Constant-adiabaticity radiofrequency pulses for generating long-lived singlet spin states in NMR

Abstract

A method is implemented to perform "fast" adiabatic variation of the spin Hamiltonian by imposing the constant adiabaticity condition. The method is applied to improve the performance of singlet-state Nuclear Magnetic Resonance (NMR) experiments, specifically, for efficient generation and readout of the singlet spin order in coupled spin pairs by applying adiabatically ramped RF-fields. Test experiments have been performed on a specially designed molecule having two strongly coupled 13 C spins and on selectively isotopically labelled glycerol having two pairs of coupled protons. Optimized RF-ramps show improved performance in comparison, for example, to linear ramps. We expect that the methods described here are useful, not only for singlet-state NMR experiments, but also for other experiments in magnetic resonance, which utilize adiabatic variation of the spin Hamiltonian.

Fast destruction of singlet order in NMR experiments

“…The NMR tube with the insert inside was filled with protonated acetone and sealed. As a result, the entire sample is located inside the NMR coil and high homogeneity of both static B 0 field and RF-field is achieved 32,33 .…”

“…The conversion pathway, |S → |T + or |S → |T − , is chosen by setting the RF-frequency. To achieve a high degree of adiabaticity with a moderate pulse duration, we use optimized shapes 33,37 of the APSOC pulses, introducing "constant adiabaticity" pulses. Finally, it is important to note that the APSOC pulse with an increasing ν 1 (t) correlates the singlet state with the |T ± states, as introduced in the "tilted" frame with the quantization axis parallel to the RF-field in the rotating frame.…”

Real-Time Nuclear Magnetic Resonance Detection of Fumarase Activity Using Parahydrogen-Hyperpolarized [1-13C]Fumarate

“…In our experiment, the proton singlet order was transformed into hyperpolarized magnetization on the 1-13 C spin by subjecting the sample to a magnetic field cycle [20,21]. Here, a 'constant adiabaticity' [22] fieldcycling profile was used. The chemical reaction and magnetic field cycle profile are shown in Fig.…”

Generalised magnetisation-to-singlet-order transfer in nuclear magnetic resonance

“…Several radio-frequency (rf) pulse sequences have been developed for this purpose. 2,6,[36][37][38][39][40][41][42] However, most pulse sequences are designed for either the near-equivalent regime (y ST E 0), or the strongly inequivalent regime (y ST E p/2). The intermediate coupling regime (y ST E p/4) is a difficult case which is not welladdressed by most existing sequences.…”

“…APSOC (adiabatic passage spin-order conversion). 41,42 Although such techniques are often efficient and robust, they have the disadvantage that there are no analytical solutions; in many cases, specific shapes must be derived for each set of spin system parameters. We do not consider these schemes further in this paper.…”