Electron Collision with DPPC Molecules

Electrons colliding with the monolayer of DPPC (1, 2-dipalmitoyl-sn-glycero-3-phosphocholine) molecules deposited on gold

R.Panajotovic
N. Mason
Department of Physics and Astronomy
Science Faculty
The Open University
Milton Keynes, United Kingdom

M. Schnietz
A. Turchanin
A. Gölzhäuser
Department of Physics
Physics of Supramolecular Systems
University of Bielefeld
Bielefeld, Germany

When the cell is exposed to high-energy ionizing radiation, the large number of secondary electrons ejected from atoms is causing a major disruption to all its parts – cell membrane, organelles and the DNA. To study the physical and chemical changes of the cell membrane exposed to these electrons, in experiment and theory, a model membrane is usually designed as a thin mono or bilayer lipid film deposited on a solid (gold, silicon, mica, etc.) surface or at the air/liquid interface.

Most popular lipids used for this purpose are phospholipids and among them a DPPC (1, 2-dipalmitoyl-sn-glycero-3-phosphocholine) molecule, as a major component of the lung tissue. When the electrons come across the well ordered thin molecular film, they are either transmitted, elastically scattered, or they will excite molecules through the collision or temporary attachment/detachment. Ordering in the film will be disrupted because of the loss of the functional groups in the polar head of the molecules (most likely loss of CH3 and breaking of the phosphodiester bond), and also because of the loss of hydrogen atoms in the alkane tails. Since the distribution and orientation of phospholipids is governed by the hydrophilic and hydrophobic forces between them, parts of the film will then collapse.

In a real-life situation, this can have major consequences on stability of the receptor proteins wrapped in the lipid matrix, as well as on permeability of the cell membrane for ions and water. In addition, in the process of breaking molecular bonds, reactive molecular fragments are formed, which may cause further damage to the cell.

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