MODELING SORPTION OF SOIL ORGANIC-MATTER ON MINERAL SURFACES - WOOD-DERIVED POLYMERS ON MICA

Molecular mechanics and molecular dynamics calculations were carried o ut on model organo-mineral composites typical of both paper products a nd soil. Sorption energy of neutral model linear chains of lignin, car bohydrate, and humic substances on muscovite mica depends on the mutua l orientation of organic and mineral components, spatial organization and functionality of the organic chain, and the presence of metal cati ons. Carbohydrates are characterized by their higher affinity towards the mineral surface than the more flexible helical aromatic polymers. In the model calculations, sorption energies are twice as high. Oxidat ion of lignin into respective humic acids does not lead to better sorp tion. Unlike metal cations, water molecules interlacing between organi c and mineral surfaces do not act as bridges and sharply decrease sorp tion energy. Flexible linear polymers may undergo drastic conformation al changes when approaching the mineral surface, to ensure a gain in t he interaction energy that more than compensates a loss in the conform ational energy proper. (C) 1998 Elsevier Science Limited.