Semiempirical energy calculations on model compounds of polypeptides. Crystal structures of DL-acetylleucine N-methylamide and DL-acetyl-amino-n-butyric acid N-methylamide
✍ Scribed by Dino R. Ferro; Jan Hermans Jr.
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1972
- Tongue
- English
- Weight
- 736 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
The sum E of the packing and conformation energies of the crystals of Dr,-acetylleucine N-met,hylamide (ALNMA) and I)r~acetyl-ol-amino-n-brrt,yric acid N-methylamide (ABAMA) is calculated as a function of the crystallographic parameters and the corifor- mational angles. The intermolecular energy is assnmed to be the pairwise sum of nonbonded and electrostatic atomic interactions, while both these terms and intrinsic terms describing barriers of internal rotat,ion contribute to t,he intramolecular energy. For ALNMA E is minimized with respect to 18 parameters: the miniomurn found when startingfrom the experimental strnctnre agrees with this within 0.07 A and 3", except, for one angle which deviates by 6"; the aver:ge deviations of the atomic coordinates are = 0.08 A. Another minimum with about the same energy shows slightly worse agreement,. A romparison between different sets of nonbonded fitnctions is made. The predirtioii of conforination and intermolerular packing of ABAMA is attempted on the basis of the knowledge of the iuiit cell and the space group. In agreement with available expeiimeiital data it is fonrid that only one-dimensional arrays of molecules linked by pairs of hydrogeii bonds are ronipal ible with the unit cell. The more stable of two possible c.otifornial,ions of the main chain agrees approximately with the experimental conformatioil. The calcnlation is not conclusive with regard to the side-chain conformation and the packing of non-hydro$eii-bonded molecules.