Proton Relaxometry of Long‐Lived Spin Order

Abstract

A study of long‐lived spin order in chlorothiophene carboxylates at both high and low magnetic fields is presented. Careful sample preparation (removal of dissolved oxygen in solution, chelating of paramagnetic impurities, reduction of convection) allows one to obtain very long‐lived singlet order of the two coupled protons in chlorothiophene derivatives, having lifetimes of about 130 s in D2O and 240 s in deuterated methanol, which are much longer than the T1‐relaxation times (18 and 30 s, respectively, at a field B0 =9.4 T). In protonated solvents the relaxation times become shorter, but the lifetime is still substantially longer than T1 . In addition, long‐lived coherences are shown to have lifetimes as long as 30 s. Thiophene derivatives can be used as molecular tags to study slow transport, slow dynamics and slow chemical processes, as has been shown in recent years.

Transport of hyperpolarized samples in dissolution-DNP experiments

“…We also performed T 1 -measurements at variable fields as described before. 26 All relaxation experiments were done using a 400 MHz NMR spectrometer with a magnetic field B 0 of 9.4 T. This spectrometer is equipped with a field-cycling device, which allows one to switch the field from B 0 to any field in the range 10 nT o B rel o 9.4 T in less than 0.4 s. To switch the field, we mechanically move the sample as described in ref. 32.…”

“…The signal decay as a function of t rel allowed us to determine T LLS or T 1 for each field B rel . The same method has been used in our earlier work 26 on field-cycling relaxometry of singlet order. It is worth noting that the adiabatically ramped RF-field was optimized separately for the pairs of protons in CTC and in Ala-Gly to have high yields of the singlet order in each case.…”

“…However, these mechanisms are often less efficient and therefore do not significantly curtail the lifetime of the TSI. For protons, the T LLS /T 1 ratio 25 can be as high as 45 and T LLS can be as long as 4 minutes; [26][27][28] for nuclei such as 13 C or 15 N in suitably designed molecules, extremely long T LLS values can be achieved, reaching 1 hour. 21,29,30 Although the TSI lifetime is reduced by the presence of paramagnetic agents (significant radical concentrations are common in D-DNP experiments) T LLS can still be longer than T 1 , since the local fields due to paramagnetic agents experienced by the two spins are partly correlated.…”

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

“…Nuclear magnetic resonance (NMR) experiments are restricted by the relaxation of longitudinal magnetization in solution, which decays with the characteristic time constant T 1 . Long-lived states (LLS) offer a promising means to alleviate this limitation [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. In pairs of spin-1/2 homonuclei, the LLS is unaffected by in pair dipole-dipole relaxation and showcases extended lifetimes with respect to T 1 .…”

“…The optimal conversion efficiency was 39.9% for 13 C 2 -I, 35.2% for 13 C-II and 17.7% for Ala-Gly. The delay between successive experiments is 65 s for 13 C 2 -I, 175 s for13 C-II and 125 s for Ala-Gly. (a) Optimization of ADAPT 18 loop number for 13 C 2 -I with D18 fixed at 0.9 ms. (b) Optimization of ADAPT 18 delay for 13 C 2 -I with m18 fixed at 53.…”