Cellular uptake of molybdenum and tungsten

Cells acquire molybdenum and tungsten as their highly soluble oxoanions, Mo^VIO₄^2? or W^VIO₄^2?, which they internalize by means of an active (i.e. energy requiring) transmembrane importer, for subsequent conversion into the metalloenzyme cofactors Moco or Wco (and FeMoco in nitrogen fixers). This import system has been studied as one of the models for the functioning of the protein complex superfamily of ABC (ATP binding cassette) transporters, but its mechanistic details are presently not clear. The complex exhibits interesting variants, known as the microbial Mod, Tup, and Wtp system, and the – less well defined – eukaryotic MOT1 system, which mutually differ in oxoanion coordination chemistry and in the control of intracellular Mo/W levels. This evolutionary diversity of Mo/W transporters has resulted in confusing nomenclature whose rectification is here proposed.     

On Eisenbud's and Wigner's R-matrix: A general approach

The main objective of this paper is to give a rigorous treatment of Wigner's and Eisenbud's R-matrix method for scattering matrices of scattering systems consisting of two selfadjoint extensions of the same symmetric operator with finite deficiency indices. In the framework of boundary triplets and associated Weyl functions an abstract generalization of the R-matrix method is developed and the results are applied to Schrödinger operators on the real axis.     

2,7,11,16-Tetra-tert-Butyl Tetraindenopyrene Revisited by an “Inverse” Synthetic Approach

A new synthetic route to tetraindenopyrene (TIP)—a bowl-shaped cut-out structure of C₇₀—is reported. The key step in this approach is a fourfold palladium-catalyzed C−H activation that increases the yield more than 50 times in comparison to the approach originally described by Scott and co-workers. Besides examination of its optoelectronic properties and study of its aggregation in solution, TIP was also re-investigated by dispersion-corrected DFT methods, which showed that dispersion interactions significantly increase the bowl-to-bowl inversion barrier. Furthermore, TIP was used as a semiconductor in p-channel thin-film transistors (TFTs).     

Ion dynamics in solid electrolytes described by the concept of mismatch and relaxation

Abstract

Below the far-infrared frequency regime, conductivity spectra of crystalline ion conductors like RbAg₄I₅ and others display remarkably uniform characteristics. Well-known approximations include the universal dynamic response (UDR) and the nearly constant loss (NCL) behaviour. We now present a new non-power-law, non-KWW master curve. Its shape is shown to be equivalent to a proportionality between two particular functions of time. These functions are interpreted as rates of mismatch relaxation via the so-called single-particle and many-particle routes. The proportionality of relaxation rates is the central statement of the concept of mismatch and relaxation (CMR).     

Comparison of chromatographic band profiles obtained under microwave irradiated and non-irradiated reversed-phase liquid chromatography column

The possible influence of the application of microwave energy to a reversed-phase liquid chromatography column on the mass transfer kinetics and the thermodynamics of equilibrium between mobile and stationary phases was examined. Chromatograms of propylbenzene and phenol were recorded under the same experimental conditions, on the same column, successively irradiated and not. The effect of microwave irradiation on the mass transfer kinetics was determined by measuring the second moment of small pulses of propylbenzene in a 70:30 (v/v) solution of methanol in water and microwave outputs of 15 and 30 W. The effect of microwave irradiation on the equilibrium thermodynamics was determined by measuring the elution time of breakthrough curves of phenol at high concentrations in a 20:80 (v/v) solution of methanol and water and microwave outputs of 15, 50, and 150 W. A qualitative comparison of the profiles of the propylbenzene peaks obtained with and without irradiation suggests that this irradiation affects significantly the peak shapes. However, a qualitative comparison of the profiles of the breakthrough curves of phenol obtained with and without irradiation suggests that this irradiation has no significant effect on their shapes. The peak sharpening observed may be due to an increase in the diffusivity, resulting from the dielectric polarization under microwave irradiation. This effect is directly related to an increase of the rate of mass transfers in the column. In contrast, the similarity of the overloaded band profiles at high concentrations suggests that the equilibrium thermodynamics is unaffected by microwave irradiation. This may be explained by the transparence of the stationary phase to microwaves at 2.45 GHz. The column temperature was measured at the column outlet under irradiation powers of 15, 30, 50, and 150 W. It increases with increasing power, the corresponding effluent temperatures being 25+/-1, 30+/-1, 35+/-1, and 45+/-1 degrees C, respectively.