Organoselenido Complexes of Tungsten

Organometallic tungsten selenido complexes of the type [cpW(CO)₃]₂Se_m; m = 2 (1), 3 (2), 4 (3), can be easily synthesized via insertion of selenium into the alkali-metal tungsten bond of LiWcp(CO)₃ in appropriate ratios and subsequent oxidation of the produced W-selenolates with O₂/SiO₂. In contrast, reactions of K₂Se₆ with [cpW(CO)₃Cl] and 18-crown-6 in DMF lead to a mixture óf [cpW(CO)₃]₂Se₄ (3), the η¹ Se-bonded selenocarbamato complex [cpW(CO)₃SeC(O)NMe₂] (4) and the ionic complex [(18-crown-6)K]⁺[cpW(Se₄)₂]^? (5). The crystal structures of 3 and 4 together with their ⁷⁷Se NMR data are presented.     

Effects of Pressure Oscillations on Drainage in an Elastic Porous Medium

The effects of seismic stimulation on the flow of two immiscible fluids in an elastic synthetic porous medium is experimentally investigated. A wetting fluid is slowly evacuated from the medium, while a pressure oscillation is applied on the injected non- wetting fluid. The amplitude and frequency of the pressure oscillations as well as the evacuation speed are kept constant throughout an experiment. The resulting morphology of the invading structure is found to be strongly dependent on the interplay between the amplitude and the frequency of the applied pressure oscillations and the elasticity of the porous medium. Different combinations of these properties yield morphologically similar structures, allowing a classification of structures that is found to depend on a proposed dimensionless number.     

Detection and characterization of silver nanoparticles in chicken meat by asymmetric flow field flow fractionation with detection by conventional or single particle ICP-MS

A method of analysis of silver nanoparticles (AgNPs) in chicken meat was developed. The homogenized chicken meat sample, which was spiked with AgNPs, was subjected to enzymolysis by Proteinase K for 40 min at 37 °C. Transmission electron microscopy and inductively coupled plasma mass spectrometry (ICP-MS) in single particle mode were used to characterize the number-based size distribution of AgNPs in the meat digestate. Because similar size distributions were found in the meat digestate and in the aqueous suspension of AgNPs used for spiking the meat, it was shown that no detectable dissolution of the AgNPs took place during the sample preparation stage. The digestate was injected into the asymmetric flow field flow fractionation (AF⁴) -ICP-MS system, which enabled fractionation of nanoparticles from the remaining meat matrix, and resulted in one large peak in the fractograms as well as two smaller peaks eluting close to the void volume. The recovery of silver contained in the large AgNP peak was around 80 %. Size determination of AgNPs in the meat matrix, based on external size calibration of the AF⁴ channel, was hampered by non-ideal (early elution) behavior of the AgNPs. Single particle ICP-MS was applied for determination of the number-based particle size distribution of AgNPs in collected fractions. The presented work describes for the first time the coupling of AF⁴ and ICP-MS for AgNP separation in a food matrix.