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United States Department of Agriculture

Agricultural Research Service


Location: Plant Polymer Research

2013 Annual Report

1a. Objectives (from AD-416):
The long-term objectives of this project are to develop new technologies and knowledge to enable expanded growth of biobased materials, new market opportunities for agricultural products, and reduced environmental impact. Objective 1: Develop and characterize electroactive materials from natural polymers that enable commercially viable technologies. Objective 2: Develop and characterize stimulus-responsive starch-based materials that enable the commercially viable technologies. Objective 3: Develop cutting-edge computational tools for starch and other natural polymers using density functional theory and empirical energy approaches that enable development of new technologies.

1b. Approach (from AD-416):
Develop new biobased materials with novel properties from starch-based commodities. Novel properties include electroactive and stimuli-responsive polymeric materials. Develop molecular modeling tools for use in rational design approaches.

3. Progress Report:
Examining the structure of glucose in the presence of water by density functional theory (DFT) has shown that no single site on glucose retains a water molecule for more than a couple of picoseconds. This is an important result because if a water molecule resides for any length of time at a particular site it could change the properties of the molecule so that its biological function would be modified. A degree of polymerization (DP)-3 molecule dimer optimization density functional theory (DFT) study is completed that will assist in understanding the formation of the amylopectin double helix found in corn. Two DP-3 dimers were optimized using our DFT methods. Our initial study using the basis set without dispersion showed a particular loosely bound configuration to be of lowest energy. However, upon further analysis we found that DFT methods with dispersion gave different, more compact configurations, as having lowest energy. This result, that dispersion parameters are required to give the correct results when evaluating the structure of dimers, was confirmed by utilizing additional methods. A density functional theory (DFT) optimization and molecular dynamics-DFT study on glucose dimers using both explicit and implicit solvents was completed. We showed that there are timing differences between explicit and implicit solvation methods, with explicit waters holding bridging positions for longer times during dynamics. It is important to understand how explicit and implicit models differ in order to use the method that is best suited for the problem. In our study the dissociation of the dimers into monomers was very different. This is due to special explicit bridging water molecules between molecules which slow down dimer dissociation more than the implicit model in which the water is treated like a dielectric medium and cannot form bridging interactions. It has been determined that biochar could be added to insulative materials, such as biobased plastics, in order to modify its electrical properties. Biochar is the carbon material produced during pyrolysis of agricultural fibrous material. Impedance analysis showed a critical concentration limit (maximum) where no further gains in conductance occurred. The addition of biochar also had an effect on the physical properties of the biobased polymers.

4. Accomplishments
1. Developing an improved understanding of the structure of starch in water. ARS Plant Polymer Research scientists at the National Center for Agricultural Utilization Research, Peoria, Illinois, examined the structure of water as it interacts with glucose (single building block of starch), oligomers (multiple glucose units), and starch (many oligomers) using sophisticated computer modeling. The chemical or biological function of starch changes in the presence of water. Examining the structure of glucose in the presence of water by computer modeling has shown that water moves around a glucose molecule very quickly. The structure of starch and its bound water determines its interaction with enzymes in the laboratory, the production plant and living organisms. This information will be of value to scientists and companies that are involved with the conversion of starch into ethanol or other value added products through the development of new chemical reactions or selection of optimized enzymes.

2. Use of biochar to improve the conductivity of plastics. Petroleum based carbon black is known to change the electrical properties of materials, including plastics, to give desired levels of conductivity. Biochar is a relatively new material that is made using renewable materials. Biochar has not been investigated as a domestic, renewable replacement for carbon black to produce conductive plastics. ARS Plant Polymer Research scientists at the National Center for Agricultural Utilization Research Peoria, Illinois, have demonstrated that biochar can be incorporated into biobased polylactic acid and its electrical properties are improved.

Review Publications
Schnupf, U., Momany, F.A. 2012. COSMO-DFTr study of cellulose fragments: Structural features, relative energy, and hydration energies. Computational and Theoretical Chemistry. 999(1):138-151.

Last Modified: 05/28/2017
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