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1.
A synthetic peptidolipid consisted of a hydrocarbon chain with a chain length of C18 and a peptide moiety of IIGLM terminated with an amine group, designated as C18IIGLM-NH2, has been employed as a biomimic model compound of amyloid peptide for exploring molecular interaction and orientation with the use of the Langmuir monolayer and Langmuir-Blodgett film techniques. Inspired by a well-known fact that a stain reagent, Congo red (CR), binds well to the amyloid-mimic part (IIGLM), inhibition of molecular aggregation of C18IIGLM-NH2 by interaction with CR was expected, and it has been investigated by use of surface pressure-area isotherm, surface dipole moment-area isotherm, Brewster-angle microscopy, and UV-vis/infrared spectroscopies. It has been revealed that monomeric CR molecules whose long axis is parallel to the Langmuir monolayer surface are penetrating the C18IIGLM-NH2 Langmuir monolayer, which plays a role of inhibition of molecular aggregation via hydrogen bonding.  相似文献   

2.
The fibril formation process of a synthetic peptidolipid compound in a Langmuir monolayer at the air-water interface has been analyzed by surface pressure and surface dipole moment-area isotherms, followed by infrared spectral analysis of related Langmuir-Blodgett films. Thus far, the analysis of randomly oriented molecular assemblies has been a difficult matter, especially for spectroscopic measurements. In the present study, the Langmuir film isotherms were discussed in detail, and they have readily been correlated to the infrared spectra. For the spectral analysis, infrared multiple-angle incidence resolution spectroscopy (MAIRS) was employed, which was compared to the results by conventional techniques. Since the peptide assemblies greatly responded to a metal surface, the reflection-absorption technique was not useful for our analysis. Instead, MAIRS was found to be powerful to reveal the anisotropic structure of the Langmuir films, and a disordered molecular architecture has been revealed via the molecular orientation analysis. As a result, the fibril-like aggregation formation process during the monolayer compression, which was suggested by previous topographical study, has been found to be due to the stiff domain formation in the Langmuir films.  相似文献   

3.
Reported here is the study on the structure of Langmuir-Blodgett (LB) films of double-armed dibenzo-18-crown-6 contain biphenyl (DACE) which are newly synthesized and mixed with stearic acid (SA). In addition, the miscibility of the two compounds was also tested by the measurement of the surface pressure-area (pi-A) isotherms of DACE and DACE/SA with various proportions. It is noted that there is no phase segregation in the mixed monolayer film of DACE/SA. Upon calculation of the excess surface area, it is concluded that the SA molecule can enter into the crown ether ring, while an 18C6 ring can host a maximum of one SA molecule. The difference of spectroscopic properties of DACE in LB films and bulk solution has been investigated by ultraviolet-visible (UV-vis) and Fourier-transfer infrared (FTIR) measurements. Molecules of DACE exist in the mixed LB films as monomers in contrast to those in the concentrated solution as aggregates. The hydrocarbon chains in DACE and DACE/SA LB films are tilted to the normal of the substrate surface, but perpendicular to the dipole moment of CO. Both CO bonds in the phenyl ethers and carboxylic ester of DACE, and the long axes of phenyl rings are aligned nearly perpendicular to the substrate surface. Infrared spectra of mixed LB films of DACE/SA present further evidence that the SA molecules enter into the crown ether rings of DACE.  相似文献   

4.
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.  相似文献   

5.
This paper reports the pi-A isotherms and spectroscopic characteristics of mixed Langmuir and Langmuir-Blodgett (LB) films of nonamphiphilic carbazole (CA) molecules mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). pi-A isotherm studies of mixed monolayer as well as the remarkable change in collapse pressure of the mixed monolayer isotherms definitely show that CA is incorporated into PMMA and SA matrices. However, CA is stacked in the PMMA/SA chains and forms microcrystalline aggregates, as is evidenced from the scanning electron micrograph picture. The nature of these aggregated species in the mixed LB films has been revealed by UV-vis absorption and fluorescence spectroscopic studies. The presence of two different kinds of band systems in the fluorescence spectra of the mixed LB films have been observed. This may be due to the formation of low-dimensional aggregates in the mixed LB films. Intensity distribution of different band systems is highly sensitive to the microenvironment of two different matrices as well as also on the film thickness.  相似文献   

6.
The monodisperse silver nanoparticles were synthesized by one-step reduction of silver ions in the alkaline subphase beneath vitamin E (VE) Langmuir monolayers. The monolayers and silver nanocomposite LB films were characterized by surface pressure-area (pi-A) isotherms, transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), selected area electron diffraction (SAED), Fourier transform infrared transmission spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that the limiting area/VE molecule on different subphases varied. The phenolic groups in the VE molecules were converted to a quinone structure, and the silver ions were mainly reduced to ellipsoidal and spherical nanoparticles. The arrangement of the nanoparticles changed from sparseness to compactness with reaction time. The electron diffraction pattern indicated that the silver nanoparticles were face-centered cubic (fcc) polycrystalline. Silver nanocomposite LB films with excellent quality could be formed on different substrates, indicating that the transfer ratio of monolayer containing silver nanoparticles is close to unity. The dynamic process of reduction of silver ions by VE LB films was also studied through monitoring the conductivity of an Ag2SO4 alkaline solution.  相似文献   

7.
Molecular structure in dip-coated films of linear poly(ethylene imine) (LPEI) on a germanium (Ge) substrate in dried and hydrated conditions have been analyzed by infrared multiple-angle incidence resolution spectrometry (IR MAIRS). The MAIRS-IP (in-plane) and -OP (out-of-plane) spectra of the dried film exhibited largely different patterns from each other, which indicated that LPEI molecules had an apparent molecular orientation with respect to the substrate surface. Although the film exhibited no peak in X-ray diffraction patterns, the low-crystallinity film has been found to have highly oriented molecular structure. Many key bands indicated that the molecules were involved in the double-stranded helix structure, which is specific to the anhydrate crystal of LPEI, with nearly perpendicular orientation. The Davydov splitting of the NH stretching vibration mode was readily captured by the IR MAIRS spectra, which also supported the helix standing model. When the film was stored in a humid condition, on the other hand, IR MAIRS spectra revealed that the helix was resolved to be straight chains, but the perpendicular orientation was kept unchanged. In addition, the MAIRS spectra also revealed molecular orientation of the water molecules of crystallization. The unique molecular arrangements are understandable by considering that the stabilization energy in the polymer monolayer directly attached on the substrate surface is minimized by the standing-molecule arrangements.  相似文献   

8.
ABSTRACT

The Langmuir monolayer is a special class of lyotropic liquid crystalline system wherein phase transition essentially depends on surface density, temperature and ion-content in the aqueous medium. The variety of surface phases can be transferred onto devices by the Langmuir–Blodgett (LB) technique. The Langmuir monolayer of pristine single-walled carbon nanotubes (SWCNTs) exhibited gas and liquid-like phases. The LB film of SWCNTs shows target surface pressure dependent interesting morphologies. The methane gas sensing using parallel alignment of SWCNTs was found to be better than that of randomly oriented SWCNTs. The SWCNTs can be functionalised chemically to enhance the ease of film processability and affinity towards analytes. These are essential parameters for the development of a sensor. In this article, we present our work on Langmuir monolayer and LB films of octadecylamine functionalised SWCNTs (ODACNTs) and its sensing application towards bio-analytes, e.g. L-aspartic acid and bovine serum albumin. The sensing performance of LB film of ODACNTs was compared with that of spin-coated films of ODACNTs. The sensing performance of LB films of ODACNTs indicated a potential platform for bio-sensing application.  相似文献   

9.
对不同链长的2-烷基-苯并咪唑衍生物(BzCn,烷基链长从C5到C15)在硝酸银亚相上的成膜行为及形成的LB膜的结构进行了研究.表面压-面积曲线的结果表明,短链(C5~C9)的2-烷基-苯并咪唑可在银离子亚相上形成稳定的单分子膜,而长链(C13和C15)衍生物则形成多层膜.利用LB技术可将上述Langmuir膜转移到固体基板上形成LB膜,其吸收光谱的结果说明了苯并咪唑和银离子配位.利用AFM、XRD及FT-IR等技术研究了烷基链长对LB膜结构的影响.实验结果表明,除了BzC15,其余的衍生物都可形成规整的层状结构.短链衍生物的单层LB膜具有均一、平整的形貌;而对于BzC15,观察到多层结构.  相似文献   

10.
In this communication we demonstrated the incorporation of water-soluble surface-active protein OVA within an insoluble cationic ODA monolayer and compared with zwitterionic (DPPC) and anionic (SA) monolayer. The incorporation of OVA is found to be more in ODA as compared to that of DPPC and SA. The kinetics of protein adsorption in lipid monolayer gives the idea that unfolding of OVA is less in case of DPPC than SA and ODA. The pi-A isotherm and compressibility study gives the information about the different states of the protein-lipid mixed monolayer. At higher pressure, OVA tend to squeeze out from the lipids monolayer. High-resolution field emission scanning electron microscope (FE-SEM) images confirm this observation. The surface morphology of DPPC-OVA LB film is far better than ODA-OVA and SA-OVA LB film. OVA forms large irregular aggregates on SA and ODA monolayer. Fluorescence study reveals that protein structure is perturbed more in SA and ODA system compared to that of DPPC. The overall results indicate that DPPC monolayer is better to get protein lipid mixed film than SA and ODA monolayer.  相似文献   

11.
The synthesis, spectroscopic characterization and surface-enhanced spectroscopy of a new electro active organic material bis (benzimidazo) thioperylene (Monothio BZP) are reported. Langmuir monolayers of Monothio BZP were successfully formed on water subphase and characterized by the pi-A surface-pressure area isotherm. Langmuir-Blodgett (LB) monomolecular layers of Monothio BZP were fabricated onto glass substrates and onto silver island films for surface-enhanced spectroscopic studies. The results of surface-enhanced resonance Raman scattering (SERRS), SERRS imaging and surface-enhanced fluorescence (SEF) studies for Monothio BZP LB monolayers are reported. Raman imaging (global imaging and point-by-point mapping) of the SERRS signal for a single monomolecular layer on silver islands were obtained using the 514.5 nm laser line. The SERRS imaging permits a visualization of the variation of the SERRS intensity across of the rough metal surface. The SEF was recorded for the excimer emission of aggregates in the LB film. The distance dependence and the enhancement factor of SEF were determined using fatty acid spacing layers. A temperature dependence study of the LB monolayer SERRS and SEF spectra was carried out between -190 degrees and + 200 degrees C confirming the thermal stability of the LB monolayer on silver. The specificity and the sensitivity of SERRS signal on metal island films was probed using mixed LB films with 0.01% molecular ratio of Monothio BZP in Arachidic Acid (AA). The micro-Raman SERRS spectra from ca. 10(-3) attomole of the dye were recorded.  相似文献   

12.
The maximum withdrawal speed of Langmuir-Blodgett (LB) film deposition of arachidic acid (AA) was investigated. The quality of LB deposited film was determined by the transfer ratio (TR), together with measurements of surface roughness using atomic force microscopy (AFM). A Langmuir mini-trough was used to provide the surface pressure versus molecular area (pi-A) curves and a flow visualization technique was applied to estimate the dynamic contact angles and to observe the fluid motion. The effects of hydrophobic and hydrophilic substrates, pH and the addition of four different ions, i.e., K+, Ba2+, Cd2+, and Al3+, on the withdrawal speed were examined. The "transition point" from liquid to solid states on the pi-A curve provided a clear indication of the maximum withdrawal speed. The lower the transition point, the higher was the maximum withdrawal speed. Stable deposition was possible only if the pH of the solution was maintained in a narrow range. The observation of dynamic contact angles and fluid motion, particularly the movement of air-liquid interface, was consistent with previous findings. Owing to the "soap effect" of the divalent ions Ba2+ and Cd2+, the maximum speed for successful LB film deposition without significant water entrainment could be extended substantially with the addition of divalent ions.  相似文献   

13.
Asymmetrically substituted poly(paraphenylene) (PhPPP) with hydrophilic and hydrophobic side chains was investigated. The polymer behavior at the air-water interface was studied on the basis of surface pressure-area (pi-A) isotherms and compression/expansion hysteresis measurements. PhPPP can form stable monolayers with an area per repeat unit of A=0.20+/-0.02 nm2 and a collapse pressure in the range of pi=25 mN/m. Then, Langmuir-Blodgett-Kuhn (LBK) films of PhPPP were prepared by horizontally and vertically transferring the Langmuir monolayers onto hydrophilic solid substrates at pi=12 mN/m. Cross-section analysis of the AFM tapping-mode topography images of a single transferred monolayer reveals a thickness of d0=0.9+/-0.1 nm. Taking into account the obtained monolayer thickness, curve-fitting calculations of angular scan data of LB monolayers measured using surface plasmon resonance (SPR) spectroscopy lead to a value for the refractive index of n=1.78+/-0.02 at lambda=632.8 nm. Next, the spontaneous formation of a PhPPP monolayer by adsorption from solution was studied ex situ by atomic force microscopy and UV-vis spectroscopy and in situ by using SPR spectroscopy. Stable self-assembled monolayers of PhPPP can be formed on hydrophilic surfaces with a thickness similar to that of the monolayer obtained using the LB method. The characterization results confirmed the amphiphilic character and the self-assembly properties of PhPPP, as well as the possibility of preparing homogeneous monolayer and multilayer films.  相似文献   

14.
Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectra have been recorded of 11-layer Langmuir-Blodgett (LB) films of stearic acid deposited at various surface pressures (0.1, 15, and 35 mN/m), and the molecular orientation angles were evaluated quantitatively, which supplied insight into the molecular order with the alkyl chains tightly packed like crystal in the LB films deposited at the zero and higher surface pressures. These experimental results indicate that, in the Langmuir film as the precursor of LB films, stearic acid molecules self-aggregate to form two-dimensional crystalline domains already even at the zero surface pressure, which results in the inhomogeneity of monolayer. The analysis of dependence of nu(C=O) intensity on the surface pressure, surface density, and subphase temperature leads to the conclusion that the defects in LB films originate from the Langmuir film and be conserved upon deposition. Annealing below 50 degrees C and cooling could improve the monolayer homogeneity, and thus a defect-free or low-defect LB films can be deposited. Furthermore, ion exchange conducted in the LB films, on the other hand, confirms the existence of structure defects in LB films of stearic acid. The polar plane microstructure, lateral transport along the polar planes and the coordination types of stearic acid/cation system may be the rate-limiting process. The results have implication on the possible uses of stearic acid LB films as ion-exchange materials or sensors. Copyright 2001 Academic Press.  相似文献   

15.
A twin-tailed, twin-chiral fatty acid, (2R,3R)-(+)-bis(decyloxy)succinic acid was synthesized and its two dimensional behavior at the air-water interface was examined. The pH of the subphase had a profound effect on the monolayer formation. On acidic subphase, stable monolayers with increased area per molecule due to hydrogen bonding and bilayers at collapse pressures were observed. Highly compressible films were formed at 40 degrees C, while stable monolayers with increased area were observed at sub-room temperatures. Langmuir monolayers formed on subphases containing 1 mM ZnCl2 and CaCl2 revealed two dimensional metal complex formation with Zn2+ forming a chelate-type complex, while Ca2+ formed an ionic-type complex. Monolayers transferred from the condensed phase onto hydrophilic Si(100) and quartz substrates revealed the formation of bilayers through transfer-induced monolayer buckling. Compression induced crystallites in 2D from monolayers and vesicle-like supramolecular structures from multilayers were the noted LB film characteristics, adopting optical imaging and electron microscopy. The interfacial monolayer structure studied through molecular dynamics simulation revealed the order and packing at a molecular level; monolayers adsorbed at various simulated specific areas of the molecule corroborated the (pi-A) isotherm and the formation of a hexagonal lattice at the air-water interface.  相似文献   

16.
Fullerene derivative C60TT, which is substituted with the low-molecular-weight organogelator tris(dodecyloxy)benzamide, formed nanowire structures on application of the Langmuir-Blodgett (LB) method. The surface morphology of the C60TT LB film was dependent on the holding time before deposition at a surface pressure of 5 mN m(-1); it changed from a homogeneous monolayer to a bilayer fibrous structure via a fibrous monolayer structure, which was estimated to have dimensions of 1.2 nm in height, 8 nm in width, and 5-10 microm in length. From the structural and spectroscopic data, it is inferred that close packing of the fullerene moiety occurs along with intermolecular hydrogen bonding within the monolayer fibrous structure. The morphological changes in the LB film are explained kinetically by the Avrami theory, based on the decrease in the surface area of the monolayer at the air/water interface. The growth of the quasi-one-dimensional fibrous monolayer structures at holding times from 0 to 0.2 h is considered to be an interface-controlled process, whereas the growth of the quasi-one-dimensional bilayer fibrous structures from 0.2 to 18 h is thought to be a diffusion-controlled process.  相似文献   

17.
The structure formation of wedge-shaped monodendrons based on symmetric benzenesulfonic acid with different lengths of peripheral alkyl chains was studied in Langmuir monolayers and Langmuir–Blodgett (LB) films. A phase transition from the liquid-expanded state to the liquid-condensed state was observed on compression of the Langmuir monolayers of the dendrons containing dodecyl lateral chains. The transition is accompanied by the formation of star-shaped aggregates visualized by Brewster angle microscopy. The three-layer LB transfer results in the reorganization of the monolayer into regions of bi-, tetra-, and hexalayers on a solid substrate with a low coverage of the surface. Homogeneous liquid-condensed mono layers are formed for the dendrons with hexa- and octadecyl chains, and the film thickness achieved by the LB transfer corresponds to the monolayer alignment of the molecules with the surface coverage up to 90%. It was determined that varying the alkyl length of wedge-shaped dendrones based on symmetric benzenesulfonic acid leads to a change in phase behavior of Langmuir monolayers as well as Langmuir–Blodgett films formed by them.  相似文献   

18.
The 3‐ferrocenoylpropanoyl group, one of the redox species, was introduced at C‐2 and/or C‐3 positions of 6‐O‐(4‐stearyloxytrityl)cellulose. The spreading behavior of the cellulose derivatives on the water surface and the properties of Langmuir–Blodgett (LB) films were investigated. The surface pressure–area isotherm of the cellulose monolayer was changed by the subphase temperature. Uniform monolayers of 6‐O‐(4‐stearyloxytrityl)cellulose 3‐ferrocene propionate (STCFc) could be deposited successively onto several substrates by the horizontal lifting method at 10 mN m?1, and this produced X‐type LB films. The successive uniform depositions of STCFc were confirmed by ultraviolet–visible absorption spectra. X‐ray diffraction measurements indicated that the thickness of the STCFc molecules in the LB films was 1.99 nm. Fourier transform infrared spectroscopy measurements supported the idea that hydrocarbon chains in the LB films were highly ordered (trans‐zigzag) and oriented considerably perpendicular to the surface of the substrate. Moreover, the C?O group of the ferrocenoyl groups was perpendicular to the surface of the substrate, and the ferrocene group was occupied in the water phase. Cyclic voltammograms for the STCFc monolayer on a gold electrode exhibited surface waves. The interfacial electron‐transfer process between the redox site incorporated into the cellulose LB monolayer and the electrode surface was fast enough at a scanning rate lower than 100 mV s?1. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5023–5031, 2005  相似文献   

19.
Langmuir films have been fabricated from 4-[4'-(4'-thioacetyl-phenyleneethynylene)-phenyleneethynylene]-aniline (NOPES) after cleavage of the thioacetyl protecting group. Characterization by surface pressure vs area per molecule isotherms and Brewster angle microscopy reveal the formation of a high quality monolayer at the air-water interface. One layer Langmuir-Blodgett (LB) films were readily fabricated by the transfer of the NOPES Langmuir film onto solid substrates. X-ray photoelectron spectroscopy (XPS), surface polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), and quartz crystal microbalance (QCM) experiments conclusively demonstrate the formation of one layer LB films in which the functional group associated with binding to the substrate can be tailored by the film transfer conditions. Using LB methods this molecule could be transferred to gold samples with either the amine or thiol group attached to the gold surface. The amine group is directly attached to the gold substrate (Au-NH(2)-OPE-SH) when the substrate is initially immersed in the subphase and withdrawn during the transfer process; in contrast, monomolecular films in which the thiolate group is attached to the gold substrate (Au-S-OPE-NH(2)) are obtained when the substrate is initially out of the subphase and immersed during the transfer process. The morphology of these films was analyzed by atomic force microscopy (AFM), showing the formation of homogeneous layers. Film homogeneity was confirmed by cyclic voltammetry, which revealed a large passivation of gold electrodes covered by NOPES monolayers. Electrical properties for both polar orientated junctions have been investigated by scanning tunnelling microscopy (STM), with both orientations featuring a nonrectifying behavior.  相似文献   

20.
A novel amphiphilic oligo(ethylene glycol)-C60-hexadecaaniline (A16) tricomponent conjugate, C60>(A16-EG43), possessing a well-defined number of repeating aniline donor units and a hydrophilic ethylene glycol oligomer chain was synthesized. The compound is composed of a covalently bound donor-acceptor chromophore structure. Molecular self-assembly of C60>(A16-EG43) at the air-water interface formed a densely packed Langmuir monolayer with all highly hydrophobic fullerene cages located above the liquid interface. The monolayer can then be transferred onto a glass substrate via Langmuir-Blodgett (LB) deposition. LB multilayered thin films formed by multiple deposition of the monolayer yielded broadened optical absorption peaks extending beyond 600 nm into the 950 nm region, suggesting strong intermolecular interactions among the C60 cages and the A16 moieties. An X-ray reflectometry study clearly reveals that the Langmuir film at the air-water interface consists of a C60 top layer and a bottom layer containing hexcadecaaniline and oligo(ethylene glycol) with gradually decreasing electron density over a distance of approximately 130 A above bulk water. The pressure isotherm shows that the packing density of the C60>(A16-EG43) monolayer, corresponding to a molecular area of approximately 95 A2/molecule, is similar to that of the surface area of the C60 monolayer. This result suggests that C60 packing plays a dominant role in guiding the formation of the monolayer structure. Further photoexcitation of hexadecaaniline moieties of aligned (C60>)-A16 layers by a flash light source induces cross linking between adjacent A16 segments forming an interlinked A16 array. Our results have demonstrated a unique fabrication method for preparing the aligned donor-acceptor array using strong intermolecular interactions between fullerenes as the molecular orientation guiding force in the Langmuir-Blodgett technique.  相似文献   

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