AB-INITIO SCF CALCULATIONS ON LOW-ENERGY CONFORMERS OF CYCLOHEXAGLYCINE

Results from ab initio self-consistent field (SCF) calculations with a 3-21G and a double-zeta-plus polarization (DZP) basis set on four low-energy conformations of cyclohexaglycine are reported. In agreement with results from semiempirical and molecular mechanics force field calculations, the lowest-energy conformation found at the DZP level is a conformation forming six C-7 turns. However, the energy difference to the beta-turn conformers is significantly smaller at the ab initio DZP level than calculated by the other methods. In contrast to the results obtained with some of the other methods, the present ab initio calculations show that both the double-type-I beta turn and the double-type-II beta-turn conformer of cyclohexaglycine are stable low-energy structures. (C) 1995 by John Wiley and Sons, Inc.