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.     

Effects of various whey protein hydrolysates on the emulsifying and surface properties of hydrolysed lecithin

Oil-in-water emulsions (30 wt% sunflower oil) containing various concentrations of commercial whey protein hydrolysates (0-4 wt%) and hydrolysed lecithin (0.4-1.8 wt%) were prepared by means of a high pressure homogeniser. The degrees of hydrolysis used ranged from 10 to 27%. The individual and interactive effects of these factors on the particle size distribution, emulsion stability, consistency and interfacial tension were investigated using a three-level factorial design according to the principle of response surface methodology. The properties of the emulsions containing both hydrolysed lecithin and whey protein hydrolysate (WPH) were significantly influenced by the degree of hydrolysis of WPH, the protein content and the second-order interaction between both. Addition of WPH, with a 10-20% degree of hydrolysis, improved the stability of lecithin-stabilised emulsions and slightly decreased the average droplet size, compared to those emulsions with only protein or hydrolysed lecithin. However, when extensively hydrolysed WPH (DH=27%) was mixed with hydrolysed lecithin, rapid coalescence and oiling-off of the emulsion droplets resulted, suggesting competition between the surface active components of this WPH and the hydrolysed lecithin. High amounts of such an extensively hydrolysed WPH, together with low lecithin concentrations, were found to be especially detrimental. The different behaviour of partially and extensively hydrolysed WPH in oil-in-water emulsions containing hydrolysed lecithin, was in good agreement with their interfacial activity, as measured by the drop volume method.     

电容法研究卵磷脂/氨基酸/H_2O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垌甘氨酸.     

Factors affecting physicochemical properties of liposomes prepared with hydrogenated purified egg yolk lecithins by the microencapsulation vesicle method

We examined hydrogenated purified egg yolk lecithins, having practical advantages over non-hydrogenated ones, as liposomal membrane materials. Liposomes were prepared by the microencapsulation vesicle (MCV) method in which liposomes are formed through two-step emulsification and dispersion. Three types of purified egg yolk lecithins with different iodine values were examined after being dissolved in one of three lipid solvents. The liposome size increased as the temperature during the second emulsification increased, being closer to the boiling temperature of the solvent. The preparation temperature in relation to the transition temperature of each lecithin was also a factor affecting liposome sizes. As for the encapsulation efficiencies of the model compound calcein in liposomes, they differed mainly depending on the solubility of each lecithin in a lipid solvent and it was more obvious in hydrogenated lecithins. A high preparation temperature resulted in lower encapsulation efficiencies, suggesting that leakage of encapsulated calcein was facilitated at high temperature in the MCV methods. There was a significant correlation between liposome sizes and encapsulation efficiencies in non-hydrogenated purified egg yolk lecithin but not in hydrogenated ones. When using hydrogenated purified egg yolk lecithins as liposomal membrane materials, it was suggested that a lipid solvent should be chosen so that a lecithin completely dissolves under the preparation condition in order to achieve a higher encapsulation efficiency. Smaller liposome particles were obtained when the second emulsification was performed at a lower temperature compared with the boiling point of the lipid solvent. These findings can be applied to control encapsulation efficiencies and particle sizes in each particular liposome preparation enclosing therapeutic agents.     

A study of the adsorption of bile salts onto model lecithin membranes

Bile salts play a central role in the promotion of cytotoxicity or cytoprotection. In this study, we examined the interaction of different bile salts with egg lecithin vesicles using 31P NMR spectroscopy. The effects of taurochenodeoxycholate (TCDC or 3alpha,7alpha,-dihydroxy-5beta-cholanoyl taurine, of tauroursodeoxycholate (TUDC) or 3alpha,7beta,-dihydroxy-5beta-cholanoyl taurine) and of taurobetamuricholate (TbetaMC or 3alpha,6beta,7beta,-trihydroxy-5beta-cholanoyl taurine), at various bile salt/lecithin ratios, were evaluated. From the percent 31P present in vesicles, the micellar capacity of bile salts to dissolve lecithin was determined. TCDC was incorporated into vesicles for bile salt/lecithin molar ratios lower than 0.62 while for TUDC and TbetaMC, the critical ratios were 0.94 and 1.1, respectively. The 31P chemical shift change was markedly larger with TCDC than that found with TUDC and TbetaMC. In order to specify the low interactions observed between hydrophilic bile salts and lecithin, we determined the intermixed micellar/vesicular bile salt concentrations (IMVC) of bile salt/lecithin solutions using rapid ultrafiltration-centrifugation for TUDC and lecithin solubility measurements for TUDC, TbetaMC and TCDC. The low IMVC obtained indicate that even hydrophilic bile salts were bound mostly to the mixed aggregates. In conclusion, the low disturbance in the arrangement of lecithin induced by TUDC and TbetaMC appears to be due to the interfacial location of these bile salts. TCDC (7alpha OH) penetrates more deeply in the membrane than the 7beta hydroxylated bile salts that may partly explain the distinct damaging effects of these bile salts.     

Phase behavior of the lecithin/water/isooctane and lecithin/water/decane systems

The isothermal pseudo-ternary-phase diagram was determined at 25 degrees C for systems composed oflecithin, water, and, as oil, either isooctane or decane. This was accomplished by a combination of polarizing microscopy, small-angle X-ray scattering, and NMR techniques. The lecithin-rich region of the phase diagram is dominated by a lamellar liquid-crystalline phase (Lalpha). For lecithin contents less than 60% and low hydration (mole ratio water/lecithin = W0 < 5.5), the system forms a viscous gel of branched cylindrical reverse micelles. With increase in the water content, the system phase separates into two phases, which is either gel in equilibrium with essentially pure isooctane (for lecithin < 25%) or a gel in equilibrium with Lalpha (for lecithin > 25%). These two-phase regions are very thin with respect to water dilution. For 8 < W0 < 54 very stable water-in-oil emulsions form. It is only after ripening for more than 1 year that the large region occupied by the emulsion reveals a complex pattern of stable phases. Moving along water dilution lines, one finds (i) the coexistence of gel, isooctane and Lalpha, (ii) equilibrium between reverse micelles and spherulites, and, finally, (iii) disconnected reverse micelles that fail to solubilize water for W0 > 54. This results in a Winsor II phase equilibrium at low lecithin content, while for lecithin > 20% the neat water is in equilibrium with a reverse hexagonal phase and an isotropic liquid-crystalline phase. The use of the decane as oil does not change the main features of the phase behavior.     

Casein adsorption on the surfaces of oil-in-water emulsions modified by lecithin

The effects of incorporating an additional component, egg-yolk lecithin, on the properties of oil-in-water emulsions stabilized by casein have been studied. The impact of lecithin on the stability of the emulsions was studied using integrated light scattering and the casein-oil-lecithin interaction was studied with photon correlation spectroscopy combined with breakdown of the adsorbed protein layers by proteolysis. Lecithin was found to enhance the stability of the emulsions at low cascin concentrations, below the limiting surface coverage of 1 mg m⁻² of casein which is found in the absence of lecithin. Conversely, small amounts of casein also stabilized flocculating oil-lecithin emulsions. The hydrodynamic thickness of the adsorbed protein layer on the hydrophobic oil surface was modified by the presence of lecithin. When the total surface area occupied by lecithin was less than 10% (5 mg lecithin for 2 ml oil), the thickness of the adsorbed casein layer was not significantly different from that in the absence of phospholipid. At higher concentrations of lecithin, the adsorbed casein layer had a lower minimum value for the layer thickness of 6.5 nm at low casein concentration and an upper plateau value of 8 nm at saturated adsorption, compared to a low limit of 5 nm and a plateau value of 10 nm in the absence of lecithin, demonstrating that the structure of the adsorbed casein layer was changed by the presence of phospholipid.     

Potentiometric Dipyridamole Sensors Based on Lipophilic Ion Pair Complexes and Native Ionic Polymer Membranes

Abstract

A new spectrofluorimetric method was developed for the determination of trace amounts of lecithin. Using enoxacine (ENX)‐terbium ion (Tb³⁺) as a fluorescent probe, in a buffer solution at pH=5.80, lecithin can remarkably reduce the fluorescence intensity of the ENX‐Tb³⁺ complex at λ=545 nm; the reduced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of lecithin. Optimum conditions for the determination of lecithin were also investigated. The linear range and detection limit for the determination of lecithin were 1.96×10^?7–9.8×10^?6 mol l^?1 and 9.74×10^?8 mol l^?1. This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to assess lecithin in serum samples.     

Effects of emulsifying agents on the safety of titanium dioxide and zinc oxide nanoparticles in sunscreens

The use of titanium oxide (TiO₂) and zinc oxide (ZnO) nanoparticles (NPs) in sunscreen formulations has increased considerably, and might pose a serious health hazard worldwide. A thorough investigation into the toxicity induced by such components is highly necessary. In this study, the effects of TiO₂ and ZnO NPs on HaCaT cells were tested in the presence and absence of emulsifiers (cyclopentasiloxane, jojoba ester, and lecithin). Cell viability results revealed that the toxicity of NPs was highly dose dependent and influenced by the emulsifier type. The emulsifiers themselves are minimally toxic. However, when used in combination with TiO₂ and ZnO, they were highly toxic to HaCaT cells. Transmission electron microscopy revealed that the cells showed least permeability to NPs dispersed in lecithin compared to other emulsifiers. In conclusion, the toxicity of NPs may be highly dependent on the emulsifier type and be varied. In particular, lecithin can be used as a potential alternative emulsifier in sunscreens.     

Al2O3纳米粒子在TEM测试中分散性的研究

对自制不同粒径范围的球形和纤维状Ａｌ２Ｏ３纳米粉在电镜（ＴＥＭ）测试中颗粒的分散性进行了研究。以卵磷脂、油酸为表面活性剂，无水乙醇为溶剂进行试验，结果表明：当卵磷脂浓度为０．５％时，能得到颗粒之间无聚集、分散性良好的ＴＥＭ照片。文中给出了可能的分散机理     

高分子微泡体系中光解水的研究：（Ⅱ）聚卵磷脂微泡在光解水中的应用

本文研究以卵磷脂为单体形成的微泡体系,以Co~(60)辐照为聚合方式,通过超声波作用将联吡啶钌和EDTA,甲基紫精和铂溶胶等光解水的试剂置于微泡的不同区域,从而获得不同的光解水效果。     

卵磷脂与四乙酰氧基苯基卟啉金属配合物的相互作用

本文用~(31)P.NMR和~1HNMR谱分析了卵磷脂的组分和结构,并以小角X射线散射法(SAXS)研究了所合成的六种四乙酰氧基卟啉金属配合物与卵磷脂的相互作用,发现卟啉分子镶嵌于磷脂双层的疏水链之间,使双分子层间距变大,而金属卟啉分子因其与磷脂的极性头基的静电相互作用,所形成的磷脂双分子层的间距介于纯卵磷脂和含有卟啉分子的卵磷脂所构成的双分子层之间.     

Interactions of lecithin and pig apolipoproteins of high density lipoproteins at the surface monolayer of reconstituted very small particles

Cosonication of egg yolk lecithin and triolein with apolipoproteins isolated from pig high density lipoprotein (apoHDL) gave us reconstituted high density lipoprotein particles (r-HDLs) of 9 nm in average diameter. They were smaller than microemulsion particles (MEs) composed of the lipids (35 nm). The protein/egg yolk lecithin ratio in the fractionated r-HDLs was higher in the smaller particles. Binding of a hydrophobic probe, 2-p-toluidinylnaphthalene-6-sulfonate (TNS), to MEs, r-HDLs and apoHDL were evaluated on the basis of Halfman and Nishida's method. The reconstitution of apoHDL into MEs led to a 68% reduction in the binding of TNS and a small increase in the alpha-helix content as compared with free apoHDL. The binding experiments also showed the condensation of lecithin molecules at the r-HDL surface. The amphipathic helixes of apoHDL are located in the surface monolayer of egg yolk lecithin surrounding the triolein core. The intercalation of the hydrophobic residues of apoHDL between egg yolk lecithin molecules brings about a pronounced curvature of the surface and a decrease in the particle diameter.     

Electrokinetic properties of noncharged lipid nanocapsules: influence of the dipolar distribution at the interface

Lipid nanocapsules (LNCs) containing poly(ethylene glycol) (PEG) were developed according to a phase inversion process without organic solvent. The distribution of PEG chains at the surface was determined due to electrokinetic properties, in order to correlate it with protein adsorption potentiality. In this aim, electrophoretic mobilities were measured as a function of ionic strength and pH, for particles differing by their size, dialysis effects, and the presence or not of lecithin in their shell. The study allowed the determination of the isoelectric point (pI) as well as the charge density (ZN) in relation with the dipolar distribution in the polyelectrolyte accessible layer (depth = 1/lambda), by using soft-particle electrophoresis analysis. These parameters pointed out that the PEG surface organization was dependent on the particle size. Moreover, this organization could be modified by dialyzing particles and/or by formulating them with or without lecithin. Lecithin was found to be present in the inner part of the polyelectrolyte layer and to play a role in the outer part disorganization. Dialyzing LNCs formulated with lecithin allowed to obtain stable and well-structured nanocapsules, ready to an in vivo use as drug delivery system.     

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.     

Stability and rheology of three types of W/O/W multiple emulsions emulsified with lecithin

Three types of multiple emulsions were prepared with lecithin. The morphology, stability, and rheological properties of the three types of W/O/W multiple emulsions were evaluated. The formulation factors, including salts and aliphatic alcohol, were further examined. The three types of multiple emulsions were formed by different emulsifiers. An excellent multiple emulsion occurred with 2?wt% lecithin concentration, stabilized by 0.05?wt% NaCl. All multiple emulsions showed shear-thinning behavior, i.e., the apparent viscosity decreased with the increase of the shear rate. With the high concentration of lecithin, the multiple emulsions exhibited the highest viscosity at low shear rate and had higher storage modulus (G′) and the loss modulus (G″). This study was conducted to reveal that different types of multiple emulsions can be formed with lecithin, and that the stability and rheological properties were different with different types of multiple emulsions.     

A new reverse wormlike micellar system: mixtures of bile salt and lecithin in organic liquids

We report a new route for forming reverse wormlike micelles (i.e., long, flexible micellar chains) in nonpolar organic liquids such as cyclohexane and n-decane. This route involves the addition of a bile salt (e.g., sodium deoxycholate) in trace amounts to solutions of the phospholipid lecithin. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique "facially amphiphilic" structure, can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than 5 orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.     

Highly sensitive spectrofluorimetric determination of trace amounts of lecithin

A new spectrofluorimetric method was developed for the determination of trace amounts of lecithin using the ciprofloxacin (CIP)–terbium (Tb³⁺) ion complex as a fluorescent probe. In a buffer solution at pH=5.60, lecithin can remarkably reduce the fluorescence intensity of the CIP–Tb³⁺ complex at λ=545 nm. The reduced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of lecithin. Optimum conditions for the determination of lecithin were also investigated. The linear range and detection limit for the determination of lecithin were 1.0×10⁻⁶–3.0×10⁻⁵ mol L⁻¹ and 3.44×10⁻⁷ mol L⁻¹, respectively. This method is simple, practical, and relatively free of interference from coexisting substances. Furthermore, it has been successfully applied to assess lecithin in serum samples.      

Photodegradation of Lecithin Liposomes by Nanoparticulate Titanium Dioxide

Abstract

Lecithin liposomes were studied by transmission electron microscopy (TEM), selected‐area electron diffraction (SAED), IR, and GC‐MS. Results indicate that titanium dioxide (TiO₂) nanoparticles can gain access into lecithin liposomes during sonication and the lecithin liposomes can be effectively decomposed upon illumination with near‐UV light.     

CHARACTERISTIC PROPERTIES OF LECITHIN AS A SURFACTANT

Characteristic solution properties of lecithin were studied in 1) water+propanol/lecithin/hexadecane and 2) ethanol/lecithin/ hexadecane systems. 1) Solvent property of water changes by added alcohol and the hydrophile-lipophile property of lecithin is balanced in 13 wt% propanol aq.-hexadecane system. Three liquid phases, i.e. aqueous alcohol, lecithin and hexadecane are found. The volume fraction of the lecithin phase increases with its concentration and at 2.3 wt%/system, all solvent molecules are swelled and one microemulsion phase is obtained. 2) In ethanol/ lecithin/hexadecane system, lecithin is also insoluble in the solvent, and swells a large amount of hexadecane.