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101.
《Journal of the European Ceramic Society》2006,26(10-11):2151-2154
BaTi5O11 thin films were grown on the poly-Si/SiO2/Si substrate using rf magnetron sputtering. The BaO-TiO2 thin film deposited on the poly-Si substrate had an amorphous phase even though the growth temperature was high at 550 °C. The amorphous film was crystallized into the BaTi5O11 phase when the film was post annealed above 800 °C. The post annealing temperature is one of the most important factors for the formation of the crystalline BaTi5O11 thin film. The homogeneous BaTi5O11 thin film was obtained when the film was grown at 550 °C and rapid thermal annealed (RTA) at 900 °C for 3 min. The dielectric constant (ɛr) of the BaTi5O11 film measured at 100 kHz was about 35 and the dissipation factors of all the films were smaller than 4.0%. The dielectric properties of the BaTi5O11 thin film were also measured at microwave frequencies. For the BaTi5O11 thin film grown at 550 °C and RTA at 900 °C for 3 min, the ɛr of 34–30 and dielectric loss of 0.025 ± 0.005 were obtained at 1–6 GHz. 相似文献
102.
G. R. Collier F. McL Collier A. Sanigorski K. Walder D. Cameron-Smith A. J. Sinclair 《Lipids》1997,32(3):317-322
Recently it has been postulated that membrane fatty acid composition may be involved in the pathogenesis of insulin resistance
and non-insulin dependent diabetes mellitus (NIDDM). The aim of this study was to determine whether alterations in tissue
phospholipid (PL) fatty acids are present in hyperglycemic and hyperinsulinemic Psammomys obesus. On a native diet of salt bush, P. obesus (Israeli sand rat) remains lean and free of diabetes; however, when placed on a normal laboratory chow, a significant proportion
of these animals develops a number of metabolic disorders associated with NIDDM, providing an ideal animal model of obesity
and NIDDM. Four groups of mature P. obesus were studied: group A; normoglycemic and normoinsulinemic; group B: normoglycemic and hyperinsulinemic; group C: hyperglycemic
and hyperinsulinemic; and group D: hyperglycemic hypoinsulinemic. In liver and red gastrocnemius muscle, there were no significant
differences between groups, A, B, and in fatty acid composition of PL. Minor differences in individual fatty acids were demonstrated
in group D animals (increased liver 20∶4n-6 and increased muscle 22∶5n-3); however, the unsaturation indices in liver and
muscle were not significantly different between any of the groups. In considering that the minor changes in group D animals
were not demonstrated in hyperinsulinemic group B animals or hyperglycemic, hyperinsulinemic group C animals, it is likely
that the differences in group D animals were secondary to the more severe disturbances in glucose homeostasis and hypoinsulinemia
present in these animals. The results of this study suggest that in this rodent diabetic model significant disturbances in
glucose homeostasis and hyperinsulinemia may develop independently of changes in tissue fatty acid composition. 相似文献
103.
Watkins SM Lin TY Davis RM Ching JR DePeters EJ Halpern GM Walzem RL German JB 《Lipids》2001,36(3):247-254
Diet and fatty acid metabolism interact in yet unknown ways to modulate membrane fatty acid composition and certain cellular
functions. For example, dietary precursors or metabolic products of n-3 fatty acid metabolism differ in their ability to modify
specific membrane components. In the present study, the effect of dietary 22∶6n−3 or its metabolic precursor, 18∶3n−3, on
the selective accumulation of 22∶6n−3 by heart was investigated. The mass and fatty acid compositions of individual phospholipids
(PL) in heart and liver were quantified in mice fed either 22∶6n−3 (from crocodile oil) or 18∶3n−3 (from soybean oil) for
13 wk. This study was conducted to determine if the selective accumulation of 22∶6n−3 in heart was due to the incorporation
of 22∶6n−3 into cardiolipin (CL), a PL most prevalent in heart and known to accumulate 22∶6n−3. Although heart was significantly
enriched with 22∶6n−3 relative to liver, the accumulation of 22∶6n−3 by CL in heart could not quantitatively account for this
difference. CL from heart did accumulate 22∶6n−3, but only in mice fed preformed 22∶6n−3. Diets rich in non-22∶6n−3 fatty
acids result in a fatty acid composition of phosphatidylcholine (PC) in heart that is unusually enriched with 22∶6n−3. In
this study, the mass of PC in heart was positively correlated with the enrichment of 22∶6n−3 into PC. The increased mass of
PC was coincident with a decrease in the mass of phosphatidylethanolamine, suggesting that 22∶6n−3 induced PC synthesis by
increasing phosphatidylethanolamine-N-methyltransferase activity in the heart. 相似文献
104.
Sawsan A. Rahimuddin Samir M. Khoja Marzoki M. Zuhair Nazlin K. Howell Jonathan E. Brown 《European Journal of Lipid Science and Technology》2007,109(7):647-655
Ultraviolet A (UVA) radiation causes oxidative damage to human skin cells. This damage may be reduced or prevented using plant compounds as photoprotectants. To investigate the relationship between chemical structure and UVA‐protective activity, three structurally related flavonoids, namely luteolin, luteolin‐7‐O‐glucoside (both present in artichoke) and luteolin‐4'‐O‐glucoside (present in wild carrot), were studied. Human skin fibroblasts exposed to UVA (250 and 500 kJ/m2) were treated with each flavonoid (30 µM) for 18 h prior to irradiation. The extent of lipid peroxidation in the cellular extracts was assessed as lipid peroxides and malondialdehyde (MDA). Luteolin and luteolin‐7‐O‐glucoside both prevented a significant increase in lipid peroxides at 250 kJ/m2, but at 500 kJ/m2 their effectiveness was clearly attenuated. Contrastingly, luteolin‐4'‐O‐glucoside was pro‐oxidant at both radiation doses. Measurements of MDA levels highlighted that luteolin was clearly more effective than the two glucosides at both 250 and 500 kJ/m2. Overall, these results show clear differences between the three flavonoids and suggest that the B ring 3',4'‐dihydroxy group, lacking in luteolin‐4'‐O‐glucoside, may be particularly important. Flavonoid: transition metal ion chelation studies confirmed the influence of the 3',4'‐dihydroxy group, which is also relevant to the quenching of singlet oxygen. These features as well as the greater lipophilic nature of luteolin together explain the superior activity of this flavonoid which may be potentially useful as a supplement in photoprotective skin preparations. 相似文献
105.
《Catalysis communications》2007,8(11):1834-1837
Benzophenone and its derivatives were prepared via Friedel–Crafts acylation reactions using ionic liquids (ILs) of BmimCl–FeCl3, BmimCl–AlCl3 and BmimCl–ZnCl2 as dual catalyst–solvent. Among them, BmimCl–FeCl3 showed much higher catalytic activity than that observed for the other two ILs, and in conventional organic solvents. In these reaction systems, good to excellent yields (up to 97%) of acylation products were obtained in a short reaction time. This method features high yield, a simple product isolation procedure, ILs reusability and reduced waste discharge, thus rendering this catalytic system both efficient and environmentally friendly. 相似文献
106.
Reaction selectivities were determined in multicompetitive reactions mediated by Burkholderia cepacia lipase (Amano PS-30) at a water activity of 0.19 in hexane. Saturated FA (C4–C18 even chain) and oleic acid (C18∶1) were
reacted with a single alcohol, glycerol, α-or β-MAG, containing C4, C10, C16, or C18∶1 individually as alcohol cosubstrate.
Similar odrinal patterns of FA selectivity, with C8, C10, and C16 preferred over others, were generally observed for incorporation
of FA into specific acylglycerol (AG) pools of the 24 specific cases evaluated. The three exceptions were enrichment of C14
and C18 in the MAG pool with α-C16-MAG, substrate, and a general suppression of >C8 incorporation into the TAG pool for reactions
with α-C10- and α-C16-MAG. PS-30 lipase selectivity toward MAG was in descending order: α/β-C4-MAG>β-C10-MAG>β-C16-MAG>α/β-C18∶1-MAG>α-C10-MAG>α-C16-MAG.
Selectivity in channeling CX of the original CX-MAG substrates into higher AG species was in descending order: α-C10-MAG∼α-C16-MAG>α-C18∶1-MAG>β-C10-MAG∼β-C16-MAG∼β-C18∶1-MAG
>α/β-C4-MAG. Generally, MAG were better acyl donors than FA for esterification reactions leading to DAG formation. These observations
are relevant to the design of biocatalytic processes intended to yield specifically structured TAG. 相似文献
107.
《Desalination》2007,202(1-3):271-277
A bench scale submerged microfiltration system coupled with high concentration of PAC (powdered activated carbon) was applied in order to purify a river water containing secondary effluent. The system was operated with four different modes: Run-1, -2, -3 and -4. The PAC concentration was set at 0, 4 and 40 g/L with same filtration rate of 1.0 m/d (42 L/m2/h) which correspond to Run-1, -2 and -3. In Run-4, the filtration rate was set at 0.5 m/d (21 L/m2/h) with PAC concentration of 40 g/L. The effluent turbidity showed below 0.1 NTU for all runs, and the removal rates more than 90% were observed. As for TOC removal, almost no removal of TOC was observed in Run-1 while the higher removal rates were obtained with the higher dosage of powdered activated carbon. Run-3 and 4 with PAC dose of 40 g/L showed the removal of 85% regardless of the filtration rates. Removal of UV254 was similar to that of TOC: removal of 13% at Run-1 and 90% at Run-3 and -4. As for the filtration efficiency, an average filtration time for TMP to reach 60 kPa was checked for each runs. The filtration time of around 5 days was observed in Run-1 and Run-2, 2 days in Run-3 and 60 days in Run-4. According to the results, the effluent water quality got better with higher dose of PAC and the filtration efficiency was enhanced with higher dose of PAC and lower filtration time. 相似文献
108.
109.
Aspartate ammonia lyase (Asp) is one of three types of ammonia lyases specific for aspartate or its derivatives as substrates, which catalyzes the reversible reaction of l-aspartate to yield fumarate and ammonia. In this paper, the catalytic mechanism of Asp has been studied by using combined quantum-mechanical/molecular-mechanical (QM/MM) approach. The calculation results indicate that the overall reaction only contains two elementary steps. The first step is the abstraction of Cβ proton of l-aspartate by Ser318, which is calculated to be rate limiting. The second step is the cleavage of CαN bond of l-aspartate to form fumarate and ammonia. Ser318 functions as the catalytic base, whereas His188 is a dispensable residue, but its protonation state can influence the active site structure and the existing form of leaving amino group, thereby influences the activity of the enzyme, which can well explain the pH dependence of enzymatic activity. Mutation of His188 to Ala only changes the active site structure and slightly elongates the distance of Cβ proton of substrate with Ser318, causing the enzyme to remain significant but reduced activity. 相似文献
110.
Selection of strategies that help reduce riverine inputs requires numerical models that accurately quantify hydrologic processes. While numerous models exist, information on how to evaluate and select the most robust models is limited. Toward this end, we developed a comprehensive approach that helps evaluate watershed models in their ability to simulate flow regimes critical to downstream ecosystem services. We demonstrated the method using the Soil and Water Assessment Tool (SWAT), the Hydrological Simulation Program–FORTRAN (HSPF) model, and Distributed Large Basin Runoff Model (DLBRM) applied to the Maumee River Basin (USA). The approach helped in identifying that each model simulated flows within acceptable ranges. However, each was limited in its ability to simulate flows triggered by extreme weather events, owing to algorithms not being optimized for such events and mismatched physiographic watershed conditions. Ultimately, we found HSPF to best predict river flow, whereas SWAT offered the most flexibility for evaluating agricultural management practices. 相似文献