Illumination of Nanoliter-NMR Spectroscopy Chips for Real-Time Photochemical Reaction Monitoring

Abstract

We report the use of a small-volume nuclear-magnetic-resonance (NMR)-spectroscopy device with integrated fiber-optics for the real-time detection of UV-vis-light-assisted chemical reactions. An optical fiber is used to guide the light from LEDs or a laser diode positioned safely outside the magnet toward the 25 nL detection volume and placed right above the microfluidic channel, irradiating the transparent back of the NMR chip. The setup presented here overcomes the limitations of conventional NMR systems for in situ UV-vis illumination, with the microchannel permitting efficient light penetration even in highly concentrated solutions, requiring lower-power light intensities, and enabling high photon flux. The efficacy of the setup is illustrated with two model reactions activated at different wavelengths.

Insights Into the Micelle-Induced β-Hairpin-to-α-Helix Transition of a LytA-Derived Peptide by Photo-CIDNP Spectroscopy

“…The NMR spectra were recorded on a Varian INOVA 500 MHz NMR spectrometer equipped with a gradient amplifier and a four-nucleus 5 mm 1 H{ 15 N- 31 P}PFG high-field indirect detection probe. NMR tubes with an external diameter of 2.5 mm (purchased from Wilmad, NJ, USA) were used for the more efficient and uniform illumination of the whole sample volume [26].…”

“…Previously [26,31], we reported the use of a laser-diode illumination device for NMR signal enhancement with unprecedented limits, illustrating the advantages of the combination of photo-CIDNP and small NMR active volumes due to the dependency between the signal enhancement observed in the photo-CIDNP spectrum and the photon flux in the sample [23,32]. However, our aim here was using this light setup for photo-CIDNP experiments with a different application, that is, as a tool for investigating the different mobility of two tyrosine residues in LytA 239-252 .…”

In situ sensors for flow reactors – a review

“…A step forward in this regard was provided by Gomez et al, 34 who assembled a novel kit with integrated planarspiral transceiver coils for in situ NMR monitoring of UV-visassisted reductive dehalogenation of α-bromoacetophenone in nanolitre scale. The described process solves the plight of low photonic efficiency encountered with large-scale photochemistry and makes reduced dimension analysis feasible (see Fig.…”

Monitoring off-resonance signals with SHARPER NMR – the MR-SHARPER experiment

“…3 However, most standard NMR spectroscopic techniques rely on maintenance of a highly stable homogenous magnetic field. This may be challenging when applied to reaction monitoring, for example if a chemical reaction evolves a gas 4 or requires additional hardware inside the magnetic field, such as in photochemical 5,6 or electrochemical 7 reactions. Several NMR experiments have been reported which are capable of compensating for magnetic field inhomogeneity, for example the UPSIF 8 experiment, which yields a broadband pure shift spectrum.…”