Interactions of hemoglobin with lecithin liposomes

In this paper, the interaction of hemoglobin (Hb) with lecithin liposomes is studied by UV-vis spectroscopy, fluorescent spectroscopy, and transmission electron microscopy. The adsorption of Hb on liposomes is likely to be related to the hydrophobic interaction between Hb and liposomes, which brings about the increase of the microenvironmental polarity (I ₁/I ₃) and the decrease of the fluorescence polarization (P) of lecithin liposomes. These results are considered to be that the adsorption of Hb on liposomes makes the spaces between the lecithin molecules increase, and a temporary gap is consequently formed in the liposomal bilayer membranes. The leakage of aqueous-space marker from the liposomes is increased with the addition of Hb.     

Formulation–composition map of a lecithin-based emulsion

Formulation–composition map is an interesting tool to predict the nature of an emulsion, stability, viscosity and nevertheless to decide the mixing protocol of its ingredients. Information based on optimum formulation (environmental conditions at which the affinity of an emulsifier for oil and for aqueous phase is same), which is depicted through hydrophilic–lipophilic deviation (HLD) concept, is necessary to make a formulation–composition map of an emulsion. In order to apply this concept in food emulsions, it is necessary to determine characteristic constants of each component of the system, i.e. the aqueous phase, the oil phase and the emulsifier at equilibrium. In this work formulation–composition map of a sunflower oil–water–lecithin system, based on the knowledge of phase behavior of lecithin at equilibrium and emulsification, was made. The shape of inversion line on formulation–composition map was not the classical stair type rather an almost vertical inversion line at water-fraction (f_w) near 0.20 was observed. It was supposed to be linked to the viscosity of oil phase which was 50 times the viscosity of aqueous phase. Additionally, emulsions were of oil-in-water (O/W) type for f_w higher than 0.20, but their viscosity and the drop size behavior with respect to salt concentration as formulation variable did not show the existence of transitional inversion line on formulation–composition map. Such map in advance can certainly facilitate the guidelines for dynamic emulsification.     

Destabilization of artificial biomembrane induced by the penetration of tryptophan

The effect of tryptophan on the membrane stability was studied by using three artificial biological membranes including liposome, Langmuir monolayer and solid supported bilayer lipid membrane (s-BLM) as models. All the results indicate that the penetration of tryptophan can destabilize different artificial biological membranes. The diameter of liposome and the leakage of calcein from liposome increased with the increase of tryptophan concentration because the penetration of tryptophan was beneficial for dehydrating the polar head groups of lipids and the formation of fusion intermediates. π-A isotherms of lecithin on the subphase of tryptophan solution further confirm that tryptophan can penetrate into lipid monolayer and reduce the stability of lipid monolayer. When the concentration of tryptophan increased from 0 to 2 × 10⁻³ mol L⁻¹, the limiting molecular area of lecithin increased from 110.5 to 138.5 Å², but the collapse pressure of the monolayer decreased from 47.6 to 42.3 mN m⁻¹, indicating the destabilization of lipid monolayer caused by the penetration of tryptophan. The resistance spectra of s-BLM demonstrate that the existence of tryptophan leads to the formation of some defects in s-BLM and the destabilization of s-BLM. The values of electron-transfer resistance and double layer capacitance respectively decreased from 5.765 × 10⁶ Ω and 3.573 × 10⁻⁸ F to 1.391 × 10⁶ Ω and 3.340 × 10⁻⁸ F when the concentration of tryptophan increased from 0 to 2 × 10⁻³ mol L⁻¹. Correspondingly, the breakdown voltage of s-BLM decreased from 2.51 to 1.72 V.     

A Uniquely Configured Acetylcholinesterase‐Lecithin Biomimetic Sensing Structure at Cyclohexane/Water Interface for Electrochemical Determination of Fenthion in Organic Solvent

An acetylcholinesterase (AChE)‐lecithin biomimetic structure was constructed at the oil/water interface for the direct determination of fenthion in cyclohexane. Indophenol acetate in oil phase was hydrolyzed by AChE at the two‐phase interface to produce indophenol. Square wave voltammetry was used to monitor the current decrease of substrate to assess AChE activity. The AChE incorporated in the lecithin‐based biomimetic layer possessed higher enzymatic activity and was more sensitive to fenthion inhibition than freestanding AChE. A linear relationship between the inhibition percentage and logarithm of fenthion concentration was obtained in a concentration range from 1 ng/mL to 1 mg/mL.     

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.     

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.      

双波长薄层扫描色谱法测定胡麻卵磷脂中磷脂酰胆碱的含量

以氯仿-甲醇-水(65∶25∶4,V∶V∶V)为展开系统,测定波长λS=235nm,参比波长λR=260nm,反射法双波长锯齿形扫描磷脂酰胆碱峰面积,外标两点法计算含量,建立了双波长薄层扫描色谱法测定胡麻卵磷脂中磷脂酰胆碱含量的分析方法。胡麻卵磷脂中磷脂酰胆碱的含量为62.4%,平均回收率为99.6%,RSD=3.42%。方法经济实用、结果可靠。     

胆固醇对卵磷脂囊泡稳定性的影响

采用透射电子显微镜研究了Gemini表面活性剂诱导卵磷脂囊泡结构改变的机理, 用Langmuir膜天平研究卵磷脂和胆固醇的不溶单分子混合膜在气-液界面的行为和混合膜分子间的相互作用, 并结合动态光散射技术和停留法探讨胆固醇对Gemini表面活性剂诱导卵磷脂囊泡结构改变的影响. 从电镜结果可以推测带正电荷的Gemini表面活性剂分子会嵌入到带负电荷的卵磷脂囊泡双分子层的外层, 囊泡的双分子层之间的相互吸引力使双分子层的厚度减少, 由于嵌入的表面活性剂分子在囊泡的双分子层中分布是不均匀的, 这种分布的不均匀性必然会导致双分子层厚度的不均匀, 从而使囊泡破裂. 混合膜的过剩面积和动力学结果表明, 胆固醇和卵磷脂是相互吸引的, 即胆固醇的加入使卵磷脂囊泡更不容易被表面活性剂破坏.     

Thinning and thickening effects induced by shearing in lecithin solutions of polymer-like micelles

 The effects of shear flow on the lecithin organogels consisting of reverse polymer-like micelles have been investigated by dynamic rheology. It was established that the shear effects depended on the molar ratio of water to lecithin that determined the micellar type in the system. For an organogel with linear flexible polymer-like micelles, thinning was observed. The main features of the rheological behavior bore a resemblance to previously investigated aqueous systems made up of similar but direct polymer-like surfactant micelles. The thinning effects are explicable on the basis of alignment of micellar aggregates along the flow direction and their disentanglement. An organogel with branched micelles did not demonstrate any notable response to the shearing. Unusual behavior was noticed in the case of a jelly-like phase that included the highest amounts of water. The applied steady shear flow induced a thickening effect. This was followed by restructuring of the micellar system at the level of polymer-like micelles and their network. The shearing effects were characterized by slow kinetics. In addition, the system did not revert to the original state after the cessation of steady shear flow even within 8 h. Measurements performed in an oscillation regime on this system showed that shearing should promote a substantial growth of the polymer-like micelles and affect their alignment. Received: 18 May 1999 Accepted: 27 March 2000