REPARAMETRIZATION OF FORCE-CONSTANTS IN MOPAC-6.0 7.0 FOR BETTER DESCRIPTION OF THE ACTIVATION BARRIER OF PEPTIDE-BOND ROTATIONS/

We have parametrised the force constants in AM1 and PM3 for better des cription of activation barriers of peptide bond rotations. A new keywo rd MMOP was introduced for special recognition of peptide bonds preced ing a proline residue or other N-dialkyl substituted amides. The bug i n the original MOPAC was corrected where in the case of amides where t he nitrogen atom is linked to two hydrogens the force field correction term is counted twice. The new parametrisation of the force constants for peptide bond rotations leads to more realistic rotational barrier s of peptide bond rotations. The PM3 optimised pyrrolidine ring in pro line adopts no longer a pyramidalised nitrogen atom but a more sp(2)-h ybridised flat peptide bond geometry.