Morphology observation of dipalmitoyl phosphatidyl choline (DPPC) monolayer on water surface by dropping method

Daisuke Yoshida,Takehisa Dewa,Takatsugu Shimoaki,Ayumi Sumino,Zameer Sheravani,Takashi Tomita,Tadayoshi Yoshida,Yasushi Yamamoto,Keijiro Taga,Takashi Yokoyama,Masato Yamamoto,Mamoru Nango

doi:10.4236/jbpc.2013.44016

Abstract

Preparation of DPPC lipid monolayer in water trough has been done by dropping method and compared with compression method. Monolayer was studied by surface pressure isotherm, fluorescence microscopy, Brewster angle microscopy, and infrared external reflection spectroscopy. Results of these measurements showed that dropping method gave better results compared to compression method. In dropping method, transition from liquid expanded state to liquid condensed is gradual compared to sharp one in compressed method. During monolayer formation, adjustment and interaction between hydrophilic part of lipid and water and among hydrophobic part of lipid molecule are slow, stable, and more natural as worked out from surface area versus pressure isotherm. At a given molecular area, surface pressure is less compared to compression method thus monolayer is in more fluidic state in dropping method than compression method. The observation was supported by all techniques described above.

Highlights

Biomembranes have fundamental fluid structures representing “fluid mosaic model” proposed by Singer and Nicolson [1], in which functional proteins are buried in bilayers consisting of various kinds of phospholipids [2]
We report morphology of dipalmitoyl phosphatidyl chorine (DPPC) monolayer formed on water surface by dropping method
Advantage of dropping method proved to be that limiting molecular area (A0) of DPPC monolayer at water interface was 0.65 ± 0.05 nm2/molecule corresponded to surface pressure 40 mN/m

Summary

INTRODUCTION

Biomembranes have fundamental fluid structures representing “fluid mosaic model” proposed by Singer and Nicolson [1], in which functional proteins are buried in bilayers consisting of various kinds of phospholipids [2]. Ohe et al [6] studied interaction between antibiotic and phospholipids monolayer at water-air interface applying vibrational sum frequency generation spectroscopy. Okahata and co-workers [7,8,9] have performed systematic studies on the molecular recognition of lipid monolayer formed on water surface using quartz crystal microbalance (QCM) method capable of nanogram order level detection. Monolayer on water surface is generally formed by compression method [10]. When first drop expands on water surface, drop is added; at intervals, drops are added continuously on water surface In this dropping method, a large volume of solution and enough time are required to make monolayer. Hydrophobic interaction is important to keep balance between hydrophilic groups in monolayer and water molecules. Dropping method is better for forming fluid monolayer on water surface which makes monolayer a good candidate to study model membrane. Role of hydrophilic interaction in monolayer formation has been discussed

Materials

Monolayer Preparation

RESULTS AND DISCUSSION

CONCLUSION