Langmuir monolayer properties of the fluorinated-hydrogenated hybrid amphiphiles with dipalmitoylphosphatidylcholine (DPPC)

Surface pressure–area (π–A), surface potential–area (ΔV–A), and dipole moment–area (μ–A) isotherms were obtained for the Langmuir monolayer of two fluorinated-hydrogenated hybrid amphiphiles (sodium phenyl 1-[(4-perfluorohexyl)-phenyl]-1-hexylphosphate (F6PH5PPhNa) and (sodium phenyl 1-[(4-perfluorooctyl)-phenyl]-1-hexylphosphate (F8PH5PPhNa)), DPPC and their two-component systems at the air/water interface. Monolayers spread on 0.02 M Tris buffer solution (pH 7.4) with 0.13 M NaCl at 298.2 K were investigated by the Wilhelmy method, ionizing electrode method and fluorescence microscopy. Moreover, the miscibility of two components was examined by plotting the variation of the molecular area and the surface potential as a function of the molar fraction for the fluorinated-hydrogenated hybrid amphiphiles on the basis of the additivity rule. The miscibility of the monlayers was also examined by construction of two-dimensional phase diagrams. Furthermore, assuming the regular surface mixture, the Joos equation for analysis of the collapse pressure of two-component monolayers allowed calculation of the interaction parameter (ξ) and the interaction energy (−Δ) between the fluorinated-hydrogenated hybrid amphiphiles and DPPC. The observations by a fluorescence microscopy also supported our interpretation as for the miscibility in the monolayer state. Comparing the monolayer behavior between the two binary systems, no remarkable difference was found among various aspects. Among the two combinations, the mole fraction dependence in monlayer properties was commonly classified into two ranges: 0 ≤ X ≤ 0.3 and 0.3 < X ≤ 1. Dependence of the chain length of fluorinated part was reflected for the molecular packing and surface potential.     

Membrane properties of mixed ganglioside GM1/phosphatidylcholine monolayers

The interaction between ganglioside G_M1 (GM1) and --dipalmitoylphosphatidylcholine (DPPC) in mixed monolayers was investigated using surface pressure measurements and atomic force microscopy (AFM), and the effects of GM1, surface pressure and temperature on the properties of the membranes were examined. Mixed GM1/DPPC monolayers were deposited on mica using the Langmuir–Blodgett (LB) technique for AFM. GM1 and DPPC were miscible below the 0.2 mole fraction of GM1 and there was attractive interaction between GM1 and DPPC. The AFM images for the GM1/DPPC monolayers (X_GM1 < 0.2) at 30 mN m⁻¹ and 25 °C indicated a percolation pattern which means a micro phase separation: namely, the mixed film composed of GM1 and DPPC phase-separated from the DPPC liquid-condensed film. The AFM images for the mixed monolayers at 33 mN m⁻¹ indicated a specific morphology when the surface pressure was varied from 30 to 40 mN m⁻¹. The percolation pattern in the AFM image at 25 °C came to be destroyed with increasing temperature and completely disappeared at 45 °C. The change in the morphology of mixed GM1/DPPC monolayers on varying the surface pressure and temperature is thought to be related to signal transduction and a preventive mechanism against viral infections in the human body.     

A monolayer study on three binary mixed systems of dipalmitoyl phosphatidyl choline with cholesterol, cholestanol and stigmasterol

The monolayer behavior of three mixed systems of dipalmitoyl phosphatidyl choline (DPPC) with sterols; cholesterol (Ch), stigmasterol (Stig), and cholestanol (Chsta) formed at the interface of air/water (phosphate buffer solution at 7.4 with addition of NaCl) was investigated in terms of surface pressure (π) and molecular occupation surface area (A) relation. A series of π–A curves at every 0.1 mol fraction of each sterol for the three combinations of mixed systems were obtained at 25.0 °C.

On the basis of the π–A curves, the additivity rule in regard to A versus sterol mole fraction (X_st) was examined at discrete surface pressures such as 5, 10, 15, 20, 25, 30 mN m⁻¹, and then from the obtained A–X_st curves the partial molecular areas (PMA) were determined. The A–X_st relation exhibited a marked negative deviation from ideal mixing in the pressure range below 10 mN m⁻¹, i.e. in the expanded liquid film region (below the transition pressure of DPPC).

The PMA of Ch at π=5 mN m⁻¹, for example, was found to be conspicuously negative in the range of X_Ch=0–0.2 (about −0.4 nm² per molecule) and slightly positive (ca. 0.1 nm² per molecule) in the range X_Ch=0.2 to 0.4. Above X_Ch=0.5, Ch’s PMA was almost the same as the surface area of pure Ch, while DPPC’s PMA was reduced to 60% of that of the pure system.

Excess Gibbs energy (ΔG_(ex)) as a function of X_st was estimated at different pressures. Applying the regular solution theory to thermodynamic analysis of ΔG_(ex), the activity coefficients (f₁ and f₂) of DPPC and the respective sterols as well as the interaction parameter (I_p) in the mixed film phase were evaluated; the results showed a marked dependence on X_st.

Compressibility C_s and elasticity C_s⁻¹ were also examined. These physical parameters directly reflected the mechanical strength of formed monolayer film.

Phase diagrams plotting the collapse pressure (π_c) against X_st were constructed, and the π_c versus X_st curves were examined for the respective mixed systems in comparison with the simulated curves of ideal mixing based on the Joos equation.

Comparing the monolayer behavior of the three mixed systems, little remarkable difference was found in regard to various aspects. In common among the three combinations, the mole fraction dependence in monolayer properties was classified into three ranges: 0<X_st<0.2, 0.2<X_st<0.4 and 0.5<X_st<1. How the difference in the chemical structure of the sterols influenced the properties was examined in detail.     

On the interaction of dipalmitoyl phosphatidylcholine with normal long-chain alcohols in a mixed monolayer: a thermodynamic study

This study investigated the mixed monolayer behavior of dipalmitoyl phosphatidylcholine (DPPC) with normal long-chain alcohols at the air/water interface. Surface pressure–area isotherms of mixed DPPC/C₁₈OH and DPPC/C₂₀OH monolayers at 37°C were obtained and compared with previous results for the mixed DPPC/C₁₆OH system. The negative deviations from additivity of the areas and the variation of the collapse pressure with composition imply that DPPC and long-chain alcohols were miscible and formed non-ideal monolayers at the interface. At lower surface pressures, it seems that the attractive intermolecular force was dominant in molecular packing in the mixed monolayers. At higher surface pressures, the data suggest that the molecular packing in mixed DPPC/C₁₆OH monolayers may be favored by the packing efficiency or geometric accommodation. Furthermore, negative values of excess free energy of mixing were obtained and became significant as the hydrocarbon chain length of alcohols increased, which indicates there were attractive interactions between DPPC and long-chain alcohols. In each free energy of mixing–composition curve, there was only one minimum and thus a phase separation did not exist for mixed DPPC/long-chain alcohol monolayers.     

Stress relaxation behaviour of dipalmitoyl phosphatidylcholine monolayers spread on the surface of a pendant drop

Dipalmitoyl phosphatidylcholine (DPPC) monolayers were characterised by surface pressure/area isotherms (π/A) and surface dilational rheological parameters at temperatures 20–40°C. The methods used were the Langmuir trough and the pendant drop micro-film balance. The latter allows accurate measurements at higher temperatures and transient drop deformation. Stable DPPC monolayers were found only for low surface pressures, π<15 mN m⁻¹. At higher monolayer compression π decreases over a long time, mainly caused by molecular rearrangement processes in the monolayer starting in the coexisting region. At π>25 mN m⁻¹ and 20°C relaxation experiments give evident of rupturing, brittle monolayer structures. At higher temperatures the monolayers became more fluid-like. π/A-isotherms determined by using both methods principally agree with each other, but show also remarkable differences, which cannot be explained so far satisfactory. Transient drop relaxation experiments were analysed for the short time range (600 s). At 20°C the dilational modulus (_r) and the surface dilational viscosity (ξ_r) passes a stationary maximum at 0.54 nm² molecule⁻¹ and increase strongly at higher surface coverage, thus indicating crystalline monolayer structure. Increasing temperature from 20 to 30°C causes a rapid decrease of _r and ξ_r and a shift of the stationary maximum to lower surface coverage. No evidence for crystalline structure is found. Further increase of temperature causes _r and ξ_r increase again. This increase is caused by a rising relaxation time, while the elasticity does not change in the same manner. Such intermediate decrease of _r and ξ_r in the range 30–40°C appears to be unusual and can be interpreted as a consequence of strong DPPC interactions and strongly pronounced retardation of monolayer deformation. The study is discussed in connection to the physiology of breathing. For pulmonary surfactants the observed behaviour seems to be understandable. It is however interesting that such complex behaviour is observed for monolayers consisting of DPPC only.     

Conductivity, calorimetry and phase diagram of the NaHSO4–KHSO4 system

Physico-chemical properties of the binary system NaHSO₄–KHSO₄ were studied by calorimetry and conductivity. The enthalpy of mixing has been measured at 505 K in the full composition range and the phase diagram calculated. The phase diagram has also been constructed from phase transition temperatures obtained by conductivity for 10 different compositions and by differential thermal analysis. The phase diagram is of the simple eutectic type, where the eutectic is found to have the composition X(KHSO₄) = 0.44 (melting point ≈ 406 K). The conductivities in the liquid region have been fitted to polynomials of the form κ(X) = A(X) + B(X)(T − T_m) + C(X)(T − T_m)², where T_m is the intermediate temperature of the measured temperature range and X, the mole fraction of KHSO₄. The possible role of this binary system as a catalyst solvent is also discussed.     

Evaluation of antitubercular drug insertion into preformed dipalmitoylphosphatidylcholine monolayers

Insertion profiles of antitubercular drugs isoniazid (INH), rifampicin (RFM) and ethambutol (ETH) into dipalmitoylphosphatidylcholine (DPPC) membrane models were evaluated by Langmuir monolayer technique. Maximum drug insertion into DPPC monolayer was observed with rifampicin with a surface pressure increase (Δπ_max) in the range of 21–33 mN/m depending upon rifampicin concentration. Isoniazid had minimal insertion resulting in a lower Δπ_max of about 2–3 mN/m, suggestive of minimal interactions between INH and DPPC. Ethambutol surface pressure increment on insertion resulted in an intermediate rise in the Δπ_max (6–10 mN/m). Antitubercular drug combination in the ratio of 2 mM:0.7 mM:4.5 mM for INH:RFM:ETH, attained Δπ_max between 25 and 33 mN/m. Insertion profiles similar to rifampicin were exhibited by the antitubercular drug mixture suggestive of predominant rifampicin insertion into the DPPC monolayer. The extent of drug insertion into the DPPC monolayer is suggestive of the drug penetration potential into biological membranes in vivo. Higher RFM Δπ_max is suggestive of excellent cell membrane penetration, which explains broad reach of the drug to all the organs including the cerebrospinal fluid while lower Δπ_max of INH suggests poor membrane penetration restricting the entry of the drug in different biological membranes. DPPC membrane destabilization was observed at higher antitubercular drug concentrations indicated by the negative slopes of the surface pressure–time curves. This may correlate with the dose related toxic effects observed in tuberculosis affected patients. Drug insertion studies offer a potential tool in understanding the pharmacotoxicological behavior of the various pharmacological agents.     

Enzymatic hydrolysis reaction of phospholipids in monolayers

The hydrolysis reaction of , and , -dipalmitoylphosphatidylcholine (DPPC) catalized by bee venom phospholipase A₂ was studied in spreading monolayer at the water/air interface. DPPC and the hydrolysis products, palmitic acid and -lysophosphatidylcholine, palmitoyl were characterized at the interface by means of surface pressure, surface potential and ellipsometric measurements. Furthermore, mixed monolayers of reagents and products were investigated to ascertain their miscibility. The results show that the hydrolysis reaction can be followed by the decrease of surface pressure with time on subphases containing β-cyclodextrin, a well-known complexing agent of many amphiphilic compounds. The order of the reaction, the kinetic constant and other kinetic parameters are deduced.     

Langmur monolayers of cerebroside with different head groups originated from sea cucumber: Binary systems with dipalmitoylphosphatidylcholine (DPPC)

Surface properties (Langmuir monolayer) of two different cerebrosides which are extracted from the sea cucumber (Bohadschia argus) were investigated. A main difference in chemical structure of cerebroside between BAC-2a and BAC-4 is their head groups (glucose and galactose, respectively). Furthermore, miscibility and interaction between dipalmitoylphosphatidylcholine (DPPC) and cerebrosides (BAC-2a and BAC-4) in the monolayer have been systematically examined. The surface pressure (π)−area (A), the surface potential (ΔV)−A, and the dipole moment (μ)−A isotherms for monolayers of DPPC, cerebrosides, and their binary combinations have been measured using the Wilhelmy method and the ionizing electrode method. BAC-4 forms a stable liquid-expanded (LE) monolayer, whereas BAC-2a has a first-order phase transition from the LE phase to the liquid-condensed (LC) state on 0.15 M NaCl at 298.2 K. The fundamental properties for each cerebroside monolayer were elucidated in terms of the surface dipole moment based on the three-layer model [R.J. Demchak, T. Fort Jr., J. Colloid Interface Sci. 46 (1974) 191–202] for both cerebrosides and the apparent molar quantity change (Δs^γ, Δh^γ, and Δu^γ) for BAC-2a. In addition, their miscibility with DPPC was examined by the variation of the molecular areas and the surface potentials as a function of cerebroside mole fractions, the additivity rule. The miscibility was also confirmed by constructing the two-dimensional phase diagrams. The phase diagrams for the both binary systems were of negative azeotropic type. That is, the two-component DPPC/BAC-2a and DPPC/BAC-4 monolayers are miscible. Furthermore, the Joos equation for the analysis of the collapse pressure of binary monolayers allowed calculation of the interaction parameter and the interaction energy between the DPPC and cerebroside monolayers. The miscibility in the monolayer state was also confirmed by the morphological observation with Brewster angle microscopy (BAM), fluorescence microscopy (FM), and atomic force microscopy (AFM).     

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution—10. A potentiometric study of aluminium(III) pyrocatecholates and aluminium(III) hydroxo pyrocatecholates in 0.6 M Na(Cl)

Equilibria between aluminium(III), pyrocatechol (1,2-dihydroxybenzene, H₂L) and OH⁻ were studied in 0.6 M Na(Cl) medium at 25°C. The measurements were performed as emf titrations (glass electrode) within the limits 1.5 ≤ − log[H⁺] ≤ 9; 0.0005 ≤ B ≤ 0.015 M; 0.006 ≤ C ≤ 0.03 M and 2 ≤ C/B ≤ 30 (B and C stand for the total concentrations of aluminium(III) and pyrocatechol respectively). All data can be explained with a main series of complexes: A1L⁺, log β_−2,1,1 = − 6.337 ± 0.005; A1L₂⁻, log β_−4,1,2 = −15.44 ± 0.017 and A1L₃³⁻, log β_−6,1,3 = − 28.62 ± 0.024 together with two minor species: Al(OH)L₂²⁻, log β_−5,1,2 = − 23.45 ± 0.079 and Al₃(OH)₃L₃, log β_−9,3,3 = − 29.91 ± 0.066. Of the two, the latter probably is a type of average composition complex principally occurring at low C/B quotients. The first acidity constant for pyrocatechol as determined in separate experiments is log β_−1,0,1 = − 9.198 ± 0.001. The standard deviations given are 3σ(log β p,q,r). Data were analyzed with the least squares computer program LETAGROPVRID. In a model calculation using kaolinite as solid phase, we compared the complexation ability of this system with that of the system Al³⁺-OH⁻-salicylic acid, reported earlier in this series.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures XIV. Binary mixtures of 4-(4-substituted phenylazo) phenyl-4-alkoxybenzoates

Binary mixtures formed from components of the five homologous series of the 4-(4-substituted phenylazo)phenyl-4-alkoxybenzoates Ia-e were prepared and their mesophase behaviour characterized. Transition temperatures of the mixtures prepared were measured by differential scanning calorimetry and identified by polarizing optical microscopy. Each binary combination was made from components bearing a terminal alkoxy group with the same number of carbon atoms (kept constant at n = 6, 8, 10, 12, 14 or 16), while the other substituent (X) was different—CH₃O, CH₃, Cl, NO₂, or CN. Phase diagrams were constructed for the various systems in order to investigate the effect of the terminal substituent X, as well as of the alkoxy chain length, on the phase behaviour of mixed systems.     

Structure and redox properties of CexPr1−xO2−δ mixed oxides and their catalytic activities for CO, CH3OH and CH4 combustion

A series of Ce_xPr_1−xO_2−δ mixed oxides were synthesized by a sol–gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO, CH₃OH and CH₄ on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO₂ was observed. The samples were greatly crystallized in the range of the value x from 0.99 to 0.80, which is due to the formation of solid solutions caused by the complete insertion of Pr into the CeO₂ crystal lattices. Raman bands at 465 and 1150 cm⁻¹ in Ce_xPr_1−xO_2−δ samples are attributed to the Raman active F_2g mode of CeO₂. The broad band at around 570 cm⁻¹ in the region of 0.3 ≤ x ≤ 0.99 can be linked to oxygen vacancies. The new band at 195 cm⁻¹ may be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies. The TPR profile of Pr₆O₁₁ shows two reduction peaks and the reduction process is followed: . The reduction temperature of Ce_xPr_1−xO_2−δ mixed oxides is lower than those of Pr₆O₁₁ or CeO₂. TPR results indicate that Ce_xPr_1−xO_2−δ mixed oxides have higher redox properties because of the formation of Ce_xPr_1−xO_2−δ solid solutions. The presence of the oxygen vacancies favors CO and CH₃OH oxidation, while the activity of CH₄ oxidation is mostly related to reduction temperatures and redox properties.     

Membrane properties of cationic liposomes composed of dipalmitoylphosphatidylcholine and dipalmityldimethylammonium bromide

Cationic liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and dipalmityldimethylammmonium bromide (DPAB) were prepared by the Bangham method and the effect of DPAB on the membrane properties was examined in terms of liposomal shape, particle size, trapping efficiency, surface potential and dispersibility. The dispersibility of the mixed DPPC/DPAB liposomes (the mole fraction of DPAB (X_DPAB)  0.05) was excellent and the dispersibility was maintained for 6 months, since the zeta-potential of the mixed liposomes was approximately +40 mV. The trapping efficiency of the mixed DPPC/DPAB liposomes (X_DPAB = 0.05) was 10 times greater than that of the DPPC liposomes, and the value was largest among the mixed liposomes (X_DPAB = 0–1.0). Freeze-fracture electron micrographs indicated that the shape of the mixed DPPC/DPAB liposomes (X_DPAB = 0.05) was that of large unilamellar vesicles (LUVs) with a diameter of approximately 2 μm, while the shape of the DPPC liposomes was that of multilamellar vesicles (MLVs). The mixed liposomes had, therefore, a high trapping efficiency. Furthermore, the shape of the mixed DPPC/DPAB liposomes (X_DPAB = 0.75) was also that of LUVs with a diameter of approximately 2 μm and these had a high trapping efficiency. Whereas, the particle size (500 nm) of the mixed DPPC/DPAB liposomes (X_DPAB = 0.25) was smaller than that of the former and had the minimum trapping efficiency. The phase transition temperature of the liposomal bilayer membranes indicated a maximum value at 0.25–0.30 mole fractions of DPAB. These facts were considered to be due to the fact that DPPC and DPAB, whose molar ratio was 7.5:2.5, were tightly packed in the liposomal bilayer membranes and that the curvature of the liposomal particle was resultantly large. Nevertheless, LUVs having a high trapping efficiency were easily obtained by mixing a small amount of DPAB with the DPPC.     

Evaluation of the interactions between lipids and γ-globulin protein at the air–liquid interface

The interactions between lipids (cholesterol, distearoylphosphatidylcholine, distearoylphosphatidylethanolamine and sphingomyelin) and the γ-globulin protein have been analyzed using the monolayer technique at the air–liquid interface. The analysis has been carried out using both state equations and an adequate thermodynamic formulation for the surface pressure (π)–molecular area (a) isotherms. Different parameters as the virial coefficients, have been estimated. For the uncharged lipid monolayers, the interactions between the molecules are of an attractive nature, at medium and long distance, and of a steric repulsive nature at short distance. At low surface pressures the lipid molecules form small domains. The net force between γ-Globulin molecules in the monolayers has been found to be attractive. Finally, it can be concluded that when the lipid monolayers are uncharged, there is practically no interaction between the protein and lipid molecules at the mentioned interface.     

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.     

Thermodynamic characteristics and Langmuir-Blodgett deposition behavior of mixed DPPA/DPPC monolayers at air/liquid interfaces

The role of dipalmitoylphosphatic acid (DPPA) as a transfer promoter to enhance the Langmuir-Blodgett (LB) deposition of a dipalmitoylphosphatidylcholine (DPPC) monolayer at air/liquid interfaces was investigated, and the effects of Ca2+ ions in the subphase were discussed. The miscibility of the two components at air/liquid interfaces was evaluated by surface pressure-area per molecule isotherms, thermodynamic analysis, and by the direct observation of Brewster angle microscopy (BAM). Multilayer LB deposition behavior of the mixed DPPA/DPPC monolayers was then studied by transferring the monolayers onto hydrophilic glass plates at a surface pressure of 30 mN/m. The results showed that the two components, DPPA and DPPC, were miscible in a monolayer on both subphases of pure water and 0.2 mM CaCl2 solution. However, an exception occurs between X(DPPA)=0.2 and 0.5 at air/CaCl2-solution interface, where a partially miscible monolayer with phase separation may occur. Negative deviations in the excess area analysis were found for the mixed monolayer system, indicating the existence of attractive interactions between DPPA and DPPC molecules in the monolayers. The monolayers were stable at the surface pressure of 30 mN/m for the following LB deposition as evaluated from the area relaxation behavior. It was found that the presence of Ca2+ ions had a stabilization effect for DPPA-rich monolayers, probably due to the association of negatively charged DPPA molecules with Ca2+ ions. Moreover, the Ca2+ ions may enhance the adhesion of DPPA polar groups to a glass surface and the interactions between DPPA polar groups in the multilayer LB film structure. As a result, Y-type multilayer LB films containing DPPC could be fabricated from the mixed DPPA/DPPC monolayers with the presence of Ca2+ ions.     

Study of the cholesterol-GM3 ganglioside interaction by surface pressure measurements and fluorescence microscopy

The nature of the cholesterol/glycolipid interaction in rafts being poorly understood, the interaction of cholesterol with the GM₃ ganglioside has been studied by surface pressure measurements and fluorescence microscopy. Results have been compared to those obtained with sphingomyelin (SM)-cholesterol and palmitoyl-oleoyl-phosphatidylcholine (POPC)–cholesterol monolayers. The analysis of (π–A) isotherms of mixed monolayers show a condensing effect of cholesterol on GM₃ molecules, in the same range than the effect observed with POPC and higher than the effect on SM. This is likely due to the similar state of GM₃ and POPC, since both molecules are in liquid expanded phases in our experimental conditions. The study of the cholesterol desorption induced by β-cyclodextrin suggests also that the GM₃–cholesterol interaction is rather weak as in the case of POPC–cholesterol interaction, and clearly lower than SM–cholesterol one. This lack of interaction is discussed in terms of nature of lipid chains and molecular shape, and suggests that no hydrogen bond is formed between GM₃ and cholesterol polar heads. Fluorescence microscopy performed on mixed GM₃–cholesterol monolayers shows the presence, at surface pressure higher than 10 mN/m, of particular blurring patterns without defined boundary, which could be due to a partial solubilization in one phase of different phases observed at lower surface pressure, whereas SM–cholesterol and POPC–cholesterol monolayers are homogeneous at the lateral resolution of our microscopy set-up.     

Syntheses of new model compounds related to an antigenic epitope from Bupleurum falcatum L. and their distributions in various ganglioside-phospholipid monolayers

6-N-[2-(Tetradecyl)hexadecanamido]hexyl beta-D-glucopyranosyluronic acid-(1-->6)-beta-D-galactopyranosyl-(1-->6)-beta-D-galactopyranoside (1) and its clustering compound (2) carrying a tetravalent sugar unit, which are new model compounds related to a major antigenic epitope from antiulcer pectic polysaccharide of Bupleurum falcatum L., were synthesized and the distributions of 1 and 2 in mixed ganglioside (GM1, GD1a or GT1b)/phospholipid (DPPC) monolayers were observed using atomic force microscopy (AFM). AFM images showed that 1 was distributed in the GM1, GD1a and GT1b region of the mixed monolayers, in which 1 was miscible with GD1a. Specific distribution of 1 was observed in the mixed GM1/DPPC monolayer. Compound 2 was miscible with GM1, while 2 formed associations with GD1a and GT1b in the mixed monolayers. The distribution mode of 1 and 2 was different among the mixed ganglioside/DPPC monolayers.     

Hydrogenmaleato bridged supramolecular double chains via π–π stacking interactions: syntheses, crystal structures and magnetic properties of ∞[Cu(phen)X(HL)2/2] with X=Cl (1), NO3 (2) and H2L=maleic acid

Two novel hydrogen maleato (HL) bridged Cu(II) complexes _∞¹[Cu(phen)Cl(HL)_2/2] 1 and _∞¹[Cu(phen)(NO₃)(HL)_2/2] 2 were obtained from reactions of 1,10-phenanthroline, maleic acid with CuCl₂·2H₂O and Cu(NO₃)₂·3H₂O, respectively, in CH₃OH/H₂O (1:1 v/v) at pH=2.0 and the crystal structures were determined by single crystal X-ray diffraction methods. Both complexes crystallize isostructurally in the monoclinic space group P2₁/n with cell dimensions: 1 a=8.639(2) Å, b=15.614(3) Å, c=11.326(2) Å, β=94.67(3)°, Z=4, D_calc=1.720 g/cm³ and 2 a=8.544(1) Å, b=15.517(2) Å, c=12.160(1) Å, β=90.84(8)°, Z=4, D_calc=1.734 g/cm³. In both complexes, the square pyramidally coordinated Cu atoms are bridged by hydrogen maleato ligands into 1D chains with the coordinating phen ligands parallel on one side. Interdigitation of the chelating phen ligands of two neighbouring chains via π–π stacking interactions forms supramolecular double chains, which are then arranged in the crystal structures according to pseudo 1D close packing patterns. Both complexes exhibit similar paramagnetic behavior obeying Curie–Weiss laws χ_m(T−θ)=0.414 cm³ mol⁻¹ K with the Weiss constants θ=−1.45, −1.0 K for 1 and 2, respectively.