The effect of glassing solvent deuteration and Gd³⁺ doping on ¹³C DNP at 5 T

Abstract

We report the influence of glassing solvent deuteration and Gd 3+ doping on 13 C dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) performed on [1-13 C] sodium acetate at B 0 ¼ 5 T and 1.2 K. Our data reveal that at 5 T, glassing solvent deuteration still results in a 40% improvement of the 13 C DNP signal when a large electron spin resonance (ESR) linewidth 4-oxo-TEMPO free radical is used, but results in a 60% decrease of the DNP signal in the case of a sample doped with small ESR linewidth trityl OX063. An addition of a trace amount of the Gd 3+ complex Gd-HP-DO3A led to a negligible slight decrease on the 13 C polarization TEMPO-doped sample, but is still relatively beneficial for the trityl-doped sample with 30% improvement of the DNP-enhanced 13 C polarization. These findings indicate that while these DNP optimization steps are still valid at 5 T, the effects are not as pronounced as observed in 13 C DNP at B 0 ¼ 3.35 T. These DNP results at 5 T are discussed thermodynamically within the framework of the thermal mixing model of DNP.

Construction and 13C hyperpolarization efficiency of a 180 GHz dissolution dynamic nuclear polarization system

“…Similar to sample preparation described before, [29] 100 μL aliquots of 3 M [1- G. 13 C microwave frequency sweeps and 13 C solid-state polarization measurements…”

Influence of Dy3+ and Tb3+ doping on 13C dynamic nuclear polarization

“…Similar to previous studies of Gd 3+ in DNP, Tb 3+ and Dy 3+ doped samples resulted in DNP spectra that had P(+) and P( ) shifted toward each other. 36,60 At the optimum concentration of Dy 3+ -DOTA (1.5 mM), both positive and negative polarization peaks were shifted by 20 MHz from the reference sample. This shift was consistent over all concentrations of Dy studied, only increasing to 25 MHz for both peaks with 4 mM Dy.…”

“…[31][32][33] Meanwhile, the trityls, particularly OX063, which have some of the narrowest EPR linewidths among free radicals, were found to be excellent polarizing agents for low-γ nuclei like 13 C. 16,34 When using these radicals, DNP enhancements may be improved further by the addition of trace amounts of gadolinium. [34][35][36][37] Recently, it was found that the addition of holmium to a trityl-doped sample results in liquid state enhancement similar to that achieved by using gadolinium. 38 While the use of these lanthanides may lead to significant polarization gains, the free ion form of these lanthanides may lead to greater toxicity of the DNP sample, which must be considered prior to in vivo biomedical application.…”

“…41 While a variety of Ln(iii) complexes have numerous biomedical applications, particularly in contrast-enhanced MRI, 45 only Gd 3+ and Ho 3+ have been studied extensively as beneficial doping agents in 13 C dissolution DNP. [35][36][37][38] This in part takes precedent from a previous preliminary study which has shown that only Gd 3+ and Ho 3+ ions have beneficial effects on 13 C DNP, while the other Ln(iii) ions appear to have no apparent effect on 13 C DNP enhancements for trityldoped samples. 37 We would like to note that the measurements in the aforementioned previous DNP study on using lanthanide ions 37 were not really extensively optimized in terms of concentration dependence and the fact that the optimum DNP microwave frequency could shift with lanthanide doping.…”

“…This is in line with previous studies which have used the same method to compare DNP performance. 32,[35][36][37][38] Build-up curves were recorded and fit with single exponential equations, and using the fit, the relative polarization at 10 000 s was extrapolated.…”