13C Radiofrequency Amplification by Stimulated Emission of Radiation Threshold Sensing of Chemical Reactions

Conventional nuclear magnetic resonance(NMR) enablesdetectionof chemicals and their transformations by exciting nuclear spin ensembleswith a radio-frequency pulse followed by detection of the precessingspins at their characteristic frequencies. The detected frequenciesreport on chemical reactions in real time and the signal amplitudesscale with concentrations of products and reactants. Here, we employRadiofrequency Amplification by Stimulated Emission of Radiation (RASER),a quantum phenomenon producing coherent emission of (13)Csignals, to detect chemical transformations. The C-13 signalsare emitted by the negatively hyperpolarized biomolecules withoutexternal radio frequency pulses and without any background signalfrom other, nonhyperpolarized spins in the ensemble. Here, we studiedthe hydrolysis of hyperpolarized ethyl-[1-C-13]-acetate tohyperpolarized [1-C-13]-acetate, which was analyzed as amodel system by conventional NMR and C-13 RASER. The chemicaltransformation of C-13 RASER-active species leads to completeand abrupt disappearance of reactant signals and delayed, abrupt reappearanceof a frequency-shifted RASER signal without destroying C-13 polarization. The experimentally observed quantumRASER threshold is supported by simulations.

Automated summary

Conventional nuclear magnetic resonance (NMR) is used to detect chemical transformations by exciting and detecting the precessing spins of nuclear spin ensembles. In this study, we employ Radiofrequency Amplification by Stimulated Emission of Radiation (RASER) to detect chemical transformations without the need for external radio frequency pulses or background signals. We investigated the hydrolysis of hyperpolarized ethyl-[1-C-13]-acetate using both conventional NMR and C-13 RASER and observed a complete disappearance and delayed reappearance of the RASER signal without destroying the C-13 polarization.