Strength of a bifurcated H bond

Esther S. Feldblum, Isaiah T. Arkin*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

105 Scopus citations


Macromolecules are characterized by their particular arrangement of H bonds. Many of these interactions involve a single donor and acceptor pair, such as the regular H-bonding pattern between carbonyl oxygens and amide H +s four residues apart in a-helices. The H-bonding potential of some acceptors, however, leads to the phenomenon of overcoordination between two donors and one acceptor. Herein, using isotope-edited Fourier transform infrared measurements and density functional theory (DFT) calculations, we measured the strength of such bifurcated H bonds in a transmembrane a-helix. Frequency shifts of the 13C=18O amide I mode were used as a reporter of the strength of the bifurcated H bond from a thiol and hydroxyl H+ at residue i + 4. DFT calculations yielded very similar frequency shifts and an energy of -2.6 and -3.4 kcal/mol for the thiol and hydroxyl bifurcated H bonds, respectively. The strength of the intrahelical bifurcated H bond is consistent with its prevalence in hydrophobic environments and is shown to significantly impact side-chain rotamer distribution.

Original languageAmerican English
Pages (from-to)4085-4090
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number11
StatePublished - 18 Mar 2014


  • FTIR
  • Membrane proteins
  • Protein structure


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