¹H Hyperpolarization of Solutions by Overhauser Dynamic Nuclear Polarization with ¹³C–¹H Polarization Transfer

Abstract

Dynamic nuclear polarization (DNP) is a method that can significantly increase the sensitivity of nuclear magnetic resonance. The only effective DNP mechanism for in situ hyperpolarization in solution is Overhauser DNP, which is inefficient for 1 H at high magnetic fields. Here we demonstrate the possibility of generating significant 1 H hyperpolarization in solution at room temperature. To counter the poor direct 1 H Overhauser DNP, we implement steady-state 13 C Overhauser DNP in solutions and then transfer the 13 C hyperpolarization to 1 H via a reverse insensitive nuclei enhanced by polarization transfer scheme. We demonstrate this approach using a 400 MHz gyrotron-equipped 3.2 mm magic angle spinning DNP system to obtain 1 H DNP enhancement factors of 48, 8, and 6 for chloroform, tetrachloroethane, and phenylacetylene, respectively, at room temperature.

Overhauser enhanced liquid state nuclear magnetic resonance spectroscopy in one and two dimensions

“…Nevertheless, chemical systems investigated so far, including halogenated solvents, metabolites 19 , 25 as well as representative amino acids 26 and lipids 21 , 27 , revealed site-specific signal enhancements. Moreover, all these studies were lacking NMR resolution as they were performed either in resonant cavities 26 , 28 , 29 , deteriorating magnetic field homogeneity, or in NMR sample tubes, where high-frequency MW penetration is largely attenuated and sample heating leads to line broadening 30 , 31 . Here, we present the realization of a setup in which liquid DNP can be performed close to optimal and standard NMR conditions.…”

Large31P-NMR enhancements in liquid state dynamic nuclear polarization through radical/target molecule non-covalent interaction

“…12 Those findings sparked new interest in the method, and now several groups are committed to tackle the open challenges to make DNP in the liquid state applicable to routine NMR spectroscopy. 13–22 Within this context, it is important to design targets and PAs whose properties are specifically tailored to maximize the attainable NMR signal enhancements. To this aim, it is essential to identify the physical mechanisms that make the polarization transfer particularly effective.…”

13C Hyperpolarization of Viscous Liquids by Transfer of Solid-Effect1H Dynamic Nuclear Polarization at High Magnetic Field

“…If the scalar coupling dominates over the dipolar one (as commonly observed for 13 C, 15 N, 19 F, or 31 P nuclei), then the Overhauser DNP can yield outstanding signal enhancements at magnetic fields of ≥1 T, − although usually it requires specific chemical systems that involve a strong contact interaction between the electron and nuclear spins. On the other hand, the dipolar Overhauser effect (as in the case of 1 H) has only limited applications owing to low DNP efficiency at high magnetic fields. , Therefore, to increase the 1 H polarization, a technique was proposed recently for transferring 13 C hyperpolarization produced by scalar Overhauser DNP to the attached 1 H spins via the polarization transfer scheme. , …”

“…This method increases the signal intensity by transferring the larger polarization of a high-γ spin onto a coupled low-γ spin. For the INEPT experiment with a single coupling constant J CH the signal enhancement can be expressed using equation slightly modified from ref : ε INEPT = I INEPT I 0 , normalC = γ normalH γ normalC n .25em sin ( 2 π J CH τ ) .25em exp ( − 2 τ T 2 H ) .25em exp ( − τ T 1 C ) where I INEPT and I 0,C are the INEPT intensity and the thermal equilibrium 13 C intensity, respectively; γ H and γ C are the gyromagnetic ratios for 1 H and 13 C, respectively; n is the bond multiplicity (CH n ); τ is the pulse delay in the INEPT sequence and equals to 1/4 J CH (for glycerol- 13 C 3 , J CH = 145 Hz and τ = 1.7 ms); and T 2 H and T 1 C are the transverse and longitudinal relaxation times of 1 H and 13 C, respectively.…”

“…35,36 Therefore, to increase the 1 H polarization, a technique was proposed recently for transferring 13 C hyperpolarization produced by scalar Overhauser DNP to the attached 1 H spins via the polarization transfer scheme. 37,38 With regard to an intermediate state between solids and liquids, viscous media, only a few DNP measurements at high magnetic fields 39,40 and a number of DNP experiments at low magnetic fields exist. 41−45 These experiments have been so far performed only on proton and fluorine nuclei via the direct transfer of spin polarization from the electron spin to the nuclear spin through the Overhauser effect or solid effect.…”