Strained heterocycles in radical chemistry

Over the last few decades the use of radicals in synthesis has witnessed an explosive growth through introduction of efficient chain and electron-transfer reactions. Strained heterocycles, in particular, have emerged as a highly versatile and readily available class of radical precursors. The generation of carbinyl radicals of heterocycles has resulted in many elegant applications of heteroatom-centered radicals, such as beta fragmentations, cyclizations, and intramolecular hydrogen atom abstractions. Direct electron transfer to strained heterocycles has been realized through the use of arene radical anions. The method combines the virtues of radical and organometallic chemistry to yield useful functionalized organolithium compounds. Epoxides have been opened with high regioselectivity by titanocene(III) reagents in either stoichiometric or catalytic quantities to yield beta-titanoxy radicals. This development has resulted in many new applications in natural product synthesis.     

From Biological towards Artificial Molecular Motors

Novel single‐molecule techniques allow the observation of single‐molecular motors in real time under physiological conditions. This enables one to gain previously inaccessible information about the mechanics of molecular motors, especially their mechano‐chemical coupling. As an example, we discuss the DNA import motor of the bacteriophage ?29 and protein import into chloroplasts. In contrast to these highly developed biological molecular motors, artificial molecular motors are still at an early stage of development. Nevertheless, they already give a wealth of information. Our review focuses on how the investigation of artificial and biological molecular motors can mutually enrich each other.     

New mechanistic insight into electronically excited CO-NiO(100): a quantum dynamical analysis

In a recent study Redlich et al. [Redlich et al., Chem. Phys. Lett. 2006, 420, 110] measured the velocity distribution of CO molecules desorbing from a NiO(100) surface after irradiation with an ultraviolet (UV) laser pulse. Due to the complexity of the involved processes no experimental evidence on the excitation and desorption mechanism could be obtained. In recent ab initio studies Mehdaoui et al. [Mehdaoui et al., Phys. Rev. Lett. 2007, 98, 037601] have shown that a 5sigma --> 2pi* (a (3)Pi) like transition within the CO adsorbate is most likely the crucial excitation step in the CO-NiO(100) system. At first sight this seems unlikely, since the interaction of CO molecules with the NiO(100) surface is very weak (-0.30 eV) and the corresponding CO gas phase transition energy is about 1.5 eV higher than the laser pulse energy of 4.66 eV used in the experiment. In this work we give further insight into relevant electronically excited states and identify the desorption mechanism by analysing the dynamical processes after laser excitation by quantum dynamical wave packet simulations on the basis of three-dimensional (3D) ab initio potential energy surfaces. The results corroborate the so far discussed excitation mechanism, which proposes the formation of a genuine C-Ni bond as the driving force for photodesorption, as the crucial excitation step.     

Simulating complex social behaviour with the genetic action tree kernel

The concept of genetic action trees combines action trees with genetic algorithms. In this paper, we create a multi-agent simulation on the base of this concept and provide the interested reader with a software package to apply genetic action trees in a multi-agent simulation to simulate complex social behaviour. An example model is introduced to conduct a feasibility study with the described method. We find that our library can be used to simulate the behaviour of agents in a complex setting and observe a convergence to a global optimum in spite of the absence of stable states.

A local conjecture on Brauer character degrees of finite groups

Recently, a new conjecture on the degrees of the irreducible Brauer characters of a finite group was presented by W. Willems. In this paper we propose a `local' version of this conjecture for blocks of finite groups, giving a lower bound for where the sum runs through the set of irreducible Brauer characters of in terms of invariants of . A slight reformulation leads to interesting open questions about traces of Cartan matrices of blocks.

We show that the local conjecture is true for blocks with one simple module, blocks of -solvable groups and blocks with cyclic defect groups. It also holds for many further examples of blocks of sporadic groups, symmetric groups or groups of Lie type. Finally we prove that the conjecture is true for blocks of tame representation type.

     

Cu/ZnO and Cu/ZrO2 interactions studied by contact angle measurement with TEM

A technique of contact angle measurement was applied to the nano-scale oxide-supported metal particles. For Cu supported on ZnO and ZrO2 the angles were found to increase and the work of adhesion to decrease with increasing particle size. Such a trend is interpreted as an effect of negative contact line tension of 2.1 x 10(-9) J m(-1) and 1.0 x 10(-9) J m(-1) in the Cu/ZnO and Cu/ZrO2 system, correspondingly. For the small-sized Cu particles the apparent work of adhesion on ZnO support is higher than that on ZrO2.     

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid--structure, function and dynamics of the V-Mo-W mixed oxides

The major objective of this research project was to reach a microscopic understanding of the structure, function and dynamics of V-Mo-(W) mixed oxides for the partial oxidation of acrolein to acrylic acid. Different model catalysts (from binary and ternary vanadium molybdenum oxides up to quaternary oxides with additional tungsten) were prepared via a solid state preparation route and hydrochemical preparation of precursors by spray-drying or crystallisation with subsequent calcination. The phase composition was investigated ex situ by XRD and HR-TEM. Solid state prepared samples are characterised by crystalline phases associated to suitable phase diagrams. Samples prepared from crystallised and spray-dried precursors show crystalline phases which are not part of the phase diagram. Amorphous or nanocrystalline structures are only found in tungsten doped samples. The kinetics of the partial oxidation as well as the catalysts' structure have been studied in situ by XAS, XRD, temperature programmed reaction and reduction as well as by a transient isotopic tracing technique (SSITKA). The reduction and re-oxidation kinetics of the bulk phase have been evaluated by XAS. A direct influence not only of the catalysts' composition but also of the preparation route is shown. Altogether correlations are drawn between structure, oxygen dynamics and the catalytic performance in terms of activity, selectivity and long-term stability. A model for the solid state behaviour under reaction conditions has been developed. Furthermore, isotope exchange experiments provided a closer image of the mechanism of the selective acrolein oxidation. Based on the in situ characterisation in combination with micro kinetic modelling a detailed reaction model which describes the oxygen exchange and the processes at the catalyst more precisely is discussed.     

Hydrogen bonding of methanol in supercritical CO2: comparison between 1H NMR spectroscopic data and molecular simulation results

Molecular dynamics simulation results on hydrogen bonding in mixtures of methanol with CO2 at supercritical, liquid-like conditions are compared to 1H NMR spectroscopic data that have recently become available. The molecular models are parametrized using vapor-liquid equilibrium data only, which they reliably describe. A new molecular model for methanol of Lennard-Jones plus point charge type is presented. This molecular methanol model is investigated in terms of its capability to yield hydrogen-bonding statistics. Simple assumptions are made regarding the assignment of NMR chemical shifts to the different types of hydrogen-bonded species. Only two state-independent parameters are fitted to the large NMR data set on the basis of hydrogen-bonding statistics from molecular simulations. Excellent agreement between the molecular simulation results and the NMR data is found. This shows that the molecular models of the simple type studied here cannot only describe thermodynamic properties but also structural effects of hydrogen bonding in solutions.