5 research outputs found
Long-Lived Nuclear Singlet Order in Near-Equivalent <sup>13</sup>C Spin Pairs
Molecules that support <sup>13</sup>C singlet states
with lifetimes
of over 10 min in solution have been designed and synthesized. The <sup>13</sup>C<sub>2</sub> spin pairs in the asymmetric alkyne derivatives
are close to magnetic equivalence, so the <sup>13</sup>C long-lived
singlet states are stable in high magnetic field and do not require
maintenance by a radiofrequency spin-locking field. We suggest a model
of singlet relaxation by fluctuating chemical shift anisotropy tensors
combined with leakage associated with slightly broken magnetic equivalence.
Theoretical estimates of singlet relaxation rates are compared with
experimental values. Relaxation due to antisymmetric shielding tensor
components is significant
Long-Lived Nuclear Singlet Order in Near-Equivalent <sup>13</sup>C Spin Pairs
Molecules that support <sup>13</sup>C singlet states
with lifetimes
of over 10 min in solution have been designed and synthesized. The <sup>13</sup>C<sub>2</sub> spin pairs in the asymmetric alkyne derivatives
are close to magnetic equivalence, so the <sup>13</sup>C long-lived
singlet states are stable in high magnetic field and do not require
maintenance by a radiofrequency spin-locking field. We suggest a model
of singlet relaxation by fluctuating chemical shift anisotropy tensors
combined with leakage associated with slightly broken magnetic equivalence.
Theoretical estimates of singlet relaxation rates are compared with
experimental values. Relaxation due to antisymmetric shielding tensor
components is significant
Long-Lived Nuclear Singlet Order in Near-Equivalent <sup>13</sup>C Spin Pairs
Molecules that support <sup>13</sup>C singlet states
with lifetimes
of over 10 min in solution have been designed and synthesized. The <sup>13</sup>C<sub>2</sub> spin pairs in the asymmetric alkyne derivatives
are close to magnetic equivalence, so the <sup>13</sup>C long-lived
singlet states are stable in high magnetic field and do not require
maintenance by a radiofrequency spin-locking field. We suggest a model
of singlet relaxation by fluctuating chemical shift anisotropy tensors
combined with leakage associated with slightly broken magnetic equivalence.
Theoretical estimates of singlet relaxation rates are compared with
experimental values. Relaxation due to antisymmetric shielding tensor
components is significant
Synthesis of an Isotopically Labeled Naphthalene Derivative That Supports a Long-Lived Nuclear Singlet State
The synthesis of an octa-alkoxy substituted
isotopically labeled
naphthalene derivative, shown to have excellent properties in singlet
NMR experiments, is described. This highly substituted naphthalene
system, which incorporates an adjacent <sup>13</sup>C spin pair, is
readily accessed from a commercially available <sup>13</sup>C<sub>2</sub>-labeled building block via sequential thermal alkynyl- and
arylcyclobutenone rearrangements. The synthetic route incorporates
a simple desymmetrization approach leading to a small difference in
the chemical shifts of the <sup>13</sup>C spin pair, a design constraint
crucial for accessing nuclear singlet order
Recycling and Imaging of Nuclear Singlet Hyperpolarization
The
strong enhancement of NMR signals achieved by hyperpolarization
decays, at best, with a time constant of a few minutes. Here, we show
that a combination of long-lived singlet states, molecular design,
magnetic field cycling, and specific radiofrequency pulse sequences
allows repeated observation of the same batch of polarized nuclei
over a period of 30 min and more. We report a recycling protocol in
which the enhanced nuclear polarization achieved by dissolution-DNP
is observed with full intensity and then returned to singlet order.
MRI experiments may be run on a portion of the available spin polarization,
while the remaining is preserved and made available for a later use.
An analogy is drawn with a “spin bank” or “resealable
container” in which highly polarized spin order may be deposited
and retrieved