Preparation of a stable double emulsion (W1/O/W2): role of the interfacial films on the stability of the system

This paper presents new protocols enabling preparation of W1/O/W2 double emulsions: one, using soybean oil as the O phase, that yields edible emulsions with industrial applications, and a second that yields emulsions with a previously unattainable concentration 15% (w/w) of surfactants in the external phase (the 15% target was chosen to meet the typical industry standard). Preparation of a stable W1/O emulsion was found to be critical for the stability of the system as a whole. Of the various low HLB primary surfactants tested, only cethyl dimethicone copolyol (Abil EM90), A-B-A block copolymer (Arlacel P135), and polyglycerol ester of ricinoleic acid (Grinstead PGR-90) yielded a stable W/O emulsion. Investigation of the surface properties of those surfactants using the monolayer technique found two significant similarities: (1) stable, compressible, and reversibly expandable monolayers; and (2) high elasticity and surface potential. The high degree of elasticity of the interfacial film between W1 and O makes it highly resilient under stress; its failure to break contributes to the stability of the emulsion. The high surface potential values observed suggest that the surfactant molecules lie flat at the O/W interfaces. In particular, in the case of PGR-90, the hydroxyl (-OH) groups on the fatty acid chains serve as anchors at the O/W interfaces and are responsible for the high surface potential. The long-term stability of the double emulsion requires a balance between the Laplace and osmotic pressures (between W1 droplets in O and between W1 droplets and the external aqueous phase W2). The presence of a thickener in the outer phase is necessary in order to reach a viscosity ratio (preferably approximately 1) between the W1/O and W2 phases, allowing dispersion of the viscous primary emulsion into the W2 aqueous phase. The thickener, which also serves as a dispersant and consequently prevents phase separation due to its thixotropic properties, must be compatible with the surfactants. Finally, the interactions between the low and high HLB emulsifiers at the O/W2 interface should not destabilize the films. It was observed that such destructive interaction for the system could be prevented by the use of two high HLB surfactants in the outer aqueous phase: an amphoteric surfactant, Betaine, and an anionic surfactant, sodium lauryl ether sulfate. The combination of such pairs of surfactants was found to contribute to the films' stability.     

Preparation and characterization of W/O/W double emulsions containing MgCl2

The aim of present study is to design food-grade W/O/W double emulsions encapsulating Mg²⁺ and investigate their stability and release properties. Prepared emulsions were characterized in terms of global stability, particle size, rheological properties, and interfacial tension. The double emulsions were sensitive to the presence of magnesium salt. The mean droplet size and viscosity of emulsions was positively correlated to MgCl₂ concentration. The microscopic pictures confirmed that the water transfer between two aqueous phases caused the reduced stability of double emulsions. It was suggested that swelling breakdown was the main mechanism in controlling the release of encapsulated Mg²⁺.     

Effects of biopolymer ratio and heat treatment on the complex formation between whey protein isolate and soluble fraction of Persian gum

Proteins and polysaccharides are the two most important natural ingredients with unique functional properties. Their interactions can be considered as a route to produce new materials of various technological applications. In this study, the effect of pH (3–7) as well as the mixing ratio of whey protein isolate (WPI)/soluble part of Persian gum (PG) (1:3, 1:1, 3:1, 6:1, and 9:1% w/w WPI/PG) on the complex formation behavior of the two polymers were studied using spectrophotometric and dynamic light scattering techniques, soluble protein measurement, and microscopic observations. Investigating the curves of turbidity versus pH showed that pHc and pH_?1, which are associated with the formation of soluble and insoluble complexes, moved toward higher pH values by increasing WPI:PG ratio. Increased solubility was observed at pHc?>?pH?>?pH_?1 for all biopolymers mixtures. In addition, lowering the pH toward pH_?1 resulted in a decrease in the size of complexes, while further decrease of pH beyond this point led to larger particles. No significant difference was noticed between pH_c and pH_?1 of heated and unheated WPI/PG mixtures, although the turbidity of heated samples increased due to the formation of larger aggregates.     

The effect of an anionic surfactant on the rheology and stability of high volume fraction O/W emulsion stabilized by PVA

The effect of the addition of an anionic surfactant (sodium dodecyl benzene sulphonate) on the rheology and storage stability of concentrated O/W emulsions stabilized by poly (vinyl alcohol) is reported. It was found that the surfactant markedly reduced the magnitudes of the storage modulii of the emulsions. This could be attributed to a reduction in the interfacial tension resulting from the formation of polyelectrolyte type complexes between the PVA and NaDBS at the O/W interface. The results were compared to the equation (given by Princen) relating concentrated emulsion rheology to the interfacial tension and droplet size. Reasonable agreement was found, though there was a small difference in the constants in the equation given by Princen and those found here. The agreement suggested that the emulsions were deforming above a critical volume fraction and that the rheological properties were dominated by the dilation of the interface during shear. Microelectrophoresis measurements showed that the addition of the surfactant conferred a charge onto the PVA stabilized droplets as a result of the formation of the polyelectrolyte complex. The NaDBS was found to reduce the long-term stability of the emulsions compared to emulsions containing PVA alone.     

Highly enantioselective hydrogenation of exocyclic double bond of N-tosyloxazolidinones catalyzed by a neutral rhodium complex and its synthetic applications

A highly enantioselective synthesis of optically active N-tosyl-4-alkyl-1,3-oxazolidin-2-ones based on the asymmetric hydrogenation of the trisubstituted exocyclic double bond of N-tosyl-4-alkylidene-1,3-oxazolidin-2-ones under the catalysis of neutral [Rh(COD)Cl]₂ (COD=1,5-cyclooctadiene) and (S)-(+)-DTBM-SEGPHOS was developed. The utility of this highly enantioselective reaction was exemplified by the synthesis of optically active amino acids, amino alcohols, and piperidine derivatives.     

Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by silicon dioxide/Zn?CoIII double metal cyanide complex hybrid catalysts with a nanolamellar structure

Air‐stable hybrid catalysts of silicon dioxide/double metal cyanide complexes (Si‐DMCCs) based on Zn₃[Co(CN)₆]₂ (ZHCC) were prepared by an in situ sol–gel method. The Si‐DMCCs showed low crystallinity and a nanolamellar structure with a thickness of ～40–60 nm. In particular, a lamellar structure of regular hexagonal shape was observed for Si‐DMCCs with low SiO₂ content. These catalysts had very high catalytic activity for alternating copolymerization of cyclohexene oxide (CHO) and carbon dioxide. A turnover number of 11,444, turnover frequency of 3815 h^?1, and apparent efficiency of 7.5 kg polymer/g ZHCC (～24.0 kg polymer/g Zn) were achieved at 3.8 MPa and 100 °C. The poly(cyclohexenylene carbonate) (PCHC) polymers obtained were completely atactic with a molecular weight (M_n) of ～10 kg/mol and polydispersity of 2.0–3.0. The PCHCs had a structure of nearly alternating CHO and CO₂ units, with a molar fraction of carbonate units of 0.44–0.47. Preliminary investigations of the mechanism suggest that nucleophilic attack by neighboring oxygen atoms is involved in copolymerization initiation with Zn? Co^III DMCCs. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3128–3139, 2008     

Electrocatalytic reduction of O2 at pyrolytic graphite electrode modified by a novel copper(II) complex with 2-[bis(2-aminoethyl)amino]ethanol and imidazole ligands

A new complex formed by Cu(II) with 2-[bis(2-aminoethyl)amino]ethanol and imidazole is prepared, and its electrochemical properties are studied. The electrochemical experiments are carried out in deaerated pH 7.0 buffer solution through cyclic voltammetry by scanning the potential from 0.1 to −0.5 V with this copper(II) complex-modified electrode as the working electrode. One redox process is observed, which could be assigned to Cu(II)/Cu(I). The formal potential E _0′ = (E _pa + E _pc)/2, where E _pa and E _pc are anodic and cathodic peak potentials, is −248 mV vs. SCE. A straight line, obtained from the plot of I _pc vs. v, indicated a surface-controlled reaction. The modified electrode is very stable and exhibits catalytic activity for oxygen reduction. The possible mechanism for the catalytic reduction of oxygen is studied by cyclic voltammetry and chronoamperometry. The results show that the dioxygen is reduced via a pathway of four-electron reduction to form water. Chronoamperometric measurements show the potentiality of the use of this working electrode as an amperometric sensor for dissolved dioxygen in aqueous media. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 8, pp. 975–979. The text was submitted by the authors in English.     

Proteomic analysis of cellular soluble proteins from human bronchial smooth muscle cells by combining nondenaturing micro 2DE and quantitative LC‐MS/MS. 2. Similarity search between protein maps for the analysis of protein complexes

Human bronchial smooth muscle cell soluble proteins were analyzed by a combined method of nondenaturing micro 2DE, grid gel‐cutting, and quantitative LC‐MS/MS and a native protein map was prepared for each of the identified 4323 proteins [1]. A method to evaluate the degree of similarity between the protein maps was developed since we expected the proteins comprising a protein complex would be separated together under nondenaturing conditions. The following procedure was employed using Excel macros; (i) maps that have three or more squares with protein quantity data were selected (2328 maps), (ii) within each map, the quantity values of the squares were normalized setting the highest value to be 1.0, (iii) in comparing a map with another map, the smaller normalized quantity in two corresponding squares was taken and summed throughout the map to give an “overlap score,” (iv) each map was compared against all the 2328 maps and the largest overlap score, obtained when a map was compared with itself, was set to be 1.0 thus providing 2328 “overlap factors,” (v) step (iv) was repeated for all maps providing 2328 × 2328 matrix of overlap factors. From the matrix, protein pairs that showed overlap factors above 0.65 from both protein sides were selected (431 protein pairs). Each protein pair was searched in a database (UniProtKB) on complex formation and 301 protein pairs, which comprise 35 protein complexes, were found to be documented. These results demonstrated that native protein maps and their similarity search would enable simultaneous analysis of multiple protein complexes in cells.