Solid-like Dynamic Nuclear Polarization Observed in the Fluid Phase of Lipid Bilayers at 9.4 T

Abstract

Dynamic nuclear polarization (DNP) is a powerful method to enhance NMR sensitivity. Much progress has been achieved recently to optimize DNP performance at high magnetic fields in solid-state samples, mostly by utilizing the solid or the cross effect. In liquids, only the Overhauser mechanism is active, which exhibits a DNP field profile matching the EPR line shape of the radical, distinguishable from other DNP mechanisms. Here, we observe DNP enhancements with a field profile indicative of the solid effect and thermal mixing at ∼320 K and a magnetic field of 9.4 T in the fluid phase of 1,2-dimyristoyl-sn-glycero-3phosphocholine (DMPC) lipid bilayers doped with the radical BDPA (1,3-bis(diphenylene)-2-phenylallyl). This interesting observation might open up new perspectives for DNP applications in macromolecular systems at ambient temperatures.

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.…”

Dynamic view of the solid-state DNP effect

“…Differently from the static picture based on level mixing and perturbation theory, the dynamical description developed here is readily extendable to liquids (Erb et al, 1958a;Leblond et al, 1971;Gizatullin et al, 2022;Kuzhelev et al, 2022) where the dipolar interaction is time-dependent. Such extension is presented in the companion paper (Paper II).…”

Three mechanisms of room temperature dynamic nuclear polarization occur simultaneously in an ionic liquid

“…However, there are also few contributions reported about OE in solids, 13 as well as solid-state DNP effects in liquids. 14 The transition between different DNP effects with temperature is described in several studies. 6,[14][15][16] While the transition between CE and SE takes place under conditions generally backing both effects, 7 allowing to achieve a level of enhancement close to the theoretical maximum, the transition between SE, or CE, and OE assumes a low level of DNP enhancement since both dynamics and relaxation parameters are least optimal for both.…”

“…14 The transition between different DNP effects with temperature is described in several studies. 6,[14][15][16] While the transition between CE and SE takes place under conditions generally backing both effects, 7 allowing to achieve a level of enhancement close to the theoretical maximum, the transition between SE, or CE, and OE assumes a low level of DNP enhancement since both dynamics and relaxation parameters are least optimal for both. On the other hand, to our best knowledge, there is no study reported about a simultaneous observation of more than two DNP effects.…”

“…If OE and SE are rather expected to appear in the viscous liquid, CE/TM is an uncommon phenomenon at ambient temperatures in liquid state samples without pronounced ''phase separation''. 14 There are indeed a few examples 1,5,7,11,14 of mixing or transition between two solid-state DNP effects in the literature. However, to the best of our knowledge, the current system is the first observation of OE, SE, and CE/TM DNP effects in the liquid state at ambient temperature.…”