Mixed Langmuir and Langmuir−Blodgett Films of a Proton Sponge and a Fatty Acid: Influence of the Subphase Nature on the Interactions between the Two Components

Langmuir and Langmuir-Blodgett technologies as nanoarchitectonic tools for the incorporation of curcumin in membrane systems

Curcumin (CCM) is a molecule of particular interest in health applications due to its wide spectrum of benefits for humans. However, its water-insoluble character and low bioavailability have so far prevented its extended use as a therapeutic agent. Incorporation of CCM in drug delivery vehicles (liposomes, vesicles, exosomes, etc.) is expected to contribute to increasing its bioavailability. Studies of the affinity of CCM with the components of the membrane systems of such vehicles and determination of factors that may enhance curcumin entrapment in biological membranes are of fundamental importance. To that end, here we take advantage of the nanoarchitectonic capabilities of the Langmuir technique for the construction of model cell membranes and determination of thermodynamic properties in mixed films. The obtained results may serve to: (i) provide some light on the miscibility of CCM with the components in the cell membrane and (ii) determine the optimal conditions for the fabrication of membrane systems incorporating CCM. For that, binary and ternary mixed Langmuir films of CCM, DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and CHOL (cholesterol) have been prepared. Whilst binary mixtures of DPPC and CCM exhibit poor miscibility and even phase segregation, CHOL has shown itself as a key element to promote the incorporation of CCM in the phospholipidic membrane containing DPPC. Both the thermodynamic studies of the ternary Langmuir films and the Atomic Force Microscopy (AFM) images of Langmuir-Blodgett films have shown that ternary mixed films with a molar fraction composition of x_DPPC/x_CHOL/x_CCM = 0.4/0.4/0.2 exhibit good miscibility, stability, and result in monolayers with a very homogeneous topography.

Influence of spacer of gemini on the interactions between cationic gemini surfactant and stearic acid in mixed monolayers

Mixed Langmuir-Blodgett (LB) films composed of a cationic gemini surfactant, [C(18)H(37)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(18)H(37)],2Br(-) (18-s-18 with s = 3, 6, 8, 10 and 12), and a fatty acid of stearic acid (SA) were studied by the pi-A isotherm measurement, as well as by AFM and FT-IR. The analysis of the mean molecular area, the excess area and the excess Gibbs free energy from pi-A isotherms suggests the existence of attractive interactions between 18-s-18 and SA molecules in the mixed monolayers. The spacer group of 18-s-18 plays a very important role in the surface properties of 18-s-18/SA mixed monolayers. When s < or = 8, 18-s-18 and SA are completely miscible, while partially miscible mixed monolayers are presented when s > 8. Especially, in the latter case, when s = 12, phase separation appears in two composition regions of X(SA) = 0.4-0.75 and X(SA) = 0.75-0.85, respectively. This miscible phenomenon is confirmed by AFM observation. The result of FT-IR indicates that when X(SA) < or = 0.67, SA could ionize completely and form a "cationic-anionic surfactant" with 18-s-18 owing to the electrostatic interaction between the head groups, while when X(SA) > 0.67, SA only partially ionizes, -COO(-) and -COOH coexist in mixed monolayers.

A monolayer study on interactions of docetaxel with model lipid membranes

Docetaxel (DCT) is an antineoplastic drug for the treatment of a wide spectrum of cancers. DCT surface properties as well as miscibility studies with l-alpha-dipalmitoyl phosphatidylcholine (DPPC), which constitutes the main component of biological membranes, are comprehensively described in this contribution. Penetration studies have revealed that when DCT is injected under DPPC monolayers compressed to different surface pressures, it penetrates into the lipid monolayer promoting an increase in the surface pressure. DCT is a surface active molecule able to decrease the surface tension of water and to form insoluble films when spread on aqueous subphases. The maximum surface pressure reached after compression of a DCT Langmuir film was 13 mN/m. Miscibility of DPPC and DCT in Langmuir films has been studied by means of thermodynamic properties as well as by Brewster angle microscopy (BAM) analysis of the mixed films at the air-water interface, concluding that DPPC and DCT are miscible and they form non-ideally mixed monolayers at the air-water interface. Helmholtz energies of mixing revealed that no phase separation occurs. In addition, Helmholtz energies of mixing become more negative with decreasing areas per molecule, which suggests that the stability of the mixed monolayers increases as the monolayers become more condensed. Compressibility values together with BAM images indicate that DCT has a fluidizing effect on DPPC monolayers.

The use of scanning polarization force microscopy to study the miscibility of a molecular wire candidate and an insulating fatty acid in mixed films

Mixed films containing a conjugated "molecular wire" candidate and an "insulating" fatty acid have been prepared by the Langmuir-Blodgett technique. Specifically, this paper reports the fabrication of mixed films as well as miscibility studies of 4-[4-(4-hexyloxyphenylethynyl)phenylethynyl]benzoic acid (HBPEB) and docosanoic (or behenic) acid (BA). Surface pressure vs. area per molecule isotherms were recorded, with excess area and excess Gibbs energy of mixing calculated. Surface potential-area per molecule isotherms were also recorded for mixtures over the whole range of mole fractions, with negative deviations from the additivity rule revealing orientational changes induced in the HBPEB molecules. The Langmuir films were transferred onto solid supports and characterized by SPM techniques, with atomic force microscopy (AFM) revealing that well-ordered, defect-free films are obtained. The use of scanning polarization force microscopy (SPFM), which provides non-contact imaging based on differences in surface charge distribution, i.e., surface potential, provides complimentary information regarding distribution of the components within the mixed films. From the comprehensive miscibility study performed, which includes thermodynamic and imaging methods, it can be concluded that the wire-like molecule and the fatty acid are miscible over the 0-0.1 and 0.8-1 ranges of HBPEB mole fraction while phase separation occurs for HBPEB mole fractions over the 0.1-0.8 range.