Relationship of hydrogen bonding energy with electrostatic and polarization energies and molecular electrostatic potentials for amino acids: An evaluation of the lock and key model

Hydrogen bonding, electrostatic, and polarization energies were computed fo r hydrogen-bonded complexes of HF with each of the 20 natural amino acids a nd also for certain complexes involving two amino acids each. The AM1 metho d was employed for the calculation of hydrogen bonding energies at the self -consistent field (SCF) level while atomic and hybridization displacement c harges obtained by the same method were used to compute the electrostatic a nd 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 polarizatio n of the enzyme and the substrate due to their hydrogen bonding. Lowest and highest surface molecular electrostatic potential (MEP) magnitudes near th e hydrogen bond accepting and donating sites of the amino acids, respective ly, are appreciably linearly related to the corresponding electrostatic int eraction energies. Thus it is shown that MEP can be used as a reliable desc riptor of hydrogen bonding. However, when more than one hydrogen bond is fo rmed 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 hydro gen bonding reliably. (C) 2000 John Wiley & Sons, Inc.