Related Experiment Video
Updated: Jul 31, 2026

Nuclear Magnetic Resonance Spectroscopy for the Identification of Multiple Phosphorylations of Intrinsically Disordered Proteins
Published on: December 27, 2016
19F NMR chemical shifts induced by a helical peptide
Matthew A Kubasik1, Erin Daly, Adam Blom
1Department of Chemistry, Fairfield University, CT 06824, USA. mkubasik@mail.fairfield.edu
Abstract:
(19)F NMR spectra of two neutral, organic-soluble helical peptide octamers, each labeled at its N terminus with either 4-fluorobenzamide or 4-trifluoromethylbenzamide, in solvents with widely varying dielectric constants have been observed. The peptides are oligomers of alpha-aminoisobutyric acid (Aib), which is a residue known to form stable 3(10) helices in organic solution. In relation to the (19)F NMR spectra of a control molecule, the peptide terminating in 4-fluorobenzamide shows a solvent-dependent downfield chemical shift of between approximately 1.5 and approximately 4 ppm, whilst the peptide terminating in 4-trifluoromethylbenzamide shows only an approximately 0.2 ppm chemical shift dependence on the solvent dielectric constant. The experimental observations were compared to calculated values of the electric field generated by the correlation of dipolar amide units through the peptide's helical conformation. We find the chemical-shift response of the 4-fluorobenzamide group to the peptide's calculated electric field is consistent with the magnitude of (19)F chemical shift dispersion observed in proteins.
Related Concept Videos
Proton (¹H) NMR: Chemical Shift
Absorption signals of all the protium nuclei in a...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
NMR Spectroscopy: Chemical Shift Overview
For instance, the proton...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
NMR Spectroscopy Of Amines
Other Nuclides: 31P, 19F, 15N NMR
While fluorine-19 and phosphorous-31 have high natural abundances (100%) and positive gyromagnetic ratios, nitrogen-15 has a low natural abundance and a negative gyromagnetic ratio. However, nitrogen-15 is still preferred over nitrogen-14 (which has a high...

