Interactions between Polymers and Lipid Monolayers at the Air/Water Interface: Surface Behavior of Poly(methyl methacrylate)−Cholesterol Mixed Films

Abstract

The behavior of mixed monolayers of cholesterol and poly(methyl methacrylate) (PMMA) with molecular weights of M(w) = 120,000 g/mol and M(w) = 15,000 g/mol was investigated at the air/water interface using Langmuir and Brewster angle microscopy techniques. From the data of surface pressure (pi)-area (A) isotherms, compressional modulus-surface pressure (C(s)(-1)-pi) curves, and film thickness, complemented with Brewster angle microscopy images, the interaction between the components was analyzed. Regardless of the surface pressure (pi = 10, 20, or 30 mN/m) at which the mean molecular/monomer areas (Am) were calculated, the Am-mole fraction plots (corresponding to X(PMMA) = 0.1, 0.3, 0.5, 0.7, and 0.9) show that all the experimental points obtained are placed on the theoretical straight line calculated according to the additivity rule. This fact, together with the existence of two collapses in the mixed monolayers and with the fact that the surface pressure of the liquid-expanded LE-L'E phase transition of PMMA does not change with the monolayer composition, demonstrates the immiscibility of the film components at the interface. The application of the Crisp phase rule to the phase diagram of PMMA-cholesterol mixed monolayers helps to explain the existence of a biphasic system, regardless of their composition and surface pressure. Besides, Brewster angle microscopy (BAM) images showed the existence of heterogeneous cholesterol domains with high reflectivity immersed in a homogeneous polymer separate phase with low reflectivity.

Oxysterols Versus Cholesterol in Model Neuronal Membrane. I. The Case of 7-Ketocholesterol. The Langmuir Monolayer Study

“…Cholesterol has been thoroughly characterized in Langmuir monolayers and the isotherms recorded herein agree very well with those published elsewhere (e.g., Cadena-Nava et al 2006 ; Minones Conde et al 2010 ). Since in the literature much less attention has been paid to 7-KC, we have thoroughly investigated this oxidized sterol in Langmuir monolayers.…”

Evaluation of the Structure–Activity Relationship of Rifabutin and Analogs: A Drug–Membrane Study

“…[17,[31][32][33][34] According to the C À1 s values obtained for EPC monolayers, described in previous works, the CHOL molecules, as expected, decrease the fluidity of the EPC monolayer. [15,35,36] The collapse pressure of 46 mN m À1 obtained for EPC:CHOL (4:1) ( Table 1) is slightly lower than that reported for pure EPC (% 50 mN m À1 ). [15] The isotherms of EPC:CHOL in the presence of the antimycobacterial compounds have different shapes to that of EPC:CHOL.…”

“…[34] Therefore, before compression of the monolayer it is possible to observe the existence of "elliptic vacuoles", which are attributed to the coexistence of two phases ( Figure 3, marked with arrows). [36,38] On compression, small circular nuclei of a presumably liquid-condensed phase are seen on the black background of a liquid-disordered phase. These liquid-condensed lipid domains exhibit a homogenous distribution.…”

Impact of the α-Methyl Group (α-CH3) on the Aggregation States and Interfacial Isotherms of Poly(acrylates) Monolayers at the Water Surface

“…Acrylate polymers (e.g., poly­(methyl acrylate), poly­(ethyl acrylate), poly­(methyl methacrylate), and poly­(ethyl methacrylate)), bearing hydrophilic ester pendent groups on the hydrophobic backbone, are the most representative polymers that can readily form stable monolayers at the water surface due to their amphiphilic nature and have been subjected to a vast number of investigations since the first publication in 1946. , A large part of these numerous studies were mainly focused on the “surface pressure–molecular area (π– A ) isotherms” of the polymer monolayer. ,− It has been revealed that both poly­(methyl acrylate) (PMA) ,,, and poly­(ethyl acrylate) (PEA) ,, monolayers exhibit the expanded-type isotherm, that is, the surface pressure is detected at a large surface area and slowly increases with decreasing of the area per repeated unit occupied on the surface (A). On the other hand, the isotherms of poly­(methyl methacrylate) (PMMA), ,, and poly­(ethyl methacrylate) (PEMA) ,, are the condensed-type one, featured as the faster increment in the surface pressure.…”