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1.
[reaction: see text] Pd[(-)-sparteine]Cl(2) catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride. 相似文献
2.
Kai Jiang Andriy Zakutayev Jason Stowers Michael D. Anderson Janet Tate David H. McIntyre David C. Johnson Douglas A. Keszler 《Solid State Sciences》2009,11(9):1692-1699
High-quality TiO2 thin films have been deposited from aqueous titanium-peroxo solutions via spin coating. The effects of precursor solution pH on the crystallization behavior, morphology, density, and refractive index of the films are reported. From X-ray diffraction measurements, the amorphous as-deposited films are found to crystallize in the anatase phase at 250 °C. Surface and cross-section SEM images reveal that films deposited from an acidic precursor are more uniform and denser than those deposited from a basic precursor. X-ray reflectivity measurements show that films with smooth surfaces and high densities (up to 87% of single-crystal anatase) can be produced at temperatures as low as 300 °C. Measured densities are consistent with high refractive indices at 633 nm of 2.24 and 2.11 for films derived from acidic and basic precursors, respectively. The uniformity and dense nature of the films have allowed fabrication of multilayer dielectric optical elements with thermal processing at only 300 °C. The distributed Bragg reflector with four bilayers exhibits a reflectance of 92% and a stop band width of 150 nm. The optical microcavity has a quality factor of 20. The optical properties of all elements agree well with theoretical models, indicating good optical quality. Use of the precursor chemistry for direct photopatterning of TiO2 films without a polymer resist is also demonstrated. 相似文献
3.
Chris C. Stowers J. Brian Robertson Hyunju Ban Robert D. Tanner Erik M. Boczko 《Applied biochemistry and biotechnology》2009,156(1-3):59-75
Four decades of work have clearly established the existence of autonomous oscillations in budding yeast culture across a range of operational parameters and in a few strains. Autonomous oscillations impact substrate conversion to biomass and products. Relatively little work has been done to quantify yield in this case. We have analyzed the yield of autonomously oscillating systems, grown under different conditions, and demonstrate that it too oscillates. Using experimental data and mathematical models of yeast growth and division, we demonstrate strategies to increase the efficient recovery of products. The analysis makes advantage of the population structure and synchrony of the system and our ability to target production within the cell cycle. While oscillatory phenomena in culture have generally been regarded with trepidation in the engineering art of bioprocess control, our results provide further evidence that autonomously oscillating systems can be a powerful tool, rather than an obstruction. 相似文献
4.
Stowers MA van Wuijckhuijse AL Marijnissen JC Scarlett B van Baar BL Kientz CE 《Rapid communications in mass spectrometry : RCM》2000,14(10):829-833
Matrix-assisted laser desorption/ionization (MALDI) mass spectra were obtained from single biological aerosol particles using an aerosol time-of-flight mass spectrometer (ATOFMS). The inlet to the ATOFMS was coupled with an evaporation/condensation flow cell that allowed the aerosol to be coated with matrix material as the sampled stream entered the spectrometer. Mass spectra were generated from aerosol composed either of gramicidin-S or erythromycin, two small biological molecules, or from aerosolised spores of Bacillus subtilis var niger. Three different matrices were used: 3-nitrobenzyl alcohol, picolinic acid and sinapinic acid. A spectrum of gramicidin-S was generated from approximately 250 attomoles of material using a molar ratio of 3-nitrobenzyl alcohol to analyte of approximately 20:1. A single peak, located at 1224 Da, was obtained from the bacterial spores. The washing liquid and extract solution from the spores were analyzed using electrospray mass spectrometry and subsequent MS/MS product ion experiments. This independent analysis suggests that the measured species represents part of the B. subtilis peptidoglycan. The on-line addition of matrix allows quasi-real-time chemical analysis of individual, aerodynamically sized particles, with an overall system residence time of less than 5 seconds. These results suggest that a MALDI-ATOFMS can provide nearly real-time identification of biological aerosols. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
5.
Hanchar RJ Teymouri F Nielson CD McCalla D Stowers MD 《Applied biochemistry and biotechnology》2007,137(1-12):313-325
A process was developed to fractionate corn fiber into glucose- and pentose-rich fractions. Corn fiber was ammonia fiber explosion treated at 90 degrees C, using 1 g anhydrous ammonia pergram of drybiomass, 60% moisture, and 30-min residence time. Twenty four hour hydrolysis of ammonia fiber explosion-treated corn fiber with cellulase converted 83% of available glucanto-glucose. In this hydrolysis the hemicellulose was partially broken down with 81% of the xylan and 68% of the arabinan being contained in the hydrolysate after filtration to remove lignin and other insoluble material. Addition of ethanol was used to precipitate and recover the solubilized hemicellulose from the hydrolysate, followed by hydrolysis with 2% (v/v) sulfuric acid to convert the recovered xylan and arabinan to monomeric sugars. Using this method, 57% of xylose and 54% of arabinose available in corn fiber were recovered in a pentose-rich stream. The carbohydrate composition of the pentose-enriched stream was 5% glucose, 57% xylose, 27% arabinose, and 11% galactose. The carbohydrate composition of the glucose-enriched stream was 87% glucose, 5% xylose, 6% arabinose, and 1% galactose, and contained 83% of glucose available from the corn fiber. 相似文献
6.
Enzyme recovery and recycling following hydrolysis of ammonia fiber explosion-treated corn stover 总被引:1,自引:0,他引:1
Bernie Steele Srini Raj John Nghiem Mark Stowers 《Applied biochemistry and biotechnology》2005,124(1-3):901-910
Both cellulase and cellobiase can be effectively recovered from hydrolyzed biomass using an ultrafiltration recovery method.
Recovery of cellulase ranged from 60 to 66.6% and for cellobiase from 76.4 to 88%. Economic analysis shows that cost savings
gained by enzyme recycling are sensitive to enzyme pricing and loading. At the demonstrated recovery of 60% and current loading
of 15 Filter paper units of cellulase/g of glucan, enzyme recycling is expected to generate a cost savings of approx 15%.
If recovery efficiency can be improved to 70%, the savings will increase to >25%, and at 90% recovery the savings will be
50%. 相似文献
7.
Rajagopalan S Ponnampalam E McCalla D Stowers M 《Applied biochemistry and biotechnology》2005,120(1):37-50
An Aspen Plus™ modeling platform was developed to evaluate the performance of the conversion process of degermed defibered
corn (DDC) to ethanol in 15- and 40-million gallons per year (MGPY) dry mill ethanol plants. Upstream corn milling equipment
in conventional dry mill ethanol plants was replaced with germ and fiber separation equipment. DDC with higher starch content
was fed to the existing saccharification and fermentation units, resulting in higher ethanol productivity than with regular
corn. The results of the DDC models were compared with those of conventional dry mill ethanol process models. A simple financial
analysis that included capital and operating costs, revenues, earnings, and return on investment was created to evaluate each
model comparatively. Case studies were performed on 15- and 40-MGPY base case models with two DDC process designs and DDC
with a mechanical oil extraction process. 相似文献
8.
9.
This communication describes a new method for the Pd/polyoxometalate-catalyzed aerobic olefination of unactivated sp(3) C-H bonds. Nitrogen heterocycles serve as directing groups, and air is used as the terminal oxidant. The products undergo reversible intramolecular Michael addition, which protects the monoalkenylated product from overfunctionalization. Hydrogenation of the Michael adducts provides access to bicyclic nitrogen-containing scaffolds that are prevalent in alkaloid natural products. Additionally, the cationic Michael adducts undergo facile elimination to release α,β-unsaturated olefins, which can be further elaborated via C-C and C-heteroatom bond-forming reactions. 相似文献
10.
As enzyme chemistry plays an increasingly important role in the chemical industry, cost analysis of these enzymes becomes
a necessity. In this paper, we examine the aspects that affect the cost of enzymes based upon enzyme activity. The basis for
this study stems from a previously developed objective function that quantifies the tradeoffs in enzyme purification via the
foam fractionation process (Cherry et al., Braz J Chem Eng 17:233–238, 2000). A generalized cost function is developed from our results that could be used to aid in both industrial and lab scale chemical
processing. The generalized cost function shows several nonobvious results that could lead to significant savings. Additionally,
the parameters involved in the operation and scaling up of enzyme processing could be optimized to minimize costs. We show
that there are typically three regimes in the enzyme cost analysis function: the low activity prelinear region, the moderate
activity linear region, and high activity power-law region. The overall form of the cost analysis function appears to robustly
fit the power law form. 相似文献