Figure 2.

Construction principle for obtaining a bilinear rotation element from an INEPT-type transfer element. The principle uses the equivalent of a heteronuclear coupled two-spin system (A) to an offset selective shaped pulse (A') as both interactions describe a rotation in a 3D Hilbert (sub)space. The previously reported construction principle from an effective point-to-point $\mathit{\pi }/\mathrm{2}$ pulse to a universal $\mathit{\pi }$ rotation (B) can then be extended to construct a BIRD bilinear rotation from a reduced INEPT sequence following essentially the same construction procedure (B'). A simple selective excitation scheme (C, top), equivalent to an on-resonant, reduced INEPT element (C', top), will then be constructed to give a selective $\mathit{\pi }$ rotation (D, top) and the corresponding bilinear rotation (D', top), respectively. Introducing a pair of 180° pulses (D', drawn in gray) results in the offset-compensated classical scheme. Corresponding offset and $J$ dependencies of excited coherences and magnetization transfers are given below the sequences. Note that the factor 2 in the offset vs. $J$ dependence results from the rotation frequency of the two interactions. Using a more elaborate INEPT-type transfer element like the reduced COB3-INEPT (E, E') highly $J$ -compensated bilinear rotations can be constructed (F, F'). Note that 30° pulses (drawn in gray) are added to the original COB3-INEPT sequence to ensure the transfer $I_z\to I_x$ for vanishing offsets or $J$ couplings, respectively (E, E', F, F'). Delays are taken from to be ${\mathrm{\Delta }}_{\mathrm{2}}=\mathrm{4.221}$ , ${\mathrm{\Delta }}_{\mathrm{3}}=\mathrm{2.0634}$ , ${\mathrm{\Delta }}_{\mathrm{4}}=\mathrm{2.14}$ , and ${\mathrm{\Delta }}_{\mathrm{5}}=\mathrm{1.075}$ ms.