Peptide models XXIX. cis-trans Isomerism of peptide bonds: ab initio studyon small peptide model compound; the 3D-Ramachandran map of formylglycinamide

Thermodynamic separations for cis and trans-amides and formylglycinamide ra nge from 0.00 to 4.77 kcal/mol as computed at various levels of theory. The barriers for trans --> cis-isomerization, for the same set of compounds, c omputed at various levels of theory, were found between 15.69 and 22.67 kca l/mol. The cis- and trans-Ramachandran maps of formylglycinamide are compar ed and the topology of the ab initio 3D-Ramachandran map is presented for t he first time. (C) 2000 Elsevier Science B.V. All rights reserved.