Abstract
Among the methods to enhance the sensitivity of nuclear magnetic resonance (NMR) spectroscopy, small-diameter NMR coils (microcoils) are promising tools to tackle the study of mass-limited samples. Alternatively, hyperpolarization schemes based on dynamic nuclear polarization techniques provide strong signal enhancements of the NMR target samples. Here we present a method to effortlessly perform photo-chemically induced dynamic nuclear polarization in microcoil setups to boost NMR signal detection down to sub-picomole detection limits in a 9.4T system (400 MHz 1H Larmor frequency). This setup is unaffected by current major drawbacks such as the use of high-power light sources to attempt uniform irradiation of the sample, and accumulation of degraded photosensitizer in the detection region. The latter is overcome with flow conditions, which in turn open avenues for complex applications requiring rapid and efficient mixing that are not easily achievable on an NMR tube without resorting to complex hardware.
Highlights
Among the methods to enhance the sensitivity of nuclear magnetic resonance (NMR) spectroscopy, small-diameter NMR coils are promising tools to tackle the study of mass-limited samples
We show that the combination of microcoils with photo-chemically induced dynamic nuclear polarization provides a breakthrough in both mass and concentration sensitivity enhancements of small-volume NMR and a concomitant renaissance of the photo-CIDNP technique, that to date has been limited to specialized labs
In the present manuscript we expand the field of applications of microcoils, showing their suitability to facilitate the performance of photo-CIDNP experiments with a number of advantages that we expect will rekindle the realm of these experiments, all this by virtue of the small active volumes afforded by these devices
Summary
Among the methods to enhance the sensitivity of nuclear magnetic resonance (NMR) spectroscopy, small-diameter NMR coils (microcoils) are promising tools to tackle the study of mass-limited samples. We present a method to effortlessly perform photo-chemically induced dynamic nuclear polarization in microcoil setups to boost NMR signal detection down to sub-picomole detection limits in a 9.4T system (400 MHz 1H Larmor frequency) This setup is unaffected by current major drawbacks such as the use of high-power light sources to attempt uniform irradiation of the sample, and accumulation of degraded photosensitizer in the detection region. We show that the combination of microcoils with photo-chemically induced dynamic nuclear polarization (photoCIDNP) provides a breakthrough in both mass and concentration sensitivity enhancements of small-volume NMR and a concomitant renaissance of the photo-CIDNP technique, that to date has been limited to specialized labs This setup provides low-cost components and excellent performance at the moderate magnetic field strengths of 9.4T, rivalling performance limits of state-ofthe-art cryoprobes at much higher field strengths. The experiments presented here are performed on a 9.4T magnet (400 MHz proton Larmor frequency), yet the homebuilt setup (Fig. 1) rivals cryoprobe sensitivity at higher fields
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