Selective Excitation of Long-Lived Nuclear Spin States

Nuclear magnetization storage, once limited by longitudinal
and
transverse relaxation lifetimes, T1 and T2, can be prolonged by symmetry-adapted nuclear
spin order, i.e. long-lived states (LLS) and long-lived coherences
(LLC), which have significantly extended relaxation time constants
compared to T1 and T2, respectively. Excitation and/or detection of LLS currently
involves pulses covering wide frequency ranges in high-magnetic-field
spectrometers. This leads to excitation of unwanted signals that may
overlap and interfere with the resonances of interest. Herein, we
present a new pulse sequence that converts longitudinal magnetization
to LLS and further to detectable magnetization using only frequency-selective
pulses. We demonstrate the suitability of this sequence for different J-coupled spin pairs in dipeptide AlaGly and protein Ubiquitin.
The newly developed method is adapted for investigations of LLS in
complex systems such as proteins and mixtures of metabolites where
selected molecular groups are to be investigated separately.