Biomedical subjects

S Magdassi

Publications and source records attributed to S Magdassi.

10 recordsLinked to original sources

PubMed1999

Chemically Modified Glucose Oxidase with Enhanced Hydrophobicity: Adsorption at Polystyrene, Silica, and Silica Coated by Lipid Monolayers.

Covalent modification of glucose oxidase from Aspergillus niger by the palmitic acid ester of N-hydroxysuccinimide at a molar ratio ester:protein of 56:1 results in the formation of the enzyme derivative with 11 attached palmitic chains. Surface hydrophobicity measurements by a fluorescent probe, 8-anilino-1-naphthalenesulfonate, indicate a drastic increase in the hydrophobicity index of glucose oxidase after such a modification. The modified glucose oxidase displays a much higher adsorption affinity for hydrophilic (silica) as well as for hydrophobic (silica coated by phosphatidyl choline and cholesterol monolayers and polystyrene latex beads) surfaces, and forms more compact surface layers compared to the native glucose oxidase. Such a difference results from a spontaneous formation of micelle-like aggregates (clusters) of the hydrophobized enzyme molecules (average size 500 nm), which come into contact with a surface. A possible structure of the glucose oxidase surface layers and the nature of the forces determining the adsorption of the enzyme on various adsorbents are discussed. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Chemically Modified Human Immunoglobulin G: Hydrophobicity and Surface Activity at Air/Solution Interface.

Covalent modification of human IgG by fatty acid esters (C8 and C16) of N-hydroxysuccinimide was carried out. Surface hydrophobicity measurements, using the fluorescent probe 8-anilino-1-naphthalenesulfonate, indicate an increase in the surface protein hydrophobicity with an increase in the number and in the length of the attached alkyl chains. The modified IgGs decrease surface tension at the air/solution interface more effectively than the native protein. The values of the molecular cross-sectional areas (DeltaA) estimated from the kinetic data are in the range of 100-300 Å2 and reflect the size of protein segments at the interface during the adsorption process. About 40-50% increase in the DeltaA was observed upon attachment of the C8 groups to the native IgG. The lengthening of the bound alkyl chain from C8 to C16 results in a further increase in this value. The influence of the overall IgG hydrophobicity and the length of the attached alkyl chain on the dimensions of the mobile protein segment at the surface are discussed. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Penetration of Glucose Oxidase and of the Hydrophobically Modified Enzyme into Phospholipid and Cholesterol Monolayers.

The penetrant ability of the native glucose oxidase, GOx, and of the hydrophobically modified enzyme GO(mod) realized by grafting to its lysine residues alkyl C16 chains, into phosphatidylcholine dibehenoyl (DBPC), phosphatidylcholine dipalmitoyl (DPPC), phosphatidyl-ethanolamine dipalmitoyl (DPPE), phosphatidyl-serine dipalmitoyl (DPPS), and cholesterol (CHOL) monolayers was assessed by surface pressure measurements at constant area by enzyme injection to the aqueous phase beneath spread monolayers. As revealed by the magnitude of surface pressure increments (DeltaPi), both the quantities and the rates of penetration of the enzymes into these monolayers were lipid chemical nature and enzyme concentration dependent. When compared with GOx, GO(mod) displayed an enhanced penetrant ability into all the studied monolayers that resulted in rapidly attained DeltaPi plateau values, characteristic of stable systems. The influence of lipid hydrocarbon chain length and of the polar headgroup charge on the efficiency and effectiveness of GOx and GO(mod) penetration into these monolayers is discussed. Copyright 1999 Academic Press.

Journal Article↗

PubMed1997

Formation of Surface Active Gelatin by Covalent Attachment of Hydrophobic Chains

Surface active gelatin was formed by covalent attachment of hydrophobic groups to gelatin molecules. The modification was carried out at various degrees of attachment and with various chain lengths. These modified gelatins (MGs) were synthesized in dry DMSO by a simple and rapid method. The new method leads to high yields and allows high degrees of modification. The MGs, which have various hydrophobicities, have better surface activity than the native gelatin, as determined by surface tension reduction. The surface tension reduction is correlated to the hydrophobicity of the modified molecule, which was determined by a fluorescent probe. It appears that both the increase in the number of the hydrophobic groups and the increase in the chain lengths lead to decreased surface tension. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗

PubMed1997

Adsorption of Hydrophobized Glucose Oxidase at Solution/Air Interface

The modification of glucose oxidase by palmitic acid ester of N -hydroxysuccinimide leads to the formation of a new hydrophobized enzyme with five covalently bound C16 groups. Such a modification was shown not to alter noticeably the native structure of the enzyme. The modified glucose oxidase displays enhanced surface activity at the water/air interface in comparison with the native enzyme. The maximum reduction of surface tension at all concentrations studied was higher for the modified glucose oxidase than for the native one. The modified enzyme also displayed a much steeper rise of the surface potential with time and a much more rapid attainment of the saturation plateau than the unmodified enzyme.

Journal Article↗

PubMed1996

Solubilization in Colloidal Immunoclusters

Micelle-like clusters of antibody molecules were prepared by covalent attachment of various hydrophobic groups to the protein molecules. These colloidal clusters were capable of solubilizing two hydrophobic probes, while the solubilizate:solubilizer molar ratio was dependent on the chain length of the hydrophobic groups, the degree of modification, and hence, on the size of the colloidal clusters. By using a fluorescent solubilizate, it was demonstrated that the immunoclusters may have a specific recognition ability.

Journal Article↗

PubMed1996

Dead Sea mineral-based cosmetics--facts and illusions.

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.

Chemistry, Pharmaceutical↗

PubMedDate not supplied

Effect of electrolytes, stirring and surfactants in the coacervation and microencapsulation processes in presence of gelatin.

The objectives of the present study were to investigate the parameters affecting simple coacervation and the ability to encapsulate oleic acid using this technique. Coacervation has been achieved using different types of gelatin (bloom number, charge) and various electrolytes. The electrolytes used for the coacervation can be divided into three groups: (1) inert salts; (2) phase separation inducers, (a) precipitation inducing agents (PIA), and (b) coacervation inducing agents (CIA); (3) coacervation inhibiting agents. The encapsulation of oleic acid was evaluated with two types of gelatin and various emulsifiers (anionic, cationic and nonionic). For positively charged gelatin, it was found that the encapsulation is incomplete in presence of cationic emulsifiers. For negatively charged gelatin no general trend was observed. The stirring rate for each step of the preparation of the microcapsules was evaluated. It was found that 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.

Capsules↗

PubMedDate not supplied

Microencapsulation of O/W emulsions by formation of a protein-surfactant insoluble complex.

A method for obtaining microcapsules of oil droplets by the formation of an insoluble complex of protein-surfactant is described. The gelatin type A studied, which is positively charged at the pH range studied, may form insoluble and soluble complexes with sodium dodecyl sulphate (SDS), an anionic surfactant. The binding isotherms were studied and the specific molar ratios of SDS to gelatin, in which the insoluble complex is formed, was determined. These specific ratios also led to the formation of microcapsules, in which the wall encapsulating the oil droplets, is composed of the insoluble gelatin SDS complex.

Drug Compounding↗

PubMedDate not supplied

Formation of positively charged microcapsules based on chitosan-lecithin interactions.

The formation of microcapsules which contain rosemary oil, is herewith described. The process is based on two steps: (a) formation of oil-in-water emulsions, by using lecithin as emulsifier, thus imparting negative charges on the oil droplets; (b) addition of a cationic biopolymer, chitosan, in conditions that favor the formation of an insoluble chitosan-lecithin complex. Zeta potential measurements revealed that addition of very low concentrations of chitosan to lecithin stabilized emulsions, led to reversal of charge. At a suitable pH range the chitosan precipitated around the oil droplets, forming positively charged microcapsules. The chitosan-lecithin insoluble complex is composed of a 1:1 molar ratio of the chitosan monomeric unit and lecithin, as evaluated by elementary analysis and turbidity measurements.

Capsules↗