A biologically friendly approach for silver nanoparticle formation and their in situ attachment to lecithin vesicles

There has been a keen interest for developing a biologically friendly approach for the preparation of silver nanoparticles for their application reasons. A biocompatible, single step method is established for the preparation of silver nanoparticles in lecithin (Egg phosphatidylcholine)/water systems where lecithin itself acts as a reductant for silver nitrate to form the silver nanoparticles. In another attempt, silver nanoparticles were successfully synthesized inside the lecithin vesicles and were found attached to the bilayers of lecithin vesicles. To the best of our knowledge, this is the first report where a biological surfactant has acted as a mild reducing agent for silver nitrate by itself to form silver nanoparticles.     

Lecithin organogels with n-alkyl-D- glucosides and n-alkly-D-lactobionamide

 Jelly-like phases formed by mixtures of soybean lecithin with pure n-dodecyl-β-D-glucopyranoside (DDPG), commercial alkylpoly-glucoside (APG) or n-dodecyl-β-D-lactobionamide (DLBA) in decane in the presence of small amounts of water were studied by oscillating rheology and FT-IR-spectroscopy. It was established that the sugar derivatives can modify the rheological properties of lecithin organogels in different ways. The viscosities, the structural relaxation times and the shear moduli decrease with increasing content of DDPG, while the same parameters increase for DLBA. For APG the modulus is increasing while the viscosity and the structural relaxation time are decreasing. By means of FT-IR spectroscopy and examination of the Cole–Cole-plots of the loss modulus vs. the storage modulus it was shown that the sugar derivatives influence both the strength of the hydrogen bonds between the molecules in the polymer-like micelles and the micellar dynamics. Received: 10 November 1997 Accepted: 11 December 1997     

Ein Kinkenblock-Modell für die Hauptumwandlung in Phospholipidschichten

Zusammenfassung In dieser Arbeit wird ein zweidimensionales Modell für das Kettenschmelzen bei der Hauptumwandlung in Lipid-Doppelschichten vorgestellt. Neben dem gestreckten Zustand sind nur Konformationen mit 2g2-Kinken zugelassen, die kompakte Kinkblöcke formieren.

---

Summary A two-dimensional lattice model for the chain melting transition in lipid bilayer was built on the assumption that the only non-straight hydrocarbon chain conformations allowed are 2g2-kinks organized in compact blocks.

     

Analyse Hydrometallurgique et Caracterisation de Miner Secondaires

Abstract

Two copper ores (containing between 1% and 2% of the metal) were analyzed by UV emission spectroscopy, infrared spectroscopy and X-ray diffraction yielding - per se - inconclusive results. The ores were subsequently classified by particle size into three “granular fractions”. Determination of copper, dissolved from each fraction by anaerobic and aerobic digestion with 5% aqueous sulphuric acid, produced illuminating information on the presence of sulfide-and oxide-type copper compounds. Fractionation was further refined by magnetic separations.     

Highly viscoelastic reverse worm-like micelles formed in a lecithin/urea/oil system

While lecithin alone can form spherical or ellipsoidal reverse micelles in oil, we found that urea can promote the growth of lecithin reverse worm-like micelles in oil. In a mixed system of urea and lecithin, the urea binds to the phosphate group of lecithin, thus reducing the interface curvature of the molecular assembly and inducing the formation of reverse worm-like micelles. The regions in which these micelles form increased with lecithin concentration. In addition, the zero-shear viscosity (η ₀) of the reverse worm-like micelles rapidly increased upon the addition of urea, reaching a maximum of 2 million times the viscosity of n-decane. We examined the change in η ₀ in detail by performing dynamic viscoelasticity measurements. Values for η ₀ increased with urea concentration because the disentanglement time of reverse worm-like micelles increased with micellar growth.     

Size-controlled magnetic nanoparticles with lecithin for biomedical applications

Lecithin-adsorbed magnetic nanoparticles were prepared by three-step process that the thermal decomposition was combined with ultrasonication. Experimental parameters were three items—molar ratio between Fe(CO)₅ and oleic acid, keeping time at decomposition temperature and lecithin concentration. As the molar ratio between Fe(CO)₅ and oleic acid, and keeping time at decomposition temperature increased, the particle size increased. However, the change of lecithin concentration did not show the remarkable particle size variation.     

Surface-modified magnetic nanoparticles with lecithin for applications in biomedicine

Magnetic nanoparticles were prepared by thermal decomposition and adsorbed with lecithin by applying ultrasonication. The size and saturation magnetization changes of magnetic nanoparticles were observed with different lecithin concentration, and the maximum tolerated dose (MTD) and toxicity of magnetic fluid was investigated through a biological test. As the added lecithin concentration increased in a weight loss test by heating of magnetic particles, the thickness of lecithin-adsorption layer increased non-linearly, and the proper adsorption amount was observed in the lecithin concentration of 20% (w/v). The dispersibility and magnetic property of lecithin-adsorbed magnetic nanoparticles was the most excellent when the ultrasonic holding time was 1.5 h. Also, the maximum tolerated concentration with best cell viability was 32 μg/ml by in vitro test, and lecithin-adsorbed magnetic fluids showed the improved biocompatibility by 1.2 times compared with pure magnetite magnetic fluids.     

Ionic transport across lipid bilayers activated by cryptands and alkyl-cryptands

The ionic flux of Na⁺ K⁺ ions across monoolein and lecithin bilayers, separating two aqueous electrolyte solutions, has been measured in the presence of 5-decyl-4,7,13,16,21-pentaoxa-1,10-diazabicyclo-(8,8,5)-tricosane, 5-decyl-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo(8,8,8)-hexacosane and their parent compounds 4,7,13,16,21-pentaoxa-1,10-diazabicyclo(8,8,5)-tricosane, 4,7,13,16,21,24-hexaoxa-1,10-diaza-bicyclo-(8,8,8)-hexacosane. Under the effects of an electric field, a significant increase of the membrane conductance, proportional to the macrocycle and/or to the electrolyte concentration, was observed. In spite of the high ion selectivity of both classes of cryptands, related to the different stability constants of the metal ion–macrobicyclic receptor complexes, alkyl cryptands show a greater efficiency to activate the ion transport across the lipid membranes than their parent compounds. Such a result has been explained taking into account the different hydrophobicity of the macrobicyclic compounds. Information on the ionic mobility and on the diffusion coefficient of the ionic species moving across the membrane have been obtained analyzing the experimental data in terms of the carrier mechanism based on the Eyring theory.     

High pressure liquid chromatography of standard and amniotic fluid phospholipids

A method for the HPLC separation of phosphatidylglycerol (PG), phosphatidylinositol (PI), phosphatidylcholine (PC), and sphingomyelin (SPH) was achieved using five in-series columns packed with LiChrosorb, Partisil, and μ-Porasil adsorbents, a solvent mixture of chloroform/methanol/ammonium hydroxide (50 : 36 : 6.7, by volume), and a Pye LCM2 Moving Wire (FID) detector. The same phospholipid mixture was also separated using four μ-Porasil columns with the same eluent and detector. The latter conditions were found to be suitable for the analysis of phospholipids obtained after centrifuging, extraction, and precipitation of surface-active lipid components of patient amniotic fluid collected at amniocentesis section. The lecithin/sphingomyelin (L/S) ratios, determined by the HPLC method, correlated well with those determined by the TLC technique in four normal pregnancies, whereas results of shake tests did not correlate too well with L/S ratios determined by the above two chromatographic methods. Besides the lecithin/sphingomyelin ratio, the present method was able to supply additional information: the concentrations of phosphatidylglycerol and phosphatidylinositol, for prediction of fetal lung maturity, and the palmitic acid content of amniotic fluid phosphatidylcholine.     

电容法研究卵磷脂/氨基酸/H2O胶束和囊泡体系

运用电容法研究卵磷脂/氨基酸/H2O胶束和囊泡体系结构与性质. 卵磷脂的临界胶束浓度和囊泡生成浓度可由体系电容-卵磷脂浓度关系曲线求得.随着卵磷脂浓度增加, 体系电容增加, 卵磷脂由胶束形成囊泡. 随着氨基酸浓度增加, 胶束、囊泡半径增大, 体系电容减小. 氨基酸能促进卵磷脂形成胶束和囊泡, 使得卵磷脂临界胶束浓度和囊泡生成浓度减小, 其影响的强弱顺序为组氨酸>色氨酸>>甘氨酸.