胆固醇与磷脂酰乙醇胺/磷脂酰胆碱混合膜的热力学特性及其单层膜形态的AFM观察

研究了不同比例下胆固醇(Chol)对磷脂酰乙醇胺/磷脂酰胆碱(PE/PC,1∶1物质的量比)混合膜的影响,并在表面压力-平均分子面积(π-A曲线)等温线基础上,通过对过量平均分子面积(ΔAex)和过量吉布斯自由能(ΔGex)的计算分析,研究了不同比例Chol与PE/PC(1∶1物质的量比)三元混合膜的热力学特性.实验结果表明:Chol在一定程度上加速了混合膜的相变,增强了膜的凝聚性;当XChol=0.2,0.6,0.8时,过量平均分子面积和过量吉布斯自由能在所研究的表面压力下都为负值,分子之间相互作用力表现为引力,促使混合膜的凝聚,而在XChol=0.4时,过量平均分子面积和过量吉布斯自由能在15,20,25,30 mN/m下为正值,分子之间相互作用力表现为斥力,促使熵的增加,并且在20 mN/m压力下出现极值.实验中利用LB膜技术制备了不同比例Chol与PE/PC(1∶1物质的量比)混合膜,并在原子力显微镜下对其结构形态进行了观测.     

胆固醇/两性霉素B混合单层膜相互作用的研究

两性霉素B (AmB)为多烯类抗真菌抗生素, 它的吸收过程与生物膜有密切联系. 选用生物膜中的重要分子胆固醇为代表, 通过Langmuir-Blodgett (LB)膜技术测得胆固醇/两性霉素B单层膜表面压力与平均分子面积(π-A)曲线, 定量分析了固定模压下的平均分子面积(A)、弹性模量(C_S^－1)、过量吉布斯自由能(ΔG_ex)等参量. 实验结果表明, 胆固醇/两性霉素B两组分物质的量比与膜压对单层膜的弹性、稳定性以及热力学特性有影响|通过单层膜相互作用参数α进一步佐证了组分间物质的量比和表面压力对混合单层膜稳定性、混合性以及分子间相互作用具有重要影响.     

鞘氨醇与DPPC, DPPE单层膜的热力学特性及形态观察

鞘氨醇(sphingosine)是生物体内合成鞘脂的母体化合物, 是生物膜中的重要组分之一. 通过分析表面压力和平均分子面积(π-A)等温线数据分别研究了鞘氨醇与二棕榈酰基磷脂酰胆碱(DPPC)和二棕榈酰基磷脂酰乙醇胺(DPPE)二元组分单层膜的热力学特性, 并在恒定膜压下制备不同摩尔比例的混合脂膜用原子力显微镜进行观测. 实验结果表明: (1)鞘氨醇与DPPC组成的系统中, XD-Sph＝0.2, 0.4, 0.6时, 过量分子面积与过量吉布斯自由能在所研究的表面压力下表现为负值, 而当XD-Sph＝0.8时, 表现为正值; (2)鞘氨醇与DPPE组成的系统中, 当表面压力 π＜25 mN•m－1时, 过量分子面积与过量吉布斯自由能在所研究的组分比例下表现为负值, 当π≥25 mN•m－1时为正值. 混合单层膜的分子面积与表面吉布斯自由能决定了分子间的相互作用, 当为负值时分子间相互作用表现为吸引力, 出现凝聚现象; 为正值时分子间相互作用表现为排斥力, 促使单层膜出现相分离现象. 过量吉布斯自由能值越小, 单层膜的热稳定性越高. 弹性系数曲线分析和AFM图片观测进一步验证了理论分析的结果.     

乌苏酸/DPPC 混合单层膜相互作用的研究

乌苏酸(UA)为五环三萜羧基酸类化合物, 是一种中药有效成分. 它进入细胞的过程与膜脂分子有密切关系. 选用生物膜系统中的膜脂分子二棕榈酰基磷脂酰胆碱(DPPC)为代表, 通过LB(Langmuir-Blodgett)膜技术获得乌苏酸与DPPC 混合单层膜的表面压力/平均分子面积(π-A)曲线. 分析了混合单层膜的平均和过量分子面积、弹性系数等热力学参量, 并用原子力显微镜进行了研究. 比较了乌苏酸/DPPC 与胆固醇/DPPC 混合单层膜的异同. 实验结果表明: 乌苏酸能促使DPPC 的凝聚; 乌苏酸/DPPC 两组分的物质的量比与混合单层膜的膜压对单层膜的压缩性、稳定性和热力学特性有影响, 对单层膜中不同组分间的混合性以及分子间的相互作用具有重要的影响.     

鞘氨醇／胆固醇单层分子膜的热力学特性及表面形态的AFM观测

脂筏是近年来在生物膜研究中发现的一种富含鞘脂、胆固醇和特殊蛋白质的动态微区结构,其结构和功能的改变,会引发多种疾病．本文利用LB膜技术模拟脂筏的动态微区结构,通过测量表面压力与平均分子面积（π-A）曲线数据,计算出鞘氨醇／胆固醇LB单层膜的过量分子面积（△A（ex））、表面过量吉布斯自由能（△G（ex））、活度系数（f1和f2）以及弹性模量（Cs^-1）,系统的研究了二元组份混合单层膜的热力学特性,并用原子力显微镜对鞘氨醇与胆固醇混合膜的形态进行观察．热力学分析表明过量分子面积和过量吉布斯自由能相对理想状态都具有负偏差作用,这说明分子间相互作用表现为吸引力,且单层膜的稳定性、弹性模量和活度系数的数值明显的依赖于胆固醇与鞘氨醇的比例．AFM观察结果表明,纯鞘氨醇单分子膜表现为小的颗粒体结构;当鞘氨醇与胆固醇按不同摩尔比混合时,随着胆固醇摩尔比例的增加,混合膜呈现出从链状结构向较大的片层与网状共存结构的转化．最终纯胆固醇形成高度紧密的膜结构．AFM实验有力的支持了理论分析的结果．     

β-谷甾醇、豆甾醇与DPPC相互作用的单分子膜研究

植物甾醇对生物膜具有重要的调节作用,甾醇尾部的饱和程度对生物膜性质的影响一直是个热点问题.通过LB技术和原子力显微镜分别研究了尾部是单键的β-谷甾醇(β-sito)和尾部是双键的豆甾醇(stig)与二棕榈酰磷脂酰胆碱(DPPC)的相互作用,深入分析了β-谷甾醇、豆甾醇对DPPC单分子膜液态扩张-液态聚集(LE-LC)相变过程的影响.实验结果表明:β-谷甾醇、豆甾醇添加到DPPC单分子膜中,膜的压缩性以及分子的排列都发生了较大变化.当植物甾醇含量Xsterols=0.8时,β-谷甾醇、豆甾醇与DPPC相互作用具有相同的规律,过量分子面积和过量吉布斯自由能均为负值,说明分子间的吸引力比排斥力更强;在低浓度下,Xsterols=0.2,0.4时,两种系统的过量分子面积和过量吉布斯自由能呈现出明显的区别,尾部是单键的β-谷甾醇和DPPC混合单分子膜的排斥力更强烈,而尾部是双键的豆甾醇和DPPC混合单分子膜的吸引力更强烈,说明尾部是双键的豆甾醇比尾部是单键的β-谷甾醇更容易和DPPC发生凝聚,AFM数据进一步证实了这些结果.     

组份可控的钌螯合物功能单分子膜

用作“表面离子”的钌螯合物Ru(dpphen)32+与脂肪酸类成膜分子以1:2混合时能够得到稳定的混合单分子膜.以十八烷基三氯硅烷（octadecayl trichloro silane, OTS）分子部分取代Ru(dpphen)32+,得到功能分子组份可控的混合单分子膜.研究表明,OTS分子在纯水表面上可以形成交联网状单分子膜结构,混入硬脂酸（SA）分子后,网状结构逐渐被破坏.SA含量增加,破坏的程度就增大,直至SA/OTS为3:1时,完全没有网状交联结构,形成可以用来沉积LB膜的均匀致密的单分子膜.表面离子Ru(dpphen)32+与OTS和SA一起构成三组份混合单分子膜,OTS和Ru(dpphen)32+为表面离子.单分子膜中混有Ru(dpphen)32+分子,可以有效地阻止OTS的交联发生,同时Ru(dpphen)32+/SA基团与OTS/SA基团是均匀共混的.改变Ru(dpphen)32+/SA基团与OTS/SA基团的混合比,即可以做到Ru(dpphen)32+的组份精确可控,得到可用来沉积LB膜的均一、稳定的单分子膜.     

脂筏微区超分子聚集体结构的稳定性

生物膜中脂筏微区结构的动态特征与稳定性决定着生物膜的功能。通过从动物细胞提取脂筏,实验不但观测到质膜微囊烧瓶状凹陷结构,而且还观测到大量的球状和椭球状结构.通过模拟脂筏微区结构,重点对二元体系和三元体系的超分子聚集体结构的多形性进行了研究和探索。研究发现随着表面压力的增加,鞘磷脂和胆固醇双层膜出现了紧密聚集不规则的微区结构,在 SM/Chol/DOPC双层膜中,SM/Chol形成的微区结构漂浮在液态DOPC小颗粒上部。当 DOPE加入到SM/Chol中,三种成份形成不稳定的双层膜结构.Ceramide促进了SM/Chol结构发生重排,微区形状从原来的不规则向着紧密聚集的圆形结构演变;混合单层膜的分子面积与表面吉布斯自由能决定了分子间的相互作用, 当过量分子面积与过量吉布斯自由能为负值时,分子间相互作用表现为吸引力, 出现凝聚现象; 为正值时,分子间相互作用表现为排斥力, 促使单层膜出现相分离现象. 过量吉布斯自由能值越小, 单层膜的热稳定性越高.通过动物细胞提取脂筏与体外模拟脂筏相结合的方法,从超分子水平阐述了脂筏微区结构与功能的生物学意义,为生物膜的研究提供了理论依据和实验支持。     

季铵盐三聚表面活性剂在空气-水界面上单分子膜的崩溃压和分子极限面积

利用Langmuir膜天平研究了季铵盐三聚表面活性剂12-2-12-2-12在空气-水界面单分子膜的表面压-分子面积(π-A)等温线, 得到它的崩溃压对应的表面张力g_collapse和分子极限面积A_limit. 与12-2-12-2-12溶液临界胶束浓度对应的表面张力g_cmc和由Gibbs吸附方程得到的分子平均面积A_cmc相比较, 发现A_limit＜A_cmc, 而且g_collapse＞g_cmc. 分析12-2-12-2-12单分子膜的表面压随时间的衰减, 表明这个现象是由于表面活性剂从铺展单分子膜向水中溶解造成的, 而且初始表面压越大, 表面压的衰减越快.     

碳纳米管修饰电极的孔性界面对电分离多巴胺和抗坏血酸的影响

制备了碳纳米管修饰电极(镶嵌、涂层),并研究了电分离多巴胺(DA)和抗坏血酸(AA)的机理.结果表明,该电极的表面有一个多孔性的立体界面层,不仅对DA和AA具有较强的电催化作用,而且二者的氧化峰电位差(ΔE_pa)达250mV以上.用循环伏安法和差示脉冲伏安法研究了影响ΔE_pa的因素.分散剂的种类对ΔE_pa有很大的影响;多层碳纳米管的管径对ΔE_pa的影响较小,碳纳米管的种类(单层、多层、螺旋型多层)则有一定的区别;同一种碳纳米管经不同氧化强度的酸截短后,对ΔE_pa产生了明显影响.这说明修饰电极的界面性质对电分离DA和AA有较大的影响.     

Analysis of interfacial and micellar behavior of sodium dioctyl sulphosuccinate salt (AOT) with zwitterionic surfactants in aqueous media

The interfacial and bulk properties of mixtures of the anionic surfactant (dioctyl sulphosuccinate sodium salt, AOT) with zwitterionic surfactants 3-(N,N-dimethyldodecylammonio) propane sulfonate (DPS), 3-(N,N-dimethyltetradecylammonio) propane sulfonate (TPS), 3-(N,N-dimethylhexadecylammonio) propane sulfonate (HPS) have been studied employing surface tension, fluorescence, and viscometric techniques in aqueous media at 25 °C. It is observed that these mixtures exhibit synergism and these synergistic interactions increase with the enhancement of the hydrocarbon chain of the zwitterionic surfactant. The various physicochemical properties such as critical micelle concentration (cmc), surface excess concentration (Г(max)), minimum area per molecule (A(min)), aggregation number (N(agg)), interaction parameters (β(σ), β(m)), and thermodynamic parameters such as standard Gibbs free energy of adsorption (ΔG(ads)(o)), excess free energy of micellization (ΔG(ex)), and standard Gibbs free energy of micellization (ΔG(m)(o)) have been evaluated. The negative values of ΔG(m)(o) and ΔG(ads)(o) show that the micelle formation and adsorption of surfactant at the air/solution interface is energetically favorable, while a negative value of ΔG(ex) ensures stability of the mixed micelles formed. The Regular Solution Approximation, Motomura and Rosen's approaches have been used to explain and compare the results. The packing parameter (p) ensures the formation of vesicles or bilayers for AOT+DPS/TPS mixtures, which can potentially be used as delivery agents for industrial applications.     

Evidence of domain formation in cardiolipin-glycerophospholipid mixed monolayers. A thermodynamic and AFM study

The interaction of the three main components of the mitochondrial membrane, namely cardiolipin, phosphatidylcholine, and phosphatidylethanolamine, has been studied investigating mixed cardiolipin-phosphatidylcholine and cardiolipin-phosphatidylethanolamine monolayers at different cardiolipin molar fractions. The thermodynamic behavior of the mixed monolayers was investigated by means of surface pressure and surface potential measurements, and atomic force microscopy was employed to characterize the morphology of the monolayers. Langmuir isotherms and surface potential curves show a regular behavior with a progressive transition toward the isotherm of the pure component. Positive deviations from ideality in the excess Gibbs energies of mixing suggest the presence of repulsive interactions in both systems. Analysis of partial molecular dipole moment indicates a discontinuity at a definite cardiolipin/phosphatidylethanolamine molar fraction, suggesting the formation of a stoichiometric complex; as a consequence, in mixed cardiolipin-phosphatidylethanolamine monolayers, a phase separation is observed at phosphatidylethanolamine excess. AFM measurements indicate the presence of two domains: one made by phosphatidylethanolamine and the other by a regular arrangement of phosphatidylethanolamine and cardiolipin at a fixed molecular ratio.     

Mode of interaction of two fluorinated-hydrogenated hybrid amphiphiles with dipalmitoylphosphatidylcholine (DPPC) at the air-water interface

Two-component Langmuir monolayers formed on 0.02M Tris buffer solution (pH 7.4) with 0.13M NaCl at 298.2K were investigated for two different fluorinated-hydrogenated hybrid amphiphiles (F6PH5PPhNa and F8PH5PPhNa or F6 and F8, respectively) with DPPC. Surface pressure (pi), surface potential (DeltaV) and dipole moment (mu( perpendicular)) as a function of molecular surface area (A) were measured by employing the Whilhelmy method and an ionizing electrode method. From the A- and DeltaV-X(F6) (or X(F8)) curves, partial molecular surface area (PMA) and apparent partial molecular surface potential (APSP) were determined as a function of surface mole fraction (X(Fn)) at discrete surface pressures. Then, the behavior of occupied surface areas and surface potentials of the respective components could be made clearer. Compressibility (C(s)), elasticity (C(s)(-1)), and excess Gibbs energy (DeltaG((ex))) as a function of X(F6) (or X(F8)) were estimated at definite pressures. These physico-chemical parameters were found to reflect the mechanical strength of monolayer films formed. The regular solution theory being applied to DeltaG((ex)), the activity coefficients (f) as well as the interaction parameter (I(p)) between DPPC and two hybrid amphiphiles in the binary monolayers were evaluated. I(p) values thus obtained indicated that F8 molecules interact more strongly with DPPC molecules than F6. Moreover, in order to better understand the morphological monolayer state, Langmuir-Blodgett (LB) films made from DPPC and fluorinated-hydrogenated hybrid amphiphiles were examined by atomic force microscopy (AFM). The miscibility of the two components in the monolayer state is evidenced by these thermodynamic quantities and AFM observations. Furthermore, AFM images demonstrated that F8 could more effectively disperse the ordered domains of DPPC than F6.     

Prediction of excess thermodynamic functions and activity coefficients of some polymeric liquid mixtures using a new equation of state

In this work, the excess thermodynamic properties, namely excess molar Gibbs energy, excess molar enthalpy, excess molar entropy, excess molar internal energy, and excess molar Helmholtz energy for four polymer mixtures and blends at different temperatures, pressures, and compositions have been calculated using the GMA equation of state. We have also calculated the activity coefficient for these polymeric mixtures using the GMA equation of state. The values of statistical parameters between experimental and calculated properties show the ability of this equation of state in reproducing and predicting the excess thermodynamic functions and activity coefficients for studied polymeric mixtures.     

Thermodynamic characterization of the prevailing molecular interactions in mixed floating monolayers of phospholipids and usnic acid

The investigation of the characteristics of mixed floating monolayers of phospholipids and usnic acid (UA), an active metabolite from lichens, can provide valuable information on how to prepare stable liposomes that could serve as carriers of UA for therapeutic proposes. The present paper is concerned with the thermodynamic analysis of the behavior of Langmuir monolayers formed by mixing different phospholipids (dibehenoylphosphatidylcholine, DBPC, dipalmitoylphosphatidylcholine, DPPC, and dioleoylphosphatidylcholine, DOPC) and UA at varied molar fractions. Relevant thermodynamic parameters such as excess areas, excess free energies and free energy of mixing were derived from the surface pressure data obtained from compression measurements performed in a Langmuir trough. For the largest lateral pressure examined (25 mN/m), negative values of the excess free energy were found only for the DOPC/UA monolayer, which should be the most stable of them. Based on the calculated values of the free energy of mixing, we note that the DBPC/UA and DPPC/UA systems present the best mixed character at low pressures and when the molar fraction of the UA is 0.5; at that relative concentration and at low values of the external pressure, the UA molecules can better mix and interact with the phospholipid molecules. The compression isotherms for mixed monolayers show no visible transitions, exhibiting a more organized phase that corresponds to a negative free energy of mixing. We have established that the most stable monolayers were those corresponding to DOPC/UA mixtures with a UA molar fraction of 0.75.     

Interaction of the Hepatitis A peptide VP3(110–121) with lipid mono and bilayer models of cellular membranes

 The surface activity of HAV-VP3(110–121) peptide was studied at different concentrations in an aqueous solution. Saturation was reached at 0.62 μM concentration. The ability of the peptide to insert into monolayers of CL, SA, DPPC, DPPC/5% CL and DPPC/5% SA was also performed. Mixed mono-layers composed of this peptide and the lipid mixtures were also studied as far as the miscibility of the two components is concerned. The mixed monolayers showing small negative deviations from ideality. The values of excess free energy of mixing (ΔG ^E _M) suggest that the energy associated to the miscibility process is almost non-significant except for a 0.2 molar fraction of DPPC/SA and 0.6 molar fraction of DPPC/CL. The peptide has an expanding effect upon the monolayers but due to its amphoteric character this interaction is not dependent on the electrical charge of the lipids. In fluorescence studies, the peptide showed some degree of interaction with the lipid polar heads, but no interactions were detected with its alkylchains. This results show that after incubation with DPPC/5% CL and DPPC/5% SA liposomes the peptide remains in the outer part of the bilayers. Received: 20 January 1997 Accepted: 28 May 1997     

The excess enthalpy of (tetrachloromethane + carbon disulphide) and (tetrachloromethane + dichloromethane) over a range of temperatures and pressures

Measurements of the excess molar enthalpy of (tetrachloromethane + carbon disulphide) and (tetrachloromethane + dichloromethane) have been made using an isothermal high-pressure flow calorimeter. The measurements for (tetrachloromethane + carbon disulphide) cover the range 283.15 to 323.15 K at pressures between 0.1 and 30 MPa. The excess molar enthalpies for (tetrachloromethane + dichloromethane) are reported at 298.15 K at 0.1, 15, and 30 MPa, and at 323.15 K at 0.2 MPa. The thermodynamic consistency of the results is shown by deriving the temperature dependence of the excess molar Gibbs free energy from them and comparing with published experimental values.     

Interfacial composition, thermodynamic properties, and structural parameters of water-in-oil microemulsions stabilized by 1-pentanol and mixed surfactants

The present study is focused on the evaluation of the interfacial composition, thermodynamic properties, and structural parameters of water-in-oil mixed surfactant microemulsions [(cetylpyridinium chloride, CPC+polyoxyethylene (20) cetyl ether, Brij-58 or polyoxyethylene (20) stearyl ether, Brij-78)/1-pentanol/n-heptane, or n-decane] under various physicochemical environments by the Schulman method of cosurfactant titration of the oil/water interface. The estimation of the number of moles of 1-pentanol at the interface (n(a)(i)) and bulk oil (n(a)(o)) and its distribution between these two domains at the threshold level of stability have been emphasized. The thermodynamics of transfer of 1-pentanol from the continuous oil phase to the interface have been evaluated. n(a)(i),n(a)(i), standard Gibbs free energy (ΔG(t)(0)), standard enthalpy (ΔH(t)(0)), and standard entropy (ΔG(t)(0)) of transfer process have been found to be dependent on the molar ratio of water to surfactant (ω), type of nonionic surfactant and its content (X(Brij-58 or Brij-78)), oil and temperature. A correlation between (ΔH(t)(0)) and (ΔS(t)(0)) is examined at different experimental temperatures. Bulk surfactant composition dependent temperature insensitive microemulsions have been reported. Associated structural parameters, such as droplet dimensions and aggregation number of surfactant and cosurfactant at the droplet interface have been evaluated using a mathematical model after suitable modifications for mixed surfactant systems. In light of these parameters, the prospect of using these microemulsion systems for the synthesis of nanoparticles and the modulation of enzyme activity has been discussed. Correlations of the results in terms of the evaluated physicochemical parameters have been attempted.     

Effects of lipid chain length on the surface properties of alkylaminomethyl rutin and of its mixture with model lecithin membrane

Three model flavonoid-based bioactive molecules with different lipid chain lengths (RuCn: n=8, 12, 18) were newly synthesized. The surface properties [surface pressure (π)-area (A), surface potential (ΔV)-surface pressure (π) and dipole moment (u(⊥))-surface pressure (π)] of pure RuCn and the lecithin membrane compounds had been investigated by using the Langmuir monolayer technology. The results suggested that the distinctive monolayer behavior of RuCn is strongly dependent on the lipid chain length. The great differences in the monolayer properties brought by the lipid chain length could be attributed to two major factors: (i) the ionization degree of the bulky hydrophilic head group (including hydroxyl and NH groups) alters its local field solely via the surface potential; (ii) tring molecular (or dipole) packing density within monolayers. The excess Gibbs energy (ΔG((ex))) calculated for the RuCn-lecithin mixed monolayers infers that higher stability of the mixed monolayer can be strengthened as the lipid chain length decreases. And the addition of RuCn into lecithin membrane may increase the total u(⊥) of the binary mixed monolayers, which could inhibit the hydration of the lecithin's hydrophilic head groups. The shorter the lipid chain length of RuCn (e.g., RuC8) is, the higher the surface activity can be. Our findings provide a molecular basis for the application of such class of biomolecules in the functional food, cosmetics and medicine.