Formation constants for complexation between atrazine and four hydrogen-bond donors and four acceptors are obtained by linear regression of nuclear magnetic resonance chemical shift data. Since the donors and acceptors were selected from among the compounds used to establish relative hydrogen-bonding scales, these formation constants provide a measure of atrazine's relative donating (am) and accepting (¡3m) parameters. The calculated parameters (am = 0.42; /3m = 0.49) show that atrazine has intermediate reactivity toward donating and accepting hydrogen bonds with monofunctional complexing agents.
Abstract--This paper describes structural models of four pyrophyllite edge faces: {010}, { 110}, { 100}, and { 130}. Water molecules chemisorbed to Lewis acid sites stabilize edge faces both crystallochemically and electrostatically. The detailed assignment of protons to surface oxygens and the orientation of OH bond-vectors both influence the surface Coulomb energy.The geometry chosen for the electrostatic calculations was infinite pyrophyllite ribbon the thickness of a single phyllosilicate layer and the width of 50 to 70 unit cells. Such a phyllosilicate ribbon has only two edges, a top and bottom, which were simulated using the edge-face models mentioned above. About 94% of the surface Coulomb energy is confined to the edge-face repeat unit. The surface Coulomb energies of the four edge faces are on the order of 2-3 n J/m, varying + 1 nJ/m with proton assignment. The Coulomb potential, measured either within the layer or parallel to the layer, has a distinct negative trend near the edge face that can be traced to chemisorbed water molecules. Finally, the correlation between proton Coulomb potentials at the edge face and the coordination environment of the protons is poor, obscured by long-range interactions.
Formation constants are determined for hydrogen-bond complexes between atrazine and compounds commonly found in soil organic matter. Weak to moderately strong complexes (K¡ = 2-30 L/mol) are formed with amine, hydroxyl, and carbonyl functional groups. Strong complexation is observed with the carboxylic acid (K{ = 212 L/mol) and amide (K¡ = 276 L/mol) functional groups, which interact cooperatively with atrazine by simultaneously donating and accepting a hydrogen bond. These results confirm that hydrogen bonding provides a mechanism for atrazine adsorption to soil surfaces and identifies functional groups that have high affinity for atrazine.
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