Publications by Type: Journal Articles

Mason D, Magdassi S, Sasson Y. Role of a third liquid phase in phase-transfer catalysis. J. Org. Chem.Journal of Organic Chemistry. 1991;56 (26) :7229 - 32.Abstract
The dehydrobromination of PhCH2CH2Br to give styrene under phase-transfer catalytic conditions was sharply accelerated if a 3-liq.-phase system could be engineered. Bu4NBr promoted such a system at >38° and at high concn., the 3rd phase being rich in catalyst. Excessively concd. NaOH (>42%) caused a drop in the reaction rate by nearly 1 order of magnitude, as did a small change in temp. Such effects were due to destabilization of the 3rd phase and pptn. of the catalyst. Neither Pr4NBr nor the tetrapentyl analog showed such behavior. The data were explained by ref. to anomalous phys. and surface chem. properties of Bu4NBr. [on SciFinder(R)]
Sela Y, Magdassi S. Surface activity and formation of liquid crystals of didecyldimethylammonium bromide in presence of ethanol. Tenside, Surfactants, Deterg.Tenside, Surfactants, Detergents. 1991;28 (2) :137 - 8.Abstract
Surface activity and formation of liq. crystals by didecyldimethylammonium bromide (I) in presence of EtOH was studied. The crit. micelle concn. and the area per mol. increased at EtOH concn. >2 M, in which a significant change in solvent properties occurs. I formed lamellar liq. crystals which were destroyed by the added EtOH, at concn. similar to that which prevented the formation of micelles. [on SciFinder(R)]
Magdassi S, Leibler D, Braun S. Adsorption of ovalbumin modified with stearyl groups on hydrophobic silica. LangmuirLangmuir. 1990;6 (2) :376 - 8.Abstract
Ovalbumin was modified to various degrees by acylation of lysine ε-amino groups with stearyl residues. Adsorption isotherms of the modified ovalbumin on hydrophobic silica were obtained. Increase in degree of modification resulted in increased amts. of adsorbed protein. At high modification degree (>40%), practically identical isotherms were obtained. The adsorption data were analyzed by using the Langmuir equation, and it appeared that increase in modification led to decrease in area per adsorbed protein mol., while the adsorption const. remained unchanged. [on SciFinder(R)]
Magdassi S, Neiroukh Z. Chitin particles as o/w emulsion stabilizers. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1990;11 (1) :69 - 74.Abstract
The use of solid chitin particles for stabilization of oil-in-water emulsions was evaluated, and it was shown that the chitin particles could adsorb at the oil-water interface. Stable emulsions of paraffin oil in water were obtained at high concns. of chitin particles (2.5% wt./wt.) when the water phase contained no surfactants. In the presence of only 0.0055% wt./wt. Tween 80, stable emulsions were obtained at 0.5% wt./wt. chitin. From zeta potential measurements, it was concluded that the stabilization of the above emulsion did not result from changes in the elec. properties of emulsion droplets. [on SciFinder(R)]
Sela Y, Magdassi S. Coacervation of didecyl(dimethyl)ammonium bromide in aqueous solutions. Tenside, Surfactants, Deterg.Tenside, Surfactants, Detergents. 1990;27 (3) :179 - 80.Abstract
The coacervation of a dialkyldimethylammonium salt was induced by various electrolytes. The electrolyte concn. in which coacervation was obsd. was in the range of 0.01-0.2M, depending on the electrolyte type. The effectiveness order for coacervation is NaSCN > NaI > NaBr > NaCl > NaF. A correlation between the ionic radii of the anion and the concn. in which coacervation is induced, is suggested. This correlation indicates that the coacervation process depends on the degree of counter ion binding to the cationic surfactant. [on SciFinder(R)]
Levy N, Bar-Or Y, Magdassi S. Flocculation of bentonite particles by a cyanobacterial bioflocculant. Colloids Surf.Colloids and Surfaces. 1990;48 (4) :337 - 49.Abstract
Flocculation of bentonite suspensions by a bioflocculant, produced by the cyanobacterium Phormidium species strain J1, was correlated with the adsorption mechanism of the flocculant on the bentonite particles in the presence of various CaCl2 concns. The optimum flocculant concn. decreased with an increase in CaCl2 concn., and the adsorption increased with an increase in CaCl2 concn. Langmuir-type isotherms are obtained and yield ΔG°ads. = - 12 kcal mol-1 at any CaCl2 concn., while max. adsorption increases with increasing CaCl2 concn. Measurements of electrophoretic mobility and Ca2+ uptake by the particles and the flocculant indicate that the role of CaCl2 is to increase the amt. of adsorbed flocculant at any given flocculant concn., thus shifting the optimal flocculant concn. toward lower values. [on SciFinder(R)]
Magdassi S, Siman-Tov A. Formation and stabilization of perfluorocarbon emulsions. Int. J. Pharm.International Journal of Pharmaceutics. 1990;59 (1) :69 - 72.Abstract
The formation and stabilization of perfluorocarbon emulsions with pluronic F-68 and soya lecithin were investigated. Greater ease of formation and stability were achieved with the soya lecithin. In general, smaller droplet size was obtained with the emulsions prepd. with lecithin, at all dispersed phase fractions. Zeta potential measurements indicated that the emulsions are stabilized via an electrostatic mechanism; the zeta potential increased with increasing lecithin concn., up to a const. high value, and decreased with increasing dispersed phase fraction. [on SciFinder(R)]
Magdassi S, Frank SG. Formation of oil in glycerol/water emulsions: effect of surfactant ethylene oxide content. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1990;11 (5) :519 - 28.Abstract
Oil-in-glycerol/water emulsions at various ratios of water to glycerol in the external phase were prepd. with polyoxyethylated octylphenols and light mineral oil. As the water concn. in the external phase decreased, oil droplet size decreased down to a min. size beyond which oil sepn. occurred. Also, the cloud points of various surfactants were depressed toward room temp. as the water content of the glycerol/water mixt. decreased. The concn. of water needed for formation of the smallest droplets was correlated to the concn. of water needed for depression of the cloud point of each surfactant to room temp. [on SciFinder(R)]
Mason D, Magdassi S, Sasson Y. Interfacial activity of quaternary salts as a guide to catalytic performance in phase-transfer catalysis. J. Org. Chem.Journal of Organic Chemistry. 1990;55 (9) :2714 - 17.Abstract
The phase transfer catalyzed ethylation of deoxybenzoin has been studied in several solvents, using sym. quaternary ammonium bromides as catalysts. In all cases the reactivity passed through a max. as the size of the catalyst increased. The catalysts also reduce the interfacial tension between the phases; this effect also passing through a max. as a function of catalyst size. A correlation was obsd. between the two parameters, such that those catalysts reducing interfacial tension most markedly were also the best catalysts. Therefore, interfacial tension can be a guide to catalytic activity in certain PTC systems. [on SciFinder(R)]
Vecht-Lifshitz SE, Magdassi S, Braun S. Pellet formation and cellular aggregation in Streptomyces tendae. Biotechnol. Bioeng.Biotechnology and Bioengineering. 1990;35 (9) :890 - 6.Abstract
In submerged cultures, S. tendae tended to form fluffy spherical pellets of the noncoagulative type. An increase in the av. pellet size could be attained by decreasing any of the following: shear rate, pH, temp., or inoculum size. Conditions leading to O2 limitation tended to reduce the av. pellet size and induced pulpy growth, whereas O2 sufficiency seemed to induce pellet formation. Factors inducing pellet formation simultaneously increased cell wall hydrophobicity. It is therefore proposed that the main forces inducing cellular aggregation in S. tendae are hydrophobic interactions of cell walls, and these interactions are controlled by availability of dissolved O2. [on SciFinder(R)]
Magdassi S, Shani A. Surface activity of quaternary ammonium salts derived from jojoba oil. J. Am. Oil Chem. Soc.Journal of the American Oil Chemists' Society. 1990;67 (9) :605 - 6.Abstract
Cis and trans quaternary ammonium salts synthesized from jojoba oil were surface active agents, reducing surface tension to ∼35 dynes/cm at very low concns. The relationship between surface activity and mol. structure is discussed. [on SciFinder(R)]
Rozenblat J, Magdassi S, Garti N. Effect of electrolytes, stirring and surfactants in the coacervation and microencapsulation processes in presence of gelatin. J. MicroencapsulationJournal of Microencapsulation. 1989;6 (4) :515 - 26.Abstract
The parameters affecting simple coacervation and the ability to encapsulate oleic acid using this technique were investigated. Coacervation was achieved using different types of gelatin (bloom no., charge) and various electrolytes. The electrolytes used for the coacervation can be divided into 3 groups: (1) inert salts; (2) phase sepn. inducers, (a) pptn. inducing agents (PIA), and (b) coacervation inducing agents (CIA); and (3) coacervation inhibiting agents. The encapsulation of oleic acid was evaluated with two types of gelatin and various emulsifiers (anionic, cationic, and nonionic). For pos. charged gelatin, the encapsulation is incomplete in presence of cationic emulsifiers. For neg. charged gelatin no general trend was obsd. The stirring rate for each step of the prepn. of the microcapsules was evaluated. High stirring is essential only in the cooling stage. The study was carried out in view of encapsulation of particular bacteria dispersed in the oil phase. [on SciFinder(R)]
Vecht-Lifshitz SE, Magdassi S, Braun S. Effects of surface active agents on pellet formation in submerged fermentations of Streptomyces tendae. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1989;10 (3) :265 - 75.Abstract
The effects of surface active agents on pellet formation in the filamentous bacterium Streptomyces tendae were investigated. Addn. of Pluronic F68 or Brij 58 at inoculation to the fermn. medium (up to 0.1% wt./wt.) induced cellular aggregation. Below this concn., the av. pellet size increased with increasing surfactant concn. Above this point inhibition of pellet formation was obsd. Both surfactants caused aggregation of dispersed mycelia when added after fermn. [on SciFinder(R)]
Magdassi S, Stawsky A. Emulsification by chemically modified ovalbumin. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1989;10 (3) :213 - 18.Abstract
Enhancement of emulsifying properties of a model protein, ovalbumin, was achieved by covalent attachment of hydrophobic groups using various esters of N-hydroxysuccinimide. The resulting modified proteins were much better emulsifiers than the native ovalbumin, even at low modification degree (20-30% of available amine groups): in tetradecane-water emulsions oil sepn. was obsd. within a few hours, when 0.7 mg/mL native ovalbumin was used, compared to ∼1 mo. until sepn. was obsd. when the modified proteins were used . The use of highly modified proteins prevented completely oil sepn. (≥2 mo.); for example, emulsions prepd. with 81% modified proteins with C8 or C6, showed no change in droplet size distribution even 50 days after prepn. The effect of chain length on emulsification was also investigated: an optimal chain length (C8) was found, for both low and high modifications. [on SciFinder(R)]
Magdassi S. Formation of oil-in-polyethylene glycol/water emulsions. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1988;9 (4) :391 - 9.Abstract
Oil-in-polyethylene glycol (PEG)/water emulsions were prepd. by using various PEG and various ratios of water to PEG. For all PEG studied, droplet size decreased with decreasing water concn., until a fast phase sepn. was obsd. The water concn. at which the phase sepn. occurs depends on the mol. wt. of the PEG. At const. water concns. in the external phase, the finest droplets were obtained with the high mol. wt. PEG. The effect of PEG concn. and mol. wt. on the cloud point of the surfactant, Tween 80, was studied. The redn. of cloud points, and hence the apparent HLB is correlated with droplet size, and phase sepn. in the emulsions. [on SciFinder(R)]
Magdassi S, Frank SG. Formation of oil-in-glycerol/water emulsions. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1986;7 (5) :599 - 612.Abstract
Oil-in-glycerol/water emulsions at various ratios of H2O to glycerol in the external phase were prepd. with Tween 80 and either light mineral oil or soybean oil. A min. in the droplet size was obsd. at ∼15 wt.% H2O in the external phase of the emulsions. At the same H2O concn., a clouding of the surfactant occurs at room temp. and the surface and interfacial tensions are minimal. It appears, therefore, that the min. droplet size of the emulsions is related to the clouding phenomenon, as a result of changes in the properties of the solvent and the surfactant. [on SciFinder(R)]
Magdassi S, Garti N. Formation of water/oil/water multiple emulsions with solid oil phase. J. Colloid Interface Sci.Journal of Colloid and Interface Science. 1986;120 (2) :537 - 9.Abstract
Two multiple emulsions, one with liq. oil and one with solid oil (paraffin wax), were prepd. Diln. of the emulsion in an electrolyte soln. (0.9% (wt./wt.) NaCl) caused a decrease in droplet size within 15 min only in the emulsion which contained the liq. oil phase, while the particle sizes of the solid multiple emulsion/dispersion remained const., confirming the existence of stable rigid oil membrane. [on SciFinder(R)]
Magdassi S, Garti N. A kinetic model for release of electrolytes from W/O/W multiple emulsions. J. Controlled ReleaseJournal of Controlled Release. 1986;3 (4) :273 - 7.Abstract
The release of electrolytes from water-oil-water (W/O/W) emulsions was studied. A significant difference was obsd. in the release of NaCl and org. ion (ephedrine-HCl [50-98-6]). The rate of release decreased with the increase of the initial concn. of the electrolyte. A kinetic model which is similar to the model for release of dispersed drugs from a polymeric matrix was suitable for the release of electrolytes from multiple emulsions. [on SciFinder(R)]
Magdassi S, Frank SG. Nonaqueous ternary systems. I: Polyethylene glycol-mineral oil and ethoxylated sorbitan monooleate. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1986;7 (3) :345 - 61.Abstract
The surface and interfacial properties of a nonionic emulsifier (Tween 80) were studied in polyethylene glycol/air and polyethylene glycol/oil systems. Micelles formed and the CMC, area per surfactant mol., and free energy of adsorption of surfactant to the interface increased as functions of ethylene oxide content of the solvent mols. These changes in the surface and interfacial properties of the surfactant are apparently a result of surfactant-solvent interactions, due to H bonding. A series of oil-in-solvent emulsions was prepd. also, and the stabilities and particle size of the emulsions were mainly dependent on the adsorption energy of the surfactant. [on SciFinder(R)]
Garti N, Magdassi S, Whitehill D. Transfer phenomena across the oil phase in water-oil-water multiple emulsions evaluated by Coulter counter. 1. Effect of primary emulsifier on water permeability. J. Colloid Interface Sci.Journal of Colloid and Interface Science. 1985;104 (2) :587 - 91.Abstract
The effect of primary emulsifier concn. (Span 80) in a system contg. Tween 80, mineral oil, and H2O on H2O transport due to an osmotic gradient was studied by a Coulter counter method. Diln. of W/O/W emulsions with dil. NaCl caused a decrease in multiple drop diam. due to loss of internal H2O. The primary mechanism appears to be micelle transport. [on SciFinder(R)]