Bulletin of the American Physical Society
Spring 2017 Meeting of the APS New England Section, held jointly with NanoWorcester
Volume 62, Number 5
Friday–Saturday, April 14–15, 2017; Worcester, Massachusetts
Session D4: Biophysics |
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Chair: Erkan Tuzel, Worcester Polytechnic Institute Room: Olin Hall 126 |
Saturday, April 15, 2017 10:15AM - 10:20AM |
D4.00001: Opening Remarks |
Saturday, April 15, 2017 10:20AM - 10:40AM |
D4.00002: Self-Assembly of End-to-Tail Associating Liquid Crystalline Polymers Michael Richter, Elena Dormidontova Self-assembly plays a central role in obtaining new responsive nanomaterials. The variety of the chemical nature of the building blocks and associating units creates a large spectrum of materials with controllable properties. To understand the self-assembly of a class of such materials we study a model rigid cylinders with attractive semi-spherical end-caps (spherocylinders). Using Monte Carlo simulations we study self-assembly of spherocylinders as a function of associating energy and spherocylinder concentration. Depending on the orientational specificity of association very different phase behaviors are observed. Systems with high orientational specificity of association form preferentially linear-shaped aggregates and are capable of achieving nematic order at sufficiently high concentration and association energy. Spherocylinders with low orientational specificity are capable of multiple associations between the end-caps, which results in network or scaffold-like structure formation depending on spherocylinder concentration. The corresponding phase behavior will be discussed. [Preview Abstract] |
Saturday, April 15, 2017 10:40AM - 11:00AM |
D4.00003: Collagen-inspired design rules for the self-assembly of twisted filaments Martin Falk, Lucy Colwell, Michael Brenner Despite developments in the capacity to engineer specific interactions and structures in synthetic systems, it is clear that there is more to be done in understanding the design rules by which nature forms structure from complex substrates. One structure whose formation has yet to be understood is the collagen triple helix. Though the sequence and structure of collagen is known, an identification of the most important features for producing collagen as nature does has remained elusive. Elucidating the design rules for collagen has appeal from a synthetic self-assembly perspective as well; previous studies of specific interactions have primarily confined their attention to colloids. Through simulation, we propose a successful scheme for the self-assembly of three-twists mediated by specific interactions. We find that the twist chirality decays with a correlation length, the result of defects involving the switching of two filaments. We explore the addition of a chiral term to our scheme, and find that we form twists of one handedness. Thus we identify design rules and obstacles for the self-assembly of twists, and strategies that natural collagen may be using to overcome those problems. [Preview Abstract] |
Saturday, April 15, 2017 11:00AM - 11:20AM |
D4.00004: Measurement of the Persistence Length of Cytoskeletal Filaments using Curvature Distributions Pattipong Wisanpitayakorn, Keith J. Mickolajczyk, William O. Hancock, Luis Vidali, Erkan Tuzel Cytoskeletal filaments such as microtubules and actin filaments play important roles in mechanical signal transduction allowing cells to respond to their environment. Measuring the mechanical properties of cytoskeletal structures is crucial for gaining insight into intracellular mechanical stresses and cellular processes. One of the ways to characterize such bio-filaments is by measuring their persistence length. Here, we show how curvature distributions can be used as a tool to quantify bio-filament deformations, and investigate how the apparent stiffness of filaments depends on the resolution and noise of the imaging system. We present analytical calculations of the scaling curvature distributions as a function of filament discretization, and test our predictions by comparing Monte Carlo simulations to results from Fourier and tangent correlation analysis. We also apply our approach to microtubules and actin filaments obtained from \textit{in vitro} gliding assay experiments with high densities of non-functional motors. Finally, we provide an ImageJ Plugin for users to measure the persistence length of bio-filaments from \textit{in vivo} or \textit{in vitro} fluorescence microscopy images. [Preview Abstract] |
Saturday, April 15, 2017 11:20AM - 11:40AM |
D4.00005: Retardation of Bulk Water Dynamics by Disaccharide Osmolytes Nimesh Shukla, Enrico Pomarico, Majed Chergui, Christina Othon The bioprotective nature of disaccharides is hypothesized to derive from the modification of the hydrogen bonding network of water which protects biomolecules through lowered water activity at the protein interface. Using ultrafast fluorescence spectroscopy, we measured the relaxation of bulk water dynamics around the induced dipole moment of two fluorescent probes (Lucifer Yellow Ethylenediamine and Tryptophan). Our results indicate a reduction in bulk water reorganization rate of approximately 30{\%}. We observe this retardation in the low concentration regime measured at 0.1 and 0.25 M, far below the onset of glassy dynamics. This reduction in water activity could be significant in crowded biological systems, contributing to global change in protein energy landscape, resulting in a significant enhancement of protein stability under environmental stress. We observed similar dynamic reduction for two disaccharide osmolytes, sucrose and trehalose, with trehalose being the more effective in reducing solvation dynamics. [Preview Abstract] |
Saturday, April 15, 2017 11:40AM - 12:00PM |
D4.00006: Role of Adhesion of Functionalized Biosynthesized Magnetite Nanoparticles for the specific Targeting of Breast Cancer J. D. Obayemi We present the results of adhesion studies between components of model ligand-conjugated magnetite nanoparticle systems and breast cancer cells (MDA-MB- 231) or normal breast cells (MCF 10A). Adhesion forces between biosynthesized magnetite nanoparticles (BMNPs), chemically synthesized magnetite nanoparticles (CMNPs), as well as their ligand-conjugated systems to MDA-MB- 231 or MCF 10A are elucidated at a nanoscale. The results showed that ligand-conjugated BMNPs had over six times higher adhesion forces to breast cancer cells than to normal breast cells. The increase in adhesion forces are mainly attributed to van der Waals interactions and the receptors (revealed via immunofluorescence staining) that are over- expressed on the surfaces of the breast cancer cells. The implications of the results are discussed for the specific targeting of breast cancer cells. [Preview Abstract] |
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