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Surfaces of thin low-density polyethylene films are chemically modified either by oxidation or by grafting with maleic acid. The oxidation is performed at constant tempera-ture by sulfuric acid and potassium chlorate mixtures of variable compositions. Grafting was carried out at constant temperature and time in the solution of maleic anhydride in acetic anhydride in the presence of benzoyl peroxide initiator. Isotherms of calcium adsorption at these surfaces have been established by the use of the radioactive tracer technique. The chemical composition (number of obtained polar sites) of these modified polyethylene surfaces is thus determined. The measurements were conducted at different pH and salt concentrations. Wettability of the modified surfaces is determined by contact angle measurements. It was found that the wettability of these films is directly related to the chemical composition of their surfaces.

Fusogenic liposomes have a wide-range of applications as DDS and gene/protein delivery into living cells. A variety of surface modifications of drug carriers, to enable fusion with cells, have been proposed, however, the mechanism of fusion has still not been determined. To further improve the efficiency of drug carriers, a simple and easily examinable model of a living cell surface is needed. In this study, the time-course of a fusion phenomena was made by measuring the surface pressure increase of a phospholipid monolayer spread at the air/water interface due to the fusion of liposomes carrying PEO-lipid (dialkyl-terminated polyethylene oxide) reconstituted on their outer surface. The kinetics of the surface pressure change appeared to be bimodal, indicating the coexistence of different fusion pathways. It was found that the presence of the PEO-lipid on the liposome surface led to a faster lipid transfer compared to non-modified DMPC liposomes. This indicated that the reconstitution of PEO-lipid provided an alternative transfer pathway to that for non-fusogenic liposomes that show only a slow lipid transfer to phospholipid monolayers. The relation between the rate of fusion and the surface pressure of the host membrane is discussed.

Targeting of proteins at interfaces via affinity ligands or specific antibodies is important for the understanding of protein functioning in biological membranes. This review brings together a great number of research works accomplished in this field in the past decade by a variety of analytical methods. It highlights two simple in situ techniques of monitoring molecular recognition processes at interfaces recently developed in the author's laboratory. The first of these techniques is based on the measurements of surface pressure increments of a protein monolayer spread at the air/water interface at a constant area resulting from the interaction with its specific ligands injected into the aqueous subphase beneath the preformed protein monolayer. The second technique takes advantage of the feature of [14C]-labeled proteins that enable in situ measurements of surface density changes of adsorbed protein molecules on a solid support resulting from the interaction with its specific antibody.

International audience; The surface properties of the neoglycolipid (GlcNAcE(3)G(28)) and of its PEO-lipid (E(3)G(28)) moiety mixed with phospholipids (dipalmitoylphosphatidylcholine, DPPC; distearoylphosphatidylcholine, DSPC; diarachidoylphosphatidylcholine, DAPC; and dibehenoylphosphatidylcholine, DBPC) were studied in Langmuir monolayers at various mixture compositions and surface pressures. The pi-A isotherms of the pure compounds revealed that because of the presence of the sugar group in its molecule, GlcNAcE3G28 collapsed at a higher surface pressure and occupied a larger molecular area than the PEO-lipid moiety. It was also observed that the presence of the PEO-lipid (E3G28) in the mixtures triggered a strong alteration of both phospholipid pi-A isotherm profiles and surface diffraction spectra, an indication that the disordering of the initially structured phospholipid monolayers took place. Unlike E3G28, GlcNAcE(3)G(28) did not disorganize phospholipid monolayers but generated a partial segregation of the film-forming components. The calculated excess free energies of mixing (Delta G(exc)) for GlcNAcE(3)G(28)-phospholipid mixtures enabled us to predict the stability of such systems.

Isotherms of surface pressure and surface potential versus mean molecular area for dibehenoylphosphatidylcholine (DBPC), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), and dioleoylphosphatidylcholine (DOPC) monolayers were shown to be greatly modified when these lipids were cospread with either Bauhinia monandra (BmoLL) or Concanavalin A (Con A) lectins. For the binary films of DBPC, DPPC, and DPPE cospread with each of these two lectins, there was both a displacement of the Pi-A and DeltaV-A isotherms toward higher molecular areas relative to pure lipids and an increase in the maximum surface potential values relative to the DeltaV-A relationships observed for the corresponding single-lectin systems. Both effects can be understood in terms of the occurrence of an explicit interaction between the lipids and the lectins. The plots of the corresponding compressibilities versus molecular areas reveal that, for all lipids but DOPC, the extent of this interaction was always larger for BmoLL than for Con A. The DPPC and DPPE mixed films with BmoLL differed in compressibility. Owing to the small DPPE polar headgroup, the DPPE-BmoLL film was much more incompressible than the DPPC-BmoLL mixed monolayer. However, for the DOPC-BmoLL and DOPC-Con A mixed films there was no evidence that an interaction between the lectins and the lipid took place, a fact attributed to the unsaturated character in the DOPC aliphatic chains, which leads to an expanded Pi-A isotherm.

The dielectric properties of the galactose-binding lectins Bauhinia monandra (BmoLL) and Concanavalin A (Con A) were assessed by surface potential measurements of their spread monolayers on an aqueous subphase containing a monovalent electrolyte. For both lectins the curves of surface potential versus mean molecular area (ΔV–A) and the independently recorded isotherms of surface pressure versus mean molecular area (Π–A) were shown to be pH-dependent. As the subphase pH changed from 2 to 9, a noticeable trend to higher surface pressures accompanied the compression of the monolayers. Conversely, the surface potentials values of both monolayers decreased with increasing pH. For Con A, with the single exception of the pH 9 case, lowering the pH yielded ΔV values higher than those for BmoLL. The contribution of the electric double layer ( Ψ 0 ) to the overall ΔV values at a given Π (15 mN/m) was calculated using a modified Davies equation and assuming that at this surface pressure the monolayers of both studied lectins were stable. While at all studied pHs the Ψ 0 values for Con A exceeded those calculated for BmoLL, for both lectins they were insensitive to pH changes. This provided evidence that the reorientation of lectin molecules, during compression predominantly contributed to the alteration of the overall ΔV values. The calculated Ψ 0 values made possible the evaluation of the dipole moments for BmoLL and Con A, and it has been estimated that the decrease in the pH of the subphase from 9 to 2 produced a 1.6-fold (twofold) increase in the value of for BmoLL (Con A). The differences in dielectric properties between the two film-forming lectins have been attributed to the differences in their structures. Indeed, the circular dichroism (CD) spectrum of Con A showed the predominance of β-plated sheet structures while that of BmoLL was typically rich in α-helix structures.

The interfacial behavior of the hypoglycemia lectin BmoLL purified from the leaves of Bauhinia monandra , and its ability to interact with lipid monolayers has been studied by surface tension ( γ ) measurements. The results of these experiments revealed that in the solution concentration range comprised between 0.2 and 1.0 mg/ml, there was an extremely pronounced increase in the BmoLL adsorption at the interface with the air phase. This adsorption at the higher studied BmoLL concentrations gave rise to a more gradual increase in the surface pressure ( π = γ 0 − γ ). The results showed also that the surface pressure of adsorbed films was pH dependent and it substantially increased at low pHs (between pH 4.0 and pH 2.5). Independently carried out ξ potential measurements demonstrated that BmoLL was negatively charged at all pHs and borne the highest charge at the pH around 5.5. The penetrant ability of BmoLL into the two different in chemical nature monolayers: (dioleoylphosphatidylcholine and octadecylamine) have been assessed measuring Δ π increments at constant area. It was observed that, whereas the monolayers of either pure dioleoylphosphatidylcholine (DOPC) or pure octadecylamine (ODA) stimulated BmoLL adsorption, the lectin adsorption within their mixtures strongly depended on both the content of positively charged octadecylamine in a mixture and on the monolayer compressibility. These findings are discussed in terms of both the electrostatic interaction involved in adsorption of BmoLL and of changes in monolayer compressibilities brought up by the addition of ODA molecules to the phospholipid. The relevance of this work to liposome preparations is indicated in the concluding remarks.

The interaction of three lectins (wheat germ, Ulex europaeus I, and Lotus tetragonolobus agglutinins: WGA, UEA-I and LTA) with either N-acetyl- d -glucosamine or l -fucose neoglycolipids incorporated into phospholipid monolayers and liposome bilayers was studied at the air/water interface and in bulk solution. The results show that for both systems studied, synthesized neoglycolipids were capable of binding their specific lectin and that, in general, the binding of lectins increased with the increase in the molar fraction of the saccharide derivative incorporated in either the monolayers or bilayers. However, whereas for UEA-I, molecular recognition was enhanced by a strong hydrophobic interaction, for WGA and LTA successful recognition was predominantly related to the distance between neighboring sugar groups. The observed lengthy adsorption times of these lectins onto their specific ligands were attributed to interfacial conformational changes occurring in the proteins upon their adsorption at the interfaces.

The effect of both lipid headgroup charge and of aqueous subphase pH on adsorption of glucose oxidase molecules (GOx) into dibehenoylphosphatidylcholine (DBPC) and octadecylamine (ODA) monolayers has been studied by surface tension and surface pressure measurements. The results revealed that whereas the extent of GOx adsorption into pure DBPC monolayers essentially depended on the area in a monolayer available to harbor adsorbing GOx molecules, enhanced enzyme penetration into a monolayer occurred at high surface densities. The kinetics of enzyme penetration was found to be dependent of the initial surface pressure of a spread monolayer. The addition of ODA to DBPC monolayers gave a dramatic boost to GOx penetration and at high molecular surface densities largely depended on the ratio of ODA in the mixed monolayers. This increase in GOx penetration was attributed to the strong attractive electrostatic interaction between the positively charged ODA and the negatively charged enzyme.

The goal of this work was to characterise the interfacial behaviour of amphiphilic β-cyclodextrins modified at the primary face. It was considered that the oil/water system with spread modified cyclodextrins at the interface adequately mimics the interface encountered in the nanoprecipitation process, used for the preparation of nanocapsules. The effect of the presence of spread amphiphilic β-cyclodextrins upon the interfacial behaviour of the Miglyol oil/water system was assessed from interfacial tension (γi) measurements at 20 °C. The results reveal the diminution of γi for all studied amphiphilic cyclodextrins. The highest reduction in γi was observed for the β-CDs modified at the primary face for which the lowering in γi was comprised between 14 and 18 mN m−1. For β-CD-C6, a β-CD substituted at the secondary face, the decay of γi was much less pronounced (about 9 mN m−1). The results show also the influence of the hydrocarbon chain length upon the reduction in γi: the cyclodextrin substituted with an aliphatic chain containing six carbons, ‘6-N-CAPRO-β-CD’, was more efficient than a β-CD substituted with the aliphatic chain containing 14 carbons (‘6-N-MYRISTO-β-CD’). The presence of a NH amine function in the skeleton of the hydrocarbon chain conferred to the studied amphiphilic molecules an increased performance in lowering γi of the system. Surface pressure (π)–area (A) compression isotherms of the modified CDs at the air/water interface provided additional light on the interfacial behaviour of these molecules. The data from the interfacial tension measurements corroborated those from the nanocapsule formation and provided evidence that substitution at the primary face with a relatively short aliphatic chain (six carbons) containing an amine function yielded homogenous and smaller in size nanocapsules.

The in situ adsorption/desorption studies of 14C-labeled human immunoglobulin G (IgG) were performed at the polyethylene (PE)/aqueous solution interface. The results reveal that the adsorbed protein molecules were predominantly packed in the end-on orientation. Desorption experiments showed that upon rinsing with buffer only minute fractions of adsorbed IgG could be removed from the PE surface. Both the competitive and the sequential adsorption measurements from the binary mixtures of hydrophobic IgG modified by attachment of 19 caprylic chains (19C8-IgG) and [14C]IgG confirm that native IgG strongly adhered to the PE films. The specific recognition ability of adsorbed human IgG layers was studied by using specific (goat anti-human) IgG and nonspecific (goat anti-rabbit) IgG. It was shown that the prevailing effect of the interaction of [14C]IgG adsorbed onto PE with the specific antibody was the increase in the surface radioactivity, which was attributed to the formation of a more densely packed layer of IgG molecules at the PE surface. It was also demonstrated that, whereas the specific antibody preadsorbed onto PE films retained the recognition ability relative to human IgG, its hydrophobic modification resulted in a substantial decrease in this ability.

Controlled inhibition of the enzyme Cu/Zn superoxide dismutase (SOD), one of the most important enzymes of the antioxidant defense system of aerobic organisms, is the subject of this paper. It is desirable in several noted medical and agricultural applications. This paper describes the synthesis of a very limited “sublibrary” of bifunctional metal chelators. The first function is the metal chelator DTC (sodium diethyldithiocarbamate (Et2DTC)), which has the sole chemical function of specific metal binding. An amphiphile (more precisely, an oligoether) is the second function and has a sole physical function: changing the physical properties of the molecule. The paper discusses novel copper chelators with variable amphiphilic properties: disubstituted dithiocarbamates (DTCs, R1(CH2CH2O)2NR2CS2Na) with one alkyl (R2 = hexyl, octyl, decyl, or dodecyl) and one oligoether (R1(CH2CH2O)2, where R1 = Et or Bu) substituent. The octanol−water distribution ratios of the dithiocarbamates (partition measurements by t...

The serotonin transporter (SERT) is the target of several important antidepressant and psychostimulant drugs. It has been shown that under defined conditions, the transporter spread at the air/water interface was able to bind its specific ligands. In this paper, the interfacial organization of the protein has been assessed from dynamic surface pressure and ellipsometric measurements. For areas comprising between 10,400 and 7,100 A(2)/molecule, ellipsometric measurements reveal an important change in the thickness of the SERT film. This change was attributed to the reorientation of the transporter molecules from a horizontal to their natural predictive transmembrane orientation. The thickness of the SERT film at 7,100 A(2)/molecule was found to be approximately equal to 84 A and coincided well with the theoretical value estimated from the calculations based on the dimensions of alpha-helices containing membrane proteins. These data suggest that the three-dimensional arrangement of the SERT may be represented as a box with lengths d(z)=83--85 A and d(y) or d(x)=41--47 A.

This review describes the interfacial behavior of biomolecules, which were converted to more hydrophobic derivatives by covalent attachment of hydrophobic chains. The molecules presented are proteins (glucose oxidase, immunoglobulin G, gelatin, ovalbumin) and polysaccharides (carboxymethylcellulose, pullulan). In general, it was found that such hydrophobically modified biomolecules have enhanced surface activity and ability to penetrate into phospholipid monolayers. In addition, it has been demonstrated, that such molecules can be used as efficient emulsifiers and foaming agents, and in unique biomedical application based on combining the surface activity and recognition ability. †Visiting Professor at Casali Institute of Applied Chemistry.

The interfacial behavior of the neoglycolipids formed of Guerbet alcohol (G(28)) bound to a triethylene glycol spacer (E(3)) and to a sugar moiety (alpha- and beta-fucose) spread at the air/water interface has been studied under dynamic conditions of compression. Although the alpha (alpha-FucE3G28)- and beta-fucose (beta-FucE3G28) derivatives possessed the same chemical structure, the positioning of the sugar moiety relative to the whole molecule had a significant influence on the organization of neoglycolipid molecules in the spread monolayers. Thus, beta-fucose molecules exhibited higher compressibilities and larger molecular areas than a alpha/beta (84/16%) mixture (alpha(84)-FucE3G28). The comparison of the compressional behavior of the fucose derivatives with that of Guerbet alcohol in the absence and in the presence of the triethylene glycol spacer shows that the presence of the E(3) chain is necessary to stabilize the lipid at the interface and that the incorporation of a sugar moiety into the molecule resulted in an important expansion of a monolayer. Despite their different interfacial behaviors, the two sugar derivatives formed ideal mixtures when cospread at the air/water interface. Conversely, in the presence of a phospholipid, such as DMPC, repulsive interactions were observed and appeared to be stronger for DMPC/alpha(84)-FucE3G28 mixed monolayers. The membrane fluidity of DMPC liposomes bearing the studied amphiphilic molecules was assessed by fluorescence depolarization measurements. The results reveal that whereas G(28) was deeply inserted into the liposome bilayers, the presence of a E(3) chain and of a sugar moiety in these bilayers induced a transfer of the amphiphilic derivatives from the hydrophobic core towards polar headgroups of phospholipid molecules.

The interfacial behavior of carboxymethylcellulose (CMC) and of hydrophobically modified CMCs has been assessed using surface tension and surface pressure measurements. The results showed that surface properties of these polymers are related to both the nature of the hydrophobic chain grafted to the polymer and the ionic strength. The observed differences in adsorption kinetics between the studied hydrophobized CMCs appeared to be controlled by packing of polymer aggregates formed in the subphase and were due to the nature of grafted hydrophobic chains. The observed uptake of proteins by CMC has been attributed to electrostatic interactions between the charged proteins (β-lactoglobulin, ovalbumin and thyroglobulin) and the polyanion. This uptake was enhanced for hydrophobically modified CMCs and for the proteins with increased molecular weights.

The interfacial behaviour of Cratylia mollis (Cra) at the air/water interface and its penetrant ability into spread phospholipid monolayers (Lipoid E80 and Epicuron 200) has been monitored by surface tension measurements. The first-order rate constants defining adsorption and rearrangement obtained from surface tension kinetics data reveal that Cra is a rather stable protein which exhibits characteristic protein adsorption patterns in which the breaking points separating diffusion–penetration and rearrangement profiles could have been easily distinguished. The penetration of Cra into Lipoid E80 and Epicuron 200 phospholipid monolayers has been inferred in terms of penetration pressure increments (ΔΠ) versus time relationships. The data clearly showed that penetrant ability of the lectin was, to a large extent, dependent on monolayer compressibilities. Thus, for Lipoid E80, which contained a rather high percentage of phosphatidylethanolamine (DPPE) in the mixture with phosphatidylcholine (DPPC), penetration of Cra at the high monolayer compression (20 mN m−1) was lower than that observed for Epicuron 200, which did not contain DPPE. Indeed, in the middle of the Π-A isotherm, DPPE was markedly less compressible than DPPC. However, at the low monolayer surface coverage (3 mN m−1), the rates of Cra penetration into both Lipoid E80 and Epicuron 200, although much higher for the latter at the beginning of adsorption, yielded similar limiting values of ΔΠ. This has been attributed to the occurrence of a hydrophobic interaction between the lectin and hydrophobic phospholipid chains that have the same length for both Lipoid E80 and Epicuron 200.

The effect of lipid hydrophobic chain lengths on adsorption of glucose oxidase (GOx) into phospholipid monolayers has been investigated. The results show that at low initial surface pressures, penetration of GOx depended both on hydrophobic interactions and on the orientation of lipid chains with respect to the interface plane. Compared with dimyristoyl-phosphatidylcholine (DMPC) and dipalmitoyl-phosphatidylcholine (DPPC), dibehenoyl-phosphatidylcholine (DBPC) favored enzyme adsorption at low surface pressures. This was attributed to its long hydrophobic chains and to their vertical orientation. At higher initial surface pressures, the fluidity and packing of these monolayers appeared to play a key role in the penetration process. The presence of a double bond in the hydrocarbon chains enhanced enzyme adsorption, and this effect was independent of the initial surface pressure of lipid monolayers.