Conformational analysis of the 20 naturally occurring amino acid residues using ECEPP

Conformational energy calculations using ECEPP (Empirical Conformational Energy Program for Peptides) were carried out on the N-acetyl-N'-methylamides of the 20 naturally occurring amino acids. Minimum-energy conformations were located, and the relative conformational energy, librational entropy, and free energy each minimum were calculated. The effects of intrinsic torsional potentials, intramolecular hydrogen bonds, and librational entropy on relative conformational energies and locations of minima are discussed. The results are categorized most easily by use of a new conformational letter code that is introduced here.