The effect of isotopic replacement of H by D in peptides and proteins on 13C and 15N NMR chemical shifts is of interest because the magnitude depends on the secondary structure of the residue. This is especially the case for the longer range interactions. This isotope shift can be computed for a specified geometry using a recently developed local mode method that has been shown to provide accurate results for rigid hydrocarbons. In order to determine if this computation is similarly reliable for peptides we investigate small rigid cyclic peptides computationally and by experiment. In the case of peptides there is an additional issue of the effect of hydrogen bonding of the peptide bond on the isotope effect on the chemical shift. This is expected to be of greatest importance for NH/ND isotope shifts. Experimentally hydrogen bonding may be reduced or enhanced by change of solvent. In non-polar solvents cyclic lactams are known to form hydrogen bonded dimers with symmetric structures. These dimeric species, or models of solvent hydrogen bonded peptides, can be used to model the effect of hydrogen bonding on the deuterium isotope chemical shift effect. The figure shows a model for solvated N-methylacetamide that has previously been used (10.1021/j100197a027; 10.1021/JP952729D) for simulation of structure and Raman effects of aqueous solvation. The results of such studies will be presented. 

Hydrogen bonding effects on deuterium isotope chemical shifts for small rigid cyclic peptides

248th National Meeting (2014)

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