Bis‐Gadolinium Complexes for Solid Effect and Cross Effect Dynamic Nuclear Polarization. Issue 15 (20th March 2017)

• Record Type: Journal Article
• Authors: Kaushik, Monu; Qi, Mian; Godt, Adelheid; Corzilius, Björn
• Is Part Of: Angewandte Chemie international edition. Volume 56:Issue 15(2017)
• Page Start: 4295
• Page End: 4299
• Publication Date: 2017-03-20
• Subjects: cross effect -- dynamic nuclear polarization -- gadolinium complexes -- polarizing agent -- solid-state NMR spectroscopy; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201612388
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: High‐spin complexes act as polarizing agents (PAs) for dynamic nuclear polarization (DNP) in solid‐state NMR spectroscopy and feature promising aspects towards biomolecular DNP. We present a study on bis(Gd‐chelate)s which enable cross effect (CE) DNP owing to spatial confinement of two dipolar‐coupled electron spins. Their well‐defined Gd⋅⋅⋅Gd distances in the range of 1.2–3.4 nm allowed us to elucidate the Gd⋅⋅⋅Gd distance dependence of the DNP mechanism and NMR signal enhancement. We found that Gd⋅⋅⋅Gd distances above 2.1 nm result in solid effect DNP while distances between 1.2 and 2.1 nm enable CE for 1 H, 13 C, and 15 N nuclear spins. We compare 263 GHz electron paramagnetic resonance (EPR) spectra with the obtained DNP field profiles and discuss possible CE matching conditions within the high‐spin system and the influence of dipolar broadening of the EPR signal. Our findings foster the understanding of the CE mechanism and the design of high‐spin PAs for specific applications of DNP. Abstract : Poles apart : Bis(Gd‐chelate)s are investigated as polarizing agents for dynamic nuclear polarization (DNP). On varying the length of the linker between two chelated Gd III ions, a transition from the solid effect to the cross effect DNP mechanism is observed. The analysis of NMR signal enhancements for 1 H, 13 C, and 15 N sheds light on the distance dependence between two electron spins for the cross effect.