Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V2: Constrained Polymers |
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Sponsoring Units: DCMP DPOLY Chair: Xaio Lun Wu, University of Pittsburgh Room: Spirit of Pittsburgh Ballroom BC |
Thursday, March 19, 2009 8:00AM - 8:36AM |
V2.00001: The low-force elasticity of single-stranded DNA Invited Speaker: Single-molecule manipulation experiments, in which a single polymer is stretched with a known force while its extension is measured, are typically described by ideal models (e.g. the worm-like chain or freely-jointed chain) that account only for the polymer's local stiffness, but ignore long-range 'excluded-volume' interactions. Yet, the basic (and successful) Flory scaling theory indicates that long-range interactions must be included to describe the zero-force self-avoiding walk structure of a polymer. Here, we reconcile single-molecule force-extension data with scaling theories of polymer elasticity: measurements of denatured single-stranded DNA show a regime where the extension grows as a non-linear power law with force, in accord with previously-unproven `tensile blob' models. Analysis of the salt dependence of this regime indicates that the polymer's Kuhn length is proportional to the Debye length. This contradicts the classic Odijk-Skolnick-Fixman theory; I will discuss possible explanations for this discrepancy. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 9:12AM |
V2.00002: Confinement Effects on the Structure of Complex Fluids Invited Speaker: Actin is a key component of the protein complex responsible for producing contractile force in skeletal muscle. Filamentous actin, called F-actin, is a two-stranded helical protofilament with a diameter of $\sim $8nm and a contour length of $\sim $10m. The experimental results show that the persistence length of the F-actin is 4 -20 m. One of interesting problems is to find the structure of a semiflexible filament in a confined space [1], such as a channel width less than the persistence length. The other interesting problem is to find the surface treatment effect on the liquid crystal structure in a confined space. The boundary conditions imposed by the walls of the microchannel generate the spatial patterning of defect domains in a smectic liquid crystal [2] and the formation of a large-area ordered structure [3] by using the structure of smectic liquid in the microchannels. We found that the F-actin undergoes a transition from a 2D randomly oriented regime to a 1D biaxially confined regime with the effective persistence length. We were able to generate defect domains that are nearly uniformly arranged in 2D ordered patterns by controlling the surface hydrophobicity. Furthermore, the formation of a large-area ordered structure of toric focal conic domains was generated. This work was done with C. R. Safinya's group at UCSB and Hee-Tae Jung's group at KAIST. \\[4pt] [1] M.C Choi at. al, Macromolecules 2005,38, 9882-9884\\[0pt] [2] M. C. Choi at. al, PNAS 2004, 101, 17340-17344\\[0pt] [3] D. K. Yoon at. al, Nature Materials, 2007, 6, 866-870 [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:48AM |
V2.00003: Is your brain wired optimally? Invited Speaker: |
Thursday, March 19, 2009 9:48AM - 10:24AM |
V2.00004: Gene brushes on a chip: From crowding and the search problem to synthetic systems Invited Speaker: We assemble DNA polymer brushes coding for entire genes on a surface by means of a new photolithographic approach. The gene density can be controlled from dilute to high density where the local concentration -- Megabase pairs per micron cubed -- is comparable to that in a bacterium. The gene brush, therefore, emulates the crowded medium of the cell, allowing us to study DNA transactions in vitro under native conditions. We find that transcription/translation from these gene brushes is highly sensitive to DNA density, orientation and composition. As a step towards multi-gene synthetic systems, we integrated on a chip two spatially separated gene brushes, and implemented a two-stage transcription/translation cascade. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 11:00AM |
V2.00005: Confinement effects on folding of proteins and RNA Invited Speaker: |
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