Low-Concentration Measurements of Nuclear Spin-Induced Optical Rotation Using SABRE Hyperpolarization

Nuclear spin-induced optical rotation (NSOR) is a promising phenomenon for molecular structure elucidation due to its sensitivity to electronic structure near atomic nuclei. It is the only experimentally verified nuclear magneto-optic effect (NMOE), so far observed usually in neat liquids or in concentrated binary mixtures, with the proportion of the minor component at least 10%. We report a method to extend the lower-concentration range of NSOR measurements by 2 orders of magnitude by employing continuous-flow SABRE (signal amplification by reversible exchange) hyperpolarization. This approach significantly increases the sensitivity of NSOR and enables its detection in dilute samples, as demonstrated with measurements of NSOR of 90 mmol/L solutions of pyridine and pyrazine. The results are compared with first-principles calculations, and good agreement is found. The possibility to measure low-concentration solutions significantly extends the pool of samples available for further studies of NMOEs.