Molecular dynamics simulations of electroporation in POPC and DPPC lipid bilayers have been carried out at different temperatures ranging from 230 K to 350 K for varying electric fields. The dynamics of pore formation, including threshold field, pore initiation time, pore growth rate, and pore closure rate after the field is switched off, was studied in both the gel and liquid crystalline (Lα) phases of the bilayers. Using an Arrhenius model of pore initiation kinetics, the activation energy for pore opening was estimated to be 25.6 kJ mol(-1) and 32.6 kJ mol(-1) in the Lα phase of POPC and DPPC lipids respectively at a field strength of 0.32 V nm(-1). The activation energy decreases to 24.2 kJ mol(-1) and 23.7 kJ mol(-1) respectively at a higher field strength of 1.1 V nm(-1). At temperatures below the melting point, the activation energy in the gel phase of POPC and DPPC increases to 28.8 kJ mol(-1) and 34.4 kJ mol(-1) respectively at the same field of 1.1 V nm(-1). The pore closing time was found to be higher in the gel than in the Lα phase. The pore growth rate increases linearly with temperature and quadratically with field, consistent with viscosity limited growth models.

Bacterial infections are a major health problem worldwide. Identification of disease-causing organisms by culture-based approaches is time-consuming and often lacks sensitivity. Molecular approaches such as PCR and microwaveaccelerated metal-enhanced fluorescence (MAMEF) assays1, are more sensitive and faster than traditional culture-based approaches, but require isolation of the target DNA. In order to determine the effect of both boiling and microwave irradiation on microbial lysing and DNA fragmentation, cultures of Neisseria gonorrhoeae and Listeria monocytogenes (108 CFU /mL) were either boiled (range 40 -70 C) or lysed in a 900-watt microwave on isolator-mounted microscope slides, both with and without the assistance of disjointed antenna gold bow-tie structures. The temperatures of cultures were obtained prior to and after lysing and the resulting lysate cultured on selective agar plates. DNA isolation and fragmentation efficiency were determined by gel electrophoresis and PCR. N. gonorrhoeae lysed at a lower temperature ( C) than L. monocytogenes. Microbial lysing and DNA fragmentation was more effectively carried out in the presence disjointed gold triangle structures, but only when small sample volume were used. Standard boiling was successful for bacterial lysing and DNA fragmentation, but required higher temperatures and longer times than microwave focusing. PCR results suggest that low power microwave irradiation is ideal for PCR methods while higher microwave powers are required to generate DNA fragments 1586-Pos Board B537 Molecular Modeling of Self-Assembly of Anticancer Drug Amphiphiles

In order to study cell electroporation in situ, polymer devices have been fabricated from poly-dimethyl siloxane with transparent indium tin oxide parallel plate electrodes in horizontal geometry. This geometry with cells located on a single focal plane at the interface of the bottom electrode allows a longer observation time in both transmitted bright-field and reflected fluorescence microscopy modes. Using propidium iodide (PI) as a marker dye, the number of electroporated cells in a typical culture volume of 10-100 μl was quantified in situ as a function of applied voltage from 10 to 90 V in a series of ~2-ms pulses across 0.5-mm electrode spacing. The electric field at the interface and device current was calculated using a model that takes into account bulk screening of the transient pulse. The voltage dependence of the number of electroporated cells could be explained using a stochastic model for the electroporation kinetics, and the free energy for pore formation was found to be 45.6 ± 0.5 kT at room temperature. With this device, the optimum electroporation conditions can be quickly determined by monitoring the uptake of PI marker dye in situ under the application of millisecond voltage pulses. The electroporation efficiency was also quantified using an ex situ fluorescence-assisted cell sorter, and the morphology of cultured cells was evaluated after the pulsing experiment. Importantly, the efficacy of the developed device was tested independently using two cell lines (C2C12 mouse myoblast cells and yeast cells) as well as in three different electroporation buffers (phosphate buffer saline, electroporation buffer and 10% glycerol).

No abstract

We have studied the structure of cetyltrimethylammonium bromide–DNA complexes using small angle x-ray diffraction and elemental analysis. These complexes exhibit a two-dimensional hexagonal phase. The diffraction data have been analyzed using electron density models based on two different structures of these complexes proposed in the literature, which differ in the micelle to DNA stoichiometry. The structure with a 1:2 micelle–DNA stoichiometry is found to be more consistent with the diffraction data. Furthermore, this structure is also supported by the stoichiometry deduced from elemental analysis. Madelung energies of the two structures, calculated from the electrostatic interaction between their cylindrical constituents, give insight into their relative stability.