Design Principles for the Development of Gd(III) Polarizing Agents for Magic Angle Spinning Dynamic Nuclear Polarization

• Published in: Journal of physical chemistry. C Vol. 126; no. 27; pp. 11310 - 11317
• Main Authors: Rao, Yu, Palumbo, Chad T., Venkatesh, Amrit, Keener, Megan, Stevanato, Gabriele, Chauvin, Anne-Sophie, Menzildjian, Georges, Kuzin, Sergei, Yulikov, Maxim, Jeschke, Gunnar, Lesage, Anne, Mazzanti, Marinella, Emsley, Lyndon
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.07.2022
• Subjects: C: Physical Properties of Materials and Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.2c01721

Nuclear magnetic resonance suffers from an intrinsically low sensitivity, which can be overcome by dynamic nuclear polarization (DNP). Gd­(III) complexes are attractive exogenous polarizing agents for magic angle spinning (MAS) DNP due to their high chemical stability in contrast to nitroxide-based radicals. However, even the state-of-the-art Gd­(III) complexes have so far provided relatively low DNP signal enhancements of ca. 36 in comparison to standard DNP biradicals, which show enhancements of over 200. Here, we report a series of new Gd­(III) complexes for DNP and show that the observed DNP enhancements of the new and existing Gd­(III) complexes are inversely proportional to the square of the zero-field splitting (ZFS) parameter D, which is in turn determined by the ligand-type and the local coordination environment. The experimental DNP enhancements at 9.4 T and the ZFS parameters measured with pulsed electron paramagnetic resonance (EPR) spectroscopy agree with the above model, paving the way for the development of more efficient Gd­(III) polarizing agents.