Heterogeneous Raney Nickel and Cobalt Catalysts for Racemization and Dynamic Kinetic Resolution of Amines

Raney metals were studied as heterogeneous catalysts for racemization and dynamic kinetic resolution (DKR) of chiral amines, as an alternative to metals like palladium or ruthenium. Both Raney nickel and cobalt were able to selectively racemize various chiral amines with high selectivity. In the racemization of benzylic primary amines, the minor formation of side products, e.g., secondary amines, can be suppressed by varying the hydrogen pressure. In the racemization of aliphatic amines over Raney catalysts, the selectivity is very high, with the enantiomeric amine as the sole product. DKR of racemic aliphatic amines can be performed with immobilized Candida antarctica lipase B and Raney nickel in one pot; for 2‐hexylamine, a yield of 95 % of the acetylated amide was achieved, with 97 % ee. Attention is devoted to the compatibility of the enzyme and the metal catalyst during the DKR. For benzylic primary amines, a two‐pot process is proposed in which the liquid is alternatingly shuttled between two vessels containing the solid racemization catalyst and the biocatalyst. After 4 such cycles, the amide of (R)‐1‐phenylethylamine was obtained with 94 % yield and more than 90 % ee.     

Antarctic research bases: local sources of polybrominated diphenyl ether (PBDE) flame retardants

Contemporary studies of chemical contamination in Antarctica commonly focus on remnants of historical local releases or long-range transport of legacy pollutants. To protect the continent's pristine status, the Antarctic Treaty's Protocol on Environmental Protection prohibits importation of persistent organic pollutants. However, some polybrominated diphenyl ether (PBDE) congeners exhibit similar properties. Many modern polymer-containing products, e.g., home/office furnishings and electronics, contain percent levels of flame retardant PBDEs. PBDE concentrations in indoor dust and wastewater sludge from the U.S. McMurdo and New Zealand-operated Scott Antarctic research bases were high. Levels tracked those in sludge and dust from their respective host countries. BDE-209, the major constituent in the commercial deca-PBDE product, was the dominant congener in sludge and dust, as well as aquatic sediments collected near the McMurdo wastewater outfall. The pattern and level of BDE-209 sediment concentrations, in conjunction with its limited environmental mobility, suggest inputs from local sources. PBDE concentrations in fish and invertebrates near the McMurdo outfall rivaled those in urbanized areas of North America and generally decreased with distance. The data indicate that reliance on wastewater maceration alone, as stipulated by the Protocol, may permit entry of substantial amounts of PBDEs and other chemicals to the Antarctic environment.     

Intravenous calcium infusion in a calving protocol disrupts calcium homeostasis compared with an oral calcium supplement

Hypocalcemia is a common postpartum condition in dairy cows, which negatively affects health and production. Intravenous Ca infusions are commonly included in calving protocols to prevent or mitigate the effect of hypocalcemia in multiparous cows. Thus, we sought to contrast the effect of intravenous Ca infusion against voluntary oral Ca intake on Ca metabolism. Serum total Ca (tCa) and whole-blood ionized Ca (iCa) were monitored in 24 multiparous Holstein cows after parturition. Precalving diets were formulated with a positive dietary cation-anion difference of 172 mEq/kg of DM and contained 4.1 g of Ca/kg of DM. At parturition, cows were blocked by calving sequence and calcemic status as either normocalcemic (cutoff threshold of iCa ≥1.10 mmol/L) or hypocalcemic (cutoff threshold of iCa <1.10 mmol/L). Cows in each block were randomly assigned to 1 of 2 treatments: either an oral source of Ca (Ca-Oral; n = 12) or an intravenous source of Ca (Ca-IV; n = 12). Cows in the Ca-Oral group were offered a 20-L commercial Ca suspension (48 g of Ca) for voluntary consumption. The supplement contained Ca carbonate, Ca formate, Ca propionate, and other minerals and vitamins (Farm-O-San Reviva, Trouw Nutrition, Amersfoort, the Netherlands). Cows in the Ca-IV group received a 450-mL intravenous Ca solution (13 g of Ca) that contained 298 mg/mL of Ca gluconate, 33 mg/mL of magnesium chloride, and 82 mg/mL of boric acid (AmosCAL, Kommer-Biopharm BV, Heiloo, the Netherlands). Both treatments were initiated within 25 ± 10 min after calving. The oral Ca suspension was offered to cows in a 25-L bucket and was available for 10 min. All cows in the Ca-Oral group voluntarily consumed the entire 20 L of the Ca suspension within 5 min. Blood samples for Ca analyses were collected at 0 (before treatment initiation), 1, 3, 10, and 18 h relative to treatment, and at 0700 and 1900 h for the next 2 consecutive days, to represent the 24-, 36-, 48-, and 60-h sampling time points. In Ca-IV cows, both iCa and tCa concentrations peaked at 1 h (1.54 mmol/L for iCa and 2.85 mmol/L for tCa) and declined to a nadir at 24 h following treatment initiation (0.94 mmol/L for iCa and 1.74 mmol/L for tCa). Although whole-blood iCa and serum tCa were higher at 1 and 3 h in Ca-IV cows, concentrations of iCa were greater for Ca-Oral cows at 18, 24, and 36 h and for tCa at 24 and 36 h. Our data indicate that intravenous Ca infusion immediately induced a state of hypercalcemia followed by lower whole-blood iCa and serum tCa concentrations 24 h later compared with oral Ca.     

Optimization of process parameters for sputtering of ceramic ZnO:Al2O3 targets for a-Si:H/μc-Si:H solar cells

Aluminum doped ZnO layers with a thickness of 800 nm were deposited dynamically by d.c. magnetron sputtering from a ceramic planar ZnO: Al₂O₃ target (1 wt.%). A wide range of process parameters, namely oxygen partial pressure, total pressure and power, was covered, while temperature was held constant at 300 °C. Visual absorption in the range of 2.3-4.7% and resistivities between 380 and 2150 µΩcm were obtained. In addition static imprints were performed to reveal the dependence of layer properties on target erosion. It was shown, that films deposited from targets with a race track deeper than 1.8 mm had very stable etching morphologies as well as optical and electrical properties in the range of the observed process parameters. In contrast, a new target yields very different etching structures and an increased resistivity.     

Modeling the combination of motion, stereo, and vergence angle cues to visual depth.

Three models of visual cue combination were simulated: a weak fusion model, a modified weak model, and a strong model. Their relative strengths and weaknesses are evaluated on the basis of their performances on the tasks of judging the depth and shape of an ellipse. The models differ in the amount of interaction that they permit among the cues of stereo, motion, and vergence angle. Results suggest that the constrained nonlinear interaction of the modified weak model allows better performance than either the linear interaction of the weak model or the unconstrained nonlinear interaction of the strong model. Further examination of the modified weak model revealed that its weighting of motion and stereo cues was dependent on the task, the viewing distance, and, to a lesser degree, the noise model. Although the dependencies were sensible from a computational viewpoint, they were sometimes inconsistent with psychophysical experimental data. In a second set of experiments, the modified weak model was given contradictory motion and stereo information. One cue was informative in the sense that it indicated an ellipse, while the other cue indicated a flat surface. The modified weak model rapidly reweighted its use of stereo and motion cues as a function of each cue's informativeness. Overall, the simulation results suggest that relative to the weak and strong models, the modified weak fusion model is a good candidate model of the combination of motion, stereo, and vergence angle cues, although the results also highlight areas in which this model needs modification or further elaboration.     

Randomized placebo-controlled crossover trial of continuous positive airway pressure for mild sleep Apnea/Hypopnea syndrome

The minimal disease severity at which patients with the sleep apnea/hypopnea syndrome (SAHS) gain benefit from treatment is not well characterized, although a pilot study of continuous positive airway pressure (CPAP) therapy showed daytime improvements in patients with 5 to 15 apneas + hypopneas per hour slept (AHI). We have thus performed a second, larger, randomized, placebo- controlled study in a prospective series of 34 patients (13 female) with mild SAHS (AHI 5 to 15) and daytime sleepiness. Patients spent 4 wk on CPAP treatment and 4 wk on an oral placebo, with randomization of treatment order, and daytime assessments on the last day of each treatment. Effective CPAP use averaged 2.8 +/- 2.1 h (mean +/- SD) per night. Compared with placebo, CPAP improved symptom score (p < 0.01), subjective (Epworth; p < 0.01) but not objective (maintenance of wakefulness test; p > 0.2) sleepiness, performances on 2 of 7 cognitive tasks (p < 0.02), depression score (p < 0.01), and five subscales of the SF-36 health/functional status questionnaire (p 相似文献   

High level accumulation of single-chain variable fragments in the cytosol of transgenic Petunia hybrida

The accumulation of five murine single-chain variable fragments, binding to dihydroflavonol 4-reductase, was analyzed in transgenic Petunia hybrida plants. The five scFv-encoding sequences were cloned in an optimized plant transformation vector for expression in the cytosol under control of the 35S promoter. In a transient expression assay we found that the scFv expression levels were reproducible and correlated with those in stably transformed petunia. Our results show that accumulation in the cytosol strongly depends on the intrinsic properties of the scFv fragment. Three of the five scFv fragments accumulated to unexpectedly high levels in the cytosol of the primary transformants, but no phenotypic effect could be detected. Experimental results indicate that one of the scFv fragments accumulated in the cytosol to 1% of the total soluble protein as a functional antigen-binding protein in the absence of disulphide bonds. This observation supports the idea that certain antibody fragments do not need disulphide bonds to be stable and functional. Such scFv scaffolds provide new opportunities to design scFv fragments for immunomodulation in the cytosol.     

Reduction of Dislocation Density by Producing Novel Structures

HgCdTe, because of its narrow band gap and low dark current, is the infrared detector material of choice for several military and commercial applications. CdZnTe is the substrate of choice for HgCdTe as it can be lattice matched, resulting in low-defect-density epitaxy. Being often small and not circular, layers grown on CdZnTe are difficult to process in standard semiconductor equipment. Furthermore, CdZnTe can often be very expensive. Alternate inexpensive large circular substrates, such as silicon or gallium arsenide, are needed to scale HgCdTe detector production. Growth of HgCdTe on these alternate substrates has its own difficulty, namely large lattice mismatch (19% for Si and 14% for GaAs). This large mismatch results in high defect density and reduced detector performance. In this paper we discuss ways to reduce the effects of dislocations by gettering these defects to the edge of a reticulated structure. These reticulated surfaces enable stress-free regions for dislocations to glide to. In this work, a novel structure was developed that allows for etch pit density of less than 4?×?10⁵/cm² for HgCdTe-on-Si. This is almost two orders of magnitude less than the as-grown etch pit density of 1.1?×?10⁷/cm². This value of 3.35?×?10⁵/cm² is below the <1?×?10⁶/cm² or even the better <5?×?10⁵/cm² target for this research, making HgCdTe-on- alternate substrate density much more like that of HgCdTe-on-CdZnTe.     

Impurity Gettering in (112)B HgCdTe/CdTe/Alternate Substrates

The crystalline structure and impurity profiles of HgCdTe/CdTe/alternate substrate (AS; Si and GaAs are possibilities) and CdTe/AS were analyzed by secondary-ion mass spectrometry, atomic force microscopy, etch pit density analysis, and scanning transmission electron microscopy. Impurities (Li, Na, and K) were shown to getter in as-grown CdTe/Si epilayers at in situ Te-stabilized thermal anneal (~500°C) interfaces. In HgCdTe/CdTe/Si epilayers, indium accumulation was observed at Te-stabilized thermal anneal interfaces. Impurity accumulation was measured at HgCdTe/CdTe and CdTe/ZnTe interfaces. Processing anneals were found to nearly eliminate the gettering effect at the in situ Te-stabilized thermal anneal interfaces. Impurities were found to redistribute to the front HgCdTe/CdTe/Si surface and p–n junction interfaces during annealing steps. We also investigated altering the in situ Te-stabilized thermal anneal process to enhance the gettering effect.