一种液晶化合物LB膜中的分子取向及膜结构

"利用LB技术制备出MPUOPM的Langmuir和LB膜．随着表面压力的升高,在?-A曲线上的可观察到一个明显的折点．通过与分子刚性基团的理论截面积相比较,发现该折点反映的是单层膜向多层膜的转变．紫外可见、偏振红外等光谱被用来研究膜的结构,发现烷基链与基片法线夹角为48o,C＝N基团互相平行,与基片法线呈51o夹角排列．"     

季铵盐型双子表面活性剂在空气-水界面的单分子膜

利用Langmuir膜天平测定不对称双子表面活性剂12-2-16和对称双子表面活性剂12-2-12在空气-水界面上形成单分子膜的表面压,通过单分子膜的π-A等温线、微分等温线和静态弹性,分析其相转变和成膜特性.结果表明,与传统阳离子表面活性剂DTAB比较,12-2-16、12-2-12比DTAB单分子膜的分子极限面积大,崩溃压高,并有较高的静态弹性,因而具有较高的凝聚性和稳定性,其中12-2-16单分子膜的凝聚性和稳定性最高.     

Ftir Studies on LB Film of Amphiphile with Schiff Base as Headgroup and Its Copper Complex

Two different ways to form monolayers and LB films (surface film and subphase film) of the complex have been used, where a novel amphiphile containing Schiff base as a headgroup was used as a ligand. the monolayer behavior at the air/water interface was characterized by π-A isotherms and two-dimensional molecular orientation of alkyl chains in LB films and thermal stability were measured by polarized and variable temperature FTIR transmission spectra, indicating that the LB film of the novel amphiphile and its copper(II) complex are very stable as well as stearic acid. Because incorporating the metal ion into the monolayer makes it more condensed, thermal stability of the LB film was enhanced. as can be compared from their structure and properties, subphase films are superior to surface films.     

Monolayer characteristics of stereoregular PMMA at the air/water interface

Behaviors of isotactic, atactic and syndiotactic poly(methyl methacrylate) (PMMA) monolayers at the air/water interface were investigated. The monolayer characteristics of the three stereoisomers were studied and compared in terms of surface pressure-area per molecule (π-A) isotherm, hysteresis and relaxation phenomena, and the phase images observed from Brewster angle microscopy (BAM). The results show that iPMMA monolayer has a more extended and compressible property, and exhibits pronounced hysteresis and relaxation phenomena among the three tactic PMMAs. Such characteristics can reasonably be attributed to the higher flexibility of chains segments of iPMMA as estimated from its lower T_g. On the other hand, sPMMA, the one with the highest T_g, forms a more condensed monolayer due to the high cohesive interaction among polymer chains. The BAM images show that PMMA molecules are not well extended on the subphase and thus, aggregative phases were observed even in a state corresponding to the gas phase. The aggregative structures are especially significant on sPMMA monolayer, which is consistent with the results estimated from the π-A isotherms. When the temperature is elevated from 25 to 40 °C, all the monolayers of the three stereoisomers become more expanded and compressible due to the increase in chain flexibility.     

Studies on behaviors of dipalmitoylposphatidylcholine and bilirubin in mixed monolayer at the air/water interface

Mixed monolayers of dipalmitoylposphatidylcholine (DPPC) and bilirubin (BR) were prepared on different subphases. The properties of DPPC/BR monolayer, such as collapse pressure (π_coll), limiting area per molecule (A_lim), surface compressibility modulus, free energy (ΔG_mix) and excess free energy (ΔG_ex), were investigated based on the analysis of the surface pressure-area isotherms on pure water. The results showed that DPPC and BR were miscible and formed non-ideal mixed monolayers at the air/water interface. With the molar fraction of BR (X_BR) increasing, the LE-LC coexistence region of DPPC monolayer was eliminated gradually. The DPPC/BR complex (M_D-B) of 1:2 stoichiometry formed as a result of the strong hydrogen bonds between the polar groups of DPPC and BR. The studies of effects of pH values and calcium ions in subphase on the DPPC/BR monolayers showed that the mixed monolayer became expanded on alkali aqueous solution and on 1 mmol/L CaCl₂ aqueous solution. The orientation of DPPC and BR at air/water interface was also discussed.     

Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface

The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics.The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine(DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine(DPPE) by analyzing the data of surface pressure–area(π–A) isotherms and surface pressure–time(π–T) curves.Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 m N/m.However,the changes of DPPE are larger than DPPC,indicating stronger interaction of lysozyme with DPPE than DPPC.The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 m N/m.Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers,which leads to self-aggregation and self-assembly,forming irregular multimers and conical multimeric.Through analysis,we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers.     

半胱胺单分子膜结构的表面增强拉曼散射研究(英文)

在金属电极表面所形成的有机分子的单分子膜或薄膜对于基础研究和实际应用都有着极其重要的意义。以化学吸附形式在金电极表面所形成的半胱胺单分子膜,常常用于蛋白质等生物大分子在金属表面进行吸附的连接层,以避免这些生物大分子在金属表面直接吸附而造成的变性、失活现象的发生。本文报道了我们采用表面增强拉曼散射光谱方法研究在金电极表面吸附的半胱胺单分子膜的结构特征。研究结果表明,在金电极表面所形成的半胱胺单分子膜中,半胱胺分子主要的构型为扭转构型。在与金表面的相互作用中,由于除巯基的结合作用以外,还存在半胱胺分子中端基氨基和金表面较强的亲和性,使得以扭转构型吸附在金表面的半胱胺单分子膜相当稳定。这是金电极表面的半胱胺单分子膜结构的主要行征。当考察外加电势对此单分子膜结构的影响时,可以发现有关扭转构型的特征谱峰其相对强度随着电位负移而减小。这一结构随电位的变化关系可以通过表面电势的变化对氨基氮原子上孤对电子与金属表面间相互作用的影响来加以阐释。     

制备条件对Langmuir－Blodgett膜中分子聚集态的影响

通过对不同制膜条件下样品的π－Ａ曲线及紫外－可见吸收光谱的测量，研究ＬＢ单分子层膜中半花菁衍生物（ｈｅｍｉｃｙａｎｉｎｅｄｅｒｉｖａｔｉｖｅ简称ＨＤ）分子的聚集状态及其形成机制。纯半花菁衍生物单分子层膜中分子以Ｈ聚集体的形式存在导致吸收峰的兰移及有效分子二阶非线性极化率β（基频波长λ＝１．０６４μｍ）的减小。实验表明聚集体的形成主要发生在压膜过程。提高压膜速度或降低压膜终极压力（拉膜压力）可显著减小分子的聚集程度，从而提高单分子层膜的光学非线性极化率。     

Effects of surface concentration on the porphine monolayers: Molecular simulations at the nanoscale water-gas interface

The effect of surface concentration on the structure and stability of porphine (PH₂) monolayers at the water-gas interface was studied by using molecular dynamics simulation. Five monolayer systems having different surface concentrations were investigated in order to cover a full range of the experimental π-A isotherm. The simulation results show that increment of a number of the PH₂ molecules not only affects the significantly decreasing water density at the interface but also the monolayer surface tensions. The calculated surface tensions of the five systems indicate that the monolayer phase transfer corresponding to gaseous, expanded, condensed, and collapsed phases are observed. The hydrogen bonding between water and the PH₂ molecules at the interface plays an important role on the monolayer film formation, especially at the lower surface concentrations. The PH₂ orientations for all surface concentrations, except the highest one, are favored to be the β-structure as observed in the copper porphyrazine (CuPz) monolayer.     

Effects of Calcium Ions on Thermodynamic Properties of Mixed Bilirubin/Cholesterol Monolayers

通过?-A等温线研究了含钙离子浓度不同的水溶液亚相上胆红素/胆固醇混合单分子膜的性质．在此基础上,采用数学方法计算了不同亚相上单分子膜的平均单分子面积、崩溃压、表面压缩系数、超额单分子面积、混合自由能和超额自由能．结果表明,在钙离子溶液亚相上混合单分子膜的结构发生扩张,并且在界面上形成非理想混合单分子膜．与理想混合时相比,这种混合单分子膜在超额单分子面积上表现为明显的正偏差．在纯水亚相上,胆红素与胆固醇的摩尔比为3:2时混合单分子膜为热力学最稳定体系．但是在钙离子浓度逐渐增大的亚相中,这种摩尔比的混合单分子膜热力学稳定性被破坏,即混合单分子膜中的不同组分间自发混合能力下降,这是由于受到钙离子与胆红素和胆固醇之间配位作用的影响．此外,在钙离子溶液亚相中,在较低的表面压下制备出的混合膜具有更好的热力学稳定性．     

Mixed 2D molecular systems: Mechanic, thermodynamic and dielectric properties

Study of Langmuir monolayers consisting of stearic acid (SA) and dipalmitoylphosphatidylcholine (DPPC) molecules was done by surface pressure-area isotherms (π-A), the Maxwell displacement current (MDC) measurement, X-ray reflectivity (XRR) and atomic force microscopy (AFM) to investigate the selected mechanic, thermodynamic and dielectric properties based on orientational structure of monolayers. On the base of π-A isotherms analysis we explain the creation of stable structures and found optimal monolayer composition. The dielectric properties represented by MDC generated monolayers were analyzed in terms of excess dipole moment, proposing the effect of dipole-dipole interaction. XRR and AFM results illustrate deposited film structure and molecular ordering.     

Assemblies, characterization, and luminescent enhancement of organized molecular films based on rare earth complexes

Langmuir-Blodgett (LB) films of different molar percentages of Eu(TTA)₃Phen (TTA=2-thenoyltrifluoroacetone; Phen=1,10-phenanthroline) with Gd(TTA)₃Phen coexisting with arachidic acid (AA) (complexes:AA=1:l, in molar ratio) were fabricated and the luminescence enhancement of Eu(III) in the films was studied in this investigation. The monolayers and LB films were characterized by π-A isotherms, fluorescence microscopy, UV-vis spectroscopy and low-angle X-ray diffraction. High-quality LB films and strongly luminescent films were obtained. It was learned from the present study that an efficient intermolecular energy transfer occurred from Gd(TTA)₃Phen to Eu(TTA)₃Phen in the films, which resulted in the luminescence enhancement effect. According to the proposed model of the “active enhancement circle” the distance of energy transfer from Gd-, Tb-, La-, and Y-complex to Eu-complex were calculated to be 1.2, 1.2, 0.7 and 1.0 nm, respectively.     

Comparison of phase behavior between water soluble and insoluble surfactants at the air-water interface

The surface phase behavior of 2-hydroxyethyl myristate (2-HEM) has been studied in Langmuir monolayers by measuring surface pressure (π)-area (A) isotherms with a film balance and observing monolayer morphology with a Brewster angle microscope (BAM). These results are compared with the phase behavior of 2-hydroxyethyl laurate (2-HEL) in Gibbs monolayers studied by measuring π-time (t) curves and observing monolayer morphology. The π-A isotherms of 2-HEM show a first-order phase transition from a liquid expanded (LE) phase to a liquid condensed (LC) phase in the temperature range between 5 and 35 °C whereas the π-t curves of 2-HEL represent a similar phase transition in the temperature range between 2 and 25 °C. The critical surface pressure, π_c necessary for the phase transitions increases with increasing temperature in both the cases. The LC domains formed in 2-HEM show circular shapes, which are independent of the temperature. In contrast, the circular domains having stripe texture formed at lower temperatures show a shape transition to fingering domains with uniform brightness at 15 °C. The amphiphile, 2-HEM having 13-carbon chain has higher line tension than 2-HEL that has 11-carbon chain as tail. Thus, for 2-HEM, this high line tension always dominates over other factors giving rise to circular domains at the all studied temperatures.     

Fibrinogen adsorption onto 316L stainless steel, Nitinol and titanium

Fibrinogen adsorption onto mechanically polished biomedical grade 316L stainless steel (316LSS), nickel titanium alloy (Nitinol) and commercially pure titanium (CpTi) surfaces were studied by measurements of adsorption isotherms and adsorption kinetics using an ex-situ wavelength dispersive spectroscopy technique (WDS). Surface composition, roughness and wettability of these materials were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle (WCA) measurements. Adsorption isotherm results showed that surface protein concentration on these materials increased with increasing concentration of fibrinogen in phosphate buffer solution. The fibrinogen adsorption isotherms were modeled by both the monolayer Langmuir isotherm and the multilayer Brunauer-Emmett-Teller (BET) isotherm. The results strongly suggest that fibrinogen forms multilayer structures on these materials when the concentration in solution is high. Complementary measurements on the absorbed fibrinogen films by spectroscopic ellipsometry (SE) support this view.     

Poly(ester)s Containing Germanium and Silicon in the Main Chain. 1. Langmuir Monolayer Characterization

Surface characterization of poly(ester)s containing germanium (Ge) or silicon (Si) in the main chain was studied. Surface pressure‐area isotherms (π‐A) at the air/water interface were obtained by monolayer compression at constant temperature. The molecular areas from the pressure‐area isotherms were estimated for all polymers. At low surface concentrations poly(ester)s the characterization of monolayers was carried out according to the variation of the surface pressure as a function of the surface concentration; the behavior observed was described by the virial expansion development. In the semidilute region, the surface pressure variation was expressed according to the scaling laws as a power function of the surface concentration. It was found that the chemical structure of the poly(ester)s studied influences the type of the isotherms. The morphology of the monolayers was observed by Brewster angle microscopy (BAM). The molecular mechanics approach was used to obtain predictions about the local interaction energies between segments and to explain the minimum area values at the collapse point.     

Analysis of the induction of the myelin basic protein binding to the plasma membrane phospholipid monolayer

Myelin basic protein(MBP) is an essential structure involved in the generation of central nervous system(CNS)myelin.Myelin shape has been described as liquid crystal structure of biological membrane.The interactions of MBP with monolayers of different lipid compositions are responsible for the multi-lamellar structure and stability of myelin.In this paper,we have designed MBP-incorporated model lipid monolayers and studied the phase behavior of MBP adsorbed on the plasma membrane at the air/water interface by thermodynamic method and atomic force microscopy(AFM).By analyzing the pressure–area(π–A) and pressure–time(π–T) isotherms,univariate linear regression equation was obtained.In addition,the elastic modulus,surface pressure increase,maximal insertion pressure,and synergy factor of monolayers were detected.These parameters can be used to modulate the monolayers binding of protein,and the results show that MBP has the strongest affinity for 1,2-dipalmitoyl-sn-glycero-3-phosphoserine(DPPS) monolayer,followed by DPPC/DPPS mixed and1,2-dipalmitoyl-sn-glycero-3-phospho-choline(DPPC) monolayers via electrostatic and hydrophobic interactions.AFM images of DPPS and DPPC/DPPS mixed monolayers in the presence of MBP(5 n M) show a phase separation texture at the surface pressure of 20 m N/m and the incorporation of MBP put into the DPPC monolayers has exerted a significant effect on the domain structure.MBP is not an integral membrane protein but,due to its positive charge,interacts with the lipid head groups and stabilizes the membranes.The interaction between MBP and phospholipid membrane to determine the nervous system of the disease has a good biophysical significance and medical value.     

Effect of chain length on the adhesion behaviour of n-alkanethiol self-assembled monolayers on Au(111): An atomic force microscopy study

The effect of chain length on the adhesion behaviour of n-alkanethiols CH₃(CH₂)_nSH, wheren = 5, 6, 7, 9, 10, 11, 14 and 15 has been followed by carrying out pull-off force measurement using atomic force microscopy (AFM). The self-assembled monolayers on Au(111) surface has been characterized by reflection absorption infra-red spectroscopy (RAIRS) and contact mode AFM. It is observed that the work of adhesion is independent of thiol chain length though the standard deviation is high for short chain length thiol-based monolayers. This may be attributed to the relatively more deformable nature of the short chain thiol films due to their heterogeneity in the monolayer structure than the long chain ones. This, in turn, increases the contact area/volume between the AFM tip and the monolayer, and hence the force of adhesion. However, in the presence of water, the force of adhesion is lower than that observed in air reflecting the effects of capillary forces/polar components associated with the surface energy.     

Self-assembling of cyano- and carboxyl-terminated monolayers using short-chain alkylsiloxane

A simple method was developed for the preparation of cyano- and carboxyl-terminated alkylsiloxane monolayers on the hydroxylated surface of the SiO₂/Si substrate through using adsorption and hydrolysis reaction of a short-chain 2-cyanoethyl triethoxysilane [(CH₃CH₂O)₃SiCH₂CH₂CN]. The contact angle and the X-ray photoelectron spectroscopy (XPS) measurements have proved that the cyano terminal group indeed formed on the substrate and was transformed into the carboxylic terminal group after hydrolysis. The ellipsometry shows the presence of an intact monolayer with thickness of around 0.7 nm before and during the hydrolysis reaction. The surface morphology was observed with atomic force microscopy (AFM) imaging. Those all indicate that uniform and ordered self-assembled monolayers (SAMs) were formed on the substrate.     

Shear viscosity of polymer and surfactant monolayers

The surface shear viscosity of monolayers formed at the surface of water by adsorbed polyethyl- eneoxyde and by stearic acid is measured as a function of the surface pressure of the monolayer using a new surface viscometer. The principle of the viscometer is the measurement of the drag force on a circular disk undergoing a uniform translation at the water surface: a hydrodynamic model based on the lubrication approximation allows a calculation of the surface viscosities from the absolute measurement of the drag forces. Received: 26 August 1999