Hydrogen bonding, soil adsorption

Alcohols are hydroxylated alkyl-compounds (R-OH) which are neutral in reaction due to their unionizable (OH) group (e.g., methanol, ethanol, isopropanol, and w-butanol). The hydroxyl of alcohols can displace water molecules in the primary hydration shell of cations adsorbed onto soil-solid and sediment-solid clay particles. The water molecule displacement depends mainly on the polarizing power of the cation. The other adsorption mechanisms of alcohol hydroxyl groups are through hydrogen bonding and cation-dipole interactions [19,65],... 

Adsorption of nonionic compounds on subsurface solid phases is subject to a series of mechanisms such as protonation, water bridging, cation bridging, ligand exchange, hydrogen bonding, and van der Waals interactions. Hasset and Banwart (1989) consider that the sorption of nonpolar organics by soils is due to enthalpy-related and entropy-related adsorption forces. 

Three types of adsorption occur between the macromolecule of the soil and pesticide compounds chemical, physical, and hydrogen bonding. 

Adsorption. Monomeric silica can be removed from solution by adsorption onto surfaces of sesquioxide minerals (e.g., AljOa, FejOa) through pH-dependent reactions that apparently involve hydrogen bonding (see Jones and Handreck, 1967, and references therein) such reactions, especially with AI2O3, seem to exert a major control over the concentration of dissolved silica in soil solutions. 

Adsorption water accounts for water molecules bound to the soil particle surfaces by electrostatic forces, hydrogen bonds and van der Waals forces. 

Moderate amounts of acidic pesticides were adsorbed to organic soil colloids, such as are present in muck soils, (51,143,147,175, 179) and to charcoal (53, 57,147,182,183). For both adsorption depended upon pH, being greater under acid conditions where the pesticides were adsorbed in the molecular form. The compounds were readily desorbed from the adsorbents with water (51, 57). Adsorption probably occurred through hydrogen bonding or weak physical adsorption. 

The adsorbing of bromacil by soil organic matter relative to several other herbicides is shown in Figure 11. The compound was adsorbed in low amounts, probably as a result of its high solubility. The pH of the system was approximately 5.7, so bromacil was present predominantly in the molecular form and was probably adsorbed through hydrogen bonding or other physical adsorption forces. 

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... 

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