Zero-phonon linewidth in CdSe/ZnS core/shell nanorods

High-resolution spectral hole-burning studies of CdSe/ZnS core/shell nanorods reveal a sharp zero-phonon line, with a line width dependent on the measurement time scale. The zero-phonon line width is attributed to contributions from radiative decay, spectral diffusion induced by surface electric field fluctuations, and phonon-assisted migration of excitons localized in the nanorods. A decoherence rate as small as 4.5 GHz has been observed, when the effects of spectral diffusion are suppressed in the spectral hole-burning measurement. Comparison between zero-phonon line widths in nanorods and spherical nanocrystals also elucidates important differences in the decoherence process between the one- and zero-dimensional nanostructures.     

Directed evolution of an esterase from Pseudomonas fluorescens yields a mutant with excellent enantioselectivity and activity for the kinetic resolution of a chiral building block

A triple mutant of an esterase from Pseudomonas fluorescens (PFE) that was created by directed evolution exhibited high enantioselectivity (E=89) in a kinetic resolution and yielded the building block (S)-but-3-yn-2-ol. Surprisingly, a mutation close to the active site caused the formation of inclusion bodies, but remote mutations were found to be responsible for the high selectivity. Back mutations gave a variant (double mutant PFE Ile76Val/Val175Ala) that showed excellent selectivity (E=96) and activity (20 min for 50% conversion, which corresponds to 1.25 U per mg of protein).     

Steps on anatase TiO2(101)

Surface defects strongly influence the surface chemistry of metal oxides, and a detailed picture of defect structures may help to understand reactivity and overall materials performance in many applications. We report first-principles calculations of step edges, the most common intrinsic defects on surfaces (and probably the predominant ones on nanoparticles). We have determined the structure, energetics, and chemistry of step edges on the (101) surface of TiO(2) anatase, an important photocatalytic material. Scanning tunnelling microscopy measurements of step-edge configurations and the contrast in atomically resolved images agree remarkably well with the theoretical predictions. Step-edge formation energies as well as the adsorption energies of water scale with the surface energy of the step facet, a trend that is expected to generally hold for metal oxide surfaces. Depending on the terrace/step configuration, this can lead to a situation where a step is less reactive than the flat terrace.     

Preparation and characterization of organic layers for UV protection of polycarbonate

In many applications, polycarbonate surfaces need to be coated as a protection against abrasion and decomposition caused by weathering. In particular, UV radiation during exposure to sunlight degrades polycarbonate, which causes delamination of the protective layer. To avoid coating delamination, the layer itself needs an absorption edge near 400 nm. One option is to use UV-absorbing organic molecules. The aim of the present study was to develop UV-protective layer stacks containing suitable organic molecules deposited in a vacuum process, with a focus on the stability of UV-absorbing organic layers during UV irradiation and their optical properties. The commercial UV absorber Tinuvin™ 360 and the organic compound N,N′-di(naphth-1-yl)-N,N′-diphenyl-benzidine were used. Thin layers of the organic materials were evaporated thermally. The optical properties and UV stability were investigated using UV-VIS and infrared spectroscopy.     

New crosslinkers for electrospun chitosan fibre mats. I. Chemical analysis

Chitosan (CS), the deacetylated form of chitin, the second most abundant, natural polysaccharide, is attractive for applications in the biomedical field because of its biocompatibility and resorption rates, which are higher than chitin. Crosslinking improves chemical and mechanical stability of CS. Here, we report the successful utilization of a new set of crosslinkers for electrospun CS. Genipin, hexamethylene-1,6-diaminocarboxysulphonate (HDACS) and epichlorohydrin (ECH) have not been previously explored for crosslinking of electrospun CS. In this first part of a two-part publication, we report the morphology, determined by field emission scanning electron microscopy (FESEM), and chemical interactions, determined by Fourier transform infrared microscopy, respectively. FESEM revealed that CS could successfully be electrospun from trifluoroacetic acid with genipin, HDACS and ECH added to the solution. Diameters were 267 ± 199 nm, 644 ± 359 nm and 896 ± 435 nm for CS–genipin, CS–HDACS and CS–ECH, respectively. Short- (15 min) and long-term (72 h) dissolution tests (T₆₀₀) were performed in acidic, neutral and basic pHs (3, 7 and 12). Post-spinning activation by heat and base to enhance crosslinking of CS–HDACS and CS–ECH decreased the fibre diameters and improved the stability. In the second part of this publication, we report the mechanical properties of the fibres.     

Directionally solidified biopolymer scaffolds: Mechanical properties and endothelial cell responses

Vascularization is a primary challenge in tissue engineering. To achieve it in a tissue scaffold, an environment with the appropriate structural, mechanical, and biochemical cues must be provided enabling endothelial cells to direct blood vessel growth. While biochemical stimuli such as growth factors can be added through the scaffold material, the culture medium, or both, a well-designed tissue engineering scaffold is required to provide the necessary local structural and mechanical cues. As chitosan is a well-known carrier for biochemical stimuli, the focus of this study was on structure-property correlations, to evaluate the effects of composition and processing conditions on the three-dimensional architecture and properties of freeze-cast scaffolds; to establish whether freeze-east scaffolds are promising candidates as constructs promoting vascularization; and to conduct initial tissue culture studies with endothelial cells on flat substrates of identical compositions as those of the scaffolds to test whether these are biocompatible and promote cell attachment and proliferation.     

Low temperature deposition of indium tin oxide films by plasma ion-assisted evaporation

Coatings of transparent conductive oxides, especially indium tin oxide (ITO), are important in different fields. So far, application of these materials has been limited to substrates with high thermal stability. We describe an improved coating process for ITO based on plasma ion-assisted evaporation at a substrate temperature below 100 degrees C, which is suitable for organic substrates. In characterizing the thin films, we used the classical Drude theory to calculate the resistivity from optical film properties and compared the data with linear four-point measurements. X-ray diffraction spectroscopy was used to determine the structural properties of the thin films.     

A New Flame Retardant for Wood Materials Tested in Wood‐Plastic Composites

A new flame retardant based on an ammonium phosphonate is studied with respect to its thermal decomposition and its mode of action in wood‐plastic composites (WPCs). The measurements are carried out by means of fire tests (cone calorimeter) and pyrolysis investigations (thermogravimetry, infrared spectroscopy). The flame retardant acts mainly in the condensed phase by increasing the amount of residue formed by the wood part in the WPC. Additional flame dilution is achieved by the release of water, ammonia and carbon dioxide during the decomposition of the flame retardant.

     

Determination of the degree of substitution of hydrolysed octenylsuccinate-derivatised starch

Aim of the present study was to compare two methods for the determination of the degree of substitution of starch esterified with octenyl succinic anhydride (OSA). A maximum degree of substitution of 0.034 was analysed in commercial samples of hydrolysed OSA starch using a method based on acidification of the free carboxyl group of the OSA-starch molecule after its optimization. In contrast a high degree of substitution up to 0.134 was determined when analysing the same samples using a method based on saponification of the OSA groups. An interference with reducing sugars was hypothesized as possible reason and confirmed by control experiments using different reducing and non reducing low molecular weight carbohydrates.     

Dioxins, dioxin-like PCBs and non-dioxin-like PCBs in dairy products on the German market and the temporal tendency in Schleswig-Holstein

140 Milcherzeugnisse aus verschiedenen Regionen Deutschlands wurden 2006 auf Dioxine, dioxin?hnliche PCB und nicht dioxin?hnliche PCB untersucht. Insgesamt wurden 66 K?se-, 23 Butter- und 51 Quark- bzw. Joghurterzeugnisse analysiert. Die Probenahme erfolgte in Superm?rkten und Einzelhandelsgesch?ften auf der Basis der Produktionsmengen in den einzelnen Bundesl?ndern der Bundesrepublik Deutschland. Die Dioxinkonzentrationen und die Summe der WHO-TEQ blieben weit unter den EU-Grenzwerten von 3 pg WHO-PCDD/F-TEQ/g Fett und 6 pg WHO-PCDD/F-PCB-TEQ/g Fett. Die Dioxingehalte lagen bei niedrigen 0,07–0,53 pg WHO-PCDD/F-TEQ/g Fett mit einem arithmetischen Mittelwert von 0,19 pg WHO-PCDD/F-TEQ/kg Fett. Die WHO-PCDD/F-PCB-TEQ Gehalte lagen zwischen 0,21 und 2,1 pg WHO-TEQ/g Fett, mit einem mittleren Gehalt von 0,76 pg WHO-TEQ/g Fett. Regionale Abh?ngigkeiten und Unterschiede zwischen den einzelnen Produktgruppen konnten nicht festgestellt werden. Langj?hrige Messungen der Dioxingehalte in Butter und K?se aus Schleswig-Holstein zeigen über den Zeitraum von 13 Jahren eine deutliche Abnahme der Gehalte von 0,43 auf 0,19 pg WHO-PCDD/F-TEQ/g Fett.