The 2D NOESY-TOCSY (NOTO) experiment is an hybrid experiment
consisting of consecutive NOESY and TOCSY building blocks. In the first
step, magnetization is transferred between protons via NOE and in the second
step, such magnetization is propagated via the scalar J coupling.
REQUIREMENTS
Easy implementation on AVANCE spectrometers.
VERSIONS
The basic pulse sequence of the NOESY-TOCSY experiment consists
of a conventional 2D NOESY pulse sequence followed
by a TOCSY building block
(
88ANG564
and
88MRC919
).
A related 2D ROESY-TOCSY experiment
(
88JMR401-77
and
88MRC919
)
has been proposed by replacing the NOESY mixing time by a ROESY
mixing time.
The 2D NOESY-TOCSY experiment can be recorded in routine/automation
modes. The most important parameter to consider is the length of the
the TOCSY and NOESY mixing periods. See 2D NOESY
and 2D TOCSY experiments for more details.
In the NOTO experiment, the two-step magnetization transfer
from a spin 1 (in F1) via spin 2 to a spin 3 (in F2) requires a NOE transfer
between 1 and 2 and a J-coupling between 2 and 3. However, the requeriments
for a transfer from spin 3 (in F1) via spin 2 to a spin 1 are different.
Thus, cross-peaks are asymetric with respect to the diagonal. Since both
NOESY and TOCSY sequences generate in-phase magnetization, the cross-peaks
will exhibit in-phase structures in both dimensions and, therefore, the
NOTO experiment is insensitive to cancellation effects. The coherence
transfer during the TOCSY spin-lock period is not limited to a single transfer
step; depending on the length of the mixing time multi-steps transfers
can also be observed. However, if the TOCSY mixing time is long enough,
cross-peaks can arise from several sifferent pathways of magnetization
transfer and, therefore, the interpretation of the resulting spectrum will
be more difficult.
