Abstract
Coupled pairs of nuclear spin-1/2 support one singlet state and three triplet states. Transitions between the singlet state and one of the triplet states may be driven by an oscillating low-frequency magnetic field, in the presence of couplings to a third nuclear spin, and a weak bias magnetic field. The oscillating field is in the same direction as the bias field and is called a WOLF (Weak Oscillating Low Field) pulse. Application of a WOLF pulse allows for the generation of strong nuclear hyperpolarization of 13C nuclei, starting from the nuclear singlet polarization of a 1H spin pair, associated with the enriched para-spin isomer of hydrogen gas. Hyperpolarization is demonstrated for two molecular systems.
Highlights
IntroductionMagnetic resonance experiments usually involve the application of a strong magnetic field (typically from a fraction of one Tesla to up to tens of Tesla) combined with radio frequency pulses (for nuclear magnetic resonance, NMR) or microwave pulses (for electron spin resonance, ESR) that are resonant with the magnetic Zeeman transitions of the system
Magnetic resonance experiments usually involve the application of a strong magnetic field combined with radio frequency pulses or microwave pulses that are resonant with the magnetic Zeeman transitions of the system
We show that the mixing of states by non-secular spin–spin couplings in the low-field regime allows selected “forbidden” transitions to be induced by oscillating magnetic fields
Summary
Magnetic resonance experiments usually involve the application of a strong magnetic field (typically from a fraction of one Tesla to up to tens of Tesla) combined with radio frequency pulses (for nuclear magnetic resonance, NMR) or microwave pulses (for electron spin resonance, ESR) that are resonant with the magnetic Zeeman transitions of the system. In these high-field conditions, the parts of the spin Hamiltonian that do not commute with the Zeeman Hamiltonian are usually removed. Fumarate, is a natural metabolite, which has been used for the characterization of cancer in magnetic resonance imaging (MRI).
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