Inhaltszusammenfassung

An overview of the variety of processes induced by the aluminum cation interacting with carboxyl and carboxylate groups is given by means of quantum chemical density functional theory (DFT) calculations. Different hydration states of Al3+ ranging from the hexaaquo complex down to the unhydrated cation and direct/indirect bonding with the polar groups is considered. The calculations reflect the amphoteric character of the hydrated aluminum complex showing in most cases its acidic...An overview of the variety of processes induced by the aluminum cation interacting with carboxyl and carboxylate groups is given by means of quantum chemical density functional theory (DFT) calculations. Different hydration states of Al3+ ranging from the hexaaquo complex down to the unhydrated cation and direct/indirect bonding with the polar groups is considered. The calculations reflect the amphoteric character of the hydrated aluminum complex showing in most cases its acidic character via proton transfer from the water molecules of the hydration shell to the carboxylate group, but in some cases also deprotonation of the carboxyl group. Several additional processes are observed such as opening of the bidentate bonding and strong hydrogen bonding between proton transfer partners. In addition to the proton transfer processes observed, dry aluminum acts as a strong Lewis acid and initiate electron transfer from the carboxylate groups to the cation at larger intermolecular distances. Comparison with analogous previous investigations on cation bridges induced by calcium and sodium shows the pronounced activity of the triply charged aluminum cation. The importance of the strong polarizing and bridging power of the aluminum cation for soil organic matter with low exchange capacities and a low concentration of charged groups is discussed.» weiterlesen» einklappen

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