Category Archives: isotopic labeling

Stable Isotope-Resolved Analysis with Quantitative Dissolution Dynamic Nuclear Polarization

Lerche, M. H., D. Yigit, A. B. Frahm, J. H. Ardenkjaer-Larsen, R. M. Malinowski, and P. R. Jensen. “Stable Isotope-Resolved Analysis with Quantitative Dissolution Dynamic Nuclear Polarization.” Analytical Chemistry 90 (January 2, 2018): 674–78.

Metabolite profiles and their isotopomer distributions can be studied noninvasively in complex mixtures with NMR. The advent of dissolution Dynamic Nuclear Polarization (dDNP) and isotope enrichment add sensitivity and resolution to such metabolic studies. Metabolic pathways and networks can be mapped and quantified if protocols that control and exploit the ex situ signal enhancement are created. We present a sample preparation method, including cell incubation, extraction and signal enhancement, to obtain reproducible and quantitative dDNP (qdDNP) NMR-based stable isotope-resolved analysis. We further illustrate how qdDNP was applied to gain metabolic insights into the phenotype of aggressive cancer cells.

13C dynamic nuclear polarization using isotopically enriched 4-oxo-TEMPO free radicals #DNPNMR

Niedbalski, Peter, Christopher Parish, Andhika Kiswandhi, and Lloyd Lumata. “13C Dynamic Nuclear Polarization Using Isotopically Enriched 4-Oxo-TEMPO Free Radicals.” Magnetic Resonance in Chemistry 54, no. 12 (2016): 962–67.

The nitroxide-based free radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) is a widely used polarizing agent in NMR signal amplification via dissolution dynamic nuclear polarization (DNP). In this study, we have thoroughly investigated the effects of 15N and/or 2H isotopic labeling of 4-oxo-TEMPO free radical on 13C DNP of 3 M [1-13C] sodium acetate samples in 1 : 1 v/v glycerol : water at 3.35 T and 1.2 K. Four variants of this free radical were used for 13C DNP: 4-oxo-TEMPO, 4-oxo-TEMPO-15N, 4-oxo-TEMPO-d16 and 4-oxo-TEMPO-15N,d16. Our results indicate that, despite the striking differences seen in the electron spin resonance (ESR) spectral features, the 13C DNP efficiency of these 15N and/or 2H-enriched 4-oxo-TEMPO free radicals are relatively the same compared with 13C DNP performance of the regular 4-oxo-TEMPO. Furthermore, when fully deuterated glassing solvents were used, the 13C DNP signals of these samples all doubled in the same manner, and the 13C polarization buildup was faster by a factor of 2 for all samples. The data here suggest that the hyperfine coupling contributions of these isotopically enriched 4-oxo-TEMPO free radicals have negligible effects on the 13C DNP efficiency at 3.35 T and 1.2 K. These results are discussed in light of the spin temperature model of DNP. Copyright © 2016 John Wiley & Sons, Ltd.

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