Amides consistent force field

I lagler A T, E Huler and S Lifson 1977. Energy Functions for Peptides and Proteins. I. Derivation of a Consistent Force Field Including the Hydrogen Bond from Amide Crystals. Journal of the American Chemical Society 96 5319-5327. 

Warshel, Levitt, and Lifson derived a partially optimised consistent force field for amides and lactams (25). It is composed of an alkane part and an amide-part. The former was taken over from analogous earlier calculations for saturated hydrocarbons (17). The potential constants of the amide-part were optimised with the help of a large number of experimental frequencies (taken from TV-methylform amide, acetamide, iV-methylacetamide, and several deuterated species) as well as experimental geometry data for 7V-methylacet-amide. The resulting force field was used for the calculation of vibrational and conformational properties of 2-pyrrolidone, 2-piperidone and e-caprolactam. 

Hagler, A.T., Huler, E., Lifson, S. Energy functions for peptides and proteins. 1. Derivation of a consistent force field including the hydrogen bond from amide crystals./. Am. Chem. Soc. 1974, 96, 5319-5327. 

Lifson S, Hagler AT, Dauben P (1979) Consistent force field studies of intermolecular forces in hydrogen bonded crystals. I. Carboxylic acids, amides and the C-O—H hydrogen bonds. J Am Chem Soc 101 5111-5121... 

S. Lifson, A. T. Hagler, and P. Dauber, /. Am. Chem. Soc., 101, 5111 (1979). Consistent Force Field Studies of Intermolecular Forces in Hydrogen-Bonded Crystals. 1. Carboxylic Acids, Amides, and the C = 0- H Hydrogen Bonds. 

Warshel, A., Levitt, M., Lifson, S. Consistent force field for calculation of vibrational spectra and conformations of some amides and lactam rings. J. Mol. Spectrosc. 33, 84-99 (1970)... 

The families of alkanes, amides and carboxylic acids contain the constituents which comprise most of the amino acid residues of protein chains, and indeed the major motivation for deriving a consistent force field for these families was its potential application for biopolymers. However, a comprehensive consistent force field for biological molecules should include more groups e.g. aromatic and heterocyclic rings, carbohydrate, phosphate and sulfur groups it should also extend considerably the consistent analysis of intramolecular energy parameters pertaining to polypeptide and polynucleotide chains. This could be done fully only if more experimental data could be accumulated to supply the specific needs of the consistent force field analysis. 

These results and conclusions contradicted the results obtained, and concepts adhered to, by quantum chemists, and were consequently either questioned (Schuster, 1976) or ignored by them. Even within the conceptual framework of the consistent force field methodology, one might argue that the amide hydrogen bond is the... 

The second dataset consists of 50 V-acetyl peptide amides (Table 2) these peptides have un-ionizable side chains and have previously been studied by Buchwald and Bodor (28). The three-dimensional structures of the di-peptides were built using the force field and partial charges of Kollman (29) as implemented in Sybyl 6.5.3. The initial random starting conformations were energy minimized in vacuo. For all calculations described herein, the dielectric of the medium was set to unity and the electrostatic cut-off distance was set to 16 A. For each molecule, the Sybyl Genetic Algorithm-based conformational search,... 

---