HR: 09:15h
AN: B11A-05    [PDF]
TI: Modeling Saccharide, Amino Acid and Organophosphate Adsorption to Silica and Fe-Hydroxides
AU: * Kubicki, J D
EM: kubicki@geosc.psu.edu
AF: The Pennsylvania State University, Dept. of Geosciences, University Park, PA 16802 United States
AU: Kwon, K
EM: kkwon@geosc.psu.edu
AF: The Pennsylvania State University, Dept. of Geosciences, University Park, PA 16802 United States
AU: Campen, R K
EM: campen@geosc.psu.edu
AF: The Pennsylvania State University, Dept. of Geosciences, University Park, PA 16802 United States
AB: Three main types of molecules exist within the extracellular material surrounding bacteria: polysaccharides, proteins and DNA. This study investigated short-range interactions between small-scale, simplified models of each of these types with silica and Fe-hydroxide surfaces. The results suggest that the strongest interaction is that between phosphate groups of DNA with Fe-hydroxides followed by amino acid/silica and polysaccharide/Fe-hydroxide. The interaction of polysaccharides with the silica surface is predicted to be negligible compared to the interaction of silica with water. The polysaccharide dextran (a model for LPS) has little attraction to silica and higher affinity to Fe-oxides. These observations have been explained by ab initio calculations on the H-bonding interactions between the monomer units of dextran and surface functional groups of silica and Fe-hydroxides. The methylated glucose was allowed to interact with both the hydrophilic Si-(OH) groups and the hydrophobic Si-O-Si groups of the same silica cluster in separate energy minimization calculations. The energy of interaction at both types of "surfaces" is less than that calculated for three water molecules interacting with the silica cluster. The affinity of the polysaccharide for Fe-oxides has been observed to depend on the concentration of surface functional groups on a crystal face. Surfaces with higher densities of relatively less acidic Fe-OH terminal groups tend to have higher affinities for this neutral polysaccharide. Consistent with experiment, the affinity of the methylated glucose for the terminal Fe-(OH) groups is higher than that for the bridging Fe-(OH)-Fe groups, but both result in favorable adsorption energies. We also calculated the interaction energy between lysine and silica in a same way as dextran monomer calculation. The minimum energy calculations showed that lysine forms much strong H-bonding (-116 kJ/mol) than dextran monomer (-42 kJ/mol). These preliminary calculations are in qualitative agreement with the colloid-probe AFM results. Energy calculations of a phosphate diester and a Fe-hydroxide dimer show a strong adsorption affinity. Recent work by Whitchurch et al. (2002, Science 295, 1487) has suggested that extracellular DNA is required for biofilm formation under some conditions. This work, combined with the work of Omoike and Chorover (2003, Abstr. ACS, in press), suggests a mechanism for binding DNA to Fe-hydroxides that could explain why extracellular DNA is a pre-conditioning agent for biofilm formation.
UR: http://www.engr.psu.edu/ce/enve/craems/
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting