The uptake of O3 by myristic acid-oleic acid mixed particles: evidence for solid surface layers

The oleic acid ozonolysis in mixed oleic and myristic acid particles was studied in a flow tube reactor using single particle mass spectrometry. The change in reactivity was investigated as a function of the myristic acid concentration in these 2 micron particles. For pure oleic acid aerosol, the reactive ozone uptake coefficient, gamma, was found to be 3.4 (+/-0.3) x 10(-4) after taking secondary reactions into account. At the myristic acid crystallization point, where only 2.5% of the particle is in the solid phase, the uptake coefficient was reduced to 9.7 (+/-1.0) x 10(-5). This dramatic drop in the uptake coefficient is explained by the presence of a crystalline monolayer of myristic acid, through which ozone diffusion is reduced by several orders of magnitude, relative to liquid oleic acid. Scanning electron microscope images of the mixed particles confirm that the particle surface is crystalline when the myristic acid mole fraction exceeds 0.125. The findings of these experiments illustrate that particle morphology is important to understanding the reactivity of species in a mixed particle. The decay of myristic acid during the course of ozonolysis is explained in terms of a reaction with stabilized Criegee intermediates, which attack the acidic groups of the oleic and myristic acids with equal rate constants.     

Measuring rates of reaction in supercooled organic particles with implications for atmospheric aerosol

The kinetics of heterogeneous reactions involving supercooled organic droplets is reported for the first time. Reactions between ozone and internally-mixed sub-micrometre particles containing an unsaturated alkenoic acid, oleic acid, and an n-alkanoic acid, myristic acid, were studied as a simple model for the oxidation of meat-cooking aerosol. The reactions were followed by monitoring the rate of oleic acid loss using an Aerosol CIMS (chemical ionization mass spectrometry) instrument for real-time particle analysis. Evidence of as much as 32 degrees C supercooling at room temperature was observed depending on particle composition. FTIR spectra of the aerosol also demonstrate features indicative of supercooling. Particles in which crystallization was induced by cooling below room temperature demonstrated decreased reactivity by a factor of 12 compared to supercooled particles of the same composition. This drastic difference in reactivity could have significant implications for the lifetimes of reactive species in ambient aerosol as well as for the accurate source apportionment of particulate matter.     

Temperature dependency of thermal conductivity of solid phases for fatty acids

Thermal conductivity variations with temperature of solid phases for lauric acid (LA), myristic acid (MA), pivalic acid (PA), and stearic acid (SA) have been measured with radial heat-flow method. Temperature dependencies of the thermal conductivity for same organic materials have been obtained by linear regression analysis. From graphs of thermal conductivity versus temperature, the thermal conductivity of solid phase at their melting temperature and temperature coefficients of thermal conductivity for LA, MA, PA, and SA have been found to be 0.37, 0.39, 0.23, and 0.35 W K^?1 m^?1 and 0.00935, 0.00446, 0.01095, and 0.00295 K^?1, respectively. The ratios of thermal conductivity of liquid phase to thermal conductivity of solid phase for LA, MA, PA, and SA have also been measured to be 0.52, 0.48, 0.25, and 0.59, respectively, with a Bridgman-type directional solidification apparatus.     

Equilibrium phase diagrams of aqueous mixtures of malonic acid and sulfate/ammonium salts

Tropospheric aerosols are usually complex mixtures of inorganic and organic components. Although the thermodynamic properties of inorganic aerosols have been widely studied, the effect of organics on such properties is still under discussion. In this study, solubility in water, water activity (a(w)) of aqueous solutions, deliquescence relative humidity (DRH), eutonic composition, and eutonic DRH were determined for bulk mixtures of malonic acid (MA) with ammonium sulfate (AS) and ammonium bisulfate (ABS) at 25 degrees C over the full range of composition (from 0 wt % to the solubility limit of the mixture components). The data were used to construct equilibrium phase diagrams, which show the phase of the mixtures as a function of total composition, dry mixture composition, water content, and ambient relative humidity (RH). This work complements previous reports on the thermodynamic properties of AS/MA mixtures because the range of concentrations investigated is larger than in any other published single study. On the other hand, this is the first report on the a(w), deliquescence, and water absorption of ABS/MA mixtures. The eutonic composition for AS/MA mixtures was found to be 66.8 MA dry wt % (MA dry wt % = MA mass x 100/(AS mass + MA mass) with a DRH of 0.437. The eutonic composition for the ABS/MA mixtures was lower than for the AS/MA mixtures: 20.9 MA dry wt % with a DRH of 0.327. Measured a(w) of liquid AS/MA and ABS/MA solutions is compared with an extended Zdanovskii-Stokes-Robinson expression, obtaining a good agreement (error < 5-6%). The expression was used to predict water uptake of mixtures and might be useful to interpret particle hygroscopic growth experiments. Comparison of the AS/MA and ABS/MA systems indicates that ABS reduces the DRH and enhances water uptake, relative to mixtures with AS. The results confirm that ambient particles containing sulfate and water-soluble organic compounds can remain liquid or partially liquid at very low ambient RH conditions, especially if the sulfate is not completely neutralized.     

Thermal energy storage and retrieval properties of form-stable phase change nanofibrous mats based on ternary fatty acid eutectics/polyacrylonitrile composite by magnetron sputtering of silver

This paper demonstrated a novel magnetron sputtering method used for the improvement in thermal energy storage and retrieval rates of phase change materials (PCMs). The ten types of ternary fatty acid eutectics (i.e., CA–LA–MA, CA–LA–PA, CA–LA–SA, CA–MA–PA, CA–MA–SA, CA–PA–SA, LA–MA–PA, LA–MA–SA, LA–PA–SA and MA–PA–SA) were firstly prepared using five fatty acids such as capric acid (CA), lauric acid (LA), myristic acid (MA), palmitic acid (PA) and stearic acid (SA) and then selected as solid–liquid PCMs. Thereafter, magnetron sputter coating was used to deposit the functional silver (Ag) nanolayers onto the surface of electrospun polyacrylonitrile (PAN) nanofibrous mats serving as supporting skeleton. Finally, a series of composite PCMs were fabricated by adsorbing the prepared ternary eutectics into three-dimensional porous network structures of Ag-coated PAN membranes. The observations by EDX determined the formation of Ag nanolayers on the PAN nanofibers surface after magnetron sputtering. The SEM images illustrated that the Ag-coated PAN nanofibers appeared to have larger fiber diameter and rougher surface. Ag-coated PAN nanofibrous mats could effectively prevent the leakage of molten ternary eutectics and help maintain form-stable structure due to surface tension forces, capillary and nanoconfinement effects. The DSC results suggested that the phase change temperatures of the ternary fatty acid eutectics were obviously lower than those of individual fatty acids and their binary eutectics. The adsorption rates of ternary fatty acid eutectics in the composite PCMs were determined to be about 89–98 %. The thermal performance test indicated that the metallic coating of Ag dramatically improved the thermal energy storage and retrieval rates of the composite PCMs.     

Ozonolysis of oleic acid adsorbed to polar and nonpolar aerosol particles

Single-particle kinetic studies of the reaction between oleic acid and O 3 have been conducted on two different types of core particles: polystyrene latex (PSL) and silica. Oleic acid was found to adsorb to both particle types in multilayer islands that resulted in an adsorbed layer of a total volume estimated to be less than one monolayer. The rate of the surface reaction between surface-adsorbed oleic acid and O 3 has been shown for the first time to be influenced by the composition of the aerosol substrate in a mixed organic/inorganic particle. A Langmuir-Hinshelwood mechanism was applied to the observed dependence of the pseudo-first-order rate constant with [O 3], and the resulting fit parameters for the ozone partition coefficient ( K O 3 ) and maximum first order rate constant ( k 1,max ) suggest that the reaction proceeded faster on the less polar PSL core at lower [O 3] due to the increased residence time of O 3 on the PSL surface, but the reaction was ultimately more efficient on the silica surface at high [O 3]. Values for the uptake coefficient, gamma oleic , for reaction of oleic acid on PSL spheres decrease from 2.5 x 10 (-5) to 1 x 10 (-5) with increasing [O 3] from 4 to 25 ppm and overlap at high [O 3] with the estimated values for gamma oleic on silica, which decrease from 1.6 x 10 (-5) to 1.3 x 10 (-5). The relationship between gamma oleic and the more common expression for gamma O 3 is discussed.     

Selectively increasing of polyunsaturated (18:2) and monounsaturated (18:1) fatty acids in Jatropha curcas seed oil by crystallization using D-optimal design

ABSTRACT: BACKGROUND: This study was done to obtain concentrated polyunsaturated fatty acid (PUFA) linoleic acid (LA; 18:2) and monounsaturated fatty acid (MUFA) oleic acid (OA; 18:1) from Jatropha curcas seed oil by urea complexation. Urea complexation is a method used by researchers to separate fatty acids (FAs) based on their molecular structure. Effects the ratio of urea-to-FAs, crystallization temperature and crystallization time on the final products of urea complexation were examined. D-optimal Design was employed to study the significance of these factors and the optimum conditions for the technique were predicted and verified. RESULTS: Optimum conditions of the experiment to obtain maximum concentration of LA were predicted at urea-to-FAs ratio (w/w) of 5:1, crystallization temperature of 10 C and 24 h of crystallization time. Under these conditions, the final non-urea complex fraction (NUCF) was predicted to contain 92.81% of LA with the NUCF yield of 7.8%. The highest percentage of OA (56.14%) was observed for samples treated with 3:1 urea-to-FAs ratio (w/w) at 10 C for 16 h. The lowest percentage of LA (8.84%) was incorporated into urea complex fraction (UCF) with 1:1 urea-to-FAs ratio (w/w) at 10 C for 8 h. CONCLUSIONS: The separation of PUFA (LA) and MUFA (OA) described here. Experimental variables should be carefully controlled in order to recover a maximum content of PUFA and MUFA of interest with reasonable yield% with a desirable purity of fatty acid of interest.     

The oxidation of oleate in submicron aqueous salt aerosols: evidence of a surface process

We have studied the oxidation of submicron aqueous aerosols consisting of internal mixtures of sodium oleate (oleic acid proxy), sodium dodecyl sulfate, and inorganic salts by O3, NO3/N2O5, and OH. Experiments were performed using an aerosol flow tube and a continuous flow photochemical reaction chamber coupled to a chemical ionization mass spectrometer (CIMS). The CIMS was fitted with a heated inlet for volatilization and detection of organics in the particle phase simultaneously with the gas phase. A differential mobility analyzer/condensation particle counter was used for determining aerosol size distributions. The oxidation of oleate by O3 follows Langmuir-Hinshelwood kinetics, with gammaO3 approximately 10(-5) calculated from the observed loss rate of oleate in the particle phase. The best fit Langmuir-Hinshelwood parameters are kImax=0.05+/-0.01 s-1 and KO3=4(+/-3)x10(-14) cm3molec-1. These parameters showed no dependence on the ionic composition of the aerosols or on the presence of alkyl surfactants. Several ozone oxidation products were observed to be particle-bound at ambient temperature, including nonanoic acid. We observed efficient processing of oleate by OH (0.1相似文献   

Ozonolysis of mixed oleic acid/n-docosane particles: the roles of phase, morphology, and metastable states

The reaction kinetics of ozone with oleic acid (OA) in submicron particles containing n-docosane has been studied using aerosol CIMS (chemical ionization mass spectrometry) to monitor changes in particle composition. Internally mixed particles with X(OA) > 0.72 were found to exist as supercooled droplets when cooled to room temperature. Partial reaction of the oleic acid was seen to completely inhibit further reaction and was attributed to the formation of a metastable solid rotator phase of the n-docosane at the surface. This reaction-induced phase change is believed to prevent further reaction by slowing ozone diffusion into the particle. When these particles were cooled to 0 degrees C before reaction, they reacted to a further extent and did not demonstrate such an inhibition. This shift in reactivity upon cooling is attributed to the formation of the thermodynamically stable form of n-docosane, the triclinic solid. This transition was accompanied by an increase in the n-docosane density, which led to the development of "cracks" through which ozone can diffuse into the particle. The aerosol with X(OA) < 0.72 consisted of an external mixture of particles containing n-docosane in either the rotator or the triclinic solid phase because of the stochastic nature of the rotator --> triclinic transition. The reactivity of the oleic acid was seen to increase with increasing n-docosane content as a larger fraction of the particles underwent the rotator --> triclinic transition and therefore contained cracks at the surface. These findings demonstrate the importance of transient, metastable phases in determining particle morphology and how such morphological changes can influence rates of reactions in organic aerosols.     

Mechanisms of competitive adsorption of albumin and sodium myristate at the silicon oxide/aqueous interface

The competitive adsorption of proteins and surfactants has applications to chromatographic systems and biological materials. Adsorption for systems of bovine serum albumin (BSA) and sodium myristate (SM) was investigated with in-situ ATR-IR spectroscopy and ex-situ ellipsometry. The results were used to determine quantitatively the surface densities of the adsorbates at the surface. For a mixture of SM and BSA at 25 degrees C in water, the adsorbed density of BSA is 0.3 mg/m2, which is much less than the value of 3.1 mg/m2 for BSA alone. Sodium myristate, some of which is protonated to myristic acid (MA) when adsorbed because of a pH decrease from 9.0 to 8.2, adsorbs to a surface density of 4.0 x 10(-6) mol/m2, which is greater than the value of 1.7 x 10(-6) mol/m2 from a solution of SM alone. Adsorbed SM and MA are removed, or desorbed, when the bulk mixture is replaced with water, with only a slight amount of SM remaining. When placed in contact with a layer of BSA, SM can displace most of the adsorbed protein, even when BSA is present in the bulk solution, with some BSA at 0.3 mg/m2 remaining adsorbed. Allowing BSA to adsorb to a layer of SM results in gamma(BSA) = 2.3 mg/m2, with little displacement of the SM layer. These results indicate that SM can remove some BSA from the surface by displacement, and that some BSA remains adsorbed in patches.     

Coordinatively induced length control and photoluminescence of W18O49 nanorods

A coordinatively induced length control of W18O49 nanorods has been developed using thermal decomposition of W(CO)6 in octyl ether solutions of single or mixed capping agents, oleic acid (OA), oleic acid/hexadecylamine (HDA), and oleic acid/trioctylphosphine oxide (TOPO). The order of length for nanorods synthesized with different capping agents was OA > OA/HDA > OA/TOPO, which was the opposite of order of their coordinating power. The order of crystalline size (diameter x length) from the TEM image was OA/HDA > OA > OA/TOPO and matched exactly with the order of crystallinity from the XRD pattern. The order of photoluminescence intensity was OA/HDA < OA < OA/TOPO and was the opposite of the order for the crystalline size or crystallinity. The strong coordinating power and steric bulkiness of TOPO is thought to interrupt the growth of the nanorods, the rearrangement of the end face atoms, and the fusion of the lateral faces and, thereby, increase the oxygen defects and the photoluminescence intensity.     

Recent progress in the determination of solid surface tensions from contact angles

Advancing contact angles of different liquids measured on the same solid surface fall very close to a smooth curve when plotted as a function of liquid surface tension, i.e., gamma(lv)costheta versus gamma(lv). Changing the solid surface, and hence gamma(sv), shifts the curve in a regular manner. These patterns suggest that gamma(lv)costheta depends only on gamma(lv) and gamma(sv). Thus, an "equation of state for the interfacial tensions" was developed to facilitate the determination of solid surface tensions from contact angles in conjunction with Young's equation. However, a close examination of the smooth curves showed that contact angles typically show a scatter of 1-3 degrees around the curves. The existence of the deviations introduces an element of uncertainty in the determination of solid surface tensions. Establishing that (i) contact angles are exclusively a material property of the coating polymer and do not depend on experimental procedures and that (ii) contact angle measurements with a sophisticated methodology, axisymmetric drop shape analysis (ADSA), are highly reproducible guarantees that the deviations are not experimental errors and must have physical causes. The contact angles of a large number of liquids on the films of four different fluoropolymers were studied to identify the causes of the deviations. Specific molecular interactions at solid-vapor and/or solid-liquid interfaces account for the minor contact angle deviations. Such interactions take place in different ways. Adsorption of vapor of the test liquid onto the solid surface is apparently the only process that influences the solid-vapor interfacial tension (gamma(sv)). The molecular interactions taking place at the solid-liquid interface are more diverse and complicated. Parallel alignment of liquid molecules at the solid surface, reorganization of liquid molecules at the solid-liquid interface, change in the configuration of polymer chains due to contact with certain probe liquids, and intermolecular interactions between solid and liquid molecules cause the solid-liquid interfacial (gamma(sl)) tension to be different from that predicted by the equation of state, i.e., gamma(sl) is not a precise function of gamma(lv) and gamma(sv). In other words, the experimental contact angles deviate from the "ideal" contact angle pattern. Specific criteria are proposed to identify probe liquids which eliminate specific molecular interactions. Octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS) are shown to meet those criteria, and therefore are the most suitable liquids to characterize surface tensions of low energy fluoropolymer films with an accuracy of +/-0.2 mJ/m2.     

Preparation and characteristics of nanostructured lipid carriers for control-releasing progesterone by melt-emulsification

Nanostructured lipid carriers (NLC) made from mixtures of solid and spatially incompatible liquid lipids were prepared by melt-emulsification. Their drug loading capacity and releasing properties of progesterone were compared with those of solid lipid nanoparticles (SLN), and the NLC prepared by solvent diffusion method. Monostearin (MS) and stearic acid (SA) were used as solid lipid, whilst the oleic acid (OA) was used as liquid lipid. Properties of carriers such as the particle size and its distribution, drug loading, drug encapsulation efficiency and drug release behavior were investigated. As a result, the drug encapsulation efficiencies were improved by adding the liquid lipid into the solid lipid of nanoparticles. The drug release behavior could be adjusted by the addition of liquid lipid, and the NLC with higher OA content showed the faster rate of drug releasing. NLC had higher efficiency of encapsulation and slower rate of drug release than those of NLC prepared by solvent diffusion method. On the other hand, the NLC with higher drug loading was obtained, though the drug encapsulation efficiency was decreased slightly due to the increase of the amount of drug. The NLC modified with polyethylene glycol (PEG) was also prepared by using polyethylene glycol monostearate (PEG-SA). It was observed that the incorporation of PEG-SA reduced the drug encapsulation efficiency, but increased the rate of drug release. A sample with almost complete drug release in 24 h was obtained by modifying with 1.30 mol% PEG-SA. It indicated that the modified NLC was a potential drug delivery system for oral administration.     

Determination of the fatty acid composition of saponified vegetable oils using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A method using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) for the determination of the fatty acid composition of vegetable oils is described and illustrated with the analysis of palm kernel oil, palm oil, olive oil, canola oil, soybean oil, vernonia oil, and castor oil. Solutions of the saponified oils, mixed with the matrix, meso-tetrakis(pentafluorophenyl)porphyrin, provided reproducible MALDI-TOF spectra in which the ions were dominated by sodiated sodium carboxylates [RCOONa + Na]+. Thus, palm kernel oil was found to contain capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid. Palm oil had a fatty acid profile including palmitic, linoleic, oleic, and stearic. The relative percentages of the fatty acids in olive oil were palmitoleic (1.2 +/- 0.5), palmitic (10.9 +/- 0.8), linoleic (0.6 +/- 0.1), linoleic (16.5 +/- 0.8), and oleic (70.5 +/- 1.2). For soybean oil, the relative percentages were: palmitoleic (0.4 +/- 0.4), palmitic (6.0 +/- 1.3), linolenic (14.5 +/- 1.8), linoleic (50.1 +/- 4.0), oleic (26.1 +/- 1.2), and stearic (2.2 +/- 0.7). This method was also applied to the analysis of two commercial soap formulations. The first soap gave a fatty acid profile that included: lauric (19.4% +/- 0.8), myristic (9.6% +/- 0.5), palmitoleic (1.9% +/- 0.3), palmitic (16.3% +/- 0.9), linoleic (5.6% +/- 0.4), oleic (37.1% +/- 0.8), and stearic (10.1% +/- 0.7) and that of the second soap was: lauric (9.3% +/- 0.3), myristic (3.8% +/- 0.5), palmitoleic (3.1% +/- 0.8), palmitic (19.4% +/- 0.8), linoleic (4.9% +/- 0.7), oleic (49.5% +/- 1.1), and stearic (10.0% +/- 0.9). The MALDI-TOFMS method described in this communication is simpler and less time-consuming than the established transesterification method that is coupled with analysis by gas chromatography/mass spectrometry (GC/MS). The new method could be used routinely to determine the qualitative fatty acid composition of vegetable oils, and, when fully validated by comparison with standard analytical methodologies, should provide a relatively fast quantitative measurement of fatty acid mixtures and/or soap formulations that contain saturated and unsaturated hydrocarbon moieties.     

Liquid–liquid extraction of thorium(IV) by fatty acids: a comparative study

In this paper, extractants that have the potential to be sustainably regenerated, are proposed for thorium(IV) removal from nitrate aqueous phases. These extractants are oleic (OA), palmitic (PA) and lauric (LA) acids. The advantages of using these acids are their sustainability, their biocompatibility and their non-toxicity, this makes these simpler and greener compared to other extractants (organophosphorus, azote derivatives, macrocyclic crown, etc…) used for metal extraction. These acids were applied as chelating agent for Th(IV) liquid–liquid extraction. The extractions were carried out in chloroform as an organic phase through the formation of thorium–OA, thorium–PA and thorium–LA complexes. The synergistic extraction of Th(IV) with these extractants in the presence of tributhylphosphine (TBP) has been investigated. The effect of different variables, such as time contact, pH of the aqueous phase, concentration of fatty acid, TBP addition on fatty acids, ionic strength and temperature, is reported. The results showed that the extraction kinetics using LA and OA were fast than with PA. The KNO₃ addition does not seem to highly influence the extraction yield, and no important synergy effect was noticed in the presence of TPB. Thermodynamic data for Th(IV) solvent extraction are also reported in this paper.     

梳型聚合物在固液界面吸附形态的Monte Carlo模拟

采用Monte Carlo模拟方法对PAA/PEO梳型聚合物在固液界面吸附形态进行了模拟,得到了聚合物在液相中聚集形态以及在固液界面上吸附形态的瞬时构型,同时获得了聚合物的吸附层厚度、均方回转半径和吸附在固液界面的各种链段数等微观信息. 结果证实：随着聚合物的接枝数Np增大,聚合物在液相中的扩散系数逐渐降低、相对粘度逐渐增大;当Np≥6时,羧基阴离子基团置于吸附层最外围,吸附层厚度近似等于PEO侧链长度,聚合物在固体表面形成空间排斥为主、静电排斥为辅的吸附状态;吸附聚合物分子密度过低或过高均不能起到良好的空间屏蔽或阻隔效应;吸附在固体粒子表面聚合物应该具有适宜的吸附-脱附自平衡能力.     

Identification of lipid binders in old oil paintings by separation of 4-bromomethyl-7-methoxycoumarin derivatives of fatty acids by liquid chromatography with fluorescence detection

A HPLC-fluorescence method for identification of drying oils from binding media or protective film used in pictorial works of art prior to conservation or restoration is proposed. Fluorescence derivatization of fatty acids released by hydrolysis of structural drying oils is studied. The derivatization reagent was 4-(bromomethyl)-7-methoxycoumarin with 18-crown-6 as catalyst. Mobile phase was programmed from methanol-water (90:10 v/v) to methanol-water (100:0 v/v) in 25 min. The excitation and emission wavelengths were 325 and 395 nm, respectively. Under these chromatographic conditions, coumarin derivatives of myristic, palmitic, oleic and stearic acids were satisfactorily resolved. The method shows good sensitivity, with a detection limit of 6.0 x 10(-8) mmol, and good linearity between 1.0 x 10(-7) and 1.8 x 10(-4) mmol of each analyte. Peak area ratios among fatty acids derivatives, especially the stearic acid/palmitic acid peak area ratio, are useful to identify the drying oils. The proposed method has been successfully applied to artistic samples from items of the cultural heritage of Valencia (Spain).     

Preparation and characteristics of nanostructured lipid carriers for control-releasing progesterone by melt-emulsification

Nanostructured lipid carriers (NLC) made from mixtures of solid and spatially incompatible liquid lipids were prepared by melt-emulsification. Their drug loading capacity and releasing properties of progesterone were compared with those of solid lipid nanoparticles (SLN), and the NLC prepared by solvent diffusion method. Monostearin (MS) and stearic acid (SA) were used as solid lipid, whilst the oleic acid (OA) was used as liquid lipid. Properties of carriers such as the particle size and its distribution, drug loading, drug encapsulation efficiency and drug release behavior were investigated. As a result, the drug encapsulation efficiencies were improved by adding the liquid lipid into the solid lipid of nanoparticles. The drug release behavior could be adjusted by the addition of liquid lipid, and the NLC with higher OA content showed the faster rate of drug releasing. NLC had higher efficiency of encapsulation and slower rate of drug release than those of NLC prepared by solvent diffusion method. On the other hand, the NLC with higher drug loading was obtained, though the drug encapsulation efficiency was decreased slightly due to the increase of the amount of drug. The NLC modified with polyethylene glycol (PEG) was also prepared by using polyethylene glycol monostearate (PEG-SA). It was observed that the incorporation of PEG-SA reduced the drug encapsulation efficiency, but increased the rate of drug release. A sample with almost complete drug release in 24 h was obtained by modifying with 1.30 mol% PEG-SA. It indicated that the modified NLC was a potential drug delivery system for oral administration.     

Surface tensions in NaCl-water-air systems from MD simulations

Surface tensions for liquid-vapor (lv), solid-liquid (sl), and solid-vapor (sv) interfaces are calculated from molecular dynamics simulations of the NaCl-water-air system. Three distinct calculation techniques based on thermodynamic properties are used to describe the multicomponent mixtures. Simulations of each bulk phase (including a liquid saturated solution) and various interfaces are carried out at both NPT and NVT conditions. The thermodynamic relation for energy difference between interface and bulk phases provides an upper bound to the surface tension, while the energy-integral and test area methods provide direct estimates. At 1 atm and 300 K, the best predictions for surface tensions are sigmasv (NaCl-air) of 114 mN m(-1), sigmasl (NaCl- soln) of 63 mN m(-1), sigmalv (soln-air) of 82 mN m(-1), and sigmalv (water-air) of 66 mN m(-1). The calculated surface tensions from simulations have uncertainties between 5 and 10%, which are higher than measurements for the liquid interfaces and lower than the measurement uncertainty for the solid interfaces. The calculated upper bounds for surface tensions of liquid interfaces compare well with experimental results but provide no improvement over existing measurements. However, the bounding values for solid interfaces lower uncertainty by as much as a factor of 10 as compared to the indirect experimental measurements currently available. The energy-integral and test area methods appear to underestimate the surface tension of water by 10%, which is consistent with previous studies using similar model potentials. The calculated upper bounds of surface tension show a weakly positive correlation with pressure in the 0.1-100 atm range for liquid-solid, liquid-vapor, and solid-vapor interfaces.     

Comparative quantitative fatty acid analysis of triacylglycerols using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and gas chromatography.

Quantitative analyses of fatty acids from five triacylglycerol products, coconut oil, palm kernel oil, palm oil, lard and cocoa butter, were carried out using two analytical methods: matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and gas chromatography (GC), in an effort to validate the application of MALDI-TOFMS in quantitative fatty acid analysis. For the GC analysis, transmethylated products were used, whereas, for the MALDI-TOF analysis, saponified products were used. Under MALDI-TOF conditions, the acids were detected as sodiated sodium carboxylates [RCOONa + Na](+) consistent with the mode of ionization that was previously reported. Thus, the MALDI-TOF mass spectrum of saponified coconut oil showed the presence of sodiated sodium salts of caprylic acid (7.5 +/- 0.67, m/z 189), capric acid (6.9 +/- 0.83, m/z 217), lauric acid (47.8 +/- 0.67, m/z 245), myristic acid (20.4 +/- 0.51, m/z 273), palmitic acid (9.8 +/- 0.47, m/z 301), linoleic acid (0.9 +/- 0.07, m/z 325), oleic acid (4.8 +/- 0.42, m/z 327) and stearic acid (2.0 +/- 0.13, m/z 329). Saponified palm kernel oil had a fatty acid profile that included caprylic acid (3.5 +/- 0.59), capric acid (4.7 +/- 0.82), lauric acid (58.6 +/- 2.3), myristic acid (20.9 +/- 1.5), palmitic acid (7.2 +/- 1.1), oleic acid (3.8 +/- 0.62) and stearic acid (1.2 +/- 0.15). Saponified palm oil gave myristic acid (0.83 +/- 0.18), palmitic acid (55.8 +/- 1.7), linoleic acid (4.2 +/- 0.51), oleic acid (34.5 +/- 1.5), stearic acid (3.8 +/- 0.26) and arachidic acid (0.80 +/- 0.22). Saponified lard showed the presence of myristic acid (1.5 +/- 0.24), palmitic acid (28.9 +/- 1.3), linoleic acid (13.7 +/- 0.67), oleic acid (38.7 +/- 1.4), stearic acid (12.8 +/- 0.64) and arachidic acid (2.4 +/- 0.35). Finally, for saponified cocoa butter, the fatty acid distribution was: palmitic acid (32.3 +/- 1.0), linoleic acid (2.6 +/- 0.35), oleic acid (34.9 +/- 1.7) and stearic acid (30.3 +/- 1.6). Quantitative gas chromatographic analysis of the corresponding methyl esters from these triacylglycerol products yielded data that were mostly in agreement with the MALDI-TOFMS data. The MALDI-TOF experiment, however, proved to be superior to the GC experiment, particularly with regard to baseline resolution of unsaturated acids. Furthermore, the ability of MALDI-TOFMS to detect low concentrations of fatty acids rendered it more sensitive than the GC methodology.