Untersuchung von Eisenpr?paraten

Ohne Zusammenfassung     

Photostabilising action of nickel(II) bis(1-phenyl-3-methyl-4-decanoyl-5-pyrazolate), (sanduvor NPU) in polypropylene. Thermal antioxidant action and its relationship to photostabilisation,importance of hydroperoxide decomposition and light stability as a function of concentration

The thermal antioxidant action of Sanduvor NPU in polypropylene film has been examined at the 0.1% w/w concentration level. Infra-red and second-order derivative u.v.-visible spectroscopic techniques were used to monitor degree of oxidation in the films and stabiliser photodecomposition behaviour respectively. Hydroperoxide analysis was employed to determine the degree of thermal oxidation of films in an air oven. It was found that the behaviour of Sanduvor NPU in polypropylene films as a thermal stabiliser parallels its mode of action when used a melt stabiliser. The metal complex is highly effective in inhibiting hydroperoxide formation during extreme oxidative conditions. Hydroperoxide decomposition appears to play no part in this behaviour due to the inability of the complex to destroy these chromophores in solution, and the effect it has is attributed to the very effective chain breaking acceptor mechanism, i.e. macroalkyl radical scavenging. The relationship between embrittlement time and concentration was studied by varying the stabiliser content of the polymer over a wide range. As in the case of other metal chelates, the relationship is not linear, a limiting concentration behaviour is observed. This effect is attributed to the formation during photooxidation of products which promote the degradation of the polymer. This effect has implications on the efficiency of commercial systems.     

Geminal bis-ureas as gelators for organic solvents: gelation properties and structural studies in solution and in the gel state

Several geminal bis-urea compounds were synthesised by means of an acid-catalysed condensation of various benzaldehydes with different monoalkylureas. Many of these compounds form thermoreversible gels with a number of organic solvents at very low concentrations (<3mM) and which are stable to temperatures higher than 100 degrees C. Electron microscopy revealed a three-dimensional (3D) network of intertwined fibres, which are several tens of micrometers long and have a width ranging from approximately 30 to 300 nm. The possible aggregate forms and aggregate symmetries were evaluated by means of molecular mechanics calculations. 1H NMR, 2D NMR, 13C NMR and 13C-CP/MAS NMR techniques were used to obtain information about the aggregation and possible aggregate symmetry of geminal bis-ureas in solution, in the gel state, and in the solid state.     

Long-range sigma-pi interactions in tetrahydro-4H-thiopyran end-capped oligo(cyclohexylidenes). Photo-electron spectroscopy, ab initio SCF MO calculations, and natural bond orbital analyses

Long-range sigma-pi interactions in tetrahydro4H-thiopyran end-capped oligo(cyclohexylidenes) were identified by He(I) photoelectron spectroscopy (PES) and ab initio RHF/6-31G* calculations. The vertical ionization energies Ivj of the highest occupied molecular orbitals (MO's) were assigned using Koopmans' theorem (Iv,j = -epsilonj) and by correlation with the ionizations of related reference compounds. The experimental (PES) and theoretical (RHF/6-31G*) results are in good agreement. For tercyclohexylidene derivatives which contain two nonconjugated pi-bonds splittings deltaIv,j of the pi-bands in the range from approximately 0.5 to 0.7 eV (delta-epsilonj approximately 0.6 to 0.9 eV). For the bi- and tercyclohexylidene compounds containing two sulfur atoms at their alpha- and omega-end positions the pi-type sulfur lone pair bands [Lppi(S)] split significantly by deltaIvj approximately 0.3 to 0.4 eV (delta-epsilonj approximately 0.3 to 0.4 eV), i.e. sigma-pi interactions over distances of ca. 8 and 12 A, respectively, occur. The magnitude of the interactions and the observed splittings are independent of the anti and syn conformations of the oligo(cyclohexylidene) hydrocarbon skeletons. RHF/6-31G* Natural Bond Orbital analyses reveal that the Hax-C-C-Hax precanonical MO's (PCMO's) centered on the cyclohexyl-type rings are paramount for the relay of the through-bond sigma-pi interactions; no through-space sigma-pi interactions were identified.     

The photo-stabilising action of metal chelates in polypropylene: Part IX—Practical synergism with other commercial systems and the importance of calcium stearate

The photo-stabilising action of three metal chelates (Cyasorb UV 1084, Irganox 1425 and Irgastab 2002) in a number of synergistic formulations with three commercial stabilising systems (Weston 618, Cyasorb UV 531 and Tinuvin 770), in polypropylene films has been examined. The results show that, although antagonistic effects are observed at some mass ratios, synergistic effects prevail at others. The effects are a function of the particular formulation.The addition of calcium stearate to the stabilising mixture can have marked effects on the observed behaviour. Thus, an antagonistic effect can become synergistic if calcium stearate is used in the formulation. The results have scientific and technological implications as calcium stearate is often used as a processing aid in the stabilisation of polypropylene.     

Active particle control through silicon using conventional optical trapping techniques

Functional integration of optical trapping techniques with silicon surfaces and environments can be realized with minimal modification of conventional optical trapping instruments offering a method to manipulate, track and position cells or non-biological particles over silicon substrates. This technique supports control and measurement advances including the optical control of silicon-based microfluidic devices and precision single molecule measurement of biological interactions at the semiconductor interface. Using a trapping laser in the near infra-red and a reflective imaging arrangement enables object control and measurement capabilities comparable to trapping through a classical glass substrate. The transmission efficiency of the silicon substrate affords the only reduction in trap stiffness. We implement conventional trap calibration, positioning, and object tracking over silicon surfaces. We demonstrate control of multiple objects including cells and complex non-spherical objects on silicon wafers and fabricated surfaces.