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.     

Micelle-vesicle transition of oleyldimethylamine oxide in water

We studied the effects of the degree of ionization() and the surfactant concentration (C_d) on the micelle–vesicle transition in salt-free oleyldimethylamine oxide (OlDMAO) aqueous solutions by the dynamic light scattering (DLS), the hydrogen ion titration, the small angle neutron scattering (SANS), the electrophoretic light scattering (ELS) and viscoelastic measurements. From the study of ionization effects, the micelle–vesicle transition was recognized as a change of aggregate size by the DLS measurement; however, the micelle–vesicle transition was not detected both in the ELS measurement and the hydrogen ion titration, suggesting that the electric properties of the worm-like micelles and the vesicles are very similar despite a large difference of shapes between them. From the results of the SANS, the DLS and the viscosity measurements, it was suggested that a concentration-dependent micelle–vesicle transition took place around C_p = 10 mmol kg⁻¹ for the solutions at = 0.5. In the concentration-range 10 mmol kg⁻¹ < C_d < 150 mmol kg⁻¹, the micelles and the vesicles coexisted. In the concentration region (C_d = 10–50 mmol kg⁻¹), the vesicle size increased with the surfactant concentration.     

Zeta potential and surface charge density of polystyrene-latex; comparison with synaptic vesicle and brush border membrane vesicle

The electrophoretic mobility of polystyrene — latex (PSL) of diameter 870 Å was determined using a Laser Zee System 3000. This instrument enables automatic measurement of the electrophoretic mobility of fine particles. Effect of pH and ionic strengthI on the PSL mobility was analyzed. It was found that the mobility as a function of pH has a minimum around pH 3–4 atI=0.1, showing no isoelectric point, and that the mobility decreases with increasing ionic strength up toI=0.1 but is almost constant forI=0.1–0.2 at pH=7.34. From the mobility date, we estimated the zeta potential of PSL. We used an approximate mobility formula derived by Ohshima, Healy and White, which is considerably more accurate than Smolchowski's and Henry's formula and is applicable for fine particles with small a ( a10), where is the Debye-Hückel parameter anda is the particle radius. Further, we calculated the surface charge density of PSL using an approximate relationship. It was found that there are 2000–4000 negative charges on the PSL surface at pH=7.34. Comparison is made with the results on synaptic vesicles (SV) from brain cerebrum cortex and brush-border-membrane vesicles (BBMV) from the small intestine.     

单十二烷基磷酸酯辅助共轭亚油酸的囊泡化研究

以共轭亚油酸(CLA)为模型脂肪酸,与安全、温和的阴离子表面活性剂单十二烷基磷酸酯(MLP)进行复配,动态激光光散射和透射电镜表征结果表明,CLA在中性至弱酸性环境中仍然能够囊泡化.通过pH滴定曲线研究了CLA和MLP 2种分子的荷电物种随pH值的变化规律,据此分析各物种间的相互作用,并推断经MLP辅助CLA能够在中性至弱酸性环境中囊泡化的动因是CLA-MLP间的氢键或离子-偶极作用.     

Facile synthesis of low-polydispersity block copolymer vesicles by azide-zwitterion cycloaddition

Polycaprolactone with azide (PCL-N₃) and polyethylene glycol with α,β-unsaturated ester (maPEG) as chain-end functional group were synthesized, respectively. Then, facile synthesis of polycaprolactone-block-polyethylene glycol (PCL-b-PEG) amphiphilic copolymer by azide-zwitterion cycloaddition of PCL-N₃ and maPEG, as the first example, was reported. The self-assembly of this amphiphilic copolymer was carried out in deionized water, and then the formation of vesicles was proven by the result of transmission electron microscope (TEM). Grainsize analyzer suggested that the diameter of the vesicles is 305 nm in average and the polydispersity of the vesicles is 0.128. The azide-zwitterion cycloaddition provides a powerful method for the post-functionalization of α,β-unsaturated ester or azide end-functionalized polymers.     

合成双分子膜三元体系的激发态能量转移

在４ （４’ 癸氧基 ４ 氧基联苯）丁基三甲基溴化铵双分子膜体系内,通过静电相互作用使达旦黄、荧光黄和四苯基卟啉磺酸阴离子键合在囊泡表面;研究了达旦黄给体通过荧光黄传递到四苯基卟啉磺酸阴离子受体的三元激发态能量转移。能量转移的结果改善了光的输出,扩展了光波的输出范围。     

Liquid crystal model of vesicle deformation in alternating electric fields

Considering the effects of osmotic pressure, elastic bending, Maxwell pressure, surface tension, as well as flexo-electric and dielectric properties of phospholipid membrane, the shape equation for sphere vesicle in alternation (AC) electric field is derived based on the liquid crystal model by minimizing the free energy due to coupled mechanical and AC electrical fields. Besides the effect of elastic bending, the influence of osmotic pressure and surface tension on the frequency dependent behavior of vesicle membrane in AC electric field is also discussed. Our theoretical results for membrane deformation are consistent with corresponding experiments. The present model provides the possibility to further disclose the frequency-depended behavior of biological cells in the coupled AC electric and different mechanical fields.     

Heterogeneity and deformation behavior of lipid vesicles

Recent studies on the deformation of lipid vesicles which is a simple model of biological membranes, and the factors that influence it are reviewed. In homogeneous vesicles, the deformation from spherical to various shapes was observed by adjusting the temperature and the osmotic pressure. This is mainly explained by a balance between the bending elasticity and the area difference energy. In phase separated vesicles, the effect of line tension makes a significant contribution to the deformation. In addition, asymmetric distribution of lipid molecules in bilayers caused by lipid sorting determines deformation behaviors including budding, pore, tube, adhesion, and self-reproduction. The change in membrane curvature due to shielding of lipid charges by electrolytes, proteins, peptides, and solid nanoparticles was also reviewed.     

部分水解聚丙烯酰胺-羟乙基纤维素的水相pH响应性自组装

为考察无规共聚物在全水相环境中的自组装行为, 合成了结构类似于无规共聚物的低相对分子质量的部分水解聚丙烯酰胺(HPAM). 尝试改变水溶液pH值来诱导HPAM与羟乙基纤维素(HEC)发生自组装, 采用透射电子显微镜(TEM)观察到不同pH值时分别获得了100 nm的似正方体胶束, 200 nm×100 nm的类椭球胶束, 100 nm的串珠状胶束以及500 nm×300 nm×50 nm的半月形胶束等pH响应性核壳型聚合物胶束. 建立了金在胶束表面原位还原耦合TEM表征方法, 用于检测低衬度聚合物胶束的纳米细节; 配合电子探针X射线微区分析(EPMA)和扫描电子显微镜(SEM), 证实了半月形聚合物胶束的精致分级构造为亲水性内囊@疏水性连续囊壁@亲水性外壳的多泡囊泡, 并证实pH=0.9时多泡囊泡崩解为疏水性内核@亲水性外壳的10 nm类球体小胶束. 通过分析链节质子化状态的pH响应性, 结合zeta电位和吸光度测定结果, 阐释了不同pH值时组成聚合物胶束的核和壳的链段归属, 获得了全水相中HPAM自组装驱动力和形貌方面的全新知识.     

胺类分子结构对油酸囊泡pH窗口的影响

基于激光丁达尔效应及浊度测定, 考察了改变二元胺的碳桥长度、 多元胺的氨基多寡、 长链伯胺的碳链长度及季铵化等因素对油酸囊泡pH窗口的影响. 结果表明, 二元胺及多元胺主要导致油酸囊泡的pH窗口向碱性方向拓宽, 而长链伯胺和十二烷基三甲基溴化铵(DTAB)不仅可使油酸囊泡的pH窗口向碱性拓宽, 而且可使油酸在酸性pH区域形成另一个介稳至稳定的新囊泡相. 氨基在不同pH下质子化和脱质子化转换是胺类分子调节油酸囊泡pH窗口的共同驱动力, 疏水作用是长链胺类的又一驱动力, 而静电吸引是季铵盐的另一种特殊驱动力. 分子间相互作用的热力学参数及结合能计算结果表明, 二乙烯三胺为代表的二元胺或多元胺在油酸囊泡表面以氢键或离子-偶极作用等非共价结合为主, 其调节功能弱于长链伯胺及DTAB与油酸的疏水共组装或DTAB与油酸的静电吸引作用.