Interactions of extracellular polymeric substances with mineral surfaces: Molecular modeling, Fourier transform infrared, atomic force microscopy, and quartz crystal microbalance with dissipation

The structures and energetics of biopolymers interacting with mineral surfaces have been investigated using both theoretical molecular modeling and experimental techniques to understand molecular-level interactions of extracellular polymeric substances (EPS) with mineral surfaces.; A complex mixture of polymers around microbes, EPS, are known important mediators between microbes and surfaces. In particular, extracellular nucleic acids recently have drawn attention as important EPS components in the interactions of EPS and thus microbes with mineral surfaces. Short-range binding features of extracellular nucleic acids with Fe-hydroxides and silica surfaces were characterized with quantum chemical calculations and spectroscopic experiments. Density functional theory (DFT) and IR spectroscopy have shown the formation of ligand exchange reactions between phosphodiester parts of DNA backbones and Fe-hydroxides. Ab initio/DFT calculations and atomic force microscopy (AFM) have shown that hydrogen bonds of phosphate parts of polymers with neutral silica surfaces are stronger than those of other functional groups of polymers.; Characterization of long-range interactions of EPS components with surfaces were also attempted with molecular dynamics (MD) simulations and quartz crystal microbalance with dissipation (QCM-D) monitoring. Dextran was used as EPS components weakly interacting with mineral surfaces. The MD simulations and QCM-D monitoring showed that dextran conformation on the silica surfaces was independent of dextran concentration, whereas dextran on the alumina surfaces experienced several conformation changes as dextran concentration increased.