Empirical ³J_HN-HA values and angular backbone constraints can be interconverted following well-known Karplus relationships:

³J_HA-N=-0.88*cos²(psi+60) - 0.61*cos(psi+60) - 0.27 ( 95JACS1810 )
³J_HA-N=-1.00*cos²(psi-120) + 0.65*cos(psi-120) - 0.15 (01JMR75-153)

where psi is the backbone torsion angle.

The expected ³J_HA-N coupling constant values found iin the secondary structure of proteins are:

• Alpha-helix: -1,4/-1.8 Hz
• 3₁₀-helix: -1.1 Hz
• Beta-strand: +0.1/-0.5 Hz

• E.COSY-type experiments
  3D HN(CO)CA-E.COSY experiment ( 94JMRB172-104 ) for ¹³C-¹⁵N labeled proteins in H₂O.
  3D TROSY-based HN(CO)CA[HA]-E.COSY experiment (01JMR75-153) for ¹³C-¹⁵N labeled proteins in H₂O.
  2D H(CA)CO[N]-E.COSY experiment ( 95JACS1810 ) for ¹³C-¹⁵N labeled proteins in D₂O
  3D HCA(CO)N-E.COSY experiment for ¹³C-¹⁵N labeled proteins in D₂O ( 98JACS6824 ).
• Quantitative J-correlation
  3D HNHB experiment.
• Spin-State selective Excitation.
  97JB181-10
  a/b-HN(CO)CA-J TROSY experiment ( 00JMR255-146 )