Several hyperpolarization techniques have emerged over the past few decades to address the sensitivity limitations of NMR. Among these techniques, Photochemically Induced Dynamic Nuclear Polarization (photoCIDNP) is one of the easiest to implement. In a simplistic way, all what is needed to enhance the signal in a photoCIDNP experiment is the addition of a photosensitizer molecule to your sample and to illuminate it with light of a suitable wavelength.Â
We have developed a setup that allows to measure such experiments in an automated way. The illumination of the sample is achieved via a laser fiber introduced from the bottom of the Spinsolve spectrometer, contrasting with standard setups where the fiber is inserted from the top into the liquid sample. This arrangement facilitates easy sample exchange using an autosampler. With laser irradiation controlled by the Spinsolve software, a series of samples can now be measured fully automatically, as depicted in the pictures below.
Here we present first results of photoCIDNP experiments acquired with a Spinsolve 80 in which we achieved a signal-to-noise enhancement of >60 for tryptophan at a concentration of only 0.2 mmol/L in photoCIDNP buffer on our Spinsolve 80 MHz spectrometer.
Figure 1: Structure of tryptophan.
Usually, at these small concentrations, 256 scans or more must be accumulated for the signals to start appearing in the spectrum. With our photoCIDNP setup we can detect the tryptophan signals with a single-scan experiment. The aromatic protons display high positive enhancements whereas the beta protons show high negative enhancement.
Figure 2: Stacked plot comparing a spectrum with 256 scans without laser illumination (bottom spectrum) and the single-scan experiment of the same sample recorded after a 6 s laser pulse (top spectrum).