STRUCTURE OF AMORPHOUS STARCH .1. AN ATOMISTIC MODEL AND X-RAY-SCATTERING STUDY

A detailed atomistic model for dry amorphous starch was simulated usin g an established method that proved useful for several technical polym ers. Two currently available force fields were tested for their abilit y to simulate carbohydrates. The model structures showed that the inte ractions between the starch molecules are dominated by the interaction s of the polar hydroxyl groups. They built hydrogen bonds, both inter- and intramolecular, and occurred in a wide variety of geometries, inc luding three-center bonds. The model corroborated the high cohesive en ergy density of starch and showed that the latter correlates with the density bf intermolecular hydrogen bonds. The differential radial dist ribution function for amorphous starch was evaluated from X-ray scatte ring measurements as well as from the model structures, and the agreem ent was good up to distances of 6 Angstrom. It was shown that this fun ction is dominated by intramolecular correlations, which overlay the i ntermolecular ones occurring mainly at hydrogen-bonding distances.