Theoretical study of blocked glycine and alanine peptide analogs

• Published in: Journal of the American Chemical Society Vol. 113; no. 16; pp. 5989 - 5997
• Main Authors: Head-Gordon, Teresa, Head-Gordon, Martin, Frisch, Michael J, Brooks, Charles L, Pople, John A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-07-1991
• Subjects: Ab initio calculations; alanine; Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Electronic structure of atoms, molecules and their ions: theory; Exact sciences and technology; Physics; Theoretical study; Molecules; Peptides; Molecular structure; Ab initio method; Organic compounds
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00016a010

We present a high-level ab initio study of the model blocked alanine and glycine dipeptide molecules, (S)- alpha -(formylamino)propanamide and alpha -(formylamino)ethanamide. Fully relaxed grids of the conventionally defined conformational space variables Phi and psi have been evaluated for each molecule at the HF/3-21G level. In order to obtain the best results currently feasible, HF/6-31+G super(*) fully optimized geometries and frequencies were obtained for all minima and transition structures observed on the HF/3-21G grid, and correlation corrections were explored with MP2/6-31+G super(**)//HF/6-31+G super(*) single-point energy calculations. The HF/3-21G structures are in reasonable agreement with the results of the larger basis, although the relative energies are sometimes poor.