PFG-ω₁-Filtered TOCSY Experiments for the Determination of Long-Range Heteronuclear and Homonuclear Coupling Constants and Estimation of J-Coupling "Crosstalk" Artifacts in 2-D ω₁-Filtered "E. COSY-Style" Spectra

We present novel one- and two-dimensional versions of the ω₁-filtered TOCSY experiment. These experiments utilize pulsed-field gradient techniques and INEPT-reverse INEPT magnetization transfer to generate heteronuclear filtering by means of coherence pathway selection. The major advantages of this approach are twofold: first, each experiment requires a reasonable number of transmitter pulses, gradient pulses, and delays to implement. Second, the use of z-axis gradients at the beginning and termination of the pulse sequences prevents the recovery of dephased magnetization prior to FID detection. This technique was incorporated into 1-D and 2-D ω₁-filtered J_XH- and J_HH-TOCSY-style experiments. As demonstrated on ¹⁵N-enriched peptide samples, the use of the pulsed-field-gradient coherence selection scheme effectively filters out unwanted magnetization components, thereby improving the overall sensitivity of the experiments. In addition to this suite of pulse sequences, we also present a method for correcting the reduction in J-coupling that results from crosspeak shifting in 2-D ω₁-filtered E. COSY-style spectra. This correction is applicable to both Lorentzian and Gaussian 2-D crosspeak lineshapes.