Abstract

MONAJJEMI, Majid; MOLLAAMIN, Fatemeh  and  KARIMKESHTEH, Tahereh. Ab Initio Study and Hydrogen Bonding Calculations of Nitrogen and Carbon Chemical Shifts in Serine-Water Complexes. J. Mex. Chem. Soc [online]. 2005, vol.49, n.4, pp.344-352. ISSN 1870-249X.

The hydrogen bonding (HB) effects on the NMR shielding of selected atoms in a few Ser-nH₂O complexes have been investigated with quantum mechanical calculations of the ¹⁵N and ¹³C tensors. Interaction with water molecules causes important changes in geometry and electronic structure of serine. Chemical shift calculations, geometry optimization and energies have been performed with ab ini-tio method at HF/6-31G* and HF/6-31G** levels with magnetic properties of the gauge-including atomic orbital method. There is evidence that intermolecular effects are important in determining the ¹⁵N chemical shifts of free amino acid residue, to assign principal axes of the tensors, and some systematic trends appear from the analysis of the calculated values. Formation of each interaction (in ten orientations) results in a change of the bridging hydrogen's chemical shifts of N...H bond that indicate the most stabilized compound. The C"H...O bond plays an important role in the interactions of amino acids residue upon the structure and function of a protein. This paper represents comparison between theoretical and experimental values of NMR resonances. Calculations at HF/6-31G** level produce results in better agreement with the experimental data.

Keywords : Isotropy and Anisotropy; chemical shift; ab initio serine; C^aH...O; hydrogen bonding.

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