PEPTIDE MODELS .12. TOPOLOGICAL FEATURES OF MOLECULAR MECHANICS AND AB-INITIO 8D-RAMACHANDRAN MAPS - CONFORMATIONAL DATA FOR AC-(L-ALA)(4)-NHME AND FOR-(L-ALA)(4)-NH2

Of the nine legitimate diagonal conformational minima (alpha(D) alpha( D) alpha(D) alpha(D), alpha(L) alpha(L) alpha(L) alpha(L), beta(L) bet a(L) beta(L) beta(L), gamma(D) gamma(D) gamma(D) gamma(D), gamma(L) ga mma(L) gamma(L) gamma(L), delta(D) delta(D) delta(D) delta(D), delta(L ) delta(L) delta(L) delta(L), epsilon(D) epsilon(D) epsilon(D) epsilon (D) and epsilon(L) epsilon(L) epsilon(L) epsilon(L)) only six conforma tions (alpha(D) alpha(D) alpha(D) alpha(D), beta(L) beta(L) beta(L) be ta(L), gamma(L) gamma(L) gamma(L) gamma(L), gamma(D) gamma(D) gamma(D) gamma(D), delta(D) delta(D) delta(D) delta(D) and epsilon(D) epsilon( D) epsilon(D) epsilon(D)) could be located by gradient optimization at the HF/3-21G level of theory. The conformational and energetic conseq uences of these findings are discussed in terms of relative stabilitie s, degree of backbone twisting or foldedness, energy of polymerization and density of conformational states.