Effects of surface pressure on the structure of the monolayer formed at the air/water interface by a non-ionic surfactant

The monolayer formed at an air/water interface by the synthetic non-ionic surfactant, 1,2-di-O-octadecyl-rac-glyceryl-3-(omega-methoxydodecakis (ethylene glycol)) (2C18E12) has been characterized using Langmuir trough measurements, Brewster angle microscopy (BAM), and neutron reflectometry. The BAM and reflectometry studies were performed at four different surface pressures (pi) in the range 15-40 mN/m. The BAM studies (which give information on the in-plane organisation of the surfactant layer) demonstrate that the 2C18E12 molecules are arranged on the water surface to form distinct, approximately circular, 5 microm diameter domains. As the surface pressure is increased these domains retain their size and shape but are made progressively more close-packed, such that the monolayer is made more or less complete at pi=40 mN/m. The neutron reflectometry measurements were made to determine the structure of the interfacial surfactant layer at pi=15, 28, 34 and 40 mN/m, providing information on the thickness of the 2C18E12 alkyl chains', head groups' and associated solvent distributions (measured along the surface normal), along with the separations between these distributions, and the effective interfacial area per molecule. Partial structure factor analyses of the reflectivity data show that the effective interfacial area occupied decreases from 217 A2 per 2C18E12 molecule at pi=15 mN/m down to 102 A2 at pi=40 mN/m. There are concomitant increases in the widths of the surfactant's alkyl chains' and head groups' distributions (modelled as Gaussians), with the former rising from 12 A (at pi=15 mN/m) up to 19 A (at pi=40 mN/m) and the latter rising from 13 A (at pi=15 mN/m) up to 24 A (at pi=40 mN/m). The compression of the monolayer is also shown to give rise to an increased surface roughness, some of which is due to the thermal roughness caused by capillary waves, but with a significant contribution also coming from the intrinsic/structural disorder in the monolayer. At all surface pressures studied, the alkyl chains and head groups of the 2C18E12 are found to exhibit a significant overlap, and this increases with increasing pi. Given the various trends noted on how the structure of the 2C18E12 monolayer changes as a function of pi, we extrapolate to consider the structure of the monolayer at pi>40 mN/m (making comparison with its single chain (CnEm) counterparts) and then relate these findings to the observations recorded on the structure and solute entrapment efficiency of 2C18E12 vesicles.     

Synthesis and characterization of shell cross-linked micelles with hydroxy-functional coronas: a pragmatic alternative to dendrimers?

Shell cross-linked (SCL) micelles with hydroxy-functional coronas have been constructed in aqueous solution by exploiting the micellar self-assembly behavior of a new thermoresponsive ABC triblock copolymer. This copolymer was prepared via atom transfer radical polymerization in a convenient one-pot synthesis and comprised a thermoresponsive core-forming poly(propylene oxide) (PPO) block, a cross-linkable central poly(2-(dimethylamino)ethyl methacrylate) (DMA) block, and a hydroxy-functional outer block based on poly(glycerol monomethacrylate) (GMA). DMF GPC analysis confirmed a unimodal molecular weight distribution for the PPO-PDMA-PGMA triblock copolymer precursor, with an M(n) of 12 100 and a polydispersity of approximately 1.26. This copolymer dissolved molecularly in aqueous solution at 5 degrees C but formed micelles with hydroxy-functional coronas above a critical micelle temperature of around 12 degrees C, which corresponded closely to the cloud point of the PPO macroinitiator. Cross-linking of the DMA residues using 1,2-bis(2-iodoethoxy)ethane produced SCL micelles that remained intact at 5 degrees C, i.e., below the cloud point of the core-forming PPO block. Dynamic light scattering studies confirmed that the SCL micelle diameter could be varied depending on the temperature employed for cross-linking: smaller, more compact SCL micelles were formed at higher temperatures, as expected. Since cross-linking involved quaternization of the DMA residues, the SCL micelles acquired cationic surface charge as judged by aqueous electrophoresis studies. These cationic SCL micelles were adsorbed onto near-monodisperse anionic silica sols, which were used as a model colloidal substrate. Thermogravimetric analyses indicated a SCL micelle mass loading of 2.5-4.4%, depending on the silica sol diameter and the initial micelle concentration. Aqueous electrophoresis measurements confirmed that surface charge reversal occurred after adsorption of the SCL micelles, and scanning electron microscopy studies revealed a uniform coating of SCL micelles on the silica particles.     

Synthesis and characterisation of new shell cross-linked micelles with amine-functional coronas

Shell cross-linked (SCL) micelles with amine-functional coronas have been constructed in aqueous solution by exploiting the micellar self-assembly of new thermo-responsive ABC triblock copolymers. These copolymers were prepared via atom transfer radical polymerisation (ATRP) in convenient one-pot syntheses and comprised a thermo-responsive core-forming poly(propylene oxide) [PPO] block, a cross-linkable central poly(glycerol monomethacrylate) [GMA] block and an amine-functional outer block based on either poly(2-(dimethylamino)ethyl methacrylate) [DMA] or poly([2-(methacryloyloxy)ethyl]trimethyl ammonium chloride) [QDMA]. DMF GPC analysis indicated an M_n of 17,700 and an M_w/M_n of 1.46 for the PPO-PGMA-PDMA triblock copolymer. The DMA residues of the PPO-PGMA-PDMA triblock copolymer were reacted with methyl iodide to prepare copolymers with differing degrees of quaternisation. Each triblock copolymer dissolved molecularly in aqueous solution at 5 °C and formed micelles with amine-functional coronas above a critical micelle temperature (CMT) of around 12 °C, which corresponded closely to the cloud point of the PPO macro-initiator. Cross-linking of the GMA residues in the inner shell using divinyl sulfone produced SCL micelles that remained intact at 5 °C, i.e. below the cloud point of the core-forming PPO block. Aqueous electrophoresis studies confirmed that these SCL micelles had considerable cationic surface charge, as expected. The cationic SCL micelles were adsorbed onto a near-monodisperse anionic silica sol, which was used as a model colloidal substrate. Thermogravimetric analyses indicated SCL micelle mass loadings of 6.1-15.5 wt.%, depending on the initial micelle concentration. Aqueous electrophoresis studies confirmed that surface charge reversal occurred on adsorption of the SCL micelles and scanning electron microscopy studies revealed the presence of SCL micelles on the silica particles.     

多响应性聚肽共混胶束的药物控释性能

合成了聚(L-谷氨酸)-b-聚氧化丙烯-b-聚(L-谷氨酸)(PLGA-b-PPO-b-PLGA)三嵌段聚肽共聚物.通过透射电镜、激光光散射与核磁共振等方法研究了其与聚乙二醇-6-聚氧化丙烯(PEG-b-PPO)两嵌段共聚物共混体系的自组装行为,使用紫外分光光度计探讨了负载阿霉素的共混聚集体在不同环境下的释药行为.结果表明:该体系形成了以PPO为内核,PLGA和PEG为壳的共混胶束,该共混胶束的释药行为不仅具有pH和温度的响应性,并且对共混胶束的组分具有依赖性.     

Surface behavior and peptide-lipid interactions of the cyclic neuropeptide melanin concentrating hormone

The kinetics and the thermodynamics of melanin concentrating hormone (MCH) adsorption, penetration, and mixing with membrane components are reported. MCH behaved as a surface active peptide, forming stable monolayers at a lipid-free air-water interface, with an equilibrium spreading pressure, a collapse pressure, and a minimal molecular area of 11 mN/m, 13 mN/m, and 140 A (2), respectively. Additional peptide interfacial stabilization was achieved in the presence of lipids, as evidenced by the expansion observed at pi > pi sp in monolayers containing premixtures of MCH with zwitterionic or charged lipids. The MCH-monolayer association and dissociation rate constants were 9.52 x 10 (-4) microM (-1) min (-1) and 8.83 x 10 (-4) min (-1), respectively. The binding of MCH to the dpPC-water interface had a K d = 930 nM at 10 mN/m. MCH penetration in lipid monolayers occurred even up to pi cutoff = 29-32 mN/m. The interaction stability, binding orientation, and miscibility of MCH in monolayers depended on the lipid type, the MCH molar fraction in the mixture, and the molecular packing of the monolayer. This predicted its heterogeneous distribution between different self-separated membrane domains. Our results demonstrated the ability of MCH to incorporate itself into biomembranes and supports the possibility that MCH affects the activity of mechanosensitive membrane proteins through mechanisms unrelated with binding to specific receptors.     

Temperature- and pH-responsive self-assembly of poly(propylene oxide)-b-poly(lysine) block copolymers in aqueous solution

A series of poly(propylene oxide)-b-poly(L-lysine) (PPO-PK) block copolymers were synthesized using Huisgen's 1,3-dipolar cycloaddition, and the solution self-assembly was studied using transmission electron microscopy, circular dichroism spectroscopy, and dynamic and static light scattering techniques. In contrast to previous studies of poly(lysine)-based block copolymers, PPO-PK exhibits a significant shift in the pH associated with the helix-coil transition of the poly(lysine) block, potentially a result of decreased hydrophobicity in the core PPO block. Given the proximity of the lower critical solution temperature of the PPO block, these materials exhibit both pH and temperature-responsive (i.e., "schizophrenic") self-assembly, the latter of which was interpreted in terms of changes in the second osmotic virial coefficient. Finally, the vesicle morphology obtained from these polymers was studied for the propensity in drug encapsulation and passive release.     

New insights into lung surfactant monolayers using vibrational sum frequency generation spectroscopy

At the air-water interface, interfacial molecular structure, intermolecular interactions, film relaxation and film respreading of model lung surfactant monolayers were studied using vibrational sum frequency generation (VSFG) spectroscopy combined with a Langmuir film balance. Chain-perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62), palmitoyloleoyl-phosphatidylglycerol (POPG), palmitic acid (PA) and tripalmitin were investigated. In the DPPC-d62-PA binary monolayer, PA showed a condensing effect on the DPPC chains. On the contrary, in the DPPC-d62-POPG binary monolayer, POPG showed a fluidizing effect on the DPPC chains. In the ternary monolayer system of DPPC-d62-POPG-PA, the balance between the fluidizing and the condensing effect was also observed. In addition, the film relaxation behavior of DPPC-d62 and the enhanced film stability of DPPC-d62 caused by the addition of tripalmitin were observed. Real-time VSFG was also employed to study the respreading properties of a complex lung surfactant mixture containing DPPC-d62, POPG, PA and KL4 (a mimic of SP-B) peptide, which revealed DPPC enrichment after film compression.     

Effects of block copolymer's architecture on its association with lipid membranes: experiments and simulations

Triblock copolymers of the form poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) have been shown to effectively interact with and restore activity of damaged cell membranes. To better understand the interaction between these polymers and cell membranes, we have modeled the outer leaflet of a cell membrane with a lipid monolayer spread at the air-water interface and injected poloxamers of varying architectures into the subphase beneath the monolayer. Subsequent interactions of the polymer with the monolayer upon compression were monitored with concurrent Langmuir isotherm and fluorescence microscopy measurements. Monte Carlo simulations were run in parallel using a coarse-grained model to capture interactions between lipids and poloxamers. Changing the ratio of the PEO to PPO block lengths (NPEO:NPPO) affects the equilibrium spreading pressure of the polymer. Poloxamers with a relatively longer central hydrophobic block are less soluble, resulting in more polymer adsorbed to the interface and therefore a higher equilibrium spreading pressure. Simulation results show that changing the poloxamer structure effectively affects its solubility. This is also reflected in the degree of lipid corralling as poloxamers with a higher chemical potential (and resulting higher equilibrium spreading pressure) cause the neighboring lipid domains to be more ordered. Upon lateral compression of the monolayers, the polymer is expelled from the film beyond a certain squeeze-out pressure. A poloxamer with a higher NPEO:NPPO ratio (with either NPEO or NPPO held constant in each series) has a lower squeeze-out pressure. Likewise when the total size of the polymer is varied with a constant hydrophilic:hydrophobic ratio, smaller poloxamers are squeezed out at a lower pressure. Our simulation results capture the trends of our experimental observations, both indicating how the interactions between lipids and poloxamers can be tuned by the polymer architecture.     

Real-time investigation of lung surfactant respreading with surface vibrational spectroscopy

The respreading of a lung surfactant monolayer at the air-water interface is investigated with broad bandwidth sum frequency generation (BBSFG) spectroscopy. The lung surfactant mixture contains chain perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62), palmitoyloleoylphosphatidylglycerol (POPG), palmitic acid (PA), and KL4 (a 21-residue polypeptide analogue to the surfactant protein SP-B). DPPC-d62 serves as a probe molecule for the spectroscopic investigation. The BBSFG spectra of DPPC-d62 in the lung surfactant mixture are obtained in the C-D stretching region in real-time during film compression and expansion in a Langmuir trough. The BBSFG intensity of the CD3 stretch peak from DPPC-d62 terminal methyl groups is used as a measure of the interfacial density of DPPC-d62 after careful consideration of orientation effects. For the first time, the interfacial loss of DPPC in a complex lung surfactant mixture is quantified. Spectroscopic results reveal that there is an 18% DPPC-d62 interfacial loss during film respreading. However, the surface pressure-area isotherm measurements demonstrate that there is a rather large trough area reduction (37%) during film expansion. The relatively small interfacial loss of DPPC-d62 and the rather large trough area reduction indicate that the respreading of DPPC and non-DPPC components in the lung surfactant is not uniform and a surface refinement process exists during film compression and expansion. This refinement process results in a DPPC-enriched monolayer with a significant depletion of non-DPPC components after film respreading. Implication for replacement surfactant design from this work is discussed.     

Lyotropic liquid-crystalline phases formed by Pluronic P123 in ethylammonium nitrate

Aggregation of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer, Pluronic P123, is promoted in a room temperature ionic liquid, ethylammonium nitrate (EAN). A series of lyotropic mesophases including normal micellar cubic (I1), normal hexagonal (H1), lamellar (Lalpha), and reverse bicontinuous cubic (V2) are identified at 25 degrees C by using polarized optical microscopy and small-angle X-ray scattering techniques. Such self-assembly behavior of P123 in EAN is similar to those observed in H2O or 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMim(+)][PF6(-)]) systems except for the presence of the V2 phase in EAN and the absence of the I 1 phase in [BMim(+)][PF6(-)]. This suggests that the ionic solvent of EAN plays similar roles as H2O and [BMim(+)][PF6(-)] during the aggregation process and solvates the PEO blocks through hydrogen-bond interaction. Furthermore, the hydrogen bonds are considered to form between the ethylammonium cations and oxygen atoms of the PEO blocks as confirmed by Fourier transform infrared spectra of P123-EAN assemblies. This deduction is also consistent with the results from differential scanning calorimetry and thermogravimetric analysis. The additional V2 phase appearing in the P123-EAN system is attributed to the higher affinity for the relatively hydrophobic PPO blocks to EAN than to water, which might reduce the effective area of the solvophilic headgroup and increase the volume of the solvophobic part. The obtained results may help us to better understand the self-assembly process for amphiphilic block copolymers in protic solvents.     

Condensing effect of palmitic acid on DPPC in mixed Langmuir monolayers

The interaction between deuterated dipalmitoylphosphatidylcholine (DPPC-d62) and palmitic acid (PA) in mixed Langmuir monolayers is studied using vibrational sum frequency generation (VSFG) spectroscopy. Palmitic acid is an additive in exogenous lung surfactant preparations such as Survanta and Surfaxin. The effect of PA on the chain conformation and orientation of DPPC in the liquid-expanded and condensed phases is explored. A condensing effect of PA on DPPC is observed with VSFG. At 12 mN/m, DPPC-d62 alone is in the liquid-expanded phase. Adding PA increases the conformational ordering of DPPC chains and causes DPPC to transition from the expanded phase into the condensed phase. At 42 mN/m, DPPC-d62 and PA form a mixed structure in the condensed phase. The presence of PA decreases the chain tilt angle of DPPC, increasing the orientational ordering of DPPC chains. At 42 mN/m, there is also evidence from the frequency red shift of the PO2- symmetric stretch that the carboxyl group of PA forms a hydrogen bond with the phosphate group of DPPC in the condensed phase. From this work the effect of PA on DPPC is 2-fold: (1) PA increases the chain ordering of DPPC and promotes the LE and TC phase separation and (2) due to the miscibility between DPPC and PA in the condensed phase, PA decreases the collapse pressure.     

Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers

In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)(2)(tmphen)]PF(6), (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air-water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as pi-A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at pi approximately equal to 37 mNm(-1). Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir-Blodgett) technique.     

聚电解质微球多级自组装制备双重药物载体

将表面带正电荷的壳聚糖(CS)微球和表面带负电荷的聚(L-谷氨酸)-b-聚氧化丙烯-b-聚(L-谷氨酸)(GPG)胶束共混,制备了CS/GPG聚集体水溶液体系.通过改变CS/GPG的共混比例,研究了CS微球和GPG胶柬形成稳定CS/GPG聚集体水溶液体系的配比范围,并对其粒径分布和表面电位进行了表征.在此基础上,将CS...     

Monoglycerides and beta-lactoglobulin adsorbed films at the air-water interface. structure, microscopic imaging, and shear characteristics

In this work we have analyzed the structural, topographical, and shear characteristics of mixed monolayers formed by adsorbed beta-lactoglobulin (beta-lg) and spread monoglyceride (monopalmitin or monoolein) on a previously adsorbed protein film. Measurements of the surface pressure (pi)-area (A) isotherm, Brewster angle microscopy (BAM), and surface shear characteristics were obtained at 20 degrees C and at pH 7 in a modified Wilhelmy-type film balance. The pi-A isotherm and BAM images deduced for adsorbed beta-lactoglobulin-monoglyceride mixed films at pi lower than the equilibrium surface pressure of beta-lactoglobulin (pi(e)(beta-lg)) indicate that beta-lactoglobulin and monoglyceride coexist at the interface. However, the interactions between protein and monoglyceride are somewhat weak. At higher surface pressures (at pi > or = pi(e)(beta-lg)) a protein displacement by the monoglyceride from the interface takes place. The surface shear viscosity (eta(s)) of mixed films is very sensitive to protein-monoglyceride interactions and displacement as a function of monolayer composition (protein/monoglyceride fraction) and surface pressure. Shear can induce change in the morphology of monoglyceride and beta-lactoglobulin domains, on the one hand, and segregation between domains of the film-forming components on the other hand. In addition, the displacement of beta-lactoglobulin by the monoglycerides is facilitated under shear conditions.     

pH/温度响应的两亲性嵌段共聚物的研究

刺激响应性两亲性嵌段共聚物由于具有多种潜在的用途而引起广泛关注。其中，pH和温度响应的嵌段共聚物被认为是较易获得并对外界环境刺激响应较敏感的一类聚合物。本文综述了利用各种可控/活性聚合方法制备不同结构刺激响应性的两亲性嵌段共聚物研究的最新进展，重点介绍聚（甲基）丙烯酸及其酯类与聚环氧乙烷(PEO)和聚环氧丙烷(PPO)类结构的两亲性嵌段共聚物的合成以及它们在水溶液中对pH值和温度变化的响应性。     

A thermodynamic study to evidence the alpha,omega-dichloroalkane/ block copolymer mixed aggregates formation: effect of the copolymer architecture

The thermodynamics of alpha,omega-dichloroalkanes in aqueous solutions of (ethylene oxide)(11)(propylene oxide)(16)(ethylene oxide)(11) (L35) and (propylene oxide)(8)(ethylene oxide)(23)(propylene oxide)(8) (10R5) was determined at 298 and 305 K. Modeling the experimental data allowed to calculate the standard free energy (DeltaG(D)(o)/w) and the volume (DeltaV(D)/w) for the additive-copolymer mixed aggregates formation per additive molecule. DeltaG(D)(o)/w for Cl(2)CH(2) and Cl(2)(CH(2))(2) evidenced that the process is controlled by the forces exercising between the chlorine atoms and the OH groups of the copolymer micelles protruded into the aqueous phase. Cl(2)(CH(2))(3) experiences both the hydrophilic and hydrophobic domains into the aggregates. The hydrophobic interactions are more significant in 10R5 whereas the hydrophilic ones are more significant in L35. Temperature increase does not influence DeltaG(D)(o)/w in 10R5, whereas, it does influence DeltaG(D)(o)/w in L35, enhancing the ability of the aggregate to extract the chlorinated compounds from the aqueous phase. The DeltaV(D)/w values are consistent with the free energy results. These insights agree with those predicted by the Flory liquid lattice theory. The calculations extended to several alpha,omega-dichloroalkanes showed that Cl(2)CH(2) and Cl(2)(CH(2))(2) prefer poly(ethylene oxide) (PEO), Cl(2)(CH(2))(3) exhibits the same affinity for both PEO and poly(propylene oxide) (PPO), whereas the more hydrophobic additives show a preference for PPO. The copolymer architecture plays a relevant role in the alpha,omega-dichloroalkane solubilization into the polymeric aggregates.     

Mechanism of gold metal ion reduction, nanoparticle growth and size control in aqueous amphiphilic block copolymer solutions at ambient conditions

Spontaneous formation and efficient stabilization of gold nanoparticles with an average diameter of 7 approximately 20 nm from hydrogen tetrachloroaureate(III) hydrate (HAuCl4.3H2O) were achieved in air-saturated aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer solutions at ambient temperature in the absence of any other reducing agent. The particle formation mechanism is considered here on the basis of the block copolymer concentration dependence of absorption spectra, the time dependence (kinetics) of AuCl4- reduction, and the block copolymer concentration dependence of particle size. The effects of block copolymer characteristics such as molecular weight (MW), PEO block length, PPO block length, and critical micelle concentration (cmc) are explored by examining several PEO-PPO-PEO block copolymers. Our observations suggest that the formation of gold nanoparticles from AuCl4- comprises three main steps: (1) reduction of metal ions by block copolymer in solution, (2) absorption of block copolymer on gold clusters and reduction of metal ions on the surface of these gold clusters, and (3) growth of metal particles stabilized by block copolymers. While both PEO and PPO blocks contribute to the AuCl4- reduction (step 1), the PEO contribution appears to be dominant. In step 2, the adsorption of block copolymers on the surface of gold clusters takes place because of the amphiphilic character of the block copolymer (hydrophobicity of PPO). The much higher efficiency of particle formation attained in the PEO-PPO-PEO block copolymer systems as compared to PEO homopolymer systems can be attributed to the adsorption and growth processes (steps 2 and 3) facilitated by the block copolymers. The size of the gold nanoparticles produced is dictated by the above mechanism; the size increases with increasing reaction activity induced by the block copolymer overall molecular weight and is limited by adsorption due to the amphiphilic character of the block copolymers.     

Adsorption behavior of glucose oxidase on a dipalmitoylphosphatic acid monolayer and the characteristics of the mixed monolayer at air/liquid interfaces

A dipalmitoylphosphatic acid (DPPA) monolayer at the air/liquid interface is used as a binding layer to incorporate glucose oxidase (GOx) from the subphase. The effects of the adsorption time of GOx on the behavior of the mixed DPPA/GOx monolayer and the relevant structure of the mixed LB film were studied using the characteristics of the pressure-area (pi-A) isotherm, Brewster angle microscopy (BAM), and atomic force microscopy (AFM). The experimental results show that two equilibrium states of GOx adsorption exist in the presence of a DPPA monolayer. The first equilibrium stage occurs at tens of minutes after spreading of DPPA, and a surface pressure of ca. 7.5 mN/m is obtained. The second equilibrium stage approaches slowly, and a higher equilibrium surface pressure (ca. 16 mN/m) was obtained at ca. 8 h after the first stage. The BAM and AFM images show that, after the second equilibrium stage is reached, a more condensed phase and rough morphology are obtained on the mixed DPPA/GOx monolayer, indicating a higher amount of GOx incorporated into the mixed film. For the first equilibrium stage of GOx adsorption, DPPA molecules can still pack regularly and closely under compression, suggesting that GOx molecules are mainly located beneath the DPPA monolayer at the compressed state. A more uniform phase was detected on a film prepared after the first equilibrium stage was reached. The present result indicates that distinct structures and properties of mixed DPPA/GOx films can be prepared from the various stages of GOx adsorption.     

Synthesis of biocompatible poly[2-(methacryloyloxy)ethyl phosphorylcholine]-coated magnetite nanoparticles

A well-defined, double-hydrophilic diblock copolymer comprising poly[2-(methacryloyloxy)ethyl phosphorylcholine]-block-(glycerol monomethacrylate) (PMPC30-PGMA30, where the numbers represent the average degrees of polymerization for each block) was evaluated for the synthesis of colloidally stable ultrafine magnetite sols. Sterically stabilized paramagnetic sols were prepared in aqueous solution by chemical coprecipitation of ferric and ferrous salts in the presence of this block copolymer. The PMPC30-PGMA30-stabilized magnetite sol had a mean transmission electron microscopy (TEM) diameter of 9.4 +/- 1.7 nm and a mean hydrodynamic diameter of 34 nm. This sol exhibited improved colloidal stability with respect to long-term storage and pH variation compared with magnetite sols prepared in the presence of alternative water-soluble homopolymers and diblock copolymers. Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry, electron spectroscopy imaging (ESI), and zeta potential studies indicate that the PMPC30-PGMA30 diblock copolymer was adsorbed onto the surface of the sol via the PGMA30 block, with the PMPC30 chains acting as the stabilizing block. Such sterically stabilized sols are expected to be improved contrast agents for magnetic resonance imaging (MRI) applications.     

Brewster angle microscopy and PMIRRAS study of DNA interactions with BGTC, a cationic lipid used for gene transfer

The lipid bis(guanidinium)-tris(2-aminoethyl)amine-cholesterol (BGTC) is a cationic cholesterol derivative bearing guanidinium polar headgroups which displays high transfection efficiency in vitro and in vivo when used alone or formulated as liposomes with the neutral colipid 1,2-di-[ cis-9-octadecenoyl]- sn-glycero-3-phosphoethanolamine (DOPE). Since transfection may be related to the structural and physicochemical properties of the self-assembled supramolecular lipid-DNA complexes, we used the Langmuir monolayer technique coupled with Brewster angle microscopy (BAM) and polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) to investigate DNA-BGTC and DNA-BGTC/DOPE interactions at the air/water interface. We herein show that BGTC forms stable monolayers at the air/water interface. When DNA is injected into the subphase, it adsorbs to BGTC at 20 mN/m. Whatever the (+/-) charge ratio of the complexes used, defined as the ratio of positive charges of BGTC in the monolayer versus negative charges of DNA injected in the subphase, the DNA interacts with the cationic lipid and forms either an incomplete (no constituent in excess) or a complete (DNA in excess) monolayer of oriented double strands parallel to the lipid monolayer plan. We also show that, under a homogeneous BGTC/DOPE (3/2) monolayer at 20 mN/m, DNA adsorbs homogeneously to form an organized but incomplete layer whatever the charge ratio used (DNA in default or in excess). Compression beyond the collapse of these mixed DNA-BGTC/DOPE systems leads to the formation of dense DNA monolayers under an asymmetric lipid bilayer with a bottom layer of BGTC in contact with DNA and a top layer mainly constituted of DOPE. These results allow a better understanding of the mechanisms underlying the formation of the supramolecular BGTC-DNA complexes efficient for gene transfection.