Category Archives: Optical Pumping

Optically generated hyperpolarization for sensitivity enhancement in solution-state NMR spectroscopy #DNPNMR

Dale, Matthew W., and Christopher J. Wedge. “Optically Generated Hyperpolarization for Sensitivity Enhancement in Solution-State NMR Spectroscopy.” Chemical Communications 52, no. 90 (2016): 13221–24.

https://doi.org/10.1039/C6CC06651H.

We show that optical excitation of radical triplet pair systems can produce a fourfold NMR signal enhancement in solution, without the need for microwave pumping. Development of optical hyperpolarization methods will significantly impact all NMR user groups by boosting sensitivity and reducing signal averaging times.

Coherent evolution of parahydrogen induced polarisation using laser pump, NMR probe spectroscopy: Theoretical framework and experimental observation

Halse, M.E., et al., Coherent evolution of parahydrogen induced polarisation using laser pump, NMR probe spectroscopy: Theoretical framework and experimental observation. J Magn Reson, 2017. 278: p. 25-38.

https://www.ncbi.nlm.nih.gov/pubmed/28347906

We recently reported a pump-probe method that uses a single laser pulse to introduce parahydrogen (p-H2) into a metal dihydride complex and then follows the time-evolution of the p-H2-derived nuclear spin states by NMR. We present here a theoretical framework to describe the oscillatory behaviour of the resultant hyperpolarised NMR signals using a product operator formalism. We consider the cases where the p-H2-derived protons form part of an AX, AXY, AXYZ or AA’XX’ spin system in the product molecule. We use this framework to predict the patterns for 2D pump-probe NMR spectra, where the indirect dimension represents the evolution during the pump-probe delay and the positions of the cross-peaks depend on the difference in chemical shift of the p-H2-derived protons and the difference in their couplings to other nuclei. The evolution of the NMR signals of the p-H2-derived protons, as well as the transfer of hyperpolarisation to other NMR-active nuclei in the product, is described. The theoretical framework is tested experimentally for a set of ruthenium dihydride complexes representing the different spin systems. Theoretical predictions and experimental results agree to within experimental error for all features of the hyperpolarised 1H and 31P pump-probe NMR spectra. Thus we establish the laser pump, NMR probe approach as a robust way to directly observe and quantitatively analyse the coherent evolution of p-H2-derived spin order over micro-to-millisecond timescales.

Proton polarization in photo-excited aromatic molecule at room temperature enhanced by intense optical source and temperature control

Sakaguchi, S., et al., Proton polarization in photo-excited aromatic molecule at room temperature enhanced by intense optical source and temperature control. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2013. 317(0): p. 679-684.

http://www.sciencedirect.com/science/article/pii/S0168583X13008872

Proton polarization at room temperature, produced in a p-terphenyl crystal by using electron population difference in a photo-excited triplet state of pentacene, was enhanced by utilizing an intense laser with an average power of 1.5 W. It was shown that keeping the sample temperature below 300 K is critically important to prevent the rise of the spin–lattice relaxation rate caused by the laser heating. It is also reported that the magnitude of proton polarization strongly depends on the time structure of the laser pulse such as its width and the time interval between them.

Proton polarization in photo-excited aromatic molecule at room temperature enhanced by intense optical source and temperature control

Sakaguchi, S., et al., Proton polarization in photo-excited aromatic molecule at room temperature enhanced by intense optical source and temperature control. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2013(0).

http://www.sciencedirect.com/science/article/pii/S0168583X13008872

Proton polarization at room temperature, produced in a p-terphenyl crystal by using electron population difference in a photo-excited triplet state of pentacene, was enhanced by utilizing an intense laser with an average power of 1.5 W. It was shown that keeping the sample temperature below 300 K is critically important to prevent the rise of the spin–lattice relaxation rate caused by the laser heating. It is also reported that the magnitude of proton polarization strongly depends on the time structure of the laser pulse such as its width and the time interval between them.

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