Bulletin of the American Physical Society
2006 Ohio Section of the APS Fall Meeting
Friday–Saturday, October 13–14, 2006; Orrville, Ohio
Session D4: Biological Applications |
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Chair: Forrest Smith, The University of Akron Room: Wayne College C113 |
Saturday, October 14, 2006 9:30AM - 9:42AM |
D4.00001: Phase Separation in Asymmetric Lipid Bilayers: Cubic and Quartic Interaction Terms Fanindra Bhatta, David Allender Previous work has considered asymmetric bilayers in which each layer contains a mixture of cholesterol and lipids, but the two layers have different lipids and different concentrations of cholesterol. In particular, one layer has concentrations such that phase separation into cholesterol rich and cholesterol poor phases is expected, but the second layer, if unaffected by the first layer, would not phase separate. Using only the leading terms of interaction between cholesterol concentration and the straightening of the hydrocarbon chains in the lipids in a given layer, plus a coupling of the two layers via their chain order, it was found that phase separation in one layer causes phase separation in the second. We have examined the effect of higher order terms in the chain ordering on phase separation behavior of the bilayer. We find a shift of the critical temperatures and cholesterol concentrations for the phase separation, but qualitatively the same behavior as in the simpler model. [Preview Abstract] |
Saturday, October 14, 2006 9:42AM - 9:54AM |
D4.00002: Simulations of Triblock Copolymer Interactions with Biomimetic Membranes Shashishekar Adiga, Peter Zapol, Millicent Firestone Association of amphiphilic triblock copolymers with lipid membranes results in versatile novel materials with enormous potential in many areas of bionanotechnology. The molecular architecture and concentration of block copolymers along with environmental variables such as temperature and pH provide means to tune these structures for desired applications and also allow for designing signal-responsive materials. Understanding interaction between block copolymers and lipid bilayers is crucial for applications in nanomedicine. Monte Carlo simulations are used to explore the effect of molecular architecture on the mode of insertion of triblock copolymers into lipid bilayers. The results are compared with small angle X-ray scattering data. [Preview Abstract] |
Saturday, October 14, 2006 9:54AM - 10:06AM |
D4.00003: Calculation of folding rates of two-state proteins supports enhanced structural cooperativity Xianghong Qi, John Portman The coarse-grained variational model is used to characterize the polymer dynamics of barrier crossing for a set of 28 non-homologous two-state small proteins. When terms that induce minor cooperativity are included in the interaction potential, we find that the behavior of calculated rates are in good agreement with experimental rates in terms of the absolute rate as well as realtionship to native topology. Generally,the structure of the transition state ensemble for the folding and unfolding routes include roughly the same residues, though the distinction between folding and unfolding residues is more pronounced. That is, the main effect of cooperativity is to sharpen the interface of the folding nucleus without significently changing the folding mechanism. Furthermore, the calculated prefactors $1/k_0$ are found to be relatively uniform, with variation in $1/k_0$ less than a factor of five.This calculation justifies the common assumption that $k_0$ is a roughly same for small two-state folding proteins. Using the barrier heights obtained from the model, we find that $1/k_0 \sim 1-5\mu$s(with average $\sim 4\mu$s). The relationship between free energy barrier and native state topology and chain length are also considered. The model can be easily to study more subtle aspects of folding such as the variation of the folding rate with stability or solvent viscosity. [Preview Abstract] |
Saturday, October 14, 2006 10:06AM - 10:18AM |
D4.00004: Getting DNA by using Silver Spears Samantha Selgraph, Tyler Laudenslager, Dongdong Jia Silver nano needles were prepared with a glancing angle magnetron sputtering deposition method. The tips of the silver needles are about 150 nm sharp. Negatively charged DNA molecules with a length of 150 nm and a width of 3 nm were suspended in a Trish-HCl buffer solution. A positive potential was applied to the silver needles. The silver needles were submerged into the buffer solution. Due to the electrical tip effect, DNA molecules were collected by Coulomb attraction force. Silver needles with DNA deposition were studied with a scanning electron microscope and an atomic force microscope. [Preview Abstract] |
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