MorphologicaObservation of Specific Condensation Effect of Cholesterol on Dipalmitoyl Phosphatidyl Choline (DPPC) Monolayer by Dropping Method

Abstract

Morphology of dipalmitoyl phosphatidyl choline (DPPC)-cholesterol (Chol) mixed monolayer formed on water surface by dropping method was investigated using surface tension measurement (STm), Brewster angle microscopy (BAM), and fluorescence microscopy (FM). STm showed strong condensation effect of Chol in fluidic DPPC monolayer. Excess area (S ex ) from mean mixing state of DPPC and Chol was about twice larger than that by general compression method in the range from x C = 0.2 to 0.4 (x C : mole fraction of Chol). BAM and FM images showed clearly that the fluidic DPPC monolayer changed to condensed rigid monolayer due to the condensation effect of Chol. At more than x C = 0.3 DPPC-Chol mixed monolayer changed to condensed state similar to the Chol monolayer. These results support previous reports by compression method that Chol molecule demonstrates the strong condensation effect to the fluidic monolayer and also indicate that dropping method enables to form unique monolayer on the water surface.

Structural Change in Dimyristoyl Phosphatidyl Choline (DMPC) Molecule Alkyl Chains on the Addition of Cholesterol to DMPC Monolayer: Specific Addition Effect of Cholesterol

“…A 0 was 0.39 ± 0.02 nm 2 /molecule at 30 mN/m of π and this value was also very similar (0.40 nm 2 /molecule at 35 mN/m) in compression method [22] [23] [24] [25]. The obtained A 0 was also identical (0.41 nm 2 /molecule at 34 mN/m) as reported previously by dropping method [11].…”

“…Therefore the deviation occurred in both the methods suggests that the DMPC-cholesterol mixed monolayer formation by dropping and compression methods are same and thus cholesterol condensation effect of the mixed monolayer is also same in both methods. The result of cholesterol condensation effect on DMPC monolayer was different from that of dipalmitoyl phosphatidyl choline (DPPC) monolayer, where the condensation effect of cholesterol on DPPC monolayer by dropping method was twice larger than compression method [11]. was brightest among all the above three π values, thereby confirmed that the completion of monolayer occurred at the water surface.…”

“…This also promotes thermal and structural stabilities of biomembrane in a wide temperature range. Many studies on the condensation effect have been performed using phospholipid-cholesterol mixtures in monolayer and bilayer systems, and liposomes [2] [5]- [11]. The techniques of thermal analysis, ATR-FTIR and NMR spectroscopy, and molecular simulation [5] [12] [13] [14] [15] [16] showed that the structure of DMPC molecule exchanged from liquid-disordered (L d ) phase to liquid-ordered (L o ) phase with an increase in cholesterol mole fraction.…”

Morphological Behavior of DPPC-DMPC Two-dimensional Mixed Monolayer on Water Surface by Dropping Method

“…Brewster angle microscopy (BAM) for visualizing the morphology of pure DPPC and DMPC and several mixed monolayers were carried out using a commercial BAM microscope (EMM633K; Filgen Inc., Nagoya, Japan) attached with an USB-CAP type (GV-USB2; I-O DATA DEVICE, INC., Kanazawa, Japan) imaging analysis software [16], [17], [18], [19], [20]. BAM shows the monolayer image arises from the difference in refractive index between the monolayer and the water phase.…”

“…However, the study of DPPC-DMPC lipid combination is a pending issue. Therefore, in this communication, we have investigated the monolayer properties of two-dimensional DPPC-DMPC mixed monolayer at various mole fractions formed by the dropping method [16], [17], [18], [19] using surface tension measurement (STm), Brewster angle microscopy (BAM), and infrared external reflection spectroscopy (IERS).…”