Clay complexes Hydrogen bonding

FIGURE 9.2 Neutron-scattering-density profiles p(z) for a lithium-substituted vermiculite. Oxygen plus clay layer is the solid line, hydrogen is the dashed line, and lithium is the stars. The molecular model above shows two sections of clay surface and an undistorted octahedral Li+(H20)6 complex. In this model all six water molecules are hydrogen bonded directly to the clay plate in practice we find that, on average, two of the six water molecules are less strongly oriented toward the plate. 

Fig. 10a-f Examples of the structural motifs of p-ferf-butylcalix[4] arene derivatives a guest-free structure b 1 1 complex c 2 1 host-guest complex d hydrogen-bonded structure with an amine guest e self-inclusion structure f 1 1 host-guest clay mimic structure. (Adopted from [44] with permission)... 

Ward and Upchurch (340) found an inverse relationship between the solubilities of 18 substituted anilines and their adsorption by nylon (R2 = 0.77) and cellulose triacetate (R = 0.80). It was suggested that steric and electronic effects of the molecules were also responsible for the adsorption differences of the compounds. Because of the low solubilities of the substituted anilines, adsorption by organic matter probably occurs at lipophilic sites through dipole-dipole interactions—e.g., hydrogen bonding or charge-transfer complexes. Low adsorption at clay surfaces probably occurs because the hydrophobic molecules do not readily associate with hydrated surfaces. Adsorption of the substituted anilines by dry clays might occur on the soil surface for instance, but in the... 

The adsorption of neutral molecules on smectites is driven by various chemical interactions hydrogen bonds, ion-dipole interactions, coordination bonds, acid-base reactions, charge transfer, and van der Waals forces. Several polar molecules, such as alcohols, amines, and acids, form intercalation complexes with montmorillonites. The intercalation can be performed from the vapor, liquid, or even solid state. In intercalation from solution, solvent molecules are generally coadsorbed in the interlayer space. Guest molecules may be intercalated in dried clay minerals or may displace the water molecules of hydrated montmorillonite. 

It is for this reason that hydrogen-bonded complexes and coacervates are formed mainly in the pH range 1-4, and especially 1.5-3.0. Also, this explains why this t>7< of attachment does not occur with the surface of colloidal aluminosilicates such zs clays and zeolites. These materials combine with nonlonic polar organic molecules, including proteins, only if the aluminum has been extracted first from the silica surface by a strong acid, or if the mineral surface is coated with a film of relatively pure silica. 

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