Hydrogen bonding, electrostatic, and polarization energies were computed for hydrogen-bonded complexes of HF with each of the 20 natural amino acids and also for certain complexes involving two amino acids each. The AM1 method was employed for the calculation of hydrogen bonding energies at the self-consistent field (SCF) level while atomic and hybridization displacement charges obtained by the same method were used to compute the electrostatic and polarization energies. It is found that hydrogen bonding, electrostatic, and polarization energies at different intermolecular distances vary with each other strongly linearly, and so the validity of the lock and key model of enzyme catalysis does not seem to be affected by electrical polarization of the enzyme and the substrate due to their hydrogen bonding. Lowest and highest surface molecular electrostatic potential (MEP) magnitudes near the hydrogen bond accepting and donating sites of the amino acids, respectively, are appreciably linearly related to the corresponding electrostatic interaction energies. Thus it is shown that MEP can be used as a reliable descriptor of hydrogen bonding. However, when more than one hydrogen bond is formed in a given region of a molecule, particularly when a cyclic structure is produced due to hydrogen bonding, only the MEP values near the hydrogen bond accepting and donating atoms would not be sufficient to describe hydrogen bonding reliably. (C) 2000 John Wiley & Sons, Inc.
