PEPTIDE MODELS .7. THE ENDING OF THE RIGHT-HANDED HELICES IN OLIGOPEPTIDES [FOR-(ALA)(N)-NH2 FOR 2-LESS-THAN-OR-EQUAL-TO-N-LESS-THAN-OR-EQUAL-TO-4] AND IN PROTEINS

The right-handed helical conformation (denoted as alpha(L)) of a singl e amino-acid diamide (e.g. HCO-NHCHCH3CO-NH2) is not a minimum energy conformation on the ab initio potential energy surface. Computations p erformed on oligopeptides [For-(Ala)(n)-NH2, for n less than or equal to 4], revealed that the helix-like conformations do exist if the back bone conformation at the carboxyl-end is of delta L type; i.e. (alpha( L))(n-1)delta(L). This suggests that according to SCF computations, th e isolated helices end in a type I beta-turn (alpha(L) beta(L)).