An Efficient and Stable Polarizing Agent for In-Cell Magic-Angle Spinning Dynamic Nuclear Polarization NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy would be a method of choice to follow biochemical events in cells because it can analyze molecules in complex environments. However, the intrinsically low sensitivity of NMR makes in-cell measurements challenging. Dynamic Nuclear Polarization (DNP) has emerged as a method to circumvent this limitation, but most polarizing agents developed for DNP are unstable in reducing cellular environments. Here, we introduce the use of Gd(III)-based DNP polarizing agents for in-cell NMR spectroscopy. Specifically, we show their persistent stability in cellular formulations, and we investigate the DNP performance of the Gd(III)-based complex [Gd(tpatcn)] in human embryonic kidney cell lysates and intact cells. For cell lysates, DNP enhancements up to -27 are obtained on the cellular signals, reproducible even after storage at room temperature for days. Mixing the [Gd(tpatcn)] solution with intact cells enables the observation of cellular signals with DNP, and DNP enhancement factors of about -40 are achieved.