Scaled quantum mechanical force field for alanyl-alanine peptide in solution.
We have obtained ab initio scale factors and assigned frequencies for the alanine-alanine peptide in water. Calculations were performed on the isolated acidic and basic Ala-Ala structures, two one-water basic Ala-Ala supermolecules, and one two-water acidic and one two-water basic Ala-Ala supermolecules. Force constants were scaled using the experimentally determined Raman and Fourier transform infrared vibrational frequencies of four isotopic species of Ala-Ala in water at pH 13 and pH 1. Most of the 4-31G scale factors were transferable from smaller molecules. All but one scale factor were directly transferable between the pH 1 and pH 13 species for coordinates unchanged by protonation in both the isolated and two-water supermolecule structures. Scale factors for nonpolar coordinates were transferable between all Ala-Ala species with only a few small changes. Good agreement was obtained between the calculated and experimental frequencies for all isotopic species and structures.
Weir
A F
AF
Department of Bioinformatics, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA.
Lowrey
A H
AH
Williams
R W
RW
D004151:Dipeptides / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman
D004151:Dipeptides; D012996:Solutions; C002956:alanylalanine