A model for establishing the ultimate enhancements (A∞) in the low to high magnetic field transfer dynamic nuclear polarization experiment

Abstract

In a preliminar 3, report, we have demonstrated transfer of a flowing bolus enhanced in low magnetic fields (e.g., 0.33 T) with dynamic nuclear polarization (DNP), but monitored in a high magnetic field (4.7 T). The advantages of the high magnetic field monitoring approach include: 1) greater chemical shift dispersion, and 2) improved signal strength in compa¡ with static low field DNP experiments. In the present study, a model is developed to predict ultimate DNP enhancements (Aoo) in this expefiment for flow liquid/liquid intermolecular transfer (L2IT). L2IT IH and 13C data is obtained for benzene and chloroform in order to test the validity of the model. The ultimate XH and 13C DNP enhancements obtained for benzene/TEMPO ate --150 and --220, respectively. For a chloroform/TEMPO (L2IT) sample, the ultimate enhancements ate close to the tH dipolar (--)30) and the 13C scalar (+2660) limit, respectively. In the latter case, the observed 13C DNP enhancement exceeds the thermal Boltzmann magnetization at 4.7 T by a factor of 21. For a 1-chlorobutane/TEMPO sample selective enhancements were observed at different sites in the molecule. For example, the C-1 carbon exhibits a large scalar enhancement, whereas, the other carbons exhibit dipolar enhancements. Data illustrating the importance of three-spin effects in 13C DNP studies is also presented. Alternative methods of sample transfer from the low to high magnetic field are also discussed.

Liquid State DNP on Metabolites at 260 GHz EPR/400 MHz NMR Frequency

“…5), it is apparently inactive. This finding is concordant with results at lower magnetic field, where direct 13 C polarization on small organic molecules without mediation via abundant proton spins was observed [20]. , partially deuterated water (middle) and 99.9 % deuterated water (right), containing 12 mM TEMPOL radical with (dotted) and without microwave irradiation (solid line), respectively.…”

Dynamic nuclear polarization of 13C in aqueous solutions under ambient conditions

“…Thus, a simplified version of Eq. [6] would be E 2 = 1 + DNP term + three-spin term. The DNP term is negative for dipolar coupling and positive for scalar coupling, due to the sign of the coupling factor and the negative c S .…”

“…Magic angle spinning-DNP (MAS-DNP) experiments on solid samples were presented originally for the purpose of investigating coal [3], then later at higher fields for studying biological samples in frozen solutions [4,5]. Since most biological processes occur in solution, there has been interest in solution-state 13 C DNP, initially demonstrated by flowing the sample from a low polarizing field to a higher NMR detection field [6], and more recently performed by polarizing in the solid state for an extended period of time at 1.2 K, then rapidly dissolving the hyperpolarized sample and delivering it to the system of interest [7]. The latter methodology, known as dissolution DNP, is particularly notable for the extremely high, three to four orders-of-magnitude signal gain.…”

Sensitivity Optimization in Continuous-Flow FTNMR

“…When there is no sensitivity enhancement, EF(2) goes to unity [as compared to the A value in DNP, which goes to zero (17)]. Magnetization M3 at the end of the transfer line is given by an equation similar to Eq.…”

“…Because NMR flow transverse-relaxation time T 2 f depends upon t(4) as shown samples are not spun, their linewidths tend to be larger than in Eq. [17]. Ernst's treatment explicitly assumes quadrature normal, favoring the assumption except at small T rep values detection, optimal filter cutoffs, and application of matched and flow rates.…”