AM‐1 molecular orbital calculations of silica–alanine–nitrogen interaction

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Abstract
Chemical binding of proteins with bioactive surfaces is modeled using a semi‐empirical molecular orbital theory (AM‐1). The model calculates the optimized molecular structures of an amino acid (L‐alanine) interacting with a cyclotetrasiloxane silica cluster (a four‐membered hydrated silica ring). The calculated heats of formation for various orientations of alanine show +5 kcal/mol difference for binding via the −NH2 group following a condensation reaction with a pentacoordinate Si intermediate. Hydrogen bonding of the alanine via the COOH group occurs with +13 to +15 kcal/mole differences in heats of formation and imposes a highly specific geometric orientation on the amino acid. Association of a diatomic N2 molecule with the silica cluster before interaction with alanine inhibits formation of an intermolecular bond, as is observed experimentally in studies of silicaalanine epitaxy. © 1994 John Wiley & Sons, Inc.