Publications by Type: Journal Articles

Magdassi S, Rodel B-Z. Flocculation of montmorillonite dispersions based on surfactant-polymer interactions. Colloids Surf., AColloids and Surfaces, A: Physicochemical and Engineering Aspects. 1996;119 (1) :51 - 56.Abstract
A two-step flocculation process is described in which a polycation (polydiallyldimethylammonium chloride) is adsorbed on to neg. charged montmorillonite particles, followed by the addn. of an anionic surfactant [sodium dodecyl sulfate (SDS)]. At a 1:1 molar ratio, optimal flocculation is obtained owing to the formation of an insol. surfactant-polymer complex in the presence of the particles. The pptn. of the insol. complex is also dependent on the SDS and polymer concns., and occurs at a 1:1 SDS:monomer molar ratio. From adsorption isotherms of the polymer-particle and surfactant-polymer systems, the adsorption energy was calcd. and subsequently a flocculation mechanism is suggested. [on SciFinder(R)]
Kamyshny A, Reuveni T, Magdassi S. Formation and properties of horseradish peroxidase colloidal clusters. J. Colloid Interface Sci.Journal of Colloid and Interface Science. 1996;181 (2) :470 - 475.Abstract
Hydrophobic modification of horseradish peroxidase by fatty acid esters (C8, C12, C16, C18) of N-hydroxysuccinimide was carried out. The degree of modification increases with an increase in the ester:enzyme molar ratio and reaches a maximal value of four modified amino groups when this ratio is 150:1. Covalent attachment of hydrophobic groups to the peroxidase mols. leads to a spontaneous formation of micelle-like colloidal clusters, which have a mean diam. of 65 nm at the maximal degree of modification by C16-ester. The fraction of the enzyme mols. which forms clusters depends on both the length of the attached hydrophobic chain and the degree of modification. The colloidal clusters, which are composed of the modified peroxidase, have about 80 and 50% lower enzymic activities for C12- and C16- modified enzymes. [on SciFinder(R)]
Magdassi S, Vinetsky Y, Relkin P. Formation and structural heat-stability of β-lactoglobulin/surfactant complexes. Colloids Surf., BColloids and Surfaces, B: Biointerfaces. 1996;6 (6) :353 - 362.Abstract
The binding of two model surfactants, SDS and dodecyltrimethylammonium bromide to β-lactoglobulin was studied at room temp. and the thermal stability of the resulting complexes was evaluated by differential scanning calorimetry (DSC) measurements. Binding isotherms indicated both ionic and hydrophobic interactions depending on both the charge of the protein and surfactant at different pHs and on the binding molar ratios of surfactant to the globular protein. Zeta potential measurements indicated charge neutralization of the protein, under suitable conditions, which also lead to aggregation and pptn. of the proteins. Surface tension measurements indicated similarity between the two types of oppositely charged protein-surfactant complexes and a difference between them when protein and surfactants are similarly charged. DSC measurements revealed different behavior in protein conformation in the presence of the two surfactants. The results obtained at room temp. and upon heating are discussed in terms of the nature of the surfactant/protein interactions involved in the complex formation. [on SciFinder(R)]
Magdassi S, Vinetsky Y. Microencapsulation of oil-in-water emulsions by proteins. Drugs Pharm. Sci.Drugs and the Pharmaceutical Sciences. 1996;73 (Microencapsulation) :21 - 33.Abstract
A review with 33 refs. Methods of encapsulation, surface activity of proteins, and possible film-forming proteins in drug delivery are discussed. [on SciFinder(R)]
Cohen S, Magdassi S. Chemiluminescence in Microemulsions: Effect of Phase Composition. LangmuirLangmuir. 1996;12 (16) :3759 - 3762.Abstract
Chemiluminescence (CL) reactions were studied in a model system based on a phase diagram which was composed of Triton X-100, 2-butanol, toluene, and H2O. The CL reaction was achieved by using trichlorophenyl oxalate, H2O2, and perylene as the fluorophore. The intensity of light (I0) and t1/2 depend on both reactant concns. and phase compn. The CL reaction was conducted in W/O microemulsions, and an inverse relation between I0 and t1/2 was found. These two parameters could also indicate the transition from a W/O (water-in-oil) emulsion to a W/O microemulsion. The effect of medium polarity was evaluated by fluorescence, absorbance, and chemiluminescence spectra. [on SciFinder(R)]
Ma'or Z, Magdassi S, Efron D, Yehuda S. Dead Sea mineral-based cosmetics--facts and illusions. Isr J Med SciIsrael journal of medical sciences. 1996;32 Suppl :S28-35.Abstract
Modern Dead Sea cosmetics have developed in order to meet the demands of new regulations, technical opportunities, and today's consumer expectations for higher quality standards and proven performance. As an example of the application of this approach, the authors describe the development of a new cosmetic formulation, based on "Osmoter", a special Dead Sea mineral composition, and the evaluation of this formulation's effect on the depth of skin wrinkles, by a controlled assay. Possible mode of action is discussed.[on SciFinder (R)]
Magdassi S, Toledano O, Zakay-Rhones Z. Formation of novel colloidal immunoclusters by surface active antibodies. J. Colloid Interface Sci.Journal of Colloid and Interface Science. 1995;175 (2) :435 - 9.Abstract
Surface active antibodies were formed by covalent attachment of hydrophobic groups to IgG mols. The modification was carried out at various degrees of attachment and various chain lengths. These modified antibodies spontaneously formed new colloidal micelle-like particles, immunoclusters, which were viewed with a transmission electron microscope and evaluated by light scattering. The size of the immunoclusters increased while either degree of attachment or chain-length were increased, and the biol. activity decreased with an increase of degree of modification. [on SciFinder(R)]
Magdassi S, Vinetsky Y. Microencapsulation of O/W emulsions by formation of a protein-surfactant insoluble complex. J. MicroencapsulationJournal of Microencapsulation. 1995;12 (5) :537 - 45.Abstract
A method for obtaining microcapsules of oil droplets by the formation of an insol. complex of protein-surfactant is described. The gelatin type A studied, which is pos. charged at the pH range studied, may form insol. and sol. complexes with sodium dodecyl sulfate (SDS), an anionic surfactant. The binding isotherms were studied and the specific molar ratios of SDS to gelatin, in which the insol. complex is formed, was detd. These specific ratios also led to the formation of microcapsules, in which the wall encapsulating the oil droplets, is composed of the insol. gelatin SDS complex. [on SciFinder(R)]
Levy N, Garti N, Magdassi S. Flocculation of bentonite suspensions with cationic guar. Colloids Surf., AColloids and Surfaces, A: Physicochemical and Engineering Aspects. 1995;97 (2) :91 - 9.Abstract
Cationic guar gums of varying molar mass and charge d. were synthesized and tested as flocculants for bentonite suspensions. The gums were fragmented using ammonium persulfate as a degrading agent, followed by pptn. of the products with ethanol. Cationic charge was added to the guar mol. by reacting it with 2,3-epoxypropyltrimethylammonium chloride. Flocculant performance was assessed by detg. the extent of polymer adsorption, by measuring both residual turbidities of the resulting supernatants and the changes in the particles' electrophoretic mobility (EM). Increasing the flocculant charge d. causes the optimal flocculation concn. (OFC), as well as the efficient flocculant concn. range, to be reduced. Above this range restabilization occurs. The OFC (for highly modified guar) is also the concn. at which the particles' EM is zero. It was found that decreasing the mol. wt. of the guar (at the same charge d.) increases the OFC and decreases the electrophoretic mobility of the clay particles in the overdose range. [on SciFinder(R)]
Sela Y, Magdassi S, Garti N. Newly designed polysiloxane-graft-poly (oxyethylene) copolymeric surfactants: preparation, surface activity and emulsification properties. Colloid Polym. Sci.Colloid and Polymer Science. 1994;272 (6) :684 - 91.Abstract
Two sets of comb-grafted polymeric surfactants based on poly(methylhydrogen siloxane) (PHMS) and/or poly(dimethylsiloxane) (PHMS-PDMS) were prepd. by silylation of the active Si-H group with an active ω-vinyl group of specially designed undecenoic-polyethylene glycol esters (UPEG) to formation "newly-designed" polysiloxane-grafted-polyethylene glycol comb-copolymeric surfactants. The hydrophilic moieties are hooked to the hydrophobic backbone through a "spacer" (undecenoic acid). The variation in the surfactants' structures were in the length and d. of the grafted hydrophilic moieties, the chain length (DP) and nature of the hydrophobic backbone. The first 12 different polymeric surfactants (set 1), termed PHMS-UPEG, were ineffective emulsifiers with limited ability to stabilize oil-in-water emulsions. The second set of surfactants, named PHMS-PDMS-UPEG comb-grafted copolymers, significantly reduced the oil-water interfacial tension and efficiently stabilized several types of oil-in-water emulsions. The best emulsifier of this set (PHMS-PDMS-52-UPEG-45), seems to be one whose anchor backbone (PHMS-PDMS) dissolves (rather than spreads) in the oil phase, and whose stabilizing moieties are sufficiently long (45 EO units) and "hooked" to the silicone backbone at high d. (52% substitution). [on SciFinder(R)]
Sela Y, Magdassi S, Garti N. Polymeric surfactants based on polysiloxanes-graft-poly(oxyethylene) for stabilization of multiple emulsions. Colloids Surf., AColloids and Surfaces, A: Physicochemical and Engineering Aspects. 1994;83 (2) :143 - 50.Abstract
Attempts have been made to produce and use new polymeric surfactants based on polysiloxane-graft-poly(oxyethylene) for stabilization of water-in-oil-in-water (W/O/W) multiple emulsions. Hydrophobic comb-grafted copolymers have been used at the inner interface to obtain stable small droplet size water-in-oil emulsions. Hydrophilic comb-grafted copolymers with similar structures but with high d. grafting and long poly(oxyethylene) chains have been used to stabilize the outer interface of the W/O/W emulsion. Stable multiple emulsion formulations with very slow release rates can be obtained when using the two types of silicone emulsifier. [on SciFinder(R)]
Magdassi S. Interactions between proteins and fluorocarbon emulsions. Abstracts of papers of the American chemical society. 1993;205 :21-COLL.
Goldstein B, Magdassi S, Rokem JS. Surface Angle bacterial Colony is Directly Correlated to Hydrophobicity of Bacterium. Microbioss. 1993;75 :181-184.
Sela Y, Garti N, Magdassi S. Surface activity and emulsification properties of new polyethylene glycol-based nonionic surfactants. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1993;14 (2) :237 - 47.Abstract
New ethoxylated monofatty acid esters are obtained by esterification of 10-undecenoic acid chloride with several well defined polyethylene glycol mono-Me ethers. The monomeric surfactants show interesting surface properties, and they are characterized and compared to other known ethoxylated alcs. (Brijs) and acids (Mirjs). The crit. micelle concn. and area per mol. at the air-water interface are much higher than the similar com. Brijs, due to the special structure of the new surfactant allowing preferred orientation at the interface. [on SciFinder(R)]
Magdassi S, Royz M, Shoshan S. Interactions between collagen and perfluorocarbon emulsions. Int. J. Pharm.International Journal of Pharmaceutics. 1992;88 (1-3) :171 - 6.Abstract
The interactions between perfluorocarbon emulsion and both dissolved collagen and suspensions of collagen fibrils were studied in a new formulation suggested for enhancement of wound healing. Since the emulsion droplets are covered with a charged phospholipid monolayer, both elec. and hydrophobic interactions may exist. Electrophoretic mobility measurements which are conducted at various pH values, and light microscopy, revealed that the emulsion droplets were adsorbed onto the collagen fibrils, thus forming a new population of particles. This phenomenon was also obsd. at the pH values of the isoelec. points of collagen or lecithin, indicating possible hydrophobic interactions between collagen and lecithin. From adsorption expts., the area of collagen mol. at the interface was calcd. This suggested formation of an end-on oriented collagen mols. layered at the water-perfluorocarbon/lecithin interface. [on SciFinder(R)]
Levy N, Magdassi S, Bar-Or Y. Physico-chemical aspects in flocculation of bentonite suspensions by a cyanobacterial bioflocculant. Water Res.Water Research. 1992;26 (2) :249 - 54.Abstract
The biopolymer produced by Anabaenopsis circularis strain PCC 6720 was an effective anionic flocculant for bentonite suspensions. The presence of CaCl2 increased the flocculation efficiency significantly. From adsorption isotherms and zeta-potential measurements, it was concluded that the flocculation process is based on the bridging mechanism. The role of CaCl2 is to increase the initial adsorption of the biopolymer on the bentonite particles. It also decreases the neg. elec. charge of the bentonite particles and of the biopolymer mols. The dominant role of the bioflocculant in the flocculation process is discussed according to the theor. interaction energy curves. [on SciFinder(R)]
Giordano JP, Magdassi S, Frank SG, Fruman DH, Zakin JL. Prediction of emulsifiability of viscous crude oils with alkali treatment from interfacial tension measurements. Speculations Sci. Technol.Speculations in Science and Technology. 1992;15 (1) :24 - 9.Abstract
Low-viscosity concd. oil-in-water emulsions were studied in relation to transportation of viscous petroleums to refineries. Of 6 heavy crudes tested, 60% oil-in-water emulsions could be prepd. from 3 of them by treatment with NaOH over a fairly wide alkali/total acid no. range. Relatively unstable emulsions over a narrow range of NaOH addn. could be formed from one crude, and emulsions could not be formed with the other 2 at any alkali level. Interfacial tension measurements of 90% crude in PhMe solns. against 0.01% NaOH solns. gave results below 3.0 × 10-3 N-m-1 for the 3 crudes that could be emulsified, and over 6.8 × 10-3 N-m-1 for the other 3, indicating that such measurements can be used to predict the feasibility of prepg. emulsions by alkali treatment. Measurements at 77% crude in PhMe confirm these findings but the abs. values are generally somewhat higher. [on SciFinder(R)]
Magdassi S, Royz M, Shoshan S. Chemical instability of phospholipids: a key factor in stabilization of perfluorocarbon emulsions. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1991;12 (1) :69 - 82.Abstract
Perfluorocarbon macroemulsions were stabilized by phospholipids which were composed mainly of phosphatidylcholine and phosphatidylethanolamine. Emulsions which were prepd. with a phosphate buffer as the external phase, were more stable than those prepd. with water only, in spite of the very high ionic strength (I = 0.4) in the former. It was found that hydrolysis of the phospholipids caused formation of lysophosphatidylcholine, and a significant decrease in the pH, in absence of the buffer. The decrease in pH led to a decrease in ζ potential, and hence decreased stability. This effect was not significant in the buffer-emulsions. However, oxidn. of the surfactant was detected for both systems, a process which resulted in oil sepn. after prolonged time (>200 days) also in the oil in buffer emulsion. [on SciFinder(R)]
Magdassi S, Middleman S. The effect of drag-reducing additives on the drop-size distribution produced by a turbulent flow field. J. Dispersion Sci. Technol.Journal of Dispersion Science and Technology. 1991;12 (1) :17 - 23.Abstract
The effect is studied of drag-reducing additives (e.g., polyacrylamide) on the drop size and drop-size distribution in turbulent flow of oil-water emulsions. A high-mol.-wt. polymer that is sol. in the continuous phase alters the mean drop size and drop-size distribution. The results can be used in the control of the drop size and drop-size distribution in the emulsion. [on SciFinder(R)]
Magdassi S, Stawski A, Braun S. Interfacial tension reduction by chemically modified ovalbumin. Tenside, Surfactants, Deterg.Tenside, Surfactants, Detergents. 1991;28 (4) :264 - 6.Abstract
Native ovalbumin was chem. modified with various alkyl chain lengths, to several extents of modification. The surface activity which was detd. by interfacial tension redn., increased with the increase in degree of modification for all alkyl chain lengths. Increasing chain length led to a gradual decrease in interfacial tension between water and tetradecane. The most significant increase in surface activity was obsd. either at low degree of modification or at proteins modified with short alkyl chains. [on SciFinder(R)]