Click chemistry on a ruthenium polypyridine complex. An efficient and versatile synthetic route for the synthesis of photoactive modular assemblies

In this Communication, we present the synthesis and use of [Ru(bpy)(2)(bpy-CCH)](2+), a versatile synthon for the construction of more sophisticated dyads by means of click chemistry. The resulting chromophore-acceptor or -donor complexes have been studied by flash photolysis and are shown to undergo efficient electron transfer to/from the chromophore. Additionally, the photophysical and chemical properties of the original chromophore remain intact, making it a very useful component for the preparation of visible-light-active dyads.     

Hafnium Trialkyls Stabilized by Bulky,Electron‐Rich Aminopyridinates

A series of hafnium aminopyridinates were synthesized and spectroscopically analyzed. In addition, selected examples of these hafnium complexes were characterized by X‐ray single crystal structure analysis. The aminopyridinato ligands used here carry an additional dialkylamine substituent to enhance the electron donating ability of the ligands. Structural data and low temperature NMR spectroscopic investigations are indicative of the increased donating ability of the ligands. Ethylene polymerization studies revealed a rather low catalytic activity most likely due to catalyst instability. Details of the deactivation reaction were investigated by NMR spectroscopy.     

Research needs in support of the European thematic strategy for soil protection

We report on a Communication of the European Commission to the Council and the European Parliament in 2002, entitled “Towards a Thematic Strategy for Soil Protection”, an operational framework for its implementation and an indicator approach, as a basis for the elaboration of priority research areas for soil protection and the management of Europe's natural resources. From this, we draw the conclusion that soil research should be integrated into comprehensive research areas (e.g., including water and sediments) in order to manage natural resources in Europe.     

Intrinsically Microporous Polyesters From Betulin – Toward Renewable Materials for Gas Separation Made From Birch Bark

Betulin, an abundant triterpene, can be extracted from birch bark and can be used as a renewable monomer in the synthesis of microporous polyesters. Cross‐linked networks and hyperbranched polymers are accessible by an A₂ + B₃ reaction, with betulin being the A₂ monomer and B₃ being a trifunctional acid chloride. Reaction of betulin with a diacid dichloride results in linear, soluble polyesters. The present communication proves that the polyreaction follows the classic schemes of polycondensation reactions. The resulting polymers are analyzed with regard to their micro‐porosity by gas sorption, NMR spectroscopy, and X‐ray scattering methods. The polymers feature intrinsic microporosity, having ultrasmall pores, which makes them candidates for gas separation membranes, e.g., for the separation of CO₂ from N₂.     

Stranski-Krastanov growth of para-sexiphenyl on Cu(110)-(2×1)O revealed by optical spectroscopy

We have studied the growth of para-sexiphenyl (p-6P) on the Cu(110)-(2×1)O surface using reflectance difference spectroscopy (RDS) in combination with scanning tunneling microscopy (STM). The evolution of the optical anisotropy reveals that the growth of p-6P on the Cu(110)-(2×1)O surface at room temperature follows the Stranski-Krastanov growth mode with a two monolayer thick wetting layer. During all stages of growth, the p-6P molecules are well orientated with their long molecular axis aligned parallel to the Cu-O rows along the [001] direction of the Cu(110) substrate. The high packing density of the p-6P molecules in the first and second monolayer evidenced by RDS and STM is believed to be responsible for the switch from layer-by-layer to three-dimensional island growth.     

The continuous spectrum for the M / M / c queue

Transient solutions for M/M/c queues are important for many purposes, in particular for staffing facilities such as call centers. In this article, we show how to use spectral analysis to find such solutions. The difficulty is that unless the number in line is bounded, one has to deal with matrices of infinite size, and hence with a countable infinite number of eigenvalues. This problem can be overcome by noting that the spectrum is dense with few exceptions. We also show how many discrete eigenvalues remain. Our theory may also work to obtain spectra for other infinite-dimensional matrices. Numerical properties of our approach are explored.     

Convergence of rational multistep methods of Adams-Padé type

Rational generalizations of multistep schemes, where the linear stiff part of a given problem is treated by an A-stable rational approximation, have been proposed by several authors, but a reasonable convergence analysis for stiff problems has not been provided so far. In this paper we directly relate this approach to exponential multistep methods, a subclass of the increasingly popular class of exponential integrators. This natural, but new interpretation of rational multistep methods enables us to prove a convergence result of the same quality as for the exponential version. In particular, we consider schemes of rational Adams type based on A-acceptable Padé approximations to the matrix exponential. A numerical example is also provided.     

An optimal symbolic calculus on Besov algebras

In this paper we consider Besov algebras on , that is Besov spaces for s>1/p. For s>1+(1/p), p>4/3, and qp we prove that the above algebras have a maximal symbolic calculus in the following sense: for any function f belonging locally to and such that f(0)=0, the associated superposition operator T_f(g):=f○g takes to itself.