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 (Sex) from mean mixing state of DPPC and Chol was about twice larger than that by general compression method in the range from xC = 0.2 to 0.4 (xC: 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 xC = 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.
Highlights
Biomembranes have fundamental fluid-structures similar to “fluid mosaic model” proposed by Singer and Nicolson [1]
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)
We have reported using various physicochemical methods that dipalmitoyl phosphatidyl choline (DPPC) monolayer formed by dropping method maintained its fluidity and flexibility and the limiting molecular area was larger than measured by general compression method
Summary
Biomembranes have fundamental fluid-structures similar to “fluid mosaic model” proposed by Singer and Nicolson [1]. Membrane-fluidity is important for functioning of membrane such as molecular recognition, transport of nutrition and various other solutes, and construction of tertiary structures of protein [3] [4]. We have reported using various physicochemical methods that dipalmitoyl phosphatidyl choline (DPPC) monolayer formed by dropping method maintained its fluidity and flexibility and the limiting molecular area was larger than measured by general compression method. Monolayer by dropping method would be likely to apply to various property investigations as bio-mimetic membrane [9] [10] In this communication, we have investigated Chol mixing-effect on fluidic DPPC monolayer formed by dropping method for various Chol mole fractions using surface tension measurement (STm), Brewster angle microscopy (BAM), and fluorescence microscopy (FM).
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