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ABSTRACT A new simulation method, dissipative particle dynamics, is applied to model biological membranes. In this method, several atoms are united into a single simulation particle. The solubility and compressibility of the various liquid components are reproduced by the simulation model. When applied to a bilayer of phosphatidylethanolamine, the membrane structure obtained matches quantitatively with full atomistic simulations and with experiments reported in the literature. The method is applied to investigate the cause of cell death when bacteria are exposed to nonionic surfactants. Mixed bilayers of lipid and nonionic surfactant were studied, and the diffusion of water through the bilayer was monitored. Small transient holes are seen to appear at 40% mole-fraction C^sub 9^E^sub 8^, which become permanent holes between 60 and 70% surfactant. When C^sub 12^E^sub 6^ is applied, permanent holes only arise at 90% mole-fraction surfactant. Some simulations have been carried out to determine the rupture properties of mixed bilayers of phosphatidylethanolamine and C^sub 12^E^sub 6^. These simulations indicate that the area of a pure lipid bilayer can be increased by a factor 2. The inclusion of surfactant considerably reduces both the extensibility and the maximum stress that the bilayer can withstand. This may explain why dividing cells are more at risk than static cells.
INTRODUCTION
Mechanisms of the action of disinfectants have been recently reviewed (Denyer and Stewart, 1998). These authors regard disinfectants as chemical biocides with a relative lack of selectivity. They regard the vegetative bacterial cell as presenting three broad regions for biocide interaction: the cell wall, cytoplasmic membrane, and cytoplasm. A particular problem resides in the elucidation of the mechanisms of action of chemical biocides; these studies often have to be carried out under conditions that may be remote from those used to determine anti-microbial action (Bloomfield, 1991). Although biocidal compounds derive from a variety of chemical classes, the final resulting damage may show considerable similarity. The target most frequently cited in the biocide literature is the cytoplasmic membrane (Denyer and Stewart, 1998).
Agents used in household cleaning compositions are composed of structurally diverse classes of chemicals, including surface active agents, phenols, and terpenoids. The cytoplasmic membrane is a complex structure, and modes of action could involve membrane lipids or membrane proteins. Protein denaturants will disrupt transmembrane protein...