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.
Department of Bioinformatics, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA.
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Weir
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Lowrey
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Williams
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