(482b) Phase Behavior Calculations of DPPC Phospholipid Bilayers

It has been experimentally shown that the nonspecific adsorption of charged nanoparticles onto the phospholipid bilayers that contain phosphocholine head groups cause a local surface modification at the points where the nanoparticle is adsorbed. When the charged species binds to the phospholipid bilayer surface, its local state of phase can be changed as a result of the reorientation and loss of degrees of freedom of the zwitterionic phosphocholine head group[1]. An accidental shift in the phase transition temperature of a phospholipid bilayer membrane can lead to fatal consequences for living systems. For example, if the presence of a negatively charged nanoparticle can significantly influence the orientation of the DPPC head group and consequently change the integrity of the fluid-like bilayer, vital properties of the bilayer such as the transport of molecules in and out of the cell can be inhibited. Therefore, it is important to understand the theoretical fundamentals of this change of phase state by explicitly taking into account the DPPC head group size, shape and orientation when proposing a molecular model for a lipid bilayer containing phospholipids such as DPPC.[2]

In our theoretical model a self consistent mean-field approach is implemented to the adsorption of a charged nanoparticle onto a DPPC containing lipid bilayer and an extension of the Poisson-Boltzmann equation is derived through the functional minimization of the total free energy. This molecular model takes into account for the first time the size, shape and orientational entropy of the DPPC lipid head group. The results show that these head group considerations are essential in order to properly predict the main chain liquid to gel phase transition of the DPPC containing lipid bilayer.[3]

References

[1] B. Wang, L.zhang, S. Bar and S. Granick, PNAS, vol.105, no. 47 ,18171 (2008)

[2] E. Mbamala, A. Fahr and S. May, Langmuir 22, 5126 (2006)

[3] R. Elliott, M. Schick, and I. Szleifer, Phys. Rev. Letters. 96, 098101 (2006).