Bulletin of the American Physical Society
81st Annual Meeting of the APS Southeastern Section
Volume 59, Number 18
Wednesday–Saturday, November 12–15, 2014; Columbia, South Carolina
Session GD: Biomagnetism and Biophysics |
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Chair: Thomas Crawford, University of South Carolina Room: Richland I |
Friday, November 14, 2014 8:30AM - 8:42AM |
GD.00001: Physical principle for the pattern formation of binary self-assembled monolayer on nanoparticle surface Xinwei Ge, Feng Ding Self-assembled monolayer (SAM) where ligand molecules spontaneously assemble on nanoparticle (NP) surface is a common approach to stabilize or functionalize NPs. It has been proposed that a binary SAM of mixing two immiscible ligands can form stripe-like patterns on NP surfaces, which may induce novel functions. Experimental characterizations and computational simulations had been performed to show this conformation could form spontaneously on gold NPs. However, previous evidences were questioned due to their limitations. The principle for pattern formation is still not conclusive yet. We applied atomistic discrete molecular dynamics (DMD) simulation to study the binary SAM on gold NPs and our results showed that pattern conformation can indeed form on NPs surface only if favorable conditions are satisfied. The formation of patterns depends on physicochemical characteristics of composite ligands and thus relative interactions between them. Temperature also plays a role here as patterns eventually disappear at high temperature where random distribution with high entropy is favorable. We proposed a simple thermodynamics-based theory that can estimate pattern formation in a binary SAM and also demonstrate the application of this principle. [Preview Abstract] |
Friday, November 14, 2014 8:42AM - 8:54AM |
GD.00002: The Structure-Function Relationship of PAMAM Dendrimers as Robust Oil Dispersants Bo Wang, Nicholas Geitner, Rachel Andorfer, David Ladner, Puchun Ke, Feng Ding Dendrimers are well-defined fractal-like polymers with a hydrophilic surface and hydrophobic interior. Their encapsulation capacity enables biomedical applications such as drug or gene delivery. Recently, PAMAM (polyamidoamine) dendrimers have also been explored as efficient and biocompatible oil dispersants for oil spill remediation. However, their high cationic surface charge has been shown to be cytotoxic. It is therefore imperative to mitigate cationic charge-induced toxicity. Synergistic experimental approach was performed to examine the effects of varying terminal surface charge on the capacity of dendrimers to disperse model liner, polycyclic aromatic, and hybrid hydrocarbons. The discrete molecular dynamics (DMD) simulations with a new MEDUSA force field were also applied to study PAMAM structure and dynamics. We validated our DMD methods by benchmarking against previous experimental and computational results. Our study indicates that uncharged dendrimers collapse by forming intra-molecular hydrogen bonds, which reduce the hosting capability. On the other hand, changing the surface charges from positive to negative greatly shifts the pKa of tertiary amines of the PAMAM dendrimer interior. As a result, the negatively charged dendrimers have a significant percentage of tertiary amines protonated, $\sim$30{\%}. This unexpected change in interior protonation state cause electrostatic interactions with the anionic terminal groups, leading to contraction and a marked decrease in hydrocarbon hosting capacity. [Preview Abstract] |
Friday, November 14, 2014 8:54AM - 9:06AM |
GD.00003: Structural and energetic determinants of tyrosylprotein sulfotransferase sulfating specificity Praveen Nedumpully-Govindan, Lin Li, Emil G. Alexov, Mark A. Blenner, Feng Ding Tyrosine sulfation is a type of post-translational modification which is catalyzed by the enzyme tyrosylprotein sulfotransferase (TPST). There is no well-defined sequence motif for tyrosine sulfation, and the selection criteria for a sequence undergoing sulfation remain elusive. We estimated the binding affinity of peptides with tyrosines to TPST and attempted to differentiate the sulfated and non-sulfated sequences. We find that sequences which undergo sulfation in general have stronger binding affinity. Even though simple binding affinity score can satisfactorily differentiate the two sets of sequences, we found that the predictions are further improved after including energy costs associated with local unfolding. These include costs for melting secondary structures and solvent exposing the peptide residues. Our results suggest that in addition to binding affinity, the thermodynamic availability of the peptide is important for sulfation specificity. Our method is expected to be useful in predicting potential sulfation sites. Since we use simple physics-based method, we expect it to be transferable to other TPST variants, and also other post-translational modification systems. [Preview Abstract] |
Friday, November 14, 2014 9:06AM - 9:42AM |
GD.00004: Synthesis of a polymer-magnetic particle platform for ``tailored'' multimodal materials for imaging and treatment Invited Speaker: Thompson Mefford Magnetic nanoparticles have been studied for many years for use in biomedicine, not only for their high surface area, but also because of its unique magnetic properties. This presentation will describe the synthesis of a multi-anchored universal ligand for iron oxide nanoparticles, with improved stability in biological environments, while also providing a platform for additional functionality. The particles reported in this talk were modified with a heterobifunctioal polyethylene oxide (PEO) with an terminal end capable of ``click'' chemistry and nitroDOPA anchors to provide strong binding to the surface and used in a mulitdentate approach provides biocompatibility and enhanced stability in fetal bovine serum and phosphate buffer saline. For demonstration purposes, these colloidally stable biocompatible polymer-particles complexes were then be modified with a near-infrared dyes (e.g. Cy5) In addition to imaging, we have also utilized the same platform for the targeting of di fferent strains of bacteria through ``clicking'' on species-specific moieties. The modified particles adhere to the targeted bacteria strains and agglomerate. Through the application of an alternating field, magnetic energy can be transformed to promote cellular death, resulting in a multi-log reduction in bacteria population. What will be presented represents the initial findings of the research opportunities available with this new platform for diagnostic and therapeutic applications. These universal magnetic nanoparticles can be modified with different fluorescent dyes imaging biofilms, carbohydrates for targeting bacteria, and other moieties for multifunctional diagnostic probes to show the versatility of this design. [Preview Abstract] |
Friday, November 14, 2014 9:42AM - 10:18AM |
GD.00005: TBD Invited Speaker: Robert Camley |
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