Department of Chemistry


Date of this Version



Worley B, Richard G, Harbison GS, Powers R (2012) 13C NMR Reveals No Evidence of n2p* Interactions in Proteins. PLoS ONE 7(8): e42075. doi:10.1371/ journal.pone.0042075


Copyright 2012 Worley et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited


An nΠ* interaction between neighboring carbonyl groups has been postulated to stabilize protein structures. Such an interaction would affect the 13C chemical shielding of the carbonyl groups, whose paramagnetic component is dominated by nΠ* and ΠΠ* excitations. Model compound calculations indicate that both the interaction energetics and the chemical shielding of the carbonyl group are instead dominated by a classical dipole-dipole interaction. A set of high resolution protein structures with associated carbonyl 13C chemical shift assignments verifies this correlation and provides no evidence for an inter-carbonyl nΠ* interaction.