Chemical Shifts of Carbonyl Carbons in Peptides and Proteins

Angel C. de Dios, Eric Oldfield

Research output: Contribution to journalArticlepeer-review


We report in this paper the results of an ab initio gauge-including atomic orbital study of the influence of hydrogen-bonding on the carbonyl carbon (13Cʹ) chemical shift in peptides and protein model systems. For N-methylacetamide (NMA) interacting with formamide, the experimentally observed trends of the 13Cʹ shielding tensor elements on hydrogen bond distance in peptides are moderately well reproduced. Shielding computations were also performed on SCF-optimized helical and β-turn N-formylpentaalaninamide structures. Here, we find the calculated helix—sheet chemical shift difference to be 4.9 ppm, with the helical site deshielded, in good agreement with experimental trends observed in proteins, where alanine 13Cʹ helical sites are typically deshielded by ~4.6 ppm when compared with sheet or sheetlike residues. The well-known 13Cʹ helix—sheet chemical shift separation is therefore attributable to hydrogen bond formation, since Φ, Ψ effects alone (in model dipeptides) result in small upfield shifts for 13Cʹ in helical sites. Unlike the situation with Cα, Cβ, NH, and 19F shielding in proteins, ab initio geometry optimization of hydrogen-bonded systems appears to be essential in order to reproduce experimental shift patterns.

Original languageEnglish (US)
Pages (from-to)11485-11488
Number of pages4
JournalJournal of the American Chemical Society
Issue number25
StatePublished - Dec 1 1994

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry


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