Arthur E. Bailey

Interaction of a charged polymer with zwitterionic lipid vesicles.

The interaction between polyethylenimine (PEI) and phospholipid bilayers plays an important role in several biophysical applications such as DNA transfection of target cells. Despite considerable investigation into the nature of the interaction between PEI and phospholipid bilayers, the physical process remains poorly understood. In this paper, we study the impact of PEI on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles as a function of salt concentration using several techniques including dynamic (DLS) and static (SLS) light scattering, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR). At low salt concentration, vesicles aggregate, leading to the formation of stable clusters whose final size depends on the PEI concentration. At high salt concentration the system does not aggregate; DSC and NMR data reveal that the PEI penetrates into the bilayer, and SLS measurements are consistent with PEI crossing the bilayer. The transfectional ability of PEI is discussed in terms of these results.

Spontaneous Domain Growth in the One-Phase Region of a Gel/Mixture System

We present results of experiments designed to investigate a novel domain state occurring in a binary fluid mixture when imbibed in dilute silica gel. This state occurs near the coexistence curve of the pure binary mixture (in the absence of gel), but above the coexistence curve of the binary mixture/gel system. The growth rate of the domains is proportional to t 1/3 and most measurements are consistent with dynamic scaling. However, there is an additional k-independent response which is observed at very early times following the quench, which is unlike the behavior of the pure system.