The determination of phi, psi backbone angles of peptides and proteins through spectroscopic means allows for solution phase identification of secondary structural features in these biomolecules. We have employed a strategy for the determination of phi, psi angles that involves strategic single and double isotopic enrichment of amide carbonyl carbon atoms with 13C. For nearest-neighbor, doubly 13C-enriched peptides, carbon-carbon coupling constants , 3J, may be determined via linear (1D) 13C NMR spectroscopy. These coupling constants may be used to determine possible phi values via modern Karplus-type relations. However, these coupling constants do not offer unambiguous phi values. To resolve the ambiguity of phi values, we collect linear (1D) FT-IR spectra of our doubly labeled peptides. These FT-IR spectra, compared against the FT-IR spectra of singly 13C-labeled analogues, allow for the determination of nearest-neighbor coupling constants for the amide oscillators. The nearest neighbor vibrational coupling constants also, in themselves, merely limit the range of phi, and psi angles for peptide structure. However, when combined with NMR data, the ambiguity is resolved. Our method will be demonstrated with applications to several short peptides.

Linear infrared and NMR spectroscopies for the determination of short peptide phi and psi angles

255th National Meeting (2018)

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