engleski

Hydrogen Bond Influence on CSA in Model Peptide

Density Functional Theory (DFT) calculations have been used to explore the hydrogen bond influence on chemical shielding anisotropy (CSA) tensors in peptide model, N-methylacetamide hydrogen-bonded with a formamide. B3LYP functional with 6-311G(d, p) and 6-311+G(3df, 3pd) basis sets were employed for geometry optimization and NMR parameters calculation, respectively. The gauge origin problem in NMR parameter calculations was treated by the Gauge Included Atomic Orbital (GIAO) approach. All calculations were completed with Gaussian 98 program package. The influence of the hydrogen bond geometry (including hydrogen bond length, hydrogen bond angles and out-of-plane angles) on the CSA tensors of the amide proton, as well as the N-15 and C-13 backbone atoms are assessed. The results indicate that the CSA tensors depend strongly on the hydrogen bond length, while weaker dependence is found for the angles.

hydrogen bond; CSA; peptide model

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