An amphiphilic C60 derivative with a tris(2,2′-bipyridine)ruthenium(II) polar head group: synthesis and incorporation in Langmuir films

An amphiphilic C₆₀ derivative with a tris(2,2′-bipyridine)ruthenium(II) polar head group has been prepared. The Langmuir film of this compound has been characterized by its surface pressure versus molecular area (Π/A) isotherm and Brewster angle microscopy (BAM) observations.     

The role of ammonium sulfate in regulation of the structure and properties of 2D films of fullerene C<Subscript>60</Subscript>

The effect of ammonium sulfate on the parameters of surface pressure isotherms (surface pressure and area per fullerene molecule) of 2D films of fullerene C₆₀ on the water/air interface has been studied by the Langmuir method. The possibility of regulation of the structure of 2D fullerene films has been shown. The maximal A ₀ value is achieved at an ammonium sulfate concentration of 1 × 10^?4 mol/L. Brewster angle microscopy shows that the presence of the electrolyte ensures the formation of a monomolecular 2D film with a lower content of defects.     

Langmuir monolayers from perfluorobutyl-n-eicosane

Perfluorobutyl-n-eicosane (abbreviated as F4H20) was spread at the air/water as Langmuir monolayers and studied under different experimental conditions, such as spreading volume, subphase temperature and compression speed. The Langmuir monolayer experiments (π-A isotherms) have been complemented with Brewster angle microscopy results, which enabled direct visualization of the monolayers’ structure and estimation of the film thickness at different stages of compression. It has been found that the molecules are oriented almost vertically (with respect to the interface) in the vicinity of film collapse. The negative sign of the measured surface potential, ΔV, is evidence for the orientation of F4H20 molecules with their perfluorinated parts exposed towards the air. In the case of F4H20 a limited fluorination relative to perfluoroeicosane also results in monolayer formation, in contrast to eicosane itself, which forms lenses.     

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

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

Formation of 2D colloidal crystals by the Langmuir-Blodgett technique monitored in situ by Brewster angle microscopy

We report a method that combines Brewster angle microscopy and Langmuir-Blodgett films technique to obtain highly ordered 2D colloidal crystals of nanospheres. The deposition of Langmuir-Blodgett films of silica spheres monitored by Brewster angle microscopy allows to determine with accuracy the best physical conditions to transfer highly ordered monolayers of nanoparticles.     

Investigations and application in piezoelectric phenol sensor of Langmuir-Schäfer films of a copper phthalocyanine derivative functionalized with bulky substituents

An octa-substituted copper phthalocyanine was dissolved in chloroform and spread on ultrapure water subphase in a Langmuir trough. The floating films were characterized at the air–water interface by the Langmuir isotherm, Brewster angle microscopy, and UV–Vis reflection spectroscopy and transferred by Langmuir–Schäfer technique on a silicon substrate, and thickness, refractive index, and extinction coefficient of the phthalocyanine derivative thin film were calculated by means of spectroscopic ellipsometry. A different number of layers were deposited using Langmuir–Schäfer method onto QCM crystals, and the active layers were tested as sensors for the detection of phenols in aqueous solution. The piezoelectric sensor response, totally reversible, is influenced by the number of transferred layers and by the nature of the substituent; on the contrary, the pK_a value of the injected analytes slightly affects the device performances. Repeatability of the sensor responses was tested, and the frequency variation appears unchanged at least for 100 days.     

Miscibility of mixed stereoregular PMMA/PVPh monolayers at the air/water interface

The mixed monolayer behavior of stereoregular poly(methyl methacrylate) (PMMA) and poly(vinyl phenol) (PVPh) was investigated from the measurements of surface pressure–area per molecule (π–A) isotherms. The π–A isotherms indicated that isotactic PMMA (iPMMA) and PVPh were miscible at the air/water interface. The miscibility and non-ideality of the mixed monolayers were examined by calculating the excess area as a function of composition, and negative deviations from ideality were observed, which suggest the existence of attractive interactions between iPMMA and PVPh. However, the π–A isotherms of mixed syndiotactic PMMA (sPMMA)/PVPh monolayers showed positive deviation from ideality, which might suggest that non-favorable interactions exist between sPMMA and PVPh.The π–A isotherms of mixed atactic PMMA (aPMMA)/PVPh monolayers exhibited complicated excess area behavior. Both positive and negative deviations from ideality were observed at various surface pressures. These isotherm results of mixed polymers correlate approximately well with the miscibility of the corresponding mixtures in the bulk state. The formation of hydrogen bonding between PMMA and PVPh was substantiated in the bulk state by means of Fourier transform infrared (FTIR). Regardless of tacticity, an increase of hydrogen-bonded carbonyl fraction was observed.     

Influence of the electrolyte composition of the subphase on the structure of 2D films of fullerene C60

The morphology of 2D films of fullerene C₆₀ on interfaces has been studied by Brewster angle microscopy and atomic force microscopy. Fullerene C₆₀ tends to aggregate, forming supramolecular structures with a surface area per C₆₀ molecule from 21.6 to 2900 Ų. As the area per C₆₀ molecule decreases, monomolecular clusters gradually transform into multiplayer structures. The introduction of an electrolyte into the system prevents the formation of fullerene globules and favors the formation of more homogeneous films.     

Langmuir–Blodgett films of octadecanethiol on gold sols subphase

An octadecanethiol monolayer was formed on an aqueous gold sols subphase, it’s LB films were characterized by means of π-A isotherms, TEM (transmission electron microscopy), XRD (X-ray diffraction) and UV–Vis spectroscopy.     

Effects of Fullerenes on Phospholipid Membranes: A Langmuir Monolayer Study

We investigate two‐component Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC)/C₆₀ by recording surface pressure/area (π/A) and surface potential/area (ΔV/A) isotherms and by direct Brewster angle microscopy (BAM) imaging. Atomic force microscopy (AFM) is employed to study morphologies of the mixed monolayers transferred to a solid substrate by the Langmuir–Blodgett technique. C₆₀ is shown to have little influence on isotherms of the DPPC/C₆₀ monolayers even at a molar fraction as high as X_C60=0.3. The elastic modulus ( ) versus π curves of the DPPC/C₆₀ monolayers almost overlay each other, as well as that of pure DPPC, that is, the elasticities of pure DPPC monolayers and DPPC/C₆₀ monolayers are remarkably similar. AFM studies reveal that fullerene flocs form at low surface pressures (π≤15 mN m^?1), are gradually disaggregated and dispersed in the DPPC monolayer with increasing surface pressure up to 35 mN m^?1, and are then progressively squeezed out to form protruded islands as the surface pressure increases up to 65 mN m^?1. Our work provides experimental support to the computational result that C₆₀ can dissolve in lipid bilayers without significantly compromising their mechanical properties, a finding which has important implications for the toxicity and development of drug vehicles from fullerene materials.     

Structural characterization of the crystalline diastereomeric complexes of enantiopure dimethylacridino-18-crown-6 ether and the enantiomers of 1-(1-naphthyl)ethylamine hydrogen perchlorate

This paper describes the X-ray crystal structure of the diastereomeric complexes formed by enantiopure dimethyl-substituted acridino-18-crown-6 ether (R,R)-1 and the enantiomers of 1-(1-naphthyl)ethylammonium perchlorate. We found that the heterochiral complex (R,R)-1–(S)-1-NEA is more stable than the homochiral one (R,R)-1–(R)-1-NEA. In the case of the heterochiral complex, the X-ray studies revealed a strong intermolecular π–π interaction between the naphthyl unit and the acridine moiety. However, in the case of the homochiral complex, π–π interaction was not found. We suggest that the existence or absence of the π–π interaction and the difference in steric repulsions in the diastereomers is responsible for the enantiomeric discrimination.     

Langmuir-Blodgett films of cyclopalladated ferrocenylimine: preparation, characterization, and application in Suzuki coupling reaction

Langmuir monolayer and Langmuir-Blodgett (LB) films of cyclopalladated ferrocenylimine 1 were prepared and characterized. The surface pressure (π)-area (A) isotherm of complex 1 indicated the formation of highly condensed monolayer on the subphase. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy showed that complex 1 monolayer was transferred successfully onto solid supports. Atomic force microscopy (AFM) image suggested that LB films transferred on the solid substrate were well-ordered, homogeneous. Cyclic voltammograms of LB films deposited on glassy carbon electrodes showed quasi-reversible oxidation/reduction waves of ferrocene moiety. From the average thickness of monolayer, the hydrocarbon chain could be fairly directed perpendicular to the substrates. Finally, LB films of complex 1 presented a largely improved catalytic efficiency for Suzuki reaction with respect to its cast films and homogeneous reactions under the same conditions. The results might have an implication on the catalytic mechanism of this reaction.     

Organized collapse structures in mixtures of chiral ethyl 2-azido-4-fluoro-3-hydroxystearates

Monolayers of enantiomeric compounds as well as diastereomeric mixtures and racemic/diastereomeric mixtures of ethyl 2-azido-4-fluoro-3-hydroxystearates have been investigated using surface pressure-area isotherms and Brewster angle microscopy. All monolayers collapse out of the liquid-expanded phase, forming 3D collapse structures which were visualized with scanning force microscopy. The enantiomeric compound and the diastereomeric mixtures form unique fiber-like network structures with heights between 20 and 40 nm. Interestingly, the shape of the enantiomeric fiber structures is straight, whereas the diastereomeric mixtures exhibit curved fibers of different sizes. The racemic mixture however forms circular 10 nm high and 20-50 microm broad structures. The shape of unconventional collapse structures could be changed by using distinct ratios of diastereomeric or racemic/diastereomeric mixed compounds.     

Monolayer behavior and BAM observaion of biphenyl liquid crystalline polysiloxane at the A/W interface

Monolayers of a chiral biphenyl liquid crystalline polysiloxane and its monomer have been studied by π–A isotherms and hysteresis measurements. Both of them can form monolayers at different temperatures. The molecular packing in the monolayers are temperature-dependent for the monomer but not for the polymer. The molecular orderings are dominated by the packing of the biphenyl mesogens. Metastable monolayers with different ordering and thickness of domains have been directly observed by Brewster Angle Microscopy (BAM) in monomer monolayers. Both of them show characteristics of rigid monolayers. A broken process of the monolayers can be observed during expansion.     

Langmuir monolayer characteristics of a perfluoroaryl surfactant: 10-Perfluorobenzyl-decan-1-ol (PBD)

A surfactant containing the perfluorobenzyl moiety attached at the 10 position of decanol (10-perfluorobenzyldecan-1-ol, PBD) was synthesized and employed for Langmuir monolayer characterization, using surface pressure (π) and electric surface potential (ΔV)-mean molecular area (A) isotherms. Both static and dynamic stability experiments demonstrate that the monolayers formed by PBD are of satisfactory stability. Characteristic dendritic structures were observed with Brewster Angle Microscope (BAM) upon the whole compression up to the vicinity of collapse, where 3D crystallites appeared. The monolayer thickness is found to be comparable to the PBD molecule length. It occurs that ΔV has negative value even at large molecular areas, and decreases gradually along the compression, reaching a minimum of ca. −500 mV. Using the Helmholtz model, the apparent dipole moment was calculated upon film compression. The measurements were complemented with semi-empirical calculations involving molecular geometry optimization and dipole moment estimation.     

Influence of the alkyl chain length of some mesogenic molecules on their Langmuir film formation ability

Langmuir films of members of two homologous series, the 4‐n‐alkyl‐4′‐cyanobiphenyls (nCB) for n = 2–14 and trans‐4‐n‐alkyl(4′‐cyanophenyl)cyclohexanes (PCHn) for n = 2–12, have been studied by recording surface pressure/area isotherms and by Brewster angle microscopy. It has been found that the compounds with very short chains (n3) and very long chains (n>12 for nCB, n>10 for PCHn) are unable to form compressible monolayers at the air–water interface. Other members of both series can form stable Langmuir films, but both their rigidity and stability as well as the molecular packing vary with the alkyl chain length. The isotherms and BAM images imply that the organization of the liquid crystal molecules in the films is to some extent correlated with their ability to form corresponding mesophase in the bulk: nematogenic compounds tend to form rounded droplet‐like domains, whereas smectogenic compounds tend to form flat domains.     

Atypical Film-Forming Behavior of Soluble Tetra-3-Nitro-Substituted Copper Phthalocyanine

Thin films of metal phthalocyanines (MPc) are known to exhibit excellent physical properties but poorly controlled morphologies. Therefore, the present work seeks to understand the film growth mechanism of a model compound for potentially usable MPc, specifically, copper tetra(3-nitro-5-tert-butyl)phthalocyanine (CuPc*). The Langmuir-Schaefer (LS) technique was applied to prepare a series of CuPc* films under different processing conditions. The film growth was examined by Brewster angle microscopy (BAM) on the water surface and small-angle X-ray scattering (SAXS) from the solid films. Neutron reflectometry (NR) measurements of the water uptake into the films and computer simulation of hydrated CuPc* were performed to substantiate an idea of colloidal MPc-water aggregates as nanoscale precursors of smooth solid films. This idea appears fruitful in terms of materials chemistry.     

有机金属聚合物/多酸纳米杂化LB膜的制备与光电性质研究

以含有共轭大π键的有机金属聚合物(OMP)作有机组分, 以Keggin结构和Dawson结构钨(钼)磷杂多酸作无机组分, 以十八胺为辅助成膜剂, 用LB技术制备了3种新型有机金属聚合物/十八铵/杂多阴离子OMP/ODA/HPA (HPA＝PMo₁₂, PW₁₂, P₂Mo₁₈)杂化LB膜. 用π-A曲线﹑UV-vis吸收光谱﹑荧光光谱﹑原子力显微镜(AFM)﹑扫描隧道显微镜(STM)和表面光电压谱(SPS)对标题LB膜的成膜性能及光电性质进行了研究, 结果表明标题杂化LB膜的崩溃压为26.8 mN/m, 在可见光区有较强的光电压响应, 并有好的发光性质. 当电压为±8.0 V时, 隧道电流是－0.1～－2.3 nA.     

Chemoenzymatic and enantioselective assembly of the (1α,3aβ,6α,7aβ)-octahydro-1,6-methano-1H-indene framework associated with 2-isocyanoallopupukeanane: validation of a new synthetic strategy and the identification of enantiomeric switching regimes

The octahydro-1,6-methano-1H-indene framework associated with the marine sesquiterpenoid 2-isocyanoallopupukeanane (1) has been prepared in enantiomerically pure form from the cis-1,2-dihydrocatechol 8 using Diels–Alder cycloaddition, oxa-di-π-methane rearrangement and intramolecular enolate alkylation steps as the key bond-forming events. Three distinct strategies for employing such sequences in the selective synthesis of either enantiomeric form of the target framework have been identified.