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Yield Decreases (yield + decrease)
Selected AbstractsSynthesis of N -Acetyl-,-aminobutyric Acid via Amidocarbonylation: A Case StudyADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2003Dirk Gördes Abstract The synthesis of N -acetyl-,-aminobutyric acid by amidocarbonylation of propionaldehyde with acetamide in the presence of palladium catalysts is studied in detail. The influence of various reaction conditions and compositions (e.g., the co-catalysts acid and bromide) on the yield of N -acetyl-,-aminobutyric acid is shown. For the first time it is demonstrated that the palladium-catalyzed amidocarbonylations of aldehydes can be run with significantly lower halide concentrations (<30 mol,%) without a major yield decrease. While phosphine-free catalyst systems give best yields at low CO pressure, phosphine-ligated palladium catalysts lead to better yields at higher CO pressure. At low palladium loadings (<0.1 mol,%), unwanted condensation reactions of propionaldehyde become increasingly competitive. [source] Ozone-induced reductions in below-ground biomass: an anatomical approach in potatoPLANT CELL & ENVIRONMENT, Issue 7 2010AMPARO ASENSI-FABADO ABSTRACT Potato plants were grown in open-top chambers under three ozone concentrations during two complete cropping seasons (93 and 77 d in 2004 and 2005, respectively). The effects of chronic exposure to ozone on leaf anatomy, cell ultrastructure and crop yield were studied. Severe cell damage was found, even at ambient ozone levels, mainly affecting the spongy parenchyma and areas near the stomata. Damage to the cell wall caused loss of cell contact, and loss of turgor pressure due to tonoplast disintegration, contributed to cell collapse. Phloem sieve plates were obstructed by callose accumulation, and damaged mesophyll cells increased their starch stores. Tuber yield fell sharply (24,44%), due to the biggest tubers becoming smaller, which affected commercial yield. These anatomical findings show the mechanisms of ozone effect on assimilate partitioning, and thus crop yield decrease, in potato. Further implications of ozone causing reductions in below-ground biomass are also discussed. [source] Switchable Fluorescent and Solvatochromic Molecular Probes Based on 4-Amino- N -methylphthalimide and a Photochromic DiaryletheneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2008Sergey F. Yan Abstract New fluorescent photochromic compounds (1 -H and 1 -Boc) have been synthesized and characterized in different solvents. The fluorescence emission can be switched "on" and "off" with visible light and UV, respectively, by means of the photochromic reaction. The emission wavelength and efficiency strongly depend on the polarity of the solvent. The compounds show a positive solvatochromic effect in the emission maxima, and their fluorescence quantum yield decreases as the solvent's polarity increases (from cyclohexane to dioxane). In solvents more polar than dioxane the emission is too weak and therefore undetectable, and thus 1 -H and 1 -Boc behave as "normal" photochromic compounds. The photochromic reaction is also sensitive to the environment. A decrease of more than an order of magnitude was found for the quantum yield of the colouring reaction (,OF,CF) for 1 -H in ethanol compared with cyclohexane, and an about threefold decrease in ,OF,CF was observed for the compound 1 -Boc in polar solvents (compared with apolar solvents). For both compounds the ring-opening reaction was found not to dependent on the solvent. The novel fluorescent molecular switches 1 -H and 1 -Boc are able to probe the polarity of their microenvironment. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Catalytic synthesis of 1,6-dicarbamate hexane over MgO/ZrO2JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2007Fang Li Abstract MgO/ZrO2 catalyst was prepared for the synthesis of 1,6-dicarbamate hexane (HDC) using dimethyl carbonate (DMC) and 1,6-diamine hexane (HDA) as raw materials. When the catalyst is calcined at 600 °C and MgO load is 6 wt%, the catalyst exhibits better activity. When the concentration of catalyst is 2 g (100 mL),1 DMC, n(HDA):n(DMC) = 1:10, reaction time is 6 h under reflux temperature, and the yield of 1,6-dicarbamate hexane is 53.1%. HDC yield decreases from 53.1% to 35.3% after MgO/ZrO2 being used for three times. The decrease in specific surface area may be attributed to deactivation of MgO/ZrO2. Copyright © 2007 Society of Chemical Industry [source] Sulfur and nitrogen supply influence growth, product appearance, and glucosinolate concentration of broccoliJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2007Ilona Schonhof Abstract The effects of insufficient and optimal sulfur (S) and nitrogen (N) supply on plant growth and glucosinolate formation were studied under controlled experimental conditions in broccoli "Monaco". Here, we report on the interaction between S and N supply, plant growth, and quality parameters and discuss the relevance of this interaction in relation to crop-management strategies. Broccoli plants supplied with insufficient amounts of S or N showed typical deficiency symptoms and yield decreases. In contrast, total glucosinolate concentrations were high at insufficient N supply, independent of the S level, and low at insufficient S supply in combination with an optimal N supply. This was mainly due to the presence of the alkyl glucosinolates glucoraphanin and glucoiberin. Furthermore, with S concentrations above 6 g (kg DM),1 and an N : S ratio lower than 10:1, the glucosinolate concentrations were on average around 0.33 g (kg fresh matter),1 and differed significantly from those plants characterized by an S concentration below 6 g (kg DM),1 and an N : S ratio above 10:1. In addition, N : S ratios between 7:1 and 10:1 promoted plant yield and enhanced overall appearance. Therefore, to produce broccoli (and potentially other Brassicaceae) with higher crop yields and enhanced product quality in the field, it is vital to establish the optimal S and N nutritional status of the plant and to integrate this information into crop-management strategy programs. [source] UV laser-induced desorption mechanism analyzed through two-layer alkali halide samplesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2008F. A. Fernández-Lima Abstract Time of flight-mass spectrometry (TOF-MS) is used to analyze positive and negative desorbed ions generated by UV laser ablation of several alkali (X) halide (Y) salts. Most of the observed desorbed cluster ions have the structure (XY)nX+ or (XY)nY,. Their desorption yields decrease as exp(,kn), where k , 2 for both series, suggesting that the neutral component (XY)n plays the dominant role in the desorption process. Mass spectrum measurements were performed for compound samples in which two salts (out of CsI, RbI, KBr, KCl and KI) are homogeneously mixed or disposed in two superposed layers. The detection of small new ion species and large cluster ions of the original salts supports the scenario that the uppermost layers are completely atomized while deep layers are emitted colder and fragmented: It is proposed that ns-pulsed laser induced desorption of ionic salts occurs via two sequential mechanisms: (1) ejection of cations and anions in the hot plume, followed by recombination into new cluster ions and (2) ejection of relatively cold preformed species originated from deep layers or from periphery of the irradiated region. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||