Substitution controlled molecular orientation and nanostructure in the Langmuir-Blodgett films of a series of amphiphilic naphthylidene-containing Schiff base derivatives

Three amphiphilic Schiff bases containing naphthylidene group, N-octadecyl-2'-hydroxy-naphthalenylideneamine (HNOA-1), N-(4'-octadecyloxy)-2'-hydroxy-naphthalenylideneaniline (HNOA-2), and N-(4'-N-octadecylbenzamide)-2'-hydroxy-naphthalenylideneaniline (HNOA-3), were designed and their interfacial assemblies were investigated. These amphiphiles have different substitution groups in the Schiff base moiety. It was observed that HNOA-1, being in lack of second aromatic ring, formed multilayer films at the air/water interface, while the other two compounds, with another aromatic ring and some hydrophilic groups, can be spread as monolayers on water surface. All of Schiff bases could coordinate with Cu(Ac)2 in situ in the spreading films. Both the spreading films from water and aqueous Cu(Ac)2 subphases were transferred onto solid substrates and their surface morphologies as well as molecular packing modes were investigated by a series of methods such as atomic force microscopy, Fourier transform infrared spectra and X-ray diffraction. Depending on the different substitutions, these amphiphiles showed different orientations in the Langmuir-Blodgett films. Particularly, during the process of complex formation at the air/water interface, great conformational change of the alkyl chain was observed for HNOA-2 in comparison with that of other compounds. In addition, nanofiber structures were observed for the Cu(II)-complexed HNOA-1 and HNOA-2 films.     

Design and interfacial behavior of two series of gemini amphiphiles with different charge positions based on imidazole moiety

Two series of gemini amphiphiles based on 2-heptadecylimidazole were designed. One is exo-BisImC17Cn (n=2, 4, 6, 8, 10), in which the positive charges are positioned on the outsides of the headgroups. The other is endo-BisImC17Cn (n = 2, 4, 6, 8, 10), whose positive charges are localized on the insides of the headgroups. The interfacial behavior at the air/water interface of these gemini amphiphiles was investigated in relation to the effect of the charge position and the spacer length. Monolayers of exo-BisImC17Cn show small differences in interfacial behavior when spread on water and aqueous Na2SO4 subphases. In contrast, significant distinctions were observed for molecules of endo-BisImC17Cn. The limiting areas of endo-BisImC17Cn monolayers on water are obviously larger than those on the aqueous Na2SO4 solution. While the limiting areas of the exo-BisImC17Cn monolayers increased monotonically with the spacer length, those of the endo-BisImC17C10 monolayer on Na2SO4 solution is obviously smaller than those of endo-BisImC17C6 and endo-BisImC17C8 monolayers, suggesting the wicket conformation of the alkyl chain in endo-BisImC17C10. On the other hand, both of the gemini amphiphiles could form complex monolayers with negatively charged TPPS at the air/water interface. The transferred complex multilayer films of the gemini amphiphiles/TPPS showed supramolecular chirality, although both of the gemini amphiphiles and TPPS are achiral. The exciton couplet was observed for the endo-BisImC17Cn/TPPS films, while no couplet was detected for the exo-BisImC17Cn/TPPS films. A reasonable comparison between the two series of geminis in relation to the effect of charge positions and the spacer lengths on the interfacial behavior and the supramolecular chirality was performed.     

Improvement of dissolution properties of a new Helicobacter pylori eradicating agent (TG44) by inclusion complexation with beta-cyclodextrin

The interaction of a newly developed Helicobacter pylori eradicating agent (TG44, 4-methylbenzyl-4'-[trans-4-(guanidinomethyl)cyclohexylcarbonyloxy]biphenyl-4-carboxlylate monohydrochloride) with beta-cyclodextrin (beta-CyD) in aqueous solution and in solid state was studied to gain insight into the high in-vivo H. pylori eradicating activity of TG44/beta-CyD complex. The interaction was studied by the solubility method, spectroscopic methods, powder X-ray diffractometry and differential scanning colorimetry (DSC). TG44 gave A(L)-type phase solubility diagram with beta-CyD in water, showing a linear increase in solubility of the drug up to 8 mM beta-CyD concentration. The solubility of TG44 (0.04 mM in water at 25 degrees C) increased about 70-folds at 8 mM beta-CyD. Ultraviolet, circular dichroism, fluorescence and (1)H-nuclear magnetic resonance spectroscopic studies indicated that TG44 forms the inclusion complex with beta-CyD in a 1:1 stoichiometry and the biphenyl moiety of TG44 is preferably included in the beta-CyD cavity in water. The Giordano plot made by monitoring changes in the fusion enthalpy of TG44 (about 184 degrees C) suggested that TG44 forms the 1:1 complex with beta-CyD in the solid state. The TG44/beta-CyD solid complex in a 1:1 stoichiometry was prepared by the grinding and spray-drying methods and confirmed by powder X-ray diffractometry and DSC that the complex is in an amorphous state. The initial dissolution rate of TG44/beta-CyD complex was significantly faster than those of the drug alone and the physical mixture of both components, maintaining higher supersaturated concentrations of the drug for a long time. The results suggested that the higher eradicating activity of TG44/beta-CyD complex to Helicobacter pylori, compared with that of the drug alone, is attributable at least partly to the faster dissolving property of the complex and its ability to maintain the supersaturated state of the drug in the gastric fluid.     

A comparative Langmuir-Blodgett study on a set of covalently linked porphyrin-based amphiphiles: a detailed atomic force microscopic study

A set of covalently linked phenyl-amidophenyl-substituted porphyrin amphiphiles with n-C15H31 tails have been synthesized and completely characterized. These amphiphiles form good Langmuir-Blodgett (LB) films at the air/water interface. Mean molecular areas for the series were measured from the isotherms and found to increase as the number of aliphatic chains increased from one to four. No influence of the subphase pH was observed on the isotherms. LB films can be transferred successfully onto different solid surfaces. The LB films were characterized using tapping mode atomic force microscopy (AFM). Bis-, tris-, and tetra-substituted porphyrins were found to be fairly good film-forming amphiphiles, whereas irregular aggregates were seen in the case of the monosubstituted porphyrin amphiphile. Multilayers were also formed with tetra-substituted amphiphiles on mica. Detailed AFM studies of tetra-substituted amphiphiles have been carried out to investigate the effect of preparation procedure and solid substrates on film formation and transfer. The absorption and fluorescence spectra for the amphiphiles in solution and LB films deposited onto mica and glass were recorded, which demonstrated the successful transfer of LB films onto the substrates and provided more information about the arrangement of porphyrin molecules within the LB films. For comparison, self-assembled monolayers (SAMs) and the cast thin films of the amphiphiles were prepared and characterized.     

In situ Coordination and Surface Morphology of Langmuir Films of Non－amphiphilic Dithizone with Metal Ions on Air／Water Interface

A spread Langmuir film on the air/water in-terface can serve as a basic model for the under-standing of organized molecular systems[1] .Gener-ally,it is considered that only those compoundsthat possess simultaneously a hydrophilic headgroup and a long- alkyl chain can be spread on theair/water interface[2— 4] .Therefore,researches onthe organized molecular films are mainly concernedwith typical amphiphiles.In order to expand thechoice in molecular film to form materials and omitthe tedious sy…     

The miscibility of poly(D,L-lactide-co-glycolide) with amphiphilic molecules and the interaction of their mixtures with DNA at air/water interface

The miscibility of poly(D,L-lactide-co-glycolide) (PLG) with three amphiphilic molecules and the interaction of the PLG/surfactant mixtures with DNA at air/water interface are investigated by pi-A isotherms, Brewster angle microscopy (BAM) and atomic force microscopy (AFM) techniques. The pi-A isotherms of the PLG mixtures with cationic C(12)AzoC(6)PyBr, and C(12)AzoC(6)N(CH(3))(3)Br, are quite different from the pi-A isotherm of pure PLG on water subphase. In contrast to the case, the pi-A isotherm of PLG mixed with nonionic C(12)AzoC(6)OPy is almost identical to the pure PLG except some increasing of molecular area. Similar phenomena are observed on DNA subphase. The in situ BAM and ex situ AFM observations demonstrate that the dispersion of PLG at air/water interface becomes good when it mixes with the two cationic surfactants, whereas quite poor due to the phase separation when it mixes with the nonionic amphiphilic molecule. Based on these results we conclude that the cationic surfactants can affect the conformation change of PLG at air/water interface and figure a well miscibility with polymer whereas the nonionic amphiphilic molecule presents poor miscibility. In addition, the even mixing of the PLG and the cationic surfactants is favorable for the adsorption to DNA more effectively.     

Synthesis and characterization of amphiphilic fullerenes and their Langmuir-Blodgett films

We report here the synthesis and characterization of three amphiphilic fullerene derivatives and their Langmuir-Blodgett thin films. Two of the C(60) amphiphiles are mono-derivatives with a long alkyl chain terminated with either -COOH (2) or NH(2) (3) as the hydrophilic headgroup, and the third one (5) is designed to bear the same NH(2) group as 3 but with 10 additional hydrophobic alkyl chains grafted on the C(60) sphere (Scheme 1). These amphiphiles form stable, ordered monolayers at the air-water interface. The molecular packing at the air-water interface and the mean area per molecule are determined by pressure isotherms at room temperature. Hysteresis of pressure isotherms of side chain C(60) (5) shows complete reversibility upon compression and decompression, which suggests that side chains on the C(60) sphere inhibit formation of aggregates at the air-water interface. Comparative studies of all three amphiphiles allow us to better determine the interaction between C(60)'s and their self-assembly kinetics at the air-water interface. Monolayers of monoderivatized amphiphiles (2 and 3) were transferred successfully onto quartz substrates as Z-type multilayered Langmuir-Blodgett films, and monolayers of 5 were transferred as Y-type films. Detailed characterization of the multilayer films (Z-type deposition) prepared from amine-terminated C(60) (3) using X-ray and neutron reflectometry reveals staggering of C(60) spheres and a head-to-head (Y-type) structure presumably due to flipping and reattaching of C(60) amphiphiles to the previous underlying C(60) layer.     

Cationic Gemini surfactant at the air/water interface

The surface properties and structures of a cationic Gemini surfactant with a rigid spacer, p-xylyl-bis(dimethyloctadecylammonium bromide) ([C(18)H(37)(CH(3))(2)N(+)CH(2)C(6)H(4)CH(2)N(+)(CH(3))(2)C(18)H(37)],2Br(-), abbreviated as 18-Ar-18,2Br(-1)), at the air/water interface were investigated. It is found that the surface pressure-molecular area isotherms observed at different temperatures do not exhibit a plateau region but display an unusual "kink" before collapse. The range of the corresponding minimum compressibility and maximum compressibility modulus indicates that the monolayer is in the liquid-expanded state. The monolayers were transferred onto mica and quartz plates by the Langmuir-Blodgett (LB) technique. The structures of monolayers at various surface pressures were studied by atomic force microscopy (AFM) and UV-vis spectroscopy, respectively. AFM measurements show that at lower surface pressures, unlike the structures of complex or hybrid films formed by Gemini amphiphiles with DNA, dye, or inorganic materials or the Langmuir film formed by the nonionic Gemini surfactant, in this case network-like labyrinthine interconnected ridges are formed. The formation of the structures can be interpreted in terms of the spinodal decomposition mechanism. With the increase of the surface pressure up to 35 mN/m, surface micelles dispersed in the network-like ridges gradually appear which might be caused by both the spinodal decomposition and dewetting. The UV-vis adsorption shows that over the whole range of surface pressures, the molecules form a J-aggregate in LB films, which implies that the spacers construct a pi-pi aromatic stacking. This pi-pi interaction between spacers and the van der Waals interaction between hydrophobic chains lead to the formation of both networks and micelles. The labyrinthine interconnected ridges are formed first because of the rapid evaporation of solvent during the spreading processes; with increasing surface pressure, some of the alkyl chains reorient from tilting to vertical, forming surface micelles dispersed in the network-like ridges due to the strong interaction among film molecules.     

Langmuir films of (alpha-amino) phosphorus amphiphiles on various ion-containing subphases

Monolayers of amphiphilic (alpha-amino)phosphonocarboxylic and (alpha-amino)phosphonic acids have been formed by adsorption at the air/water interface. The influence of both the ionic strength and the pH of the subphase on the stability and compactness of the monolayers have been studied. The stability and the compactness of the Langmuir films are enhanced by introduction of metallic ions such as Ca(2+) or Mg(2+) in the subphases. These effects are more pronounced with Ca(2+). These metal ions can form dimeric complexes with the phosphorus moieties of the surfactant polar heads and therefore bring the amphiphiles closer. For the less hydrophobic derivative, complexation with Ca(2+) or Mg(2+) is required to ensure the formation of a stable monomolecular film. For both phosphonocarboxylic and phosphonic compounds, models have been proposed to represent the complexation phenomenon at the air/water interface.     

含磺酸盐基两性分子／聚乙烯亚胺LB膜的聚集结构

气液界面聚离子复合结构的形成能减弱两性分手亲水基间静电排斥作用，增加单分子膜的稳定性和累积性能．Ｘ－射线衍射结果表明，纯水和聚乙烯亚胺水溶液表面上的ＺＣ１４ＳＮａ单分子膜在聚苯乙烯基片上累积成Ｙ型膜，两种ＬＢ膜的等同周期差约为０．３０ｕｍ．     

Fabrication of chiral Langmuir-Schaefer films of achiral amphiphilic Schiff base derivatives through an interfacial organization

Supramolecular chirality in the Langmuir-Schaefer (LS) films of two achiral amphiphilic Schiff bases, 2-(2'-benzimidazolyliminomethyl)-4-octadecyloxyphenol (BSC18) and 2-(2'-benzthiazolyliminomethyl)-4-octadecyloxyphenol (TSC18), was investigated. Both of these amphiphiles could form LS films from the water surface or coordinate with Ag(I) in the subphase to form Ag(I)-coordinated LS films. Although both of these amphiphiles were achiral, TSC18 formed a chiral LS film from the water surface, while BSC18 formed a chiral Ag(I)-coordinated LS film from the aqueous AgNO3 subphase. The supramolecular chirality in these LS films was suggested to be due to a cooperative stereoregular pi-pi stacking of the functional groups together with the long alkyl chains in a helical sense. The relationship between the chirality of the LS films and the molecular structures of TSC18 and BSC18 as well as their H-bond or coordination behaviors was discussed. The Schiff base films showed a reversible color change upon exposure to HCl and NH3 gas alternatively; however, the supramolecular chirality was irreversible during these processes.     

Interfacial assemblies of cyanine dyes and gemini amphiphiles with rigid spacers: regulation and interconversion of the aggregates

A series of gemini amphiphiles with a pyridinium headgroup and rigid spacers were designed, and their interfacial assemblies with cyanine dyes, 3,3-disulfopropyl-9-methyl-selenacarbocyanine (SeCy) and 3,3-disulfopropyl-4,5,4',5'-dibenzo-9-methyl-thiocarbocyanine (MTC), through the air/water interface were investigated. Although the dyes have intrinsic tendencies to form J- or H-aggregates in aqueous solutions, their aggregation could be regulated in the complex films. Depending on the spacer, both J- and H-aggregates were formed for SeCy, whereas an H-aggregate with different absorption bands was obtained for MTC. Furthermore, the formed aggregates in the films could be reversibly switched by treating the complex films with HCl, NH3 gas, or water vapor. The J-aggregates of SeCy could be changed into H-aggregates and recovered through an alternative HCl/NH3 exposure in the films. The H-aggregate of the MTC film could be changed into J-aggregate upon exposure to HCl gas and subsequently put into air or NH 3 gas, and the thus-formed J-aggregate could be changed into H-aggregate under hot water vapor. In addition, such a reversible switch between different aggregates of MTC was only observed when the gemini amphiphiles with rigid spacers were applied. A possible explanation related to the protonation of the dye and the reorganizations in the film during the interconversion between different aggregates was proposed.     

Supramolecular assemblies of a new series of gemini-type schiff base amphiphiles at the air/water interface: in situ coordination, interfacial nanoarchitectures, and spacer effect

Great interest has been devoted to the gemini amphiphiles because of their unique properties. In this article, we report some interesting properties of the interfacial films formed by a series of newly designed gemini amphiphiles containing the Schiff base moiety. This novel series of gemini amphiphiles with their Schiff base headgroups linked by a hydrophobic alkyl spacer (BisSBC18Cn, n = 2, 4, 6, 8, 10) could be spread to form stable monolayers and coordinated with Cu(Ac)(2) in situ in the monolayer. The alkyl spacer in the amphiphiles has a great effect on the regulation of the properties of the Langmuir monolayers. A maximum limiting molecular area was observed for the monolayers of the gemini amphiphile with the spacer length of hexa- or octamethylene groups. Both the monolayers on water and on the aqueous Cu(Ac)(2) subphase were transferred onto solid substrates, and different morphologies were observed for films with different spacers. Nanonail and tapelike morphologies were observed for amphiphile films with shorter spacers (n = 2 and 4) on the water surface. Wormlike morphologies were observed for gemini films with longer spacers of C(8) and C(10) when coordinated with Cu(Ac)(2). An interdigitated layer structure was supposed to form in the multilayer films transferred from water or the aqueous Cu(Ac)(2) subphase.     

Investigation in monolayers of double-chain fluorocarbon amphiphiles Effect of headgroups on molecular packing and interaction between hydrocarbon and fluorocarbon monolayers

The surface pressure-area diagrams of double-chain fluorocarbon amphiphiles with different headgroup compositions show that the amphiphiles arrange almost perpendicularly to the water subphase and the structure of headgroups exerts significant influence on the amphiphile packing. Strong hydrogen bonding and weak electrostatic interaction favor the formation of stable monolayers. Perfluorooctanoic acid (FOA) cannot form monolayer at water/air interface and can only form liquid monolayer in subphase of calcium nitrate solution. Complete phase separation of palmitic acid and a fluorocarbon amphiphile with shorter hydrocarbon spacer group, 1, could be demonstrated in monolayers by using the phase rule of Crisp. The creation of phase-separated monolayers is possible when the monolayer is composed of a mixture of palmitic acid and a fluorocarbon amphiphile with longer hydrocarbon spacer group, 2. It can be suggested that the miscibility of hydrocarbon amphiphiles with fluorocarbon amphiphiles is determined by the hydrocarbon fraction of fluorocarbon amphiphiles.     

Langmuir-Blodgett films and chiroptical switch of an azobenzene-containing dendron regulated by the in situ host-guest reaction at the air/water interface

An amphiphilic dendron containing an azobenzene ring at the focal point and the l-glutamate peripheral groups was designed. Its monolayer formation and host-guest reaction with cyclodextrins at the air/water interface and the properties of the transferred Langmuir-Blodgett (LB) films were investigated. The individual dendron, although without any long alkyl chains, could still form a stable monolayer at the air/water interface because of the good balance between hydrophilic and hydrophobic parts within the molecule. When cyclodextrin (CyD) was added to the subphase, a host-guest reaction occurred in situ at the air/water interface. The inclusion of the focal azobenzene moiety into the cavity of cyclodextrin decreased the packing of the aromatic ring and also led to the diminishment of the molecular area. Both the films formed at the surface of pure water and aqueous cyclodextrins were transferred onto solid substrates. Nanofiber structures were obtained for the film from the water surface as a result of the packing of the azobenzene groups, and circular domains were obtained for the film transferred from the aqueous CyD phases. The film transferred from the water surface showed an exciton couplet in the absorption band of azobenzene, whereas a negative Cotton effect was obtained for the film from CyD subphases. It was found that the supramolecular chirality in the LB film transferred from water was due to the transfer of the molecular chirality to the assemblies whereas that from the CyD subphase was due to the inclusion of azobenzene into the chiral cavity. Interestingly, the film from the water surface was photoinactive, whereas a reversible optical and chiroptical switch could be obtained for the film from the α-CyD subphase. The work provided a way to regulate the assembly and functions of organized molecular films by taking advantage of the interfacial host-guest reaction.     

Biquinolino-modified beta-cyclodextrin dimers and their metal complexes as efficient fluorescent sensors for the molecular recognition of steroids

A series of bridged beta-cyclodextrin (beta-CyD) dimers possessing functional tethers of various lengths was synthesized in moderate yield by the treatment of 2,2'-biquinoline- 4,4'-dicarboxylic dichloride with beta-CyD or mono[6-oligo(ethylenediamino)-6-deoxy]-beta-CyDs. The products were 2,2'-biquinoline-4,4'-dicarboxy-bridged bis(6-O-beta-CyD) (8), N,N'-bis(2-aminoethyl)-2,2'-biquinoline-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-beta-CyD) (9), and N,N'-bis(5-amino-3-azapentyl)-2,2'-biquinoline-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-beta-CyD) (10). The reaction of 8-10 with copper perchlorate give their copper(II) complexes 11-13 in satisfactory yields of over 77 %. All the bis(beta-CyD)s 8-13 act as efficient fluorescent sensors and display remarkable fluorescence enhancement upon addition of optically inert steroids. The inclusion complexation behaviors of 8-13 when treated with the representative steroids cholate (14), deoxycholate (15), and glycocholate (16) in aqueous solution at 25 degrees C were investigated by means of UV/Vis spectroscopy, conductivity and fluorescence measurements, circular dichroism spectroscopy, and 2D NMR spectroscopy. The tether length of bis(beta-CyD) 9 allows it to adopt a cooperative host-tether-guest binding mode in which the spacer and guest are co-included in the two CyD cavities. As a result of this cooperation, 9 has a stability constant (K(s)) about 2x10(2) times higher than that of monomodified beta-CyD 4 for inclusion complexation with cholate. Metallooligo(beta-CyD)s with four beta-CyD units have enhanced binding abilities compared with monomodified beta-CyDs. These metallo compounds have binding affinities for guest steroids that are up to 50-4.1x10(3) times higher than those of CyDs 2-4. The guest-induced fluorescence enhancement of bis(CyD)s opens a new channel for the design of sensor materials. The complex stability constants of these compounds are discussed from the viewpoint of induced-fit interaction and cooperative multiple binding between host and guest.     

Unique rodlike surface morphologies in trisilanolcyclohexyl polyhedral oligomeric silsesquioxane films

A trisilanol derivative of polyhedral oligomeric silsesquioxane (POSS), trisilanolisobutyl-POSS, has recently been reported to form stable monolayers at the air/water interface. This paper explores the mono- and multilayer properties of another POSS derivative, trisilanolcyclohexyl-POSS, with pi-A isotherm and Brewster angle microscopy measurements. Results show that with continuously increasing surface concentration via symmetrical compression, trisilanolcyclohexyl-POSS amphiphiles at the air/water interface undergo a series of phase transitions from traditional Langmuir monolayers (one-POSS-molecule thick) to unique rodlike hydrophobic aggregates in multilayer films (approximately eight-POSS-molecules thick) that are dramatically different from "collapsed" morphologies seen in other systems. Stable and hydrophobic rodlike structure formation on water is presumably due to trisilanolcyclohexyl-POSS' unique molecular structure and strong tendency to form intermolecular hydrogen bonds in the solid state. This result is consistent with existing POSS/polymer composite research, which shows that POSS molecules tend to aggregate and crystallize into lamellar nanocrystals.     

气/液界面上β-环糊精与十六烷基三甲基溴化铵包结物形成的分子动力学模拟

利用分子动力学模拟的方法从分子水平上研究了气/液界面上β-环糊精(β-CD)与十六烷基三甲基溴化铵(CTAB)包结物的形成. 对β-CD与CTAB摩尔比分别为1∶1和2∶1的两个体系进行了模拟研究, 体系的能量、径向分布函数和均方根位移变化的结果表明, β-CD与CTAB分子可以在气/液界面上形成包结物, 相对而言, 更易形成1∶1型包结物.     

Microanalyses of beta-cyclodextrin in plasma by high-performance liquid chromatography

Procedures for the micro-determination of beta-cyclodextrin (beta-CyD) in plasma were investigated by four methods using high-performance liquid chromatography (HPLC). In methods A and B, underivatized beta-CyD was detected with a refractive index detector and determined by the absolute calibration graph method. An NH2-bonded silica/acetonitrile-water system was used in A and a C18-bonded silica/methanol-water system in B. In method C, the percarbanilate of beta-CyD was separated on a C8-bonded silica column with acetonitrile-water and determined using gamma-CyD as the internal standard with a UV detector at 231 nm. In method D, the per[1-14C]acetate of beta-CyD was fractionated on a silica column with n-hexane-ethanol containing 1% of water and the radioactivity of each fraction was measured with a liquid scintillation counter. gamma-CyD was used as the internal standard. Interfering plasma proteins were removed by centrifugal ultrafiltration with an MPS-1 micro-partition system. Method B was superior to the other methods with respect to ease of sample preparation, sensitivity and time required for analysis. The cumulative amount of beta-CyD in the mesenteric vein absorbed from the rat intestinal lumen after administration of phenobarbital-beta-CyD complex in a closed loop method was determined by the use of method B.     

Mixed monolayers of Gemini surfactants and stearic acid at the air/water interface

The properties of mixed monolayers composed of the cationic Gemini surfactant ([C(18)H(37)(CH(3))(2)N(+)(CH(2))(3)N(+)(CH(3))(2)C(18)H(37)],2Br(+), abbreviated as 18-3-18,2Br(-1)) and stearic acid (SA) at the air/water interface were investigated by using a Langmuir film balance. The excess areas at the different mixed monolayer compositions were obtained and used to evaluate the miscibility and nonideality of mixing. Due to the electrostatic attractive interactions between 18-3-18,2Br(-1) and SA, the excess areas indicated negative deviations from ideal mixing. Moreover, 18-3-18,2Br(-1) and SA were miscible at the air/water interface, as was confirmed by atomic force microscopy (AFM) images of the LB films transferred onto mica substrates. The attenuated total reflectance (ATR) infrared spectra showed that SA in the mixed monolayers was ionized completely at a composition X(SA)=0.67 and formed a "cationic-anionic surfactant," i.e., the carboxylate, with 18-3-18,2Br(-1) owing to the electrostatic interaction between the head groups.