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| - Torsion Angle Determination in Solid 13C-Labeled AminoAcids and Peptides by Separated-Local-Field Double-QuantumNMR
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| - A novel two-dimensional double-quantum NMR technique fordetermining the torsion angle ψ in doubly-13C-labeled amino acid residues of solid peptides ispresented. The intensity pattern in the two-dimensionalNMRspectrum reflects the orientation of the Cα−H bond withrespect to the carbonyl moiety, by correlating theCα−Hdipolar coupling with the CO chemical-shift anisotropy. Thisapproach eliminates problems caused by13C−14Ndipolar couplings and the relatively small chemical-shift anisotropy ofthe Cα carbon in two-dimensional double-quantum spectra based only on chemical-shift anisotropies. Thedouble-quantum selection achieves isolated-spinbackground suppression and increases the spectral resolution bypartially removing the inhomogeneous spectralbroadening. The experiment is demonstrated on13Cα−13CO-labeled leucine.With 50 mg, a useful spectrum wasobtained in 3 h. The potential of the technique for distinguishingdifferent secondary structures in peptides isdemonstrated by spectral simulations.
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