Optimal transfer of spin-order between a singlet nuclear pair and a heteronucleus

Abstract

Intramolecular spin-order transfer is a useful technique for signal enhancement of insensitive and low-concentration molecular species. We present a closed-form, optimized pulse sequence which maximizes the efficiency of transfer between a singlet (para) nuclear pair and a vicinal heteronucleus. Neglecting the decay of coherences while the nuclei are in the transverse plane, the scheme is unity efficient for all combinations of internuclear scalar couplings. Efficiency loss due to T2-like decay is also minimized by keeping the sequence as short as possible. We expect this result to be useful for hyperpolarization experiments in which the spin-order originates in parahydrogen, as well as studies of singlet state decay aimed at longer-term storage of spin-order in hyperpolarized Magnetic Resonance Imaging.

On the spin order transfer from parahydrogen to another nucleus

“…Kadlecek et al assumed a magnetic field low enough (%mT) to neglect chemical shift differences between the (former para-) 1 H nuclei, resulting in weak heteronuclear interaction between 1 H and X (J 13 , J 23 ), and strong homonuclear 1 H-1 H coupling (J 12 ) [17,19]. At high field (%T), Haake et al assumed weak 1 H-X and 1 H-1 H couplings [8].…”

“…For hyperpolarization at low field, Goldman and Johannesson [17] and Kadlecek et al [19] assumed that the full singlet-state density matrix is preserved. This is achieved by applying decoupling pulses throughout the hydrogenation reaction until the SOT is played out: [8] suggested to start from the high-field, timeaveraged density matrix.…”

“…by means of r.f. pulses or field-cycling, transform this order to an observable nuclear polarization [8,[17][18][19][20].…”

“…Here, we investigate the SOT sequences developed by Goldman et al, Kadlecek et al, and Haake et al [8,17,19]. Goldman's and Kadlecek's SOT sequences have been employed for in vivo 13 C imaging using the agents succinate (SUC) and hydroxyethylpropionate (HEP) [20,[24][25][26].…”

“…Kadlecek et al [19] derived explicit formulas for the SOT sequence parameters, which can be readily applied to arbitrary molecules.…”