Relation between calculated amide frequencies and solution structure in Ala-X peptides
✍ Scribed by Robert W. Williams; James L. Weaver; Alfred H. Lowrey
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1990
- Tongue
- English
- Weight
- 915 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0006-3525
No coin nor oath required. For personal study only.
✦ Synopsis
Computational techniques have been used to aid interpretation of observed systematic shifts in the amide I11 frequencies of Ala-X peptides. Optimized structures and frequencies have been calculated for Ala-X peptides using GAUSSIAN86/88 with the 4-31G basis, MOPAC, and normal mode methods based on empirical force fields. We observe the fol- lowing: ( 1 ) Frequencies calculated using scaled GAUSSIAN86 force constants correlate well with the experimental results. ( 2 ) Structures of the Ala-X peptides optimized by GAUSSIAN show a clear trend toward lower values of the dihedral angle 4 as the X side chain becomes larger, while structures optimized here using semiempirical and empirical force fields do not show trends. ( 3 ) Computational changes in peptide conformations from @-sheet to a-helix produce large changes in both amide I and amide I11 frequencies that are inconsistent with the experimental results. ( 4 ) Computational changes in the dihedral angle 4 of Ala-Ala produce a change in the amide I11 frequency consistent with the experimental results. ( 5 ) The experimental frequency shifts cannot be attributed directly to the effects of changing mass.