Shape induced symmetry in self-assembled mesocrystals of iron oxide nanocubes

Grazing incidence small-angle scattering and electron microscopy have been used to show for the first time that nonspherical nanoparticles can assemble into highly ordered body-centered tetragonal mesocrystals. Energy models accounting for the directionality and magnitude of the van der Waals and dipolar interactions as a function of the degree of truncation of the nanocubes illustrated the importance of the directional dipolar forces for the formation of the initial nanocube clusters and the dominance of the van der Waals multibody interactions in the dense packed arrays.     

Silicon field effect transistors as dual-use sensor-heater hybrids

We demonstrate the temperature mediated applications of a previously proposed novel localized dielectric heating method on the surface of dual purpose silicon field effect transistor (FET) sensor-heaters and perform modeling and characterization of the underlying mechanisms. The FETs are first shown to operate as electrical sensors via sensitivity to changes in pH in ionic fluids. The same devices are then demonstrated as highly localized heaters via investigation of experimental heating profiles and comparison to simulation results. These results offer further insight into the heating mechanism and help determine the spatial resolution of the technique. Two important biosensor platform applications spanning different temperature ranges are then demonstrated: a localized heat-mediated DNA exchange reaction and a method for dense selective functionalization of probe molecules via the heat catalyzed complete desorption and reattachment of chemical functionalization to the transistor surfaces. Our results show that the use of silicon transistors can be extended beyond electrical switching and field-effect sensing to performing localized temperature controlled chemical reactions on the transistor itself.     

Lanthanide concentrations in freshwater plants and molluscs, related to those in surface water, pore water and sediment. A case study in The Netherlands

Industrial emissions of lanthanides to aquatic ecosystems increase, but knowledge of the environmental fate of these metals is limited. Here we focus attention upon the distribution of lanthanides in freshwater ecosystems, describing lanthanide partitioning between sediment, water and biota. Since lanthanides are often used as oxidation-state analogues for actinides, their distribution can reflect long-term behaviour of the radioactive transuranics. Concentrations of all 14 naturally occurring lanthanides were measured by ICP-MS in Sago pondweed (Potamogeton pectinatus), common duckweed (Lemna minor), seven different mollusc species (tissue and shell), two sediment fractions (< 2 mm and < 63 microm), surface water and sediment pore water from five locations in The Netherlands. In all samples, the typical 'saw-tooth' lanthanide pattern was observed, which implies that lanthanides are transported as a coherent group through aquatic ecosystems. Typical deviations from this pattern were found for Ce and Eu and could be explained by their redox chemistry. The variation in concentrations in abiotic fractions was limited, i.e. within one order of magnitude. However, variations of up to three orders of magnitude were observed in biotic samples, suggesting different affinities among organisms for lanthanides as a group, with significant differences only among molluscs and pondweed samples in relation to sampling location. For P. pectinatus it was shown that pore water was the most important lanthanide source, and for snails, food (plants) seems to be the dominant lanthanide source. Lanthanides were not equally distributed between mollusc shell and tissue and the ratio of lanthanide concentrations in shell and tissue were dependent on the sampling location. Shells contained much lower concentrations and were relatively enriched in Eu, and to a lesser extent in Ce. Bioconcentration factors for lanthanides in plants and snails relative to surface water were typically between 10000 and 100000 l x kg(-1) dry matter, while sediment-water partition coefficients were between 100000 and 3000000 l x kg(-1) dry matter. There was a low extent of biomagnification in the plant-to-snail system, with a maximum biomagnification factor of 5.5. Many distribution coefficients displayed a slight decrease with atomic number. This can be attributed to the general increase in ligand stability constants with atomic number, keeping the heavier lanthanides preferentially in solution.     

Mobility determination of lead isotopes in glass for retrospective radon measurements

In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470-620 degrees C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 +/- 0.2 eV, and also the pre-exponential factor D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.     

Evaluation of cooling strategies for pumping of milk - impact of fatty acid composition on free fatty acid levels

Cooling strategies for pumping of raw milk were evaluated. Milk was pumped for 450 s at 31 degrees C, or pumped after cooling to 4 degrees C and subsequently subjected to various incubation times. Two types of milk were used; i.e. milk from cows fed a diet high in saturated fat supplements resulting in significantly larger milk fat globules than the other type of milk which comes from cows fed a low-fat diet that stimulates high de novo fat synthesis. The content of liquid fat was determined by low-field 1H NMR, which showed that milk from cows given the saturated fat diet also contained less liquid fat at both 4 degrees and 31 degrees C than the other type of milk. This can be ascribed to the differences in the fatty acid composition of the milk as a result of the fatty acid composition of the diets. After pumping of the milk at 31 degrees C, measurement of fat globule size distribution revealed a significant coalescence of milk fat globules in the milk obtained from the saturated fat diet due to pumping. Pumping at 4 degrees C or pumping the other type of milk did not result in coalescence of milk fat globules. Formation of free fatty acids increased significantly in both types of milk by pumping at 31 degrees C. Cooling the milk to 4 degrees C immediately before pumping inhibited an increased content of free fatty acids. However, when the milk was incubated at 4 degrees C for 60 min after cooling and then subjected to pumping, a significant increase in the formation of free fatty acids was observed in both types of milk. It is suggested that this increase in free fatty acids is caused by transition of polymorphic crystal forms or higher level of attached lipoprotein lipases to the milk fat globule before pumping.     

Dispersing WC–Co powders in aqueous media with polyethylenimine

The use of aqueous WC–Co suspensions for powder metallurgical processing of hard metal powders is expected to have environmental as well as economic advantages over the currently used systems with organic solvents. Without a suitable dispersing agent, however, poor mixing and aggregation of the different particulate constituents will occur in water and requirements on homogeneity and colloidal stability of the hard metal slurry cannot be met. We evaluated the effect of polyethylenimine (PEI) on the flow properties of concentrated aqueous WC–Co suspensions. The investigated parameters were polymer concentration, polymer molecular weight, pH, powder solubility, and ageing time. We found that simple mixing of powder, water, and PEI (at concentrations above 0.3 wt%) is sufficient to obtain well-dispersed, low-viscous suspensions without the need for pH adjustment or further additives. Almost identical flow behavior was observed over the investigated pH range 7–10.8. Effects of ageing and powder solubility on the colloidal stability were negligible over the investigated time span of 36 h. Adsorption of PEI with M_w=10,000 results in thinner adsorbed layers as compared to PEI with M_w=25,000, which is reflected by a lower suspension viscosity at high solids loading (40 vol%).     

A General and Convenient Method for the Rhodium‐Catalyzed Decarbonylation of Aldehydes

A practical protocol for the decarbonylation of a wide range of aldehydes has been developed by using commercially available RhCl₃⋅3 H₂O and dppp in a diglyme solution. This method gives rise to decarbonylated products in good to high yield and is particularly useful because of its experimental simplicity, high generality and excellent level of functional group tolerance. The reaction has been applied in a tandem Oppenauer oxidation‐decarbonylation sequence, which removes a hydroxymethyl group in one operation.