In situ illumination of liquid-state NMR samples opens a field for studies of light-dependent chemical or biological interactions. Among those studies, the light-driven reactions between amino acid and dye molecule, studied by photochemical induced nuclear polarization (photo-CIDNP) in solution, have been investigated to show characteristic changes in spin polarization upon various magnetic fields. The applications of photo-CIDNP, such as detecting aromatic amino acids or proteins in solution in the low micro-molar to nano-molar concentration range, are getting compelling simultaneously.
The time sequence shows how to perform the irradiation along with the NMR sequence. For low-field irradiation, the sample travels to the low field for irradiation and shuttles back immediately for pulsing and acquisition.
Due to the narrow bore of most commercial standard liquid-state NMR spectrometers, there was challenging to place a light source directly inside the magnet. Conventionally, the light source and control unit were outside of the spectrometer. The light, from lasers, or LED, was coupled through the long optical fiber to samples. The major drawback of this manner is that the long optical fiber confines the movement of the NMR sample. It would be severe for field-cycling NMR applications. For non-field-cycling studies, light homogeneity is also an issue for light coupling from the long thin optical fiber.
Hence, we have developed compact and high-precision shuttling equipment that shuttles and illuminates the sample at the stray field in a high-field NMR spectrometer to obtain high-resolution spectra containing the effect of field-dependent CIDNP, Field Cycling NMR illuminator. For non-field-cycling NMR users, we have also designed a compact illuminator installed directly on the sample tube, in-situ NMR illuminator.
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