The effects of vitamin C are determined in the oil-in-water(0/ W) and water-in-oil(W/ 0) microemulsion regions of CTAB/ pentanol/ p-xylene/ H20 system. The addition of Vc joins the O/ W and W/ O areas in the phase diagram and expands the bicontinous region by reducing the lamellar liquid crystal one. The results show that the “ coupling action” of Vc is in fact a structural transition from lamellar crystal to isotropic phase with W/ O, O/ W and bicontinous structure. 相似文献
A study was carried out on the mechanism of electrical conductivity percolation of H2O/C16EO20/n-butanol/heptane microemulsions. Electrical conductivity, UV-vis spectroscopy and FTIR spectra were used to study the diluted “dry” microemulsions with the mass ratio of C16EO20/n-butanol/heptane = 3:3:4. The results of electrical conductivity showed that the percolation occurred around φw = 20 wt% and the transition of w/o microemulsions to bicontinueous microemulsions happened when φw = 45 wt%. From the UV-vis absorption spectra, it was found that the absorption of methyl orange (MO) in microemulsions shifted red than that of in oil phase, but the maximal absorption peak (λmax) remained unchanged when φw > 20 wt%. It implied that the position of MO solubilized in microemulsions was unvaried after free water appeared in the core. FTIR spectra revealed that the OH band of water in microemulsions moved to high frequency at low φw (< 20 wt%) and became broader at high φw. It indicated that the added water only caused the hydration of EO at low φw, the hydration completed when φw > 20 wt% and then the residual water entered into the core with properties similar to bulk water. The presence of free water as ions exchange medium will cause the electrical conductance increased. The percolation appeared after the hydration of EO completed. 相似文献
This report describes the use of PDMS ME coupled with amperometric detection for rapid separation of ascorbic, gallic , ferulic, p‐coumaric acids using reverse polarity. ME devices were fabricated in PDMS by soft lithography and detection was accomplished using an integrated carbon fiber working electrode aligned in the end‐channel configuration. Separation and detection parameters were investigated and the best conditions were obtained using a run buffer consisting of 5 mM phosphate buffer (pH 6.9) and a detection voltage of 1.0 V versus Ag/AgCl reference electrode. All compounds were separated within 70 s using gated injection mode with baseline resolution and separation efficiencies between 1200 and 9000 plates. Calibration curves exhibited good linearity and the LODs achieved ranged from 1.7 to 9.7 μM. The precision for migration time and peak height provided maximum values of 4% for the intrachip studies. Lastly, the analytical method was successfully applied for the analysis of ascorbic and gallic acids in commercial beverage samples. The results achieved using ME coupled with amperometric detection were in good agreement with the values provided by the supplier. Based on the data reported here, the proposed method shows suitability to be applied for the routine analysis of beverage samples. 相似文献
A number of 5′-O-dicarboxylic fatty acyl monoester derivatives of 3′-azido-3′-deoxythymidine (zidovudine, AZT), 2′,3′-didehydro-2′,3′-dideoxythymidine (stavudine, d4T), and 3′-fluoro-3′-deoxythymidine (alovudine, FLT) were synthesized to improve the lipophilicity and potentially the cellular delivery of parent polar 2′,3′-dideoxynucleoside (ddN) analogs. The compounds were evaluated for their anti-HIV activity. Three different fatty acids with varying chain length of suberic acid (octanedioic acid), sebacic acid (decanedioic acid), and dodecanedioic acid were used for the conjugation with the nucleosides. The compounds were evaluated for anti-HIV activity and cytotoxicity. All dicarboxylic ester conjugates of nucleosides exhibited significantly higher anti-HIV activity than that of the corresponding parent nucleoside analogs. Among all the tested conjugates, 5′-O-suberate derivative of AZT (EC50 = 0.10 nM) was found to be the most potent compound and showed 80-fold higher anti-HIV activity than AZT without any significant toxicity (TC50 >500 nM). 相似文献
The objective of the present investigation was to develop microemulsion-based transdermal systems of highly water soluble drug, Atenolol, by quality by design technique. Atenolol-loaded W/O microemulsions were optimized using D-optimal design with concentrations of oil, surfactants mixture, and water as independent variables, which was converted into microemulsion-based gel (MBG). The results of in vitro permeation of the optimized batch of Atenolol-loaded MBG revealed significant increase in permeability parameters as compared to its convention gel. All results suggested suitability of W/O type MEs as carriers for transdermal delivery of highly water soluble drug, Atenolol. 相似文献
Tween-80–n–butanol–diesel–water microemulsion systems with various surfactant:cosurfactant (S:C) ratio have been reported as a class of alternative diesel fuel from their phase behavior, clouding phenomena, conductivity, turbidity, and inflammation studies. Temperature induced clouding of microemulsion containing 2% brine at an S:C ratio of 1:1 from a suitable turbid zone has been examined to see the stability of the diesel–water microemulsion systems. Regression models have been proposed to understand the impact of various components of the microemulsion on their cloud point (CP) values. Conductivity of the microemulsions at various S:C ratio increases with the volume of brine having two cut points depicting the presence of three microheterogenous phases within the system, whereas turbidity shows a linear increase. Dye-probed investigation of water-rich and oil-rich zones of the microemulsions indicates the involvement of a dynamic mass transfer process within the various zones. The intensities of flames produced during burning of the microemulsions with various O:E:W weight percentages selected from the isotropic regions of the phase diagrams have been estimated using MATLAB image processing method and the impacts of various components on the fuel use of the microemulsions have been analyzed. 相似文献
The effect of branching point structures and densities is studied between azido‐containing hyperbranched polymers and cross‐linked nanogels on their loading efficiency of alkynyl‐containing dendron molecules. Hyperbranched polymers that contained “T”‐shaped branching linkage from which three chains radiated out and cross‐linked nanogels that contained “X”‐shaped branching linkage with four radiating chains are synthesized in microemulsion using either atom transfer radical polymerization (ATRP) or conventional radical polymerization (RP) technique. Both polymers have similar density of azido groups in the structure and exhibit similar hydrodynamic diameter in latexes before purification. Subsequent copper‐catalyzed azide–alkyne cycloaddition reactions between these polymers and alkynyl‐containing dendrons in various sizes (G1–G3) demonstrate an order of dendron loading efficiencies (i.e., final conversion of alkynyl‐containing dendron) as hyperbranched polymers > nanogels synthesized by ATRP > nanogels synthesized by RP. Decreasing the branching density or using smaller dendron molecules increases the click efficiency of both polymers. When G2 dendrons with a molecular weight of 627 Da are used to click with the hyperbranched polymers composed of 100% inimer, a maximum loading efficiency of G2 in the loaded hyperbranched polymer is 58% of G2 by weight. These results represent the first comparison between hyperbranched polymers and cross‐linked nanogels to explore the effect of branching structures on their loading efficiencies.
Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min?1 providing a sample throughput of more than 15 samples h?1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components. 相似文献