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Talk- Shih-Hsein Liu

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  • cmb seminar
When Dec 04, 2017
from 11:00 AM to 12:30 PM
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Molecular Dynamics Simulations of Zinc Therapeutics for Citrus Greening and Poplar Lignin Acetylation for Biomass Breakdown

Citrus greening, also known as huanglongbing (HLB), is a devastating threat to citrus industry in the United States.  HLB is caused by gram-negative bacteria: Candidatus Liberibacter, which are phloem-limited and spread via Asian Citrus Psyllid.  To cure the disease, one of the latest techniques is employing multifunctional surface/sub-surface/systemic therapeutic (MS3T) technology with antimicrobial zinc ions.  The systemic component of MS3T, ternary solutes (TSOL), contains zinc nitrate, urea, and hydrogen peroxide in an aqueous solution.  However, its structure-property relationships have not been fully understood.  To better understand the behavior of TSOL, all-atom classical molecular dynamics (MD) simulations were performed.  The force fields for hydrogen peroxide and zinc ions were re-parameterized to better match their free energy of solvation.  With the force fields for each component ready for simulations, five different initial TSOL configurations were probed in an NPT ensemble.  For each set of initial configurations, the radial distribution functions (RDF) were analyzed after equilibration.  The RDF analyses all reveal strong binding between zinc ion and oxygen in urea as well as no association between zinc ion, which agree with recent FTIR and Raman measurements.  Free energy of binding of urea to zinc ion in solution was also calculated to quantify the stability of urea-zinc complex.  Future studies aim at resolving the interactions of TSOL with lignin and cellulose in plant cell walls and, ultimately, the bacteria in phloem. 


The second part of current research focuses on the effect of poplar lignin acetylation on its behavior in various solution environments: water, tetrahydrofuran (THF), and mixture of water/THF.  The force fields associated with acetylation groups were first parameterized, and classical MD simulations were performed to analyze their radius of gyration (Rg) as a function of time.  Further analyses are being conducted to compare simulation results with small-angle neutron scattering (SANS) experiments to resolve poplar lignin structures for more efficient biomass breakdown.

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