Fast destruction of singlet order in NMR experiments

Abstract

Some nuclear spin systems support long-lived states, which display greatly extended relaxation times relative to the relaxation time of nuclear spin magnetization. In spin-1/2 pairs, the such a long-lived state is given by singlet order, representing the difference of the population of the nuclear singlet state and the mean population of the three triplets. In many cases, the experiments with long-lived singlet order are very time-consuming because of the need to wait for singlet order decay before the experiment can be repeated; otherwise spin order remaining from a previous measurement may lead to experimental artefacts. Here we propose techniques for fast and efficient singlet order destruction. These methods exploit coherent singlet-triplet conversion; in some cases, multiple conversion steps are introduced. We demonstrate that singlet order destruction enables a dramatic reduction of the waiting time between consecutive experiments and suggest to use this approach in singlet-state NMR experiments with nearly equivalent spins.

Single-scan measurements of nuclear spin singlet order decay rates

“…NMR methodologies that exploit various aspects of long-lived nuclear spin singlet order -all groupable under the name singlet NMR -are under constant development. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The three main properties of this form of spin order -NMR silent, accessible on demand and long-lived -have found a variety of applications including: quantification, with enhanced sensitivity, of ligand binding; 18,19 measurements of very slow translational dynamics; [20][21][22][23][24][25] and their exploitation as molecular tags that can preserve information over a long time. [26][27][28][29][30][31][32][33][34][35][36] Long-lived spin order is exploited as a vehicle to preserve spin hyperpolarization gained through techniques such as PHIP, 37 SABRE 38 and dissolution-DNP.…”

“…nr = 7 and t i = [0, 30,60,90,120,150,180] min; under these conditions the total experimental time would result in T 4 32 h per scan (ns = 1). This time can be reduced to B11 h if the singlet order is destroyed 6 at each of the nr repetitions such that t 0 could be kept of the order of 3T 1 (T 1 is assumed 30 s in this example) rather than 3T S . Experiments to measure T S in low-gamma singlet spin pairs can therefore take several days because of the combined need for taking many transients and the many minutes long typical T S values.…”

Nuclear Spin Relaxation of Longitudinal and Singlet Order in Liquid-CO2 Solutions

“…All longitudinal decay constants (T 1 ) reported in this paper have been measured with a standard inversion recovery experiment. To measure singlet order decay constants (T S ) we have used a sequence (Figure 4) where firstly any singlet order possibly present in the sample from the previous scan is destroyed (Rodin et al, 2019), singlet order is subsequently produced with either a M2S (Pileio et al, 2010) or gM2S (Bengs et al, 2020) pulse sequence, depending on the actual spin system features. The singlet order is then allowed to relax in a specific magnetic field for some variable delay time before being reconverted back into transverse magnetization by a S2M or gS2M and acquired.…”

Algorithmic cooling of nuclear spins using long-lived singlet order

“…After pumping the singlet order by nP /2 cycles, the system is allowed to relax for a delay τ , followed by an APSOC(+) pulse to generate observable transverse magnetization. In all cases, a singlet-order-destruction (SOD) sequence was applied after signal detection, in order to allow faster repetition of the experiments 65 (not shown).…”