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 w ith results from semiempirical and molecular mechanics force field cal culations, 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 result s obtained with some of the other methods, the present ab initio calcu lations show that both the double-type-I beta turn and the double-type -II beta-turn conformer of cyclohexaglycine are stable low-energy stru ctures. (C) 1995 by John Wiley and Sons, Inc.