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United States Department of Agriculture

Agricultural Research Service

2010 Annual Report

1a.Objectives (from AD-416)
The goal of this research is to develop new biobased materials from starch and new fundamental knowledge of their properties. Objectives of this work fall into three topic areas: materials development, molecular modeling and simulations, and analysis techniques.

1b.Approach (from AD-416)
Develop new biobased materials from starches with novel properties, utilizing the inherent properties of starch so that it is an active component rather than a low cost, biodegradable filler. Develop molecular modeling tools for use in rational design approaches. Develop novel sophisticated instrumental analytical techniques to characterize the structures and properties of multicomponent biobased materials.

3.Progress Report
ARS Scientists determined structure-function properties of agriculturally based polymers. The co-products of a food-grade lactic acid bacterium, Leuconostoc mesenteroides, is becoming increasingly important as a source of enzymes, carbohydrates, and polymers. Specifically, we studied NRRL B-1355 exopolysaccharide as a corrosion inhibitor but the far-ranging applications could be biosensors, environmentally sensitive membranes, artificial muscles, actuators, electronic shielding, visual displays, solar materials, and components in high-energy batteries. Our goal was to describe the formation of bio-based coatings on metal substrates. A thermodynamic perspective of polysaccharide film formation creates a universal mainframe for the interpretation of properties. This description takes into account macroscopic variables such as temperature and polymer concentration to study energy conversions during polymer chain deposition on substrates. Atomic force microscopy (AFM) measurements provide accurate evidence of amount and topography of deposition while attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR) complementarily allows for direct measurement of energy of formation with noticeable temperature dependence. Molecular modeling tools were optimized and used to describe the hydration behavior of the building blocks of bio-base polymers. Studies were carried out using a reduced basis set discovered in this laboratory to enhance the speed of Density Functional Theory (DFT) computations significantly. Glucose (as the base molecule) as well as cellobiose, iso-maltose, amylose, and cyclodextrins were hydrated (solvated) implicitly and explicitly and then optimized for their energetically favored configuration(s). Another application of molecular modeling provided structure information about an agriculturally important pheromone. The experimental studies cannot unambiguously determine which of the hundreds of possible conformations of the chemical structure are bio-active. The models were used to predict the NMR spectra for the conformers, and a direct comparison to the experimental NMR results confirmed that the structures chosen likely correspond to the actual molecule. Four separate ring conformations found to be important, and calculations were performed to confirm that it is possible for the molecule to convert between these conformations at room temperature. Knowledge of the precise structure of the molecule is important in biological systems, as it is believed that the insect responds to one particular conformation of the pheromone molecule. The ability to synthesize this molecule will allow scientists to monitor where the beetles are present, and learn more about their habits and populations. This type of analysis was used to aid ARS Scientists to find solutions to practical problems.

1. ARS scientists demonstrated that thin, nanoscale, biobased polymer coatings provided protection to steel substrates in corrosive environments such as salt and acid and provided fundamental information regarding film formation and integrity. They showed that films could be self-repairing in aqueous environments and described the fundamental properties of thin exopolymer films including thermodynamic properties, film-formation kinetics, and diffusion characteristics. The anticorrosive coatings are produced from renewable resources and are nontoxic. Corrosion of metals is a serious and challenging global problem faced by industry. Many anticorrosive systems are hazardous and breakdown quickly once the coating is damaged. This work may help by providing environmentally friendly additives or coatings that self-repair to prevent corrosion of metals.

2. ARS scientists determined the exact structure of agriculturally important molecules (such as pheromones) using sophisticated molecular modeling tools. There are several different structures proposed for the pheromones, and ARS scientists determined the active structure that gives rise to the biologically active component. This work will assist organic chemists to synthesize similar molecules to serve the same purposes, perhaps more efficiently than the naturally occurring pheromones.

Review Publications
Finkenstadt, V.L., Tisserat, B. 2010. Poly(lactic acid) and Osage Orange Wood Fiber Composites for Agricultural Mulch Films. Industrial Crops and Products. 31(2):316-320.

Schnupf, U., Willett, J.L., Momany, F.A. 2010. DFTMD Studies of Glucose and Epimers: Anomeric Ratios Rotamer Populations, and Hydration Energies. Carbohydrate Research. 345(1):503-511.

Last Modified: 7/2/2015
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