压缩速度对Surfactin在单分子膜内聚集行为的影响

研究了一种微生物脂肽——Surfactin(表面活性素)在气/液界面形成的单分子膜性质, 测定了压缩速度对其单分子膜的表面压-分子面积(π-A)曲线的影响. 结果表明, Surfactin单分子膜铺展在pH＝2酸性亚相上的过程是一个亚稳过程. 通过原子力显微镜(AFM)观察了不同压缩速度时在25 mN•m－1下转移的Langmuir-Blodgett (LB)膜. 在中等压缩速度(0.6 nm2•mol－1• min－1)时转移的LB膜表面观察到分布均匀、排列规则、类似球形的表面聚集体, 而在其它压缩速度下, 形成了按一定规则分布的表面团簇结构. 结合π-A曲线和AFM图像, 提出了Surfactin表面聚集体在气/液界面上的形成机制.     

微生物脂肽与磷脂的混合单分子膜性质

研究了一种微生物脂肽--表面活性素与二肉豆蔻酰磷脂酰胆碱(DMPC)在气,液界面形成的混合单分子膜性质.测定了混合单分子膜的表面压.分子面积(л-A)曲线,根据л-A曲线获得了不同表面压下混合单分子膜的过剩面积(Aex)和混合过剩自由能(△Gmex)与混合单分子膜中表面活性素摩尔分数的关系.Aex和△Gmex的计算结果均表明,表面活性素与DMPC在纯水亚相上形成的混合单分子膜中不相容,二者之间 的相互作用主要是排斥力.通过原子力显微镜观察了在表面压15mN/m下的混合单分子膜的LB膜,发现表面活性素与DMPC发生了微相分离,说明二者在混合膜中的烷基链取向不同,这可能是二者发生排斥作用的主要原因之一.此外,还研究了亚相pH对混合单分子膜相容性的影响,发现表面活性素与DMPC在混合单分子膜中的相容性在碱性环境下增强,这可能与二者极性头基之间的相互作用有关.     

水溶性菁染料与类脂物混合单分子膜中J-聚集体形成的研究

报道了具有相同发色团,并有不同电荷的二种菁染料单分子膜中J-聚集体的形成。测定了单分子膜的π/A,△V/A曲线,反射光谱及吸收光谱。从实验结果得出:带正电荷的染料与花生酸混合形成单分子膜后,膜中染料的二聚体与J-聚集体随着表面压力改变存在着一个平衡。而带负电荷的染料与二十烷基胺成膜后,即使在很低的表面压下也有J-聚集体形成。同时染料分子在水面上的取向是各向异性。     

Langmuir单分子膜在海洋飞沫气溶胶表面特性研究中的应用

被表面活性有机物包裹的液相气溶胶,如海洋飞沫气溶胶(SSA),通常具有反胶束的结构,它由有机分子形成的疏水表面和一个水相内核构成。SSA界面有机膜的组分和形态对其物理、化学和光学特性有重要的影响。Langmuir单分子膜是由脂肪酸、脂肪醇和磷脂等具有低挥发性的长链表面活性有机物在空气-水界面上扩散形成的单层分子薄膜。采用Langmuir槽可以测定水-气界面的单组分或复合组分单分子膜的表面压随分子面积变化的曲线(π-A曲线),从而揭示相应单分子膜的界面特性,进而预测表面活性剂在实际SSA中的命运和行为。本文综述了常用大气气溶胶界面表征技术、基于单分子膜建立的SSA模型以及有机膜对SSA大气行为的影响。虽然目前对SSA相关单分子膜的物理性质和形貌变化已有深入的研究,但是对于反应性气体、光照和生物活性物质等环境因素引起的界面变化却很少有关注,本文为未来的实验室模拟和模式研究提供了新的思路。     

带相反电荷高分子和表面活性剂复合物膜在空气/水界面上的特性

利用原子力显微镜技术、表面压松弛法对带相反电荷高分子和表面活性剂在气/水界面形成的界面复合物膜进行了特性研究.原子力显微镜研究结果表明,部分水解聚丙烯酰胺(HPAM)/十六烷基三甲基溴化铵(CTAB)所形成的界面复合物膜呈现出“团”状聚集体形貌.两性聚丙烯酰胺与CTAB形成的界面复合物膜呈现出“纤维丝”的聚集体形貌.亚相中盐的存在对界面复合物的形貌有很大影响.表面压松弛实验则进一步表明界面复合物膜形貌结构的变化对其膜稳定性有直接的影响.     

TPPS和Gemini表面活性剂的复合膜及其手性的研究

研究了一种新的gemini表面活性剂(C12H24-α,ω-(C12H25N＋(CH3)2Br－)2, （简写为C12-C12-C12）和TPPS在气液界面上形成的复合膜及其手性.实验发现,单独C12-C12-C12不能在纯水表面形成稳定的单分子膜，但当亚相中存在TPPS时，可形成稳定的单分子膜.通过水平提拉法将复合膜转移到固体基板上，发现在适当的pH值条件下，TPPS可在复合膜中形成J-聚集体，并且发现，尽管Gemini表面活性剂和TPPS 都 是非手性的，TPPS的J-聚集体表现出强烈的Cotton效应.另外，gemini表面活性剂的两个正电荷中心对TPPS的J-聚集体的手性并不能表现出协同效应.     

Gemini表面活性剂对疏水缔合聚丙烯酰胺界面吸附膜扩张流变性质的影响

采用小幅低频振荡和界面张力弛豫技术, 考察了疏水缔合水溶性聚丙烯酰胺(HMPAM)在正癸烷-水界面上的扩张黏弹性质, 研究了不对称Gemini表面活性剂C₁₂COONa-p-C₉SO₃Na对其界面扩张性质的影响. 研究发现, 疏水链段的存在, 使HMPAM在界面层中具有较快的弛豫过程, 扩张弹性显示出明显的频率依赖性. 表面活性剂分子可以通过疏水相互作用与聚合物的疏水嵌段在界面上形成类似于混合胶束的特殊聚集体. 表面活性剂分子与界面聚集体之间存在快速交换过程, 可以大大降低聚合物的扩张弹性. 同时, 聚合物分子链能够削弱表面活性剂分子长烷基链之间的强相互作用, 导致混合吸附膜的扩张弹性远低于单独表面活性剂吸附膜.     

杯[4]芳烃双咪唑季铵盐的Langmuir-Blodgett膜性质

合成了杯[4]芳烃构建的双咪唑季铵盐化合物1(BIQ-Calix),利用表面压一面积(π-A)等温线、压缩/扩张循环等温线与膜弛豫等温线、紫外与红外光谱、原子力显微镜等手段研究了该化合物在空气/水相界面、空气/二元羧酸水溶液界面的成膜性能。结果表明:化合物1在水或者二元羧酸乙二酸,丙二酸,丁二酸水溶液的亚相表面均能很好的形成稳定的Langmuir膜,其崩溃压分别为24 mN·m-1,30 mN·m-1,33 mN·m-1和28 mN·m-1,平均单分子面积分别为2.0 nm2,2.3 nm2,2.5 nm2和2.2 nm2,并能与二元羧酸阴离子一起转移到固体基片上形成LB膜,且化合物1形成的LB膜为H-聚集体。     

髓鞘碱性蛋白对细胞膜脂质分子DPPC、DPPE单层膜影响机理研究

本文通过Langmuir单层膜的表面压力-平均分子面积(π-A)曲线的测定与分析,分别对髓鞘碱性蛋白(MBP)与细胞膜中不同头部基团脂质分子二棕榈酰基磷脂胆碱(DPPC)和二棕榈酰基磷脂酰乙醇胺(DPPE)在空气/液体界面上的相互作用过程进行了系统研究.实验结果表明:(1)当界面上脂质含量一定时,亚相中随着MBP浓度的增大,DPPC、DPPE单层膜的等温线向平均分子面积较大的方向移动;(2)在单层膜表面压力为10 mN/m时,一个MBP分子分别结合140±3个DPPC分子和100±3个DPPE分子,随着表面压力增大,当MBP分子分别与两种磷脂分子相互作用时,MBP插入到磷脂单层界面的个数逐渐减少;(3)随着蛋白质浓度的增加,脂分子形成的单层膜变得较为疏松,且MBP分子易于插入到分子头部较小的DPPE单层膜中;(4)蛋白质的存在使DPPC单层膜的表面压力逐渐减小,且蛋白质浓度越大表面压力降低越多,DPPC被MBP带入到亚相中越多;(5)对于DPPE单层膜,蛋白质通过与DPPE相互作用插入到界面膜中,引起表面压力增大,且蛋白质浓度越高,压力变化量越大.     

卟啉、酞菁L-B膜中取代基的定向作用研究

由Π-A 曲线研究了五种具有不同取代基的卟啉、酞菁金属配合物不溶物膜的水/空气界面性质, 根据分子截面积和分子模型推断了单层膜中卟啉、酞菁环的可能取向及取代基的定向作用. 以偏振紫外测定了L-B 多层膜中大环的取向, 结果表明卟啉, 酞菁环以与它们在亚相表面相同的取向转移到固体基片上, 证明了取代基的性质和致目不同对分子大环的定向作用不同.     

Polystyrene-b-poly(tert-butyl acrylate) and polystyrene-b-poly(acrylic acid) dendrimer-like copolymers: two-dimensional self-assembly at the air-water interface

The two-dimensional self-assembly at the air/water (A/W) interface of two dendrimer-like copolymers based on polystyrene and poly(tert-butyl acrylate) (PS-b-PtBA) or poly(acrylic acid) (PS-b-PAA) was investigated through surface pressure measurements (isotherms, isochores, and compression-expansion hysteresis experiments) and atomic force microscopy (AFM) imaging. The two dendrimer-like block copolymers have an 8-arm PS core (Mn = 10 000 g/mol, approximately 12 styrene repeat units per arm) with a 16-arm PtBA (Mn = 230 000 g/mol, approximately 112 tert-butyl acrylate repeat units per arm) or PAA (Mn = 129 000 g/mol, approximately 112 acrylic acid repeat units per arm) corona. The PS-b-PtBA sample forms stable Langmuir monolayers and aggregates into circular surface micelles up to a plateau observed in the corresponding isotherm around 24 mN/m. Beyond this threshold, the monolayers collapse above the interface, resulting in the formation of large and irregular desorbed aggregates. The PS-b-PAA sample has ionizable carboxylic acid groups, and its A/W interfacial self-assembly was therefore investigated for various subphase pH values. Under basic conditions (pH = 11), the carboxylic acid groups are deprotonated, and the PS-b-PAA sample is therefore highly water-soluble and does not form stable monolayers, instead irreversibly dissolving in the aqueous subphase. Under acidic conditions (pH = 2.5), the PS-b-PAA sample is less water-soluble and becomes surface-active. The pseudoplateau observed in the isotherm around 5 mN/m corresponds to a pancake-to-brush transition with the PAA chains dissolving in the water subphase and stretching underneath the anchoring PS cores. AFM imaging revealed the presence of circular surface micelles for low surface pressures, whereas the biphasic nature of the pseudoplateau region was confirmed with the gradual aggregation of the micellar PS cores above the PAA chains. The aggregation numbers for both samples were estimated around 3-5 dendrimer-like copolymers per circular surface micelle. These rather low values confirmed the tremendous influence of molecular architecture on the two-dimensional self-assembly of block copolymers.     

Monolayer behavior of a pyridyl head-group-containing amphiphile and its miscibility with poly(D,L-lactide-co-glycolide) on different pH subphase

In this paper, we investigated the Langmuir film and Langmuir-Blodgett (LB) monolayer film of a nonionic amphiphilic molecule, 4-(6-p-pyridyloxyl)hexyloxyl-4'-dodecyloxylazobenzene (C(12)AzoC(6)Py) and its mixture with poly(D,L-lactide-co-glycolide) (PLG) at different subphase pH values (2.0, 2.6, 3.3, 4.4, and 6.5, respectively) by surface pressure-area (pi-A) isotherms, in situ interface Brewster angle microscopy (BAM), and ex situ atomic force microscopy (AFM). For pure C(12)AzoC(6)Py, its pi-A isotherms display a plateau when the subphase pH value is lower than 3.0. The pressure of the plateau increases with the decrease of pH until 2.0. Over the plateau, the pi-A isotherms become almost identical to the one under neutral conditions. The appearance of such a plateau can be explained as the coexistence of protonation and unprotonation of pyridyl head groups of the employed amphiphile. In contrast to the homogeneous surface morphology of pure C(12)AzoC(6)Py near the plateau by BAM observation, the surface in the case of its mixing with PLG exhibits a dendritic crystalline state under low surface pressure at subphase pH lower than 3.0. The crystalline state becomes soft and gradually melts into homogeneous aggregates with surface pressure increasing to a higher value than that of the plateau. Meanwhile, the hydrolysis of PLG in the mixture system at the interface has been affirmed to be restrained to a very large extent. And the PLG was believed to be compelled to the up layer of the LB film due to the phase separation, which is examined by AFM. Based on the experimental results, the corresponding discussion was also performed.     

Study of the Air-Water Interfacial Properties of Biodegradable Polyesters and Their Block Copolymers with Poly(ethylene glycol)

It has been reported that the surface pressure-area isotherm of poly(d,l-lactic acid-ran-glycolic acid) (PLGA) at the air-water interface exhibits several interesting features: (1) a plateau at intermediate compression levels, (2) a sharp rise in surface pressure upon further compression, and (3) marked surface pressure-area hysteresis during compression-expansion cycles. To investigate the molecular origin of this behavior, we conducted an extensive set of surface pressure and AFM imaging measurements with PLGA materials having several different molecular weights and also a poly(d,l-lactic acid-ran-glycolic acid-ran-caprolactone) (PLGACL) material in which the caprolactone monomers were incorporated as a plasticizing component. The results suggest that (i) the plateau in the surface pressure-area isotherm of PLGA (or PLGACL) occurs because of the formation (and collapse) of a continuous monolayer of the polymer under continuous compression; (ii) the PLGA monolayer becomes significantly resistant to compression at high compression because under that condition the collapsed domains become large enough to become glassy (such behavior was not observed in the nonglassy PLGACL sample); and (iii) the isotherm hysteresis is due to a coarsening of the collapsed domains that occurs under high-compression conditions. We also investigated the monolayer properties of PEG-PLGA and PEG-PLGACL diblock copolymers. The results demonstrate that the tendency of PLGA (or PLGACL) to spread on water allows the polymer to be used as an anchoring block to form a smooth biodegradable monolayer of block copolymers at the air-water interface. These diblock copolymer monolayers exhibit protein resistance.     

Polymerization of a cysteinyl peptidolipid Langmuir film

The surface pressure-area isotherm of a cysteinyl peptidolipid on a pure water subphase (pH 5.8) was compared with that on a water subphase saturated with oxygen and buffered with ammonium bicarbonate (pH 7.8). A reduction of the limiting molecular area was observed for the isotherm measured on the subphase saturated with oxygen. Hysteresis in the compression-decompression cycles of the Langmuir film was also observed. Taking into consideration the chemical structure of the peptidolipid, we rationalized that the free sulfhydryl groups of the peptidolipid were oxidized in the presence of oxygen in the alkaline subphase to form intermolecular disulfide bonds at the air-water interface. The surface topography of the peptidolipid Langmuir film was observed by epi-fluorescence microscopy and the Langmuir-Blodgett film by environmental scanning electron microscopy (ESEM). The micrographs showed evidence of the polymerization of the cysteinyl peptidolipid at the air-water interface. Furthermore, the XPS spectra of the Langmuir-Blodgett films also proved the existence of disulfide bonds. The control peptidolipid C(18)-Ser-Gly-Ser-OH showed identical surface pressure-area isotherms in the presence or absence of an oxygen-saturated subphase.     

Memory effects on the interfacial characteristics of dioctadecyldimethylammonium bromide monolayers at the air-water interface

The structural and dynamic characteristics of dioctadecyldimethylammonium bromide (DODAB) monolayers on a pure water subphase were investigated by surface film balance, Brewster angle microscopy, and relaxation in area and surface pressure at constant surface pressure and area, respectively. The first compression-expansion cycle of the monolayer is not reversible and the second pi-A compression isotherm deviates to larger molecular areas relative to the first one. At a microscopic level this hysteresis may be assigned to an irreversible hydration of the ammonium groups of DODAB. The morphology and reflectivity of DODAB monolayers during compression and expansion on the monolayer depend on the monolayer history. Bright domains randomly dispersed were observed during compression before collapse. Surprisingly, this random distribution of domains changes into a fractal-like structure during the monolayer expansion in a narrow range of surface pressures. This morphology does not form when the monolayer is previously compressed above the collapse surface pressure. 2D foam-like structure is often observed when the film is expanded at maximum area. Relaxation phenomena in DODAB monolayers are attributed to monolayer reorganization and nucleation of liquid-condensed domains from the liquid-expanded phase. These time-dependent processes are irreversible.     

在气液界面上压缩诱导聚(L-乳酸)膜的结构变化

聚乳酸(PLA)是一种环境友好及生物可降解的聚合物, 其界面性质受到了广泛关注. 本文以Langmuir-Blodgett (LB)膜天平、原子力显微镜(AFM)研究了聚(L-乳酸) (PLLA)在气液界面上的性质. 表面压-面积(π-A)等温曲线的结果表明, 在膜压缩的初始阶段, 表面压逐渐增大; 当膜压为9.0 mN·m^-1时, 曲线出现了一个平台,其重复单元的面积大约在0.11-0.17 nm²之间. 原子力显微镜的结果发现, 在压缩过程中, 膜结构发生了明显的变化: 平台刚出现时, 膜内出现了大量的纤维结构; 在平台区内, 界面上出现了多层膜结构. 特别地, 当表面压为20.0 mN·m^-1时, PLLA在界面上可形成约6.0 nm厚的薄膜. 由此可见, PLLA等温线中的平台与其膜结构的变化紧密相关. 这有别于普通双亲分子的性质, 即这类双亲分子π-A等温线中的平台通常表示它们在二维空间上发生了单分子膜的相转变.     

The behavior of poly(ε -caprolactone) and poly(ethylene oxide)-b-poly(ε -caprolactone) grafted to a poly(glycerol adipate) backbone at the air/water interface

The behavior of crystallizable poly(ε-caprolactone) (PCL) and poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) is studied at the air/water interface prior and after grafting to an amorphous poly(glycerol adipate) (PGA) backbone (PGA-g-PCL, PGA-g-(PCL-b-PEO)). Langmuir isotherms are measured and the structure formation in the monolayers on the water surface is followed by Brewster angle microscopy (BAM) and in Langmuir–Blodgett films after a transfer to silicon substrates by atomic force microscopy (AFM). It is observed that PGA-g-PCL forms significantly smaller crystals on the water surface and has smaller crystallization rate compared to PCL homopolymers of identical molar masses as the grafted chains. In contrast to crystals formed by linear PCL, the crystals formed by grafted PCL in PGA-g-PCL do not melt (readsorb at the water surface) in an expansion cycle on the Langmuir trough. Additionally, increasing the subphase temperature at constant surface area significantly above the melting point of linear PCL in bulk results in the formation of a mesophase, and it does lead to the disappearance of crystals. The isotherms of PGA-g-(PCL-b-PEO) show a transition at the surface pressure of ～10 mN/m. This is related to the fact that PEO chains leave the water surface and submerge into the subphase and/or the crystallization of PCL chains. The monolayer collapse appears in an extended plateau region starting at π values of ～30 mN/m. AFM images of Langmuir–Blodgett films reveal that PCL chains in PGA-g-PCL and PGA-g-(PCL-b-PEO) form lamellar crystals with a disk-shape and interconnected platelets, respectively.     

A study of the interaction between polyelectrolyte-coated nanostructured CaCO<Subscript>3</Subscript> particles and a stearic acid monolayer spread at the water/air interface

The influence of nanostructured CaCO₃ particles, both uncoated and coated with a polyelectrolyte (poly(diallyldimethylammonium chloride), polyethyleneimine, fluorescein-5-isothiocyanate-labeled poly(allylamine hydrochloride), or sodium polystyrene sulfonate), on a stearic acid monolayer spread on the surface of an aqueous subphase has been studied. The interaction of the particles present in the subphase with the monolayer as depending on the presence and composition of a polymer coating has been estimated with the help of compression isotherms and the Brewster angle microscopy. The monolayers were transferred from the aqueous subphase onto a solid substrate and studied by scanning electron microscopy. Strong interaction has been revealed between the calcium carbonate particles and the stearic acid monolayer. It has been shown that the transfer of the monolayer from the aqueous suspension surface onto the solid substrate may be accompanied by the detachment of the polymer coating from the surface of CaCO₃ particles or their transfer together with the monolayer.     

Influence of environmental conditions on the interfacial organisation of fengycin, a bioactive lipopeptide produced by Bacillus subtilis

The effect of the environmental conditions both on the behaviour of fengycin at the air-aqueous interface and on its interaction with DPPC was studied using surface pressure-area isotherms and AFM. The ionisation state of fengycin is at the origin of its monolayer interfacial properties. The most organised interfacial arrangement is obtained when fengycin behaves as if having zero net charge (pH 2). In a fully ionised state (pH 7.4), the organisation and the stability of fengycin monolayers depend on the ionic strength in the subphase. This can modulate the surface potential of fengycin and consequently the electrostatic repulsions inside the interfacial monolayer, as well as the lipopeptide interaction with the layer of water molecules forming the air-water interface. Intermolecular interactions of fengycin with DPPC are also strongly affected by the ionisation state of lipopeptide and the surface pressure (Pi) of the monolayer. A better miscibility between both interfacial components is observed at pH 2, while negatively charged lipopeptide molecules are segregated from the DPPC phase. A progressive desorption of fengycin from the interface is observed at pH 7.4 when Pi increases while at pH 2, fengycin desorption brutally occurs when Pi rises above Pi value of the intermediate plateau.