The role played by coordinates in the formulation of an absolute spacetime theory is assessed. It is shown that recent criticism on previous work of ours is wrong. 相似文献
The interaction between glucose oxidase (GOx) and phospholipid monolayers is studied at the 1,2-dichloroethane/water interface by electrochemical impedance spectroscopy. Electrochemical experiments show that the presence of GOx induces changes in the capacitance curves at both negative and positive potentials, which are successfully explained by a theoretical model based on the solution of the Poisson-Boltzmann equation. These changes are ascribed to a reduced partition coefficient of GOx and an increase of the permittivity of the lipid hydrocarbon domain. Our results show that the presence of lipid molecules enhances the adsorption of GOx molecules at the liquid/liquid interface. At low lipid concentrations, the adsorption of GOx is probably the first step preceding its penetration into the lipid monolayer. The experimental results indicate that GOx penetrates better and forms more stable monolayers for lipids with longer hydrophobic tails. At high GOx concentrations, the formation of multilayers is observed. The phenomenon described here is strongly dependent on 1) the GOx and lipid concentrations, 2) the nature of the lipid, and 3) the potential drop across the interface. 相似文献
In this work, a capillary electrophoresis (CE) method using indirect UV detection (214nm) for the simultaneous determination of monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diethylethanolamine (DEEA), monocyclohexylamine (MCHA) and dicyclohexylamine (DCHA) in water/ethanol extracts of wrapping materials containing volatile corrosion inhibitors (VCIs) was described. A running buffer consisting of 0.010 molL(-1) imidazole, 0.010 molL(-1) 2-hydroxyisobutyric acid (HIBA) and 0.010 molL(-1) 18-crown-6 ether enabled separation of the analytes in less than 7 min. A few method validation parameters were determined revealing good migration time repeatability (<0.7% RSD) and area repeatability (< 1.8% RSD). Limits of detection were in the range of 0.52-1.54 mg L(-1). Recovery values were in the range of 94.8-100.9%. The methodology was successfully applied to the analysis of three commercial products (VCI treated paper, foam and plastic). The concentration of amines in these materials varied from 0.050 to 22.3% (w/w). 相似文献
The disrupting effect of three different ionic carbohydrates (xanthan, pectin and gum arabic) on the formation of tannin-protein insoluble aggregates was assessed by nephelometry using bovine serum albumin (BSA) and several procyanidin fractions previously extracted from grape seeds. The presence in solution of any of the carbohydrates studied was found to restrain the formation of insoluble protein-tannin aggregates for every procyanidin fraction used. Xanthan was the most effective carbohydrate, whereas gum arabic was the least effective. The present work has revealed that the disrupting effect of carbohydrates is quite different depending on the procyanidin structure complexity. In general, the three carbohydrates studied revealed a similar trend in that their disrupting effect on tannin-BSA aggregate formation decreased with increase of the procyanidin degree of polymerization. 相似文献
N,N,N‐trimethylchitosan (TMC) was prepared by reacting purified chitosan with iodomethane, in the presence of sodium hydroxide, water and sodium iodide, at room temperature. The reaction medium was N‐methyl‐2‐pyrrolidone. Different samples of TMC were obtained by adding to the reaction medium a fixed volume (5.5 mL) of aqueous NaOH solutions at different concentrations (15, 20, 30 and 40 wt.‐%) and carrying out the reactions for 9 or 24 h. The features observed in the 1H and 13C NMR spectra of these chitosan derivatives, in respect of the chemical shift, number and relative intensity of the signals, depended strongly on the excess of NaOH and H3CI added to the reaction medium, but when the lowest excess was employed, the characteristics of the derivative were not affected by the reaction time to the same extent. The average degree of quaternization of these N‐methylated derivatives of chitosan ranged from 10.5% to 44.8%, according to the reaction conditions. Increasing the excess of NaOH, in reactions carried out for 9 h, resulted in TMC samples with progressively higher content of trimethylated sites however, the reaction yields were correspondingly lower and O‐alkylation was favored in these cases.
1H NMR spectrum of sample [AX]24h dissolved in D2O (Cp = 10 g/L). 相似文献
Molecular distillation was studied for the separation of tocopherols from soya sludge, both experimentally and by simulation,
under different operating conditions, with good agreement. Evaporator temperatures varied from 100°C to 160°C and feed flow
rates ranged from 0.1 to 0.8 kg/h. The process pressure was maintained at 10−6 bar, the feed temperature at 50°C, the condenser temperature at 60°C, and the stirring at 350 rpm. For each process condition,
samples of both streams (distillate and residue) were collected and stored at −18°C before tocopherols analyses. Owing to
the differences between molecular weights and vapor pressures of free fatty acids and tocopherols, tocopherols preferentially
remained in the residue at evaporator temperatures of 100°C and 120°C, whereas for higher temperatures (140°C and 160°C) and
lower feed flow rate, tocopherols tended to migrate to the distillate stream. 相似文献
We have investigated the EPR and DNP behavior of a molecularly doped polymer modeling those used to transport electronic charge in electrophotography. The EPR spectra show no evidence of the superexchange reported for a closely related system based on tri-p-tolylamine. The difference may be due to larger charge-transfer matrix elements in the latter system. An unambiguous interpretation of the observed 1H DNP was rendered difficult by the unanticipated asymmetry of the EPR spectra. We report extensive data on the "three-spin" effect evident in the DNP-enhanced 13C NMR spectra, and comment on its potential for characterizing polymer interfaces. 相似文献
In this Letter, we report the structural and luminescent properties of Tb:Ce:Al2O3 crystalline ceramic powders prepared through combustion synthesis at low temperature (280 °C). The presence of Ce3+ (1.0 mol%) in the sample resulted in an enhancement of Tb3+ (1.0 mol%) overall emission intensity by a factor of 50. The analysis of the luminescence dynamics for the 5D4 → 7F6 transition (545 nm) of Tb3+ demonstrated that the mechanism responsible for the large enhancement of luminescence observed is efficient energy transfer from Ce3+ to Tb3+. 相似文献