Analysis of Molecular Interactions between Components in Phospholipid-Immunosuppressant-Antioxidant Mixed Langmuir Films

Abstract

The study of Langmuir monolayers incorporating biomimetic and bioactive substances plays an important role today in assessing the properties and quality of the molecular films for potential biomedical applications. Here, miscibility of binary and ternary monolayers of phospholipid (dioleoyl phosphatidylcholine, DOPC), immunosuppressant (cyclosporine A, CsA), and antioxidant (lauryl gallate, LG) of varying molar fractions was analyzed by means of the Langmuir technique coupled with a surface potential (ΔV) module at the air–water interface. The surface pressure–area per molecule (π–A) isotherms provided information on the physical state of the films at a given surface pressure, the monolayer packing and ordering, and the type and strength of intermolecular interactions. Surface potential–area (ΔV–A) isotherms revealed the molecular orientation changes at the interface upon compression. In addition, the apparent dipole moment of the monolayer-forming molecules was determined from the surface potential isotherms. The obtained results indicated that the film compression provoked subsequent changes of CsA conformation and/or orientation, conferring better affinity for the hydrocarbon environment. The mutual interactions between the components were analyzed here in terms of the excess and total Gibbs energy of mixing, whose values depended on the stoichiometry of the mixed films. The strongest attraction, thus the highest thermodynamic stability, was found for a DOPC–CsA–LG mixture with a 1:1:2 molar ratio. Based on these results, a molecular model for the organization of the molecules within the Langmuir film was proposed. Through this model, we elucidated the significant role of LG in improving the miscibility of CsA in the model DOPC membrane and thus in increasing the stability of self-assembled monolayers by noncovalent interactions, such as H-bonds and Lifshitz–van der Waals forces. The above 1:1:2 combination of three components is revealed as the most promising film composition for the modification of implant device surfaces to improve their biocompatibility. Further insight into mechanisms concerning drug–membrane interactions at the molecular level is provided, which results in great importance for biocoating design and development as well as for drug release at target sites.

Interaction of a Phospholipid and a Coagulating Protein: Potential Candidate for Bioelectronic Applications

“…The analysis of compressibility values also indicates that lipid molecules attain maximum ordered and compact organization within the Langmuir films in the presence of PS for a waiting time of 120 min and when the PS amount present in the subphase is 1.75 mL. We have also drawn the compression modulus vs surface pressure ( C s –1 –π) curves from the isotherm characteristics using the formula, 72 , 73 …”

Simple Does Not Mean Trivial: Behavior of Phosphatidic Acid in Lipid Mono- and Bilayers

“…The excess free energy of mixing (∆G ex m ) was calculated for π-A isotherms for pure and mixed monolayers following the established protocols [55][56][57]. The values were calculated in the range from 0 to 33 mN/m.…”

The Influence of Polysaccharides/TiO2 on the Model Membranes of Dipalmitoylphosphatidylglycerol and Bacterial Lipids

“…On the other hand, at π > 20 mN/m, domains in the form of bright points began to appear, and their amount increased with the progress of compression. The highest quantity was observed at π = 35-40 mN/m, which could indicate partial miscibility of the lipid components in the monolayer and possible ejection of those having a lower collapse surface pressure value [40]. Both π = f(A) and C S −1 = f(π) relationships plotted for this lipid film suggest that its collapse took place above surface pressure value, π > 45 mN/m.…”

“…In turn, the graph of the compression modulus as a function of surface pressure plotted two maxima of values at π value 25 mN/m and 53 mN/m. On the other hand, the observed minimum at 40 mN/m indicates partial miscibility and/or expulsion of one kind of the components (phosphatidylethanolamine (PE), CL, or PG) from the monolayer, rather than phase transition, because the C S −1 value does not drop to zero [40]. When such a situation takes place, in the monolayer the coexisting areas with packed and not-condensed domains can be observed.…”