Use of dissolved hyperpolarized species in NMR: Practical considerations.

Hyperpolarization techniques that can transiently boost nuclear spin polarization are generally carried out at low temperature - as in the case of dynamic nuclear polarization - or at high temperature in the gaseous state - as in the case of optically pumped noble gases. This review aims at describing the various issues and challenges that have been encountered during dissolution of hyperpolarized species, and solutions to these problems that have been or are currently proposed in the literature. During the transport of molecules from the polarizer to the NMR detection region, and when the hyperpolarized species or a precursor of hyperpolarization (e.g. parahydrogen) is introduced into the solution of interest, several obstacles need to be overcome to keep a high level of final magnetization. The choice of the magnetic field, the design of the dissolution setup, and ways to isolate hyperpolarized compounds from relaxation agents will be presented. Due to the non-equilibrium character of the hyperpolarization, new NMR pulse sequences that perform better than the classical ones will be described. Finally, three applications in the field of biology will be briefly mentioned.

Inductive Coupling and Flow for Increased NMR Sensitivity.

A device is proposed to enhance the NMR sensitivity of slowly relaxing nuclei, taking advantage of a controlled solution flow within a microfluidic circuit and microsized NMR detection. Unlike our previous work ( Carret et al. Anal. Chem. 2017 , 89 ( 5 ), 2995 - 3000 ), this setup can be easily installed on any commercial NMR probehead as it uses induction between the commercial antenna and the microcoil. Such a system leads to a significant gain in sensitivity per time unit for slowly relaxing nuclei while preserving the capabilities of the host probehead.

Enhancing NMR of Nonrelaxing Species Using a Controlled Flow Motion and a Miniaturized Circuit.

In this article we show that circulation of the sample in a closed-loop circuit combined to microsized detection can lead to a significant signal NMR enhancement. We present an optimized NMR device based on a mini bubble-pump associated with fluidics and microdetection that can be installed on a commercial NMR spectrometer. In addition to a significant signal enhancement for slowly relaxing nuclei, we show that it enables more precise and frequent monitoring of chemical reactions. An additional modification leads to a stopped-flow system very efficient for instance for 2D NMR experiments with long mixing times.

The presence of an air-water interface affects formation and elongation of α-Synuclein fibrils.

The aggregation of human α-Synuclein (α-Syn) into amyloid fibrils is related to the onset of multiple diseases termed synucleinopathies. Substantial evidence suggests that hydrophobic-hydrophilic interfaces promote the aggregation of amyloidogenic proteins and peptides in vitro. In this work the effect of the air-water interface (AWI) on α-Syn aggregation is investigated by means of thioflavin T binding measurements, dynamic light scattering, size-exclusion chromatography, electron microscopy, and atomic force microscopy. Measurements were performed with the monomeric protein alone or together with preformed seeds. In presence of the AWI, α-Syn aggregates readily into amyloid fibrils that remain adsorbed to the AWI. Instead, when the AWI is removed from the samples by replacing it with a solid-liquid interface, the interfacial aggregation of monomeric α-Syn is greatly reduced and no significant increase in ThT fluorescence is detected in the bulk, even at 900 µM concentration. Bulk aggregation is observed only when a sufficient amount of preformed seeds is added, and the initial slope of the kinetics scales with the amount of seeds as expected for first order kinetics. By contrast, in seeded experiments with the AWI, the initial slope is one order of magnitude lower and secondary nucleation pathways appear instead to be dominant. Thus, interfaces play multiple roles in the aggregation of α-Syn, influencing primary nucleation, aggregate elongation, and secondary nucleation processes. Interfacial effects must therefore be taken into account to achieve a complete understanding of protein aggregation events in vitro as well as in vivo.