Backbone Psi Angle Determination

A direct determination of the backbone angle can be obtained by the tensor correlation of the and C -N +i) vectors. One possibility is to excite the 

DQ coherence between C (,-) and C m and then let the DQ coherence evolve under the influence of the heteronuclear I3C-15N dipole-dipole interaction [181, 182]. The virtue of this design is that it can be easily combined with other resolution enhancement technique such as INADEQUATE [183]. Alternatively, the magnetization of C (,) dephased under the 13C-15N dipolar coupling can be transferred to C (j) for another period of 13C-15N dipolar dephasing [183]. This idea can be combined with the NCOCA experiment so that the superior resolution provided by the C (,-)-N(j+i) correlation could be exploited. The overall efficiency, however, is relatively low due to the use of two polarization-transfer steps, viz. 15N — 13C and 13C — 13C [183]. In comparison with the techniques, the advan- 

1 Echo Formation Between Two Correlated Anisotropic Interactions 

The experimental strategy discussed above was applied to determine the dihedral angle of uniformly 13C and 15N labeled L-alanine and /V-acetyl-o,L-valine (NAV) samples. The 13C C peak intensities of three separate experiments 

---