Homonuclear ADAPT: A general preparation route to long-lived nuclear singlet order

Abstract

We introduce a simple strategy to access and readout nuclear singlet order based on the alternate repetition of hard pulses and delays. We demonstrate the general applicability of the method by accessing nuclear singlet order in spin systems characterized by diverse coupling regimes. We show that the method is highly efficient in the strong-coupling and chemical equivalence regimes, and can overcome some limitations of other well-established and more elaborated pulse sequences. A simulation package is provided which allows the determination of pulse sequence parameters.

Singlet-filtered NMR spectroscopy

“…Over the years, several NMR sequences were invented to access singlet states (3,4,8,18,(24)(25)(26)(27). The available sequences generally tend to perform better in some spin systems than in others depending on spin couplings and on off-resonance effects of the pulses.…”

Experimental evidence for the role of paramagnetic oxygen concentration on the decay of long-lived nuclear spin order

“…The experimental proton NMR spectrum can be well simulated using the following parameters: 51 J HH ¼ 16.9 AE 0.3 Hz; Dn ¼ 8.8 AE 0.1 Hz, which are in approximate agreement with the literature. 52 The small proton chemical shi difference allows access to the long-lived nuclear singlet order, by using pulsed methods, [52][53][54] and their variants, 46,[55][56][57][58][59] which operate efficiently in the near-chemical equivalence regime. In the current study, we employed a modied version of the spin-locking induced crossing (SLIC) pulse sequence, 54 as shown in Fig.…”

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

“…48 An alternative method is the homonuclear ADAPT (Alternating Delays Achieve Polarization Transfer) technique. 49,50 This sequence consists of a repetitive sequence of short pulses. Simulations show that in ideal circumstances this sequence performs well for mixing angles given by 0 o y ST t 751.…”

“…As mentioned in ref. 50, the ADAPT sequence suffers from strong interference from off-resonance effects and radio-frequency field inhomogeneity. The performance of ADAPT is explored in more detail in the ESI.…”

“…The performance of gM2S with respect to resonance offsets and rf field variations is explored in the ESI, † where it is contrasted with the ADAPT scheme. 50…”