Ab Initio Study and Hydrogen Bonding Calculations of Nitrogen and Carbon Chemical Shifts in Serine-Water Complexes

Abstract

Recibido el 18 de junio del 2005; aceptado el 30 de noviembre del 2005 Abstract. The hydrogen bonding (HB) effects on the NMR shielding of selected atoms in a few Ser-nH2O complexes have been investiga- ted with quantum mechanical calculations of the 15 N and 13 C tensors. Interaction with water molecules causes important changes in geo- metry 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 pro- perties of the gauge-including atomic orbital method. There is eviden- ce that intermolecular effects are important in determining the 15 N 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 indi- cate the most stabilized compound. The C α 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.