The determination of φ, ψ 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 φ, ψ angles combining 13C NMR and FT-IR spectroscopy, involving the 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 ψ values. To resolve the ambiguity of ψ values, we collected linear (1D) FT-IR spectra of doubly 13C-labeled peptides. These FT-IR spectra, compared against the FT-IR spectra of singly 13C -labeled analogs, 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 ψ angles for peptide structure. However, when combined with NMR data, the ambiguity is significantly reduced. Our method will be demonstrated with applications to several short peptides.

Linear infrared and NMR spectroscopies for the determination of φ, ψ angles in peptides and proteins

2019 Spring National Meeting

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