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ECE PhD Defense: "Study of cellulose hierarchical architecture by x-ray scattering and diffraction pattern simulation," Yan Zhang

25
Jul

540 Holmes

July 25, 2016 9:00 am
July 25, 2016 9:00 am

Abstract:

X-ray scattering is used to study the cellulose hierarchical architecture in native and chemical pretreated maize in three length-scales. USAXS shows that cellulose fibril bundle ∼ 0.1 μm is resistance to deconstruction but by any pretreatment which leads to disorientation. The intermediate fibril ∼ 30 nm is sensitive to acid plus iron by VSAXS data. The cellulose crystallite microfibril size remains unchanged however with increasing amorphous cellulose in dilute acid pretreatment by WAXS study. A multi-angle Guinier analysis supports these results. A highly efficient fast-Debye method is developed to simulate scattering intensities and diffraction patterns from large and complex cellulose molecules. This method sorts interatomic distances into arrays with atom-type labels and use compressed pair-distances with probability mass distribution to represent the whole pair-distances dataset. The number of iterations in Debye formula is significantly reduced. A library of cellulose structures of different shapes, number of chains and twist are simulated by CHARMM program. Their scattering intensities and diffraction patterns are simulated using fast-Debye method, which provides much insight for cellulose microfibril studies. A multi-component model utilizing this library of structures is proposed to calculate the structural weights in native and pretreated maize samples. The library of cellulose structures and intensities is ready for download and will be a contribution to the research community. SXMD data of Arabidopsis stem and Alzeimer’s brain issue are analyzed by clustering methods. The clustering results of large amount of SXMD data clearly show the distribution of molecular constituents and structural heterogeneity in Arabidopsis stem and Alzeimer’s brain tissue. This strategy is shown to reduce the amount of pre-processing work needed to analyze SXMD data.

Advisor: Professor Lee Makowski

Committee:
Professor Lee Makowski
Professor Mark Niedre
Professor Qianqian Fang