PULSARTechnical Note

Using Pulsar to measure spin-lattice relaxation data to determine thelongevity of polarised spin-states produced by a parahydrogen based
hyperpolarisation techniqueDavid Ashworth, Lisa Clayton and Dr Ryan Mewis, Manchester Metropolitan University.

Introduction

Experimental Set-Up

The measurement of T1 (spin-lattice) relaxation times is used

A Young’s capped NMR tube (5 mm diameter) was charged

to evaluate the longevity of a polarised state produced bywith 5 μL of pyridine in 600 μL of d4-methanol. This was thenhyperpolarisation techniques, which are applied to NMR andplaced in the Pulsar benchtop NMR instrument, which wasMRI. These measurements are typically performed at highthen tuned and matched. A standard 1H NMR spectrum wasmagnetic field (typically around 9.4 T), but it is becoming

acquired to give an indication of the sweep width required forincreasingly more prudent to apply these techniques tothe T1 measurement. Following this the T1 measurement wasobtaining images and spectra on low-field devices.

then completed.

SABRE (Signal Amplification By Reversible Exchange), aThe sample was subsequently used for other measurements,parahydrogen based hyperpolarisation technique, is used

in which either the atmosphere above the sample, or thefor the production of molecules with non-Boltzmann

chemical composition of the solution were altered. Further

distributions. An iridium centred complex is used to catalysemeasurements are made using the original sample, in thethe spin-transfer. As the molecules that are typically polarised

absence of air, and with the addition of 2 mg of [Ir(COD)(IMes)by this method are N-heterocycles, the aromatic region ofCl] (spin-transfer catalyst, COD = cyclooctadiene,

the H NMR spectrum can be crowded in that some chemical

IMes = 1,3-Bis(2,4,6-trimethylphenyl)imidazole-2-ylidene)

shifts are super-imposed on one another.

under an atmosphere of air or hydrogen.

1

This application note describes the use of the Pulsar
benchtop NMR instrument, in conjunction with the MNOVA
software package for processing of acquired NMR data, toshow that the T1’s of pyridine are readily ascertained under arange of physical constraints.

Sample insertion point.

Results
T1 measurements of pyridine were successfully performed
using the Pulsar benchtop NMR instrument. The data wasthen processed using MNOVA. The signals observed in the 1H
NMR spectrum are a lot wider at 60 MHz than they are at 400
MHz. This is because the J-coupling of the signals is ~7 times
larger in units of chemical shift. Despite this, the three distinct
regions for pyridine are readily identifiable, facilitating thecalculation of T1 values for the three different 1H signals.

Figure 1: 1H NMR T1 data of a sample consisting of 5 μL of pyridine in 600 μL of d4-methanol in the presence of air. The chemical shift scale
has not been referenced to TMS. The variable delays used to collect the 15 different spectra were 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 7.5, 10,15, 20, 25 and 30 s. Using the data analysis function within MNOVA, the data integrals for the three 1H signals of pyridine (ortho (Y), meta(Y2) and para (Y1)) were fitted to a T1 decay. This gave the values of T1 for the ortho-, meta- and para-protons of pyridine as 4.8, 4.9 and 5.3 s
respectively.Figure 2: 1H NMR T1 data of a sample consisting of 5 μL of pyridine and 2 mg [Ir(COD)(IMes)Cl] in 600 μL of d4-methanol which has beendegassed. The variable delays used to collect the 18 different spectra were 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 7.5, 10, 15, 20, 25, 30, 40, 50 and
60 s. Using the data analysis function within MNOVA, the data integrals for the three 1H signals of pyridine (ortho (Y), meta (Y2) and para (Y1))
were fitted to a T1 decay. This gave the values of T1 for the ortho-, meta- and para-protons of pyridine as 25.4, 19.6 and 22.0 s respectively.

The T1 data collected in the absence of air, but in the presenceof catalyst gave much longer T1 times. This is due to theabsence of oxygen, which increases spin-lattice relaxation
because it is paramagnetic. Even with the added complexityof the spin-transfer catalyst in solution, the three proton
environments of pyridine are readily observed and the T1
values calculated. The measurement of T1 can also be used toascertain the effect of deuteration on a spin-system. Undera hydrogen atmosphere, the spin-transfer catalyst becomes
active and promotes both spin-transfer and hydrogendeuterium exchange. The latter is slow, but over long time
periods, the 1H signals of pyridine (in particular the orthopeak) will decrease. Measurement of T1 shows the effectof reducing the number of spins within a spin-system andthus its role in promoting longer lived polarised states whenhyperpolarisation methods, such as SABRE, are employed.

Figure 3: 1H NMR T1 data of a sample consisting of 5 μL of pyridine and 2 mg [Ir(COD)(IMes)Cl] in 600 μL of d4-methanol which has been undera hydrogen atmosphere for circa one week. The variable delays used to collect the 20 different spectra were 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5,7.5, 10, 12,15, 17.5, 20, 25, 30, 40, 50 and 60 s. Using the data analysis function within MNOVA, the data integrals for the three 1H signalsof pyridine (ortho (Y), meta (Y2) and para (Y1)) were fitted to a T1 decay. This gave the values of T1 for the ortho-, meta- and para-protons ofpyridine as 27.1, 35.0 and 32.8 s respectively.

Conclusion
The Pulsar system is fully capable of measuring T1 data which is of interest in the employment of hyperpolarisation based
techniques on low-field instrumentation. It also enables the deuteration of a molecule to be tracked and the subsequent change
in the T1 value to be monitored.

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