Controlling self-assembled perovskite-spinel nanostructures

We report a discovery that self-assembled perovskite-spinel nanostructures can be controlled simply by selecting single-crystal substrates with different orientations. In a model BiFeO(3)-CoFe(2)O(4) system, a (001) substrate results in rectangular-shaped CoFe(2)O(4) nanopillars in a BiFeO(3) matrix; in contrast, a (111) substrate leads to triangular-shaped BiFeO(3) nanopillars in a CoFe(2)O(4) matrix, irrespective of the volume fraction of the two phases. This dramatic reversal is attributed to the surface energy anisotropy as an intrinsic property of a crystal.     

Cellular dynamics of Ku: characterization and purification of Ku-eGFP

Ku is a predominantly nuclear protein that functions as a DNA double-strand-break (DSB) binding protein and regulatory subunit of the DNA-dependent protein kinase (DNA-PK). DNA-PK is involved in synapsis and remodeling of broken DNA ends during nonhomologous end-joining (NHEJ) of DNA DSBs. It has also recently been demonstrated that Ku plays roles in cytoplasmic and membrane processes, namely: interaction with matrix metalloproteinase 9, acting as a co-receptor for parvoviral infection, and also interacting with cell polarity protein, Par3. We present a method for creating stable expression of Ku-eGFP in CHO cells and extend the procedure to purify Ku-eGFP for in vitro assaying. We demonstrated that Ku-eGFP localizes to the nucleus of HeLa cells upon microinjection into the cytoplasm as well as localizing to laser induced DNA damage. We also characterized the diffusional dynamics of Ku in the nucleus and in the cytoplasm using fluorescence correlation spectroscopy (FCS). The FCS data suggest that whereas the majority of Ku (70%) in the nucleus is mobile and freely diffusing, in a cellular context, there also exists a significant slow process fraction (30%). Strikingly, in the cytoplasm, this immobile/slow moving fraction is even more pronounced (45%).     

Preparation of near-infrared absorbing composites comprised of conjugated macroligands on the surface of PbS nanoparticles

We report a facile macroligand strategy towards the synthesis of low-bandgap inorganic-organic composites comprised of semiconductor PbS nanoparticles and functional copolymers. For this, thiol-functional thiophene-based macroligands have been used as coligands for PbS nanoparticles. Thus, solution processable organic-inorganic hybrid materials with absorption in the near-infrared have been obtained. The resulting nanoparticle-polymer composites were characterized in detail by optical and FT-IR spectroscopy as well as TEM showing their potential as novel functional inorganic-organic hybrid materials when applied in initial proof-of-concept hybrid photovoltaic devices.     

The significance of defect chemistry for the rate of gas–solid reactions: three examples

Three examples are revisited in which the reaction rate could be reliably correlated with point defect chemistry highlighting the role of point defects as acid–base active centers. In the case of dehydrohalogenation of tertiary butyl chloride, AgCl becomes increasingly active as heterogeneous catalyst, if AgCl is homogeneously or heterogeneously doped. By such a procedure the silver vacancy concentration is adequately increased. The oxygen incorporation into SrTiO₃ offers an example in which the surface mechanism in terms of adsorbed species, oxygen vacancies and electronic centers has been elucidated. Appropriate surface coatings give rise to significant catalytic effects. Increasing iron (acceptor) doping not only changes the point defect chemistry but also the nature of the rate determining step. Lastly, the electrocatalytic function of Sr-doped LaMnO₃ is considered as regards oxygen reduction reaction and O²⁻ incorporation into Y-doped ZrO₂ in the context of solid oxide fuel cells. Again the defect chemistry is of prime importance for the reaction rate.     

Effect of several additives and their admixtures on the physico-chemical properties of a calcium phosphate cement

Combinations of citrate (C₆H₅O ₇ ^3-– ), pyrophosphate (P₂O ₇ ^4– ) and sulfate (SO ₄ ^2– ) ions were used to modify the physico-chemical properties of a calcium phosphate cement (CPC) composed of -tricalcium phosphate (-TCP) and phosphoric acid (PA) solution. The results obtained with only one additive at a time are similar to those previously published. New facts are: the positive effect of C₆H₅O ₇ ^3– ions on cement failure strain and their negative effect on cement pH. The position of the setting time maximum measured at an SO ₄ ^2– concentration of 0.09 M was not displaced by the addition of C₆H₅O ₇ ^3– and P₂O ₇ ^4– ions. However, the effect of SO ₄ ^2– ions on the setting time was depressed by C₆H₅O ₇ ^3– ions. Moreover, no increase in tensile strength was observed when increasing amounts of SO ₄ ^2– were added into a C₆H₅O ₇ ^3– -containing cement. The latter results suggest a competitive effect of C₆H₅O ₇ ^3– and SO ₄ ^2– on setting time and tensile strength. Anhydrous dicalcium phosphate (DCP; CaHPO₄) appeared in cement samples dried just after setting, but not in cement samples incubated for 24 h in deionized water before the drying step. It is believed that the setting reaction is stopped by the drying step, leaving a low internal pH in the sample, hence providing favorable conditions for the transformation of dicalcium phosphate dihydrate (DCPD) into DCP. Interestingly, even though C₆H₅O ₇ ^3– ions dramatically lowered the equilibrium pH of the cement with 5 ml of deionized water, they still prevented the occurrence of the transformation of DCPD into DCP.     

Size-dependent absolute quantum yields for size-separated colloidally-stable silicon nanocrystals

Size-selective precipitation was used to successfully separate colloidally stable allylbenzene-capped silicon nanocrystals into several visible emitting monodisperse fractions traversing the quantum size effect range of 1-5 nm. This enabled the measurement of the absolute quantum yield and lifetime of photoluminescence of allylbenzene-capped silicon nanocrystals as a function of size. The absolute quantum yield and lifetime are found to monotonically decrease with decreasing nanocrystal size, which implies that nonradiative vibrational and surface defect effects overwhelm spatial confinement effects that favor radiative relaxation. Visible emission absolute quantum yields as high as 43% speak well for the development of "green" silicon nanocrystal color-tunable light emitting diodes that can potentially match the performance of their toxic heavy metal chalcogenide counterparts.