pz = pyrazine) in Fe(CN)₅H₂O^3? have been studied in micellar aqueous solutions of sodium dodecylsulfate (SDS). Experimental results are discussed by using an approach based on the transition‐state theory. This approach is better than others based on the pseudophase model, which can also be used, because it is able to give a clear meaning to the parameters of the model. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants to the micelles (Ru(NH₃)₅pz²⁺ in the present work). This association is governed by an equilibrium constant that depends on the electrostatic potential at the surface of the micelles. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 627–633, 2004     

A study of the charge-exchange reaction pp → nΔ++(1232) at ISR energies

We report on a study of the charge-exchange reaction pp → nΔ⁺⁺(1232) at the CERN intersecting storage rings (ISR) in the energy range √s = 23 to 53 GeV. From our analysis of the energy dependence of the total cross-section, of the differential cross-section dσ/dt and of the decay angular distributions we find evidence that pion exchange is dominant up to √s = 23 GeV and that (?+A₂) exchange dominates the reaction for √s ? 30 GeV, as described by simple Regge-pole models.     

p(↑)+p(↑) → π+d at 515 and 578 MeV

The polarization asymmetries A_0y and A_y0, and the spin correlation parameter A_yy have been measured at SIN at 515 and 578 MeV using a transversally polarized proton beam and target. The results are compared with various theoretical models.     

Charakteristik der Methansulfonyloxygruppe als ein desaktivierender o-,p-dirigierender Substituent durch ihr UV-Absorptionsspektrum

Ohne ZusammenfassungMit 1 Abbildung     

Study of a market model with conservative exchanges on complex networks

Many models of market dynamics make use of the idea of conservative wealth exchanges among economic agents. A few years ago an exchange model using extremal dynamics was developed and a very interesting result was obtained: a self-generated minimum wealth or poverty line. On the other hand, the wealth distribution exhibited an exponential shape as a function of the square of the wealth. These results have been obtained both considering exchanges between nearest neighbors or in a mean field scheme. In the present paper we study the effect of distributing the agents on a complex network. We have considered archetypical complex networks: Erdös–Rényi random networks and scale-free networks. The presence of a poverty line with finite wealth is preserved but spatial correlations are important, particularly between the degree of the node and the wealth. We present a detailed study of the correlations, as well as the changes in the Gini coefficient, that measures the inequality, as a function of the type and average degree of the considered networks.